Image forming apparatus, power supply device, and control method

A step-down circuit lowers a voltage outputted from a commercial power supply. A step-down-output control and charge control circuit controls a step-down voltage and charges a capacitor bank based on a step-down voltage outputted. A constant-voltage generating circuit generates a constant voltage based on an output of the capacitor bank or an output of the step-down circuit. An image-forming-apparatus control circuit supplies the constant voltage to a load that performs an image forming operation.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present document incorporates by reference the entire contents of Japanese priority documents, 2006-063180 filed in Japan on Mar. 8, 2006 and 2006-166567 filed in Japan on Jun. 15, 2006.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an image forming apparatus, a power supply device, and a control method. More particularly, the present invention relates to power control including charge accumulating means.

2. Description of the Related Art

In recent years, according to increasing environmental protection activities, energy saving for image forming apparatuses is demanded. An image forming apparatus including a fixing device of a heat roller system that presses and heats a sheet, a film, and the like having toner images formed thereon consumes a particularly large amount of electric power.

In an image forming apparatus with high image formation speed, to prevent a temperature fall in a fixing roller of a heating unit at the time of an image forming operation, a fixing roller with a large heat capacity may be adopted. In such a case, since a warm-up time as long as several minutes is necessary to raise the temperature of the fixing roller to a usable temperature, a copy waiting time is long. To reduce a heat-up time of the fixing roller, a fixing roller with a reduced heat capacity may be adopted. In such a case, a temperature fall of the fixing roller occurs at the time of the image forming operation. It is possible to solve these problems if the temperature of the fixing roller can be raised quickly by using a 200-volts power supply to increase a power capacity of a heating member such as a halogen heater and increase a transport current. However, as a general commercial power supply for offices in Japan, a power supply with 100 volts and 15 A is used. To adapt the power supply to the voltage at 200 volts, it is necessary to apply special work to a facility in which the power supply is installed. This does not provide a general solution for the problems.

As a method of reducing power consumption of the fixing device on standby, in general, the temperature of the fixing device on standby is kept at fixed temperature slightly lower than a fixing temperature and immediately raised to the usable temperature when the fixing device is used to reduce time for waiting for heat-up of the fixing roller. In this case, even when the fixing device is not used, since a certain degree of power is supplied, energy is consumed unnecessarily. The energy consumption of the fixing device on standby is as high as about 70% to 80% of energy consumption of the apparatus.

As a technology for solving such a problem, in a technology disclosed in Japanese Patent Application Laid-Open No. 2003-297526, an auxiliary heater is provided separately from a fixing heater driven by a commercial power supply and electric power accumulated in a capacitor with a large capacity is supplied to the auxiliary heater to input large power to the fixing heater, reduce a warm-up time of the fixing device, and reduce a temperature change of the fixing device.

In a technology disclosed in Japanese Patent Application Laid-Open No. 2004-266984, a charge accumulating unit (a capacitor) is charged by a voltage supplied from a commercial power supply and electric power is supplied to a load using the voltage charged.

However, in the technology disclosed in Japanese Patent Application Laid-Open No. 2003-297526, temperature detecting units corresponding to a plurality of heaters and a control unit that controls the heaters according to a result of temperature detection by the temperature detecting unit are necessary. This complicates a structure of the fixing device.

In the technology disclosed in Japanese Patent Application Laid-Open No. 2004-266984, it is necessary to use a capacity with a large capacity that charges power at a high voltage. This undesirably increases cost.

SUMMARY OF THE INVENTION

According to an aspect of the present invention, an image forming apparatus includes a charge accumulating unit that is chargeable and dischargeable with electric charge and outputs a first output; a step-down unit that steps down a voltage of a commercial power supply and outputs a step-down voltage as a second output; a step-down and charge control unit that controls the step-down unit so that the step-down unit outputs a voltage having certain level as the second output and controls the charge accumulating unit so that the charge accumulating unit accumulates an electric change that corresponds to the level of the second output; a constant-voltage generating unit that generates a constant voltage based on any one of the first output and the second output; and a voltage-supply control unit that supplies the constant voltage to a load that performs an image forming operation.

According to another aspect of the present invention, an image forming apparatus includes a charge accumulating unit that is chargeable and dischargeable with electric charge and outputs a first output; a charging unit that charges the charge accumulating unit with a voltage outputted from a commercial power supply; a constant-voltage generating unit that generates a constant voltage based on an output of the charge accumulating unit; and a voltage-supply control unit that supplies the constant voltage to a load that performs an image forming operation.

According to still another aspect of the present invention, a power supply device that supplies electric power to an external load includes a charge accumulating unit that is chargeable and dischargeable with electric charge and outputs a first output; a step-down unit that steps down a voltage of a commercial power supply and outputs a step-down voltage as a second output; a step-down and charge control unit that controls the step-down unit so that the step-down unit outputs a voltage having certain level as the second output and controls the charge accumulating unit so that the charge accumulating unit accumulates an electric change that corresponds to the level of the second output; a constant-voltage generating unit that generates a constant voltage based on any one of the first output and the second output; a first switching unit that inputs the second output to one of the constant-voltage generating unit and the charge accumulating unit; a second switching unit that inputs one of the first output and the second output to the constant-voltage generating unit, wherein the step-down and charge control unit supplies the constant voltage to the load.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An engine power supply unit of an image forming apparatus according to a first embodiment of the present invention steps down a voltage outputted from a commercial power supply and charges a charge accumulating unit. The engine power supply unit changes a voltage outputted from the commercial power supply or a voltage outputted from the charge accumulating unit to a constant voltage using a constant-voltage generating circuit to supply the voltage to a load.

An example of a structure of an engine power supply unit of a printer as an example of an image forming apparatus, to which the present invention is applied, is explained with reference toFIGS. 1 and 2. In this example, the printer is explained as an example of the image forming apparatus. It is possible to apply the present invention to image forming apparatuses such as a copying machine other than the printer, a facsimile apparatus, and a multi function peripheral (MFP) in which a copying function, a printer function, and a facsimile function are combined. It is also possible to apply the present invention to a power supply device that supplies electric power to some load unit.

FIG. 1is a circuit diagram of a circuit configuration of an engine power supply unit of a printer according to the first embodiment.FIG. 2is a detailed circuit diagram of a detailed circuit configuration of the engine power supply unit of the printer according to the first embodiment.

An engine power supply unit100includes a filter1, a full-wave rectifying circuit2, a step-down chopper circuit50, a step-down-voltage detecting circuit19, a charge accumulating unit (hereinafter, “capacitor bank”)9, a charge-voltage detecting circuit16, a constant-voltage generating circuit13, a charge-current detecting circuit12, an image-forming-apparatus control circuit (hereinafter, “engine control unit”)10, a step-down-output control and charge control circuit7, a load20, AC fixing heaters29and30, heating-unit-temperature detecting circuits33and34, an AC-fixing-heater control circuit39, a first switching circuit55, and a second switching circuit56.

A commercial power supply is inputted to the filter1via a main power supply switch3(seeFIG. 2). An output of the filter1is connected to the full-wave rectifying circuit2and subjected to full-wave rectification. The output subjected to full-wave rectification is connected to a smoothing capacitor C2. A ripple component and the like of the output are removed by the smoothing capacitor C2. A DC output of the full-wave rectifying circuit2is connected to a drain side of a field effect transistor (FET)51of a step-down chopper circuit (a step-down circuit)50.

The step-down chopper circuit50steps down an output from the commercial power supply. The step-down chopper circuit50includes the FET51provided on an input side, a choke coil52connected to an output side, that is, a source side of the FET51, a current feedback diode53provided between the output of the FET51and the choke coil52, and a smoothing capacitor54provided on the output side of the choke coil52. The step-down chopper circuit50is connected in parallel between terminals of the capacitor bank9via the first switching circuit55.

In the step-down chopper circuit50, when the FET51is turned on by a pulse width modulation signal (PWM signal) outputted from a PWM-signal generating circuit7eof the step-down-output control and charge control circuit7described later, an electric current flows to the choke coil52. A part of input electric power is accumulated in the choke coil52. Subsequently, when the FET51is turned off by the PWM signal, the electric power accumulated in the choke coil52in the ON period of the FET51is discharged through the current feedback diode53.

A voltage is stepped down according to repetition of this operation and the voltage stepped down is smoothed by the smoothing capacitor54. The smoothed voltage is supplied to the capacitor bank9via the first switching circuit55and respective capacitor cells of the capacitor bank9are charged. An output of the capacitor bank9is supplied to an input of the constant-voltage generating circuit13via the second switching circuit56and changed to a constant voltage. The output changed to the constant voltage by the constant-voltage generating circuit13is inputted to the load20and a post-processing apparatus22.

An output of the step-down chopper circuit50depends on a ratio of an ON period and an OFF period of the FET51(a duty ratio D/T) and an input voltage to the step-down chopper circuit50. When the duty ratio D/T is 100%, an output voltage and an input voltage are equal. When the duty ratio D/T is 50%, an output voltage is 50% of an input voltage. It is possible to control an output of the step-down chopper circuit50by controlling a duty ratio (PWM) of the FET51.

The voltage stepped down by the step-down chopper circuit50is detected by the step-down-voltage detecting circuit19subjected to voltage division by a resistor R4and a resistor R5and fed back to the step-down-output control and charge control circuit7. The voltage is also inputted to an analog/digital (A/D) converter10bof the engine control unit10. The voltage stepped down and smoothed by the step-down chopper circuit50is monitored by the step-down-output control and charge control circuit7and controlled according to a change of an ON duty of the PWM signal.

The capacitor bank9accumulates electric power. In the capacitor bank9, fourteen capacitor cells (electric double layer capacitor cells), each of which has 2.5 volts when fully charged, are connected in series. Therefore, when the fourteen capacitor cells are fully charged, a voltage at 35 volts is accumulated.

The charge-voltage detecting circuit16detects a charge voltage at the capacitor bank9. An inter-terminal voltage at the capacitor bank9is detected by the charge-voltage detecting circuit16in which a voltage dividing circuit is formed by a resistor R2and a resistor R3. An output of the capacitor bank9is inputted to an A/D converter7cof the step-down-output control and charge control circuit7and the A/D converter10bof the engine control unit10.

The charge-current detecting circuit12detects a charge current of the capacitor bank9. In the detection of the charge current of the capacitor bank9, an electric current flowing through a resistor R1connected in series to the capacitor bank9is detected as an inter-terminal voltage. An output of the charge-current detecting circuit12is inputted to a charge-current detecting circuit7dof the step-down-output control and charge control circuit7.

An equalizing circuit17detects full-charge of the respective capacitor cells, actuates bypass circuits17a, and equalizes charge voltages at the respective capacitor cells. A capacitor cell9ais charged by the step-down-output control and charge control circuit7. When the capacitor cell9ais charged to the full charge of 2.5 volts, an equalizing circuit17bypasses a charge current. Bypass circuits connected to the other capacitor cells in parallel perform the same operation. Charge voltages at the respective capacitor cells are equalized. When the equalizing circuit17detects full-charge of any one of the capacitor cells and actuates one of the bypass circuits, the equalizing circuit17outputs a single-cell full-charge signal5to the step-down-output control and charge control circuit7. When the equalizing circuit17detects full-charge of all the capacitor cells and actuates all the bypass circuits, the equalizing circuit17outputs a full-charge signal6for all the capacitor cells to the step-down-output control and charge control circuit7.

The step-down-output control and charge control circuit7detects a charge voltage at the capacitor bank9, detects a charge current, and detects an operation of the bypass circuits. The step-down-output control and charge control circuit7applies constant current charge or constant power charge to the capacitor bank9. The step-down-output control and charge control circuit7has a function of generating a PWM signal for applying constant current charge and constant power charge to the capacitor bank9and a function of generating a PWM signal for supplying a step-down voltage to the constant-voltage generating circuit13via the first switching circuit55and the second switching circuit56. The step-down-output control and charge control circuit7includes a CPU7a, a serial controller (SIC)7b, the A/D converter7c, the charge-current detecting circuit7d, the PWM-signal generating circuit7e, a ROM, a RAM, a timer, an interrupt control circuit, and an input/output port.

The step-down-output control and charge control circuit7detects an inter-terminal voltage at the capacitor bank9according to an output of the charge-voltage detecting circuit16. When the inter-terminal voltage at the capacitor bank9is lower than a value set in advance, the step-down-output control and charge control circuit7detects inter-terminal voltages at the resistor R1connected to the capacitor bank9in series one by one. To perform constant current charge set in advance, the step-down-output control and charge control circuit7outputs a PWM signal corresponding to the inter-terminal voltage detected to a gate of the FET51. To calculate the PWM signal for performing the constant current charge set in advance, the step-down-output control and charge control circuit7may use a table in which the inter-terminal voltage at the resistor R1and the ON duty of the PWM signal are associated. The step-down-output control and charge control circuit7may calculate the PWM signal according to an arithmetic operation. The step-down-output control and charge control circuit7may control the PWM signal with reference to only a charge current to obtain a charge current set in advance. When the capacitor bank9is not charged, to prevent a large rush current from flowing to the capacitor bank9, the step-down-output control and charge control circuit7may output the PWM signal to set a step-down voltage low and gradually increase the step-down voltage.

When the inter-terminal voltage at the capacitor bank9is equal to or higher than the value set in advance, to perform constant power charge, the step-down-output control and charge control circuit7detects charge currents of the capacitor bank9and inter-terminal voltages at the capacitor bank9one by one. The step-down-output control and charge control circuit7detects a charge current of the capacitor bank9and an inter-terminal voltage at the capacitor bank9, calculates a PWM signal for performing constant power charge set in advance from the charge current and the charge voltage detected, and determines the PWM signal.

When the step-down-output control and charge control circuit7detects any one of the single-cell full-charge signals5, the step-down-output control and charge control circuit7outputs the PWM signal for performing constant current charge set in advance to the gate of the FET51again. When the step-down-output control and charge control circuit7detects full-charge signals6of all the capacitors, the step-down-output control and charge control circuit7outputs a signal for stopping the charge operation to the gate of the FET51.

Processing by the step-down chopper circuit50for supplying electric power to the load20and the post-processing apparatus22via the constant-voltage generating circuit13is explained. When a signal for supplying electric power to the load20is outputted from a CPU10aof the engine control unit10to the CPU7a, the step-down-output control and charge control circuit7outputs a PWM signal set in advance by the PWM-signal generating circuit7eto the gate of the FET51. The step-down chopper circuit50generates a step-down voltage according to the PWM signal outputted and supplies the step-down voltage to the input of the constant-voltage generating circuit13via the first switching circuit55and the second switching circuit56. A PWM signal of a fixed duty ratio may be outputted to the step-down chopper circuit50. The step-down chopper circuit50may detect a step-down voltage with the step-down-voltage detecting circuit19and feeds back the step-down voltage to the step-down-output control and charge control circuit7to generate a constant voltage. A voltage value to be stepped down may be outputted from the CPU10aof the engine control unit10to the CPU7aof the step-down-output control and charge control circuit7and determined.

FIG. 3is a detailed circuit diagram of a circuit configuration of another step-down circuit. The step-down chopper circuit50may generate a step-down voltage with a structure shown inFIG. 3. The step-down chopper circuit50switches a primary coil50bof a high-frequency transformer50ausing a FET50dand rectifies a voltage induced in a secondary coil50cto generate a step-down voltage.

The engine control unit10outputs a signal to a first switching circuit and a second switching circuit to switch the circuit and control supply of electric power. The engine control unit10constitutes a voltage-supply control unit according to the present invention. The engine control unit10includes a serial controller (SIC)10dconnected to the CPU10a, an input/output port10c, the A/D converter10b, a ROM, a RAM, a timer, and an interrupt control circuit (INT).

The heating-unit-temperature detecting circuits33and34that detect a surface temperature (a fixing temperature) of a fixing roller of a fixing device (not shown) are connected to the A/D port10bof the CPU10a. The heating-unit-temperature detecting circuit33includes a resistor R11connected to an AC-heater thermistor33ain series. The heating-unit-temperature detecting circuit33detects the temperature in a measurement area corresponding to the AC fixing heater29. The temperature detecting circuit34includes a resistor R12connected to an AC-heater thermistor34ain series. The temperature detecting circuit34detects the temperature in a measurement area corresponding to the AD fixing heater30.

The AC-fixing-AC heater control circuit39that supplies electric power to the AC fixing heaters29and30according to temperature detection results of the heating-unit-temperature detecting circuits33and34, loads20and21such as a motor, a solenoid, and a clutch necessary for performing an image forming operation, a sensor necessary for performing an image forming operation, a switch circuit15, and the like are connected to the input/output port10c. The load21is a load of a power system that requires large electric power such as a conveying motor, a development motor, and the like. The load20is a load supplied from a separate power supply. The load20needs to hold a display LED and rotation of a pulse motor that always need supply of power. It goes without saying that it is unnecessary to supply the load from the separate power supply when it is possible to supply electric power to the load even at the time of charge.

The CPU10atransmits a signal to and receives a signal from the step-down-output control and charge control circuit7via the serial controller (SIC)10d. The CPU10atransmits a charge permission signal, a charge current for charging, a patter of a PWM signal, or the like to the step-down-output control and charge control circuit7when discharge is not performed, at the time of standby, at the time of an energy saving mode, or the like. The CPU10adetects an inter-terminal voltage at the capacitor bank9with the charge-voltage detecting circuit16and judges whether power discharge of the capacitor bank9is possible. The CPU10adetects a step-down voltage with the step-down-voltage detecting circuit19and instructs the step-down-output control and charge control circuit7to control the step-down voltage.

When the heating-unit-temperature detecting circuits33and34detect whether the temperature is equal to or lower than temperature set in advance, the CPU10aoutputs a signal for turning on photo-triacs35aand36ato photo-triac drive circuits35and36from ports1and3. Consequently, electric power is supplied to the AC fixing heaters29and30. When the heating-unit-temperature detecting circuits33and34detect whether the temperature is equal to or higher than the temperature set in advance, the CPU10aoutputs a signal for turning off the photo-triacs35and36to the photo-triac drive circuits35and36from the ports1and3. Consequently, the supply of electric power to the AC fixing heaters29and30is stopped.

The first switching circuit55includes a relay55a. The second switching circuit56includes a relay56a. The first switching circuit and the second switching circuit according to this embodiment include relays. It goes without saying that an opening and closing circuit including an FET, an insulated Gate Bipolar Transistor (IGBT), or the like may be used. The relays55aand56aare set to be connected to the commercial power supply (the step-down chopper circuit50) side in a normal close state (a state in which a coil is not conductive). Therefore, when a main power supply is off, discharge from the capacitor bank9is stopped.

The CPU10aenergizes the relay55aor stops the energization of the relay55aaccording to a signal outputted from a port5and controls switching of the first switching circuit55. The CPU10aenergizes the relay56aor stops the energization of the relay56aaccording to a signal outputted from a port6and controls switching of the second switching circuit56.

When electric power is unnecessary at the time of standby, the energy saving mode, or the like, to charge the capacitor bank9, the CPU10aoutputs a signal for energizing the relay55afrom the port5and outputs a signal for stopping the energization of the relay56afrom the port6. When electric power exceeds an AC power rating of the commercial power supply or when flicker occurs because of sudden fluctuation in a load on the image forming apparatus side, to use accumulated electric power in the capacitor bank9, the CPU10aoutputs a signal for stopping the energization of the relay55afrom the port5and outputs a signal for energizing the relay56afrom the port6.

At the normal time other than charge or discharge, the CPU10aoutputs a signal for stopping the energization of the relay55afrom the port5and outputs a signal for stopping the energization of the relay56afrom the port6. Consequently, the output of the step-down chopper circuit50is connected to the input of the constant-voltage generating circuit13. After the image forming operation is finished, since the image forming apparatus enters the energy saving mode when a fixed time elapses, the CPU10aoutputs a signal for stopping a part of power output to a DC/DC converter14from the port2. When an energy saving release switch (SW)24(a platen open SW, an original detection SW of an ADF, etc.) returns to a normal operation and the energy saving mode is released.

A power use table T1defines an image forming operation that cannot be managed by supplied power from the commercial power supply and an accumulated electric power use time necessary for performing processing of the image forming operation.FIG. 4is a diagram for explaining an example of a data structure of the power use table T1. The power use table T1stores an image forming operation that requires electric power equal to or larger than normal supplied power and an accumulated electric power use time in association with each other. The image forming operation that requires power equal to or larger than the normal supplied power is, for example, a combination of a sheet size and the number of sheets that makes it impossible to continuously perform an image forming operation because the temperature of the fixing device falls when the image forming operation for a plurality of sheets is performed according to supply of normal electric power from the commercial power supply. The accumulated electric power use time is time during which electric power is supplied from the capacitor bank9to perform image formation processing under a condition exceeding the normal supplied power. By referring to the power use table T1, it is possible to supply necessary electric power from the capacitor bank9and carry out an image forming operation with short waiting time before the image forming operation that cannot be managed by the normal electric power is performed. Since it is possible to prevent a fixing temperature from falling, it is possible to improve a quality of image formation and prevent flicker.

A power use table T2defines post processing that requires supply of electric power.FIG. 5is a diagram for explaining an example of a data structure of the power use table T2. The power use table T2stores a post-processing type that requires supply of electric power. By referring to the power use table T2, it is possible to judge whether supply of electric power is necessary for post processing to be executed and supply electric power when the post processing is performed.

A control circuit8controls the entire image forming apparatus. The control circuit8includes a CPU8athat controls the entire image forming apparatus, a serial controller (SIC)8dconnected to the CPU8a, a ROM, a RAM, a work memory for image expansion used in a printer, a frame memory that temporarily stores image data of a writing image, an application specific integrated circuit (ASIC) mounted with a function of controlling the periphery of the CPUs, and an interface circuit for the ASIC. An input unit to which a user inputs system setting by operating a panel, a display unit that shows a state of setting details of the system to the user, an operation-unit control circuit that controls the input unit, and the engine control unit10are connected to the CPU8avia a serial controller (SIC).

FIGS. 6A to 6Dare flowcharts of a procedure of operation mode control processing performed by the engine control unit of the image forming apparatus.

When DC power is supplied according to power-on of the main power supply or release of the energy saving mode, the CPU10aof the engine control unit10performs initial setting related to the CPU10aof the engine control unit10, a peripheral circuit of the CPU10a, and the memories (step S601). The CPU10ajudges from a result of detection by the charge-voltage detecting circuit16whether a charge voltage is 35 volts, i.e., whether the capacitor cells are in the full-charge state (step S602). When it is judged that the capacitor cells are fully charged (“Yes” at step S602), the CPU10aperforms opening-and-closing-circuit control processing P1(step S603). Consequently, it is possible to stop supply of electric power from the commercial power supply and supply electric power accumulated in the capacitor bank9to the constant-voltage generating circuit13. As a result, excess electric power is supplied to the heating unit of the fixing device (step S604). At the time of the normal operation, electric power is not supplied at 100% duty. Electric power may be supplied only at the time of warm-up of the fixing heater30as an auxiliary heater or at the time when a fixing temperature falls. When it is judged that the capacitor cells are not fully charged (“No” at step S602), the processing proceeds to step S604.

The CPU10ajudges from a result of detection by the charge-voltage detecting circuit16whether a charge voltage is equal to or higher than 28 volts (step S605). When it is judged that the charge voltage is equal to or higher than 28 volts (“Yes” at step S605), the CPU10ajudges that it is possible to use accumulated electric power and judges whether a heating unit temperature is equal to or higher than temperature set in advance (e.g., 175° C.) (step S606). When it is judged that the heating unit temperature has not reached the temperature set in advance (“No” at step S606), the CPU10areturns to step S604. The CPU10acontinues to supply maximum electric power of the heater rating to the AC fixing heaters29and30.

When it is judged that the heating unit temperature is equal to or higher than the temperature set in advance (“Yes” at step S606) or when it is judged that the charge voltage at the capacitor bank9is lower than 28 volts (“No” at step S605), the CPU10aperforms opening-and-closing-circuit control processing P2(step S607). Consequently, electric power is supplied from the commercial power supply (the step-down chopper circuit50) to the load.

The CPU10asupplies electric power at the normal time set in advance to the AC fixing heaters29and30of the fixing device (step S608). The CPU10ajudges whether the heating unit has a reload temperature (e.g., 180° C.) (step S609). When it is judged that the heating unit does not have the reload temperature (“No” at step S609), the CPU10areturns to step S608. The electric power at the normal time set in advance is continuously supplied to the AC fixing heaters29and30. When it is judged that the heating unit has the reload temperature (“Yes” at step S609), the fixing device comes into a standby state. The electric power at the normal time set in advance is supplied to the fixing heaters and normal temperature control is carried out (step S610).

The CPU10ajudges whether the fixing device is in the standby state again (step S611). When it is judged that the fixing device is in the standby state (“Yes” at step S611), the CPU10ajudges whether a charge voltage is lower than 35 volts, i.e., whether the capacitor cells are in the full-charge state (step S612). When it is judged that the charge voltage is lower than 35 volts, i.e., the capacitor cells are not in the full-charge state (“Yes” at step S612), the CPU10aperforms opening-and-closing-circuit control processing P3(step S613) and returns to step S610. Consequently, the capacitor bank9is charged. When it is judged that the charge voltage is not lower than 35 volts, i.e., the capacitor cells are in the full-charge state (“No” at step S612), the CPU10aperforms the opening-and-closing-circuit control processing P2(step S614) and returns to step S610. Consequently, electric power is supplied from the commercial power supply (the step-down chopper circuit50) to the load.

When it is judged at step S611that the fixing device is not in the standby state (“No” at step S611), the CPU10asets an operation mode or an operation condition for using accumulated electric power with reference to the power use tables T1and T2defining use of accumulated electric power for each operation mode and image forming operation process (step S615). For example, the CPU10aacquires, from the power use tables T1and T2, setting of the number of copies with which the temperature of the heating unit falls according to the number of continuous copies, a timer count of time when the temperature of the heating unit recovers when maximum power is supplied to the fixing heaters, i.e., accumulated electric power of the capacitor bank9is used, and post-processing that requires supply of electric power and sets the setting of the number of copies, the timer count, and the post-processing.

The CPU10ajudges whether the image forming apparatus is performing a copy operation (step S616). When it is judged that the image forming apparatus is performing a copy operation (“Yes” at step S616), the CPU10ajudges whether there is the setting of the number of copies acquired from the power use tables T1and T2(step S617). When it is judged that there is the setting of the number of copies (“Yes” at step S617), the CPU10aperforms plural copy processing (step S618). Details of the plural copy processing are described later.

The CPU10aperforms the opening-and-closing-circuit control processing P2(step S619). Consequently, electric power is supplied from the commercial power supply (the step-down chopper circuit50) to the load. The load continuously performs the image forming operation and normal electric power is supplied to the fixing heaters (step S620). The CPU10ajudges whether sheets of a number corresponding to one job have been discharged (step S621). When it is judged that the sheets of the number corresponding to one job have not been discharged (“No” at step S621), the CPU10areturns to step S620. The load continues the image forming operation. When it is judged that the sheets of the number corresponding to one job have been discharged (“Yes” at step S621), the CPU10ajudges whether supply of electric power is necessary for post-processing (step S622).

When it is judged that supply of electric power is necessary for post-processing (“Yes” at step S622), to increase an output of the DC power supply, the CPU10aperforms the opening-and-closing-circuit control processing P1(step S623). Consequently, power accumulated in the capacitor bank9is supplied to the constant-voltage generating circuit13. A post-processing peripheral apparatus supplied with the electric power carries out a post-processing operation (step S624). The CPU10areturns to step S610. When it is judged that supply of electric power to the post-processing is unnecessary (“No” at step S622), since the copy operation is finished, the CPU10areturns to step S610).

When it is judged at step S616that the image forming apparatus is not performing the copy operation (“No” at step S616), the CPU10ajudges whether the image forming apparatus is in the energy saving mode (step S625). When it is judged that the image forming apparatus is not in the energy saving mode (“No” at step S625), the CPU10areturns to step S610. When it is judged that the image forming apparatus is in the energy saving mode (“Yes” at step S625), the CPU10ajudges whether a charge voltage is lower than 35 volts, i.e., whether the capacitor cells are in the full-charge state (step S626). When it is judged that the charge voltage is lower than 35 volts, i.e., the capacitor cells are in the full-charge state (“Yes” at step S626), to charge the capacitor bank9, the CPU10aperforms the opening-and-closing-circuit control processing P3(step S627) and returns to step S625. Although not shown in this flowchart, when this charge operation is finished, the image forming apparatus control unit also shifts to the energy saving mode. When it is judged that the charge voltage is not lower than 35 volts, i.e., the capacitor cells are in the full-charge state (“No” at step S626), the CPU10aswitches the first switching circuit to the commercial power supply side (step S628), switches the second switching circuit to the commercial power supply side (step S629), and returns to step S625.

The CPU10aof the engine control unit10performs the opening-and-closing-circuit control processing P2(step S701). Consequently, electric power is supplied from the commercial power supply (the step-down chopper circuit50) to the load. The load carries out an image forming operation and normal electric power is supplied to the AC fixing heaters29and30(step S702). The CPU10ajudges whether copying for the number of copies N acquired from the power use tables has been carried out (step S703). When it is judged that copying for the number of copies N has not been carried out (“No” at step S703), the CPU10areturns to step S702. The load repeats the image forming operation. When it is judged that copying for the number of copies N has been carried out (“Yes” at step S703), the CPU10aperforms the opening-and-closing-circuit control processing P1(step S704). Consequently, the supply of electric power from the commercial power supply is stopped, electric power accumulated in the capacitor bank9is supplied to the constant-voltage generating circuit13, and excess electric power is supplied to the heating unit of the fixing device. As a result, it is possible to supply the maximum power of the heater rating to the AC fixing heaters29and30. It is possible to prevent the temperature of the heating unit from falling to be lower than a fixed image guarantee temperature.

The CPU10acontinues the state in which the maximum power is supplied to the AC fixing heaters29and30and continues the image forming operation (step S705). The CPU10ajudges whether the timer counter is M (step S706). When it is judged that the timer counter is not M (“No” at step S706), the CPU10areturns to step S705. When it is judged that the timer counter is M (“Yes” at step S706), the CPU10aleaves the processing.

The temperature fall of the heating unit of the fixing device occurs because heat of a fixing pressure roller moves to a sheet when sheet supply is started. Therefore, when this pressure roller is warmed, the temperature fall is solved. The time M until the pressure roller is warmed is acquired from the power use table T2and set as the timer count. Thus, it is possible to supply the maximum power of the heater rating to the fixing heaters until the time M comes.

FIG. 8is a flowchart of a procedure of the opening-and-closing-circuit control processing P1performed by the engine control unit of the image forming apparatus. According to this processing, electric power is supplied from the capacitor bank9. The constant-voltage generating circuit13outputs a constant voltage and supplies electric power to the load.

The CPU10atransmits a signal for using electric power of the charge accumulating unit to the CPU7aof the step-down-output control and charge control circuit7(step S801). The CPU10aswitches the first switching circuit to the commercial power supply side (step S802) and switches the second switching circuit to the charge accumulating unit side (step S803).

In this way, it is possible to supply electric power from the charge accumulating unit. Thus, it is possible to supplement shortage of electric power supplied from the commercial power supply.

FIG. 9is a flowchart of a procedure of the opening-and-closing-circuit control processing P2performed by the engine control unit of the image forming apparatus. According to this processing, electric power is supplied from the commercial power supply (the step-down chopper circuit50) to the load.

The CPU10atransmits a signal for supplying electric power to the load to the CPU7aof the step-down-output control and charge control circuit7(step S901). The CPU10aswitches the first switching circuit to the commercial power supply side (step S902) and switches the second switching circuit to the commercial power supply side (step S903).

In this way, it is possible to interrupt supply of electric power from the charge accumulating unit when electric power is supplied from the commercial power supply. Thus, it is possible to effectively utilize accumulated electric power of the charge accumulating unit.

FIG. 10is a flowchart of a procedure of the opening-and-closing-circuit control processing P3performed by the engine control unit of the image forming apparatus. According to this processing, the capacitor bank9is charged.

The CPU10aswitches the first switching circuit to the charge accumulating unit side (step S1001) and switches the second switching circuit to the commercial power supply side (step S1002). The CPU10atransmits a charge permission signal (step S1003).

In this way, it is possible to charge the charge accumulating unit when electric power is unnecessary for the load. Thus, it is possible to perform leveling of electric power use.

FIGS. 11A and 11Bare flowcharts of a procedure of step-down-voltage control and charge control processing by the step-down-output control and charge control circuit of the image forming apparatus. According to this processing, the capacitor bank9is charged and an output of the commercial power supply is stepped down by the step-down chopper circuit50.

The CPU7aof the step-down-output control and charge control circuit7judges whether a charge permission signal is transmitted from the CPU10aof the engine control unit10(step S1101). When it is judged that the charge permission signal is transmitted (“Yes” at step S1101), the CPU7ajudges whether a charge voltage has reached 35 volts (step S1102). Specifically, the CPU7achecks a charge voltage from a detection result of the charge-voltage detecting circuit16and judges whether the capacitor cells are in the full-charge state. When it is judged that the charge voltage has reached 35 volts (“Yes” at step S1102), since it is unnecessary to charge the charge accumulating unit, the CPU7atransmits a full-charge voltage signal to the CPU10aof the engine control unit10(step S1103) and finishes the processing.

When it is judged that the charge voltage has not reached 35 volts (“No” at step S1102), to perform a charge operation, the CPU7atransmits a charge operation signal to the CPU10aof the engine control unit10(step S1104). The CPU7ajudges whether the charge voltage is equal to or lower than 24 volts (step S1105). When it is judged that the charge voltage is equal to or lower than 24 volts (“Yes” at step S1105), the CPU7adetects a charge current of the charge accumulating unit, i.e., the capacitor bank9(step S1106). The CPU7aoutputs a PWM signal corresponding to the charge current detected for performing constant current charge to the gate of the FET51of the step-down chopper circuit50(step S1107). Returning to step S1105, the CPU7ajudges whether the charge voltage is equal to or lower than 24 volts. When it is judged that the charge voltage is equal to or lower than 24 volts, the CPU7arepeats the charge operation described above.

When it is judged at step S1105that the charge voltage is not equal to or lower than 24 volts (“No” at step S1105), the CPU7aperforms detection of a charge current and a charge voltage at the charge accumulating unit, i.e., the capacitor bank9(step S1108). To perform constant power charge, the CPU7aoutputs a PWM signal corresponding to the charge current and the charge voltage detected to the gate of the FET51(step S1109). The CPU7ajudges whether there is any one of single-cell full-charge signals (step S1110). When it is judged that there is no single-cell full-charge signal (“No” at step S1110), the CPU7areturns to step S1108.

When it is judged that there is any one of the single-cell full-charge signals (“Yes” at step S1110), the CPU7acarries out constant current charge (step S1111). The CPU7ajudges whether there is an all-cell full-charge signal (step S1112). When it is judged that there is the all-cell full-charge signal (“Yes” at step S1112), to stop the charge operation, the CPU7aoutputs a PWM signal to the gate of the FET51(step S1113). The CPU7atransmits the all-cell full-charge signal to the CPU10a(step S1114) and finishes the processing. When it is judged that there is no all-cell full-charge signal (“No” at step S1112), the CPU7areturns to step S1111and performs constant current charge.

When it is judged at step S1101that the charge permission signal is not transmitted (“No” at step S1101), the CPU7ajudges whether there is an image forming operation signal, i.e., whether the image forming operation signal is outputted from the CPU10a(step S1115). When it is judged that there is the image forming operation signal (“Yes” at step S1115), the CPU7adetects a voltage outputted from the step-down chopper circuit50with the step-down-voltage detecting circuit19(step S1116). The CPU7ajudges whether the voltage outputted from the step-down chopper circuit50is 30 volts (step S1117). This step-down voltage is set in advance to be lower than a charge voltage at the capacitor bank9. In fully charging the respective capacitor cells, a voltage at the capacitor bank9is higher than 30 volts of the step-down voltage.

When it is judged that the voltage outputted from the step-down chopper circuit50is not 30 volts (“No” at step S1117), the CPU7aoutputs a PWM signal corresponding to the step-down voltage detected to set the step-down voltage to 30 volts (step S1118). As this PWM signal, a PWM signal associated with the step-down voltage detected may be set in a table in advance. A PWM signal may be generated by an analog circuit by comparing a comparative-signal generating circuit (a triangular wave) and an analog voltage set in advance (a voltage for outputting 30 volts).

When it is judged that the voltage outputted from the step-down chopper circuit50is 30 volts (“Yes” at step S1117), the CPU7areturns to step S1116. The CPU7arepeats such an operation to maintain the step-down voltage at 30 volts with the PWM-signal generating circuit7e.

When it is judged at step S1115that there is no image forming operation signal (“No” at step S1115), the CPU7ajudges whether there is a load power supply signal, i.e., whether the load power supply signal is outputted from the CPU10a(step S1119). When it is judged that there is no load power supply signal (“No” at step S1119), the CPU7aproceeds to step S1116. When it is judged that there is the load power supply signal (“Yes” at step S1119), the CPU7ajudges whether there is a power use signal for using electric power of the charge accumulating unit, i.e., whether the power use signal for using electric power of the charge accumulating unit is outputted from the CPU10a(step S1120). When it is judged that there is no power use signal for using electric power of the charge accumulating unit (“No” at step S1120), the CPU7afinishes the processing.

When it is judged that there is the power use signal for using electric power of the charge accumulating unit (“Yes” at step S1120), the CPU7adetects a voltage outputted from the step-down chopper circuit50with the step-down-voltage detecting circuit19(step S1121). The CPU7ajudges whether the voltage outputted from the step-down chopper circuit50is 28 volts (step S1122). This step-down voltage is a voltage set such that the capacitor bank9starts discharge and the voltage falls to a voltage equal to or lower than 28 volts, the output of the step-down chopper circuit50automatically changes to the input of the constant-voltage generating circuit13.

When it is judged that the voltage outputted from the step-down chopper circuit50is not 28 volts (“No” at step S1122), the CPU7aoutputs a PWM signal corresponding to the detected step-down voltage from the PWM-signal generating circuit7eto the gate of the FET51of the step-down chopper circuit50to set the step-down voltage to 28 volts (step S1123). As this PWM signal, a PWM signal associated with the step-down voltage detected may be set in a table in advance. A PWM signal may be generated by an analog circuit by comparing a comparative-signal generating circuit (a triangular wave) and an analog voltage set in advance (a voltage for outputting 28 volts). When it is judged that the voltage outputted from the step-down chopper circuit50is 28 volts (“Yes” at step S1122), the CPU7areturns to step S1121. The CPU7arepeats such an operation to maintain the step-down voltage at 28 volts with the PWM-signal generating circuit7e.

In this way, a constant voltage is generated by the constant-voltage generating circuit13from an output of the capacitor bank9charged by the commercial power supply or an output of the commercial power supply and the constant voltage generated is supplied to the load. Thus, it is possible to realize a plurality of functions, which are realized by a plurality of circuits in the past, with one constant-voltage generating circuit13. This makes it possible to reduce a warm-up time of the fixing device using the commercial power supply for general offices in Japan without applying special work related to a power supply and simplify a circuit configuration of the power supply device including the charge accumulating unit. Since the circuit configuration of the power supply device including the charge accumulating unit is simplified, it is possible to reduce manufacturing cost for the image forming apparatus. Since a complicated structure is not adopted for the circuit configuration of the power supply device, it is possible to realize improvement of a quality of the apparatus and improvement of easiness of maintenance.

Since a voltage at the commercial power supply is stepped down and the capacitor bank9is charged with the voltage stepped down, it is possible to reduce the number of capacitor cells connected in series. It is possible to accumulate an accumulated charge amount (equal to or higher than DC 30 volts) acceptable as a voltage at the fixing device (a halogen heater).

FIG. 12is a graph for explaining a temperature characteristic of the fixing device at the time of warm-up and copying performed by using the capacitor bank. In this embodiment, since the structure described above is adopted, a warm-up time until the fixing device at the time of start of the image forming apparatus reaches a predetermined temperature is shorter than a warm-up time at the time when the capacitor cells are not provided. Temperature fall is reduced by performing image formation processing. Since the structure using the capacitor bank charged by the commercial power supply is adopted, it is possible to reduce time during which the image formation processing is impossible by using the commercial power supply used in general offices in Japan.

The present invention is not limited to the embodiment described above. Other embodiments are explained below.

As in the first embodiment, an engine power supply unit of an image forming apparatus according to a second embodiment of the present invention steps down a voltage outputted from the commercial power supply to charge a charge accumulating unit and changes a voltage outputted from the commercial power supply and a voltage outputted from the charge accumulating unit to constant voltages with a constant-voltage generating circuit to supply the voltages to the load. The second embodiment is different from the first embodiment in that a first opening and closing circuit is used instead of the first switching circuit and a second opening and closing circuit and a third opening and closing circuit are used instead of the second switching circuit.

Concerning an example of a structure of an engine power supply unit200to which the present invention is applied, differences from the first embodiment are explained. Explanations of components identical with those in the first embodiment are omitted.FIG. 13is a circuit diagram of a circuit configuration of an engine power supply unit of a printer according to the second embodiment.FIG. 14is a detailed circuit diagram of a detailed circuit configuration of the engine power supply unit of the printer according to the second embodiment.

The engine power supply unit200of the printer according to this embodiment includes the filter1, the full-wave rectifying circuit2, the step-down chopper circuit50, the step-down-voltage detecting circuit19, the capacitor bank9, the charge-voltage detecting circuit16, the constant-voltage generating circuit13, the charge-current detecting circuit12, the engine control unit10, the step-down-output control and charge control circuit7, the load20, the AC fixing heaters29and30, the heating-unit-temperature detecting circuits33and34, the AC-fixing-heater control circuit39, a first opening and closing circuit40, a second opening and closing circuit41, and a third opening and closing circuit42.

Structures and functions of the filter1, the full-wave rectifying circuit2, the step-down chopper circuit50, the step-down-voltage detecting circuit19, the capacitor bank9, the charge-voltage detecting circuit16, the constant-voltage generating circuit13, the charge-current detecting circuit12, the engine control unit10, the step-down-output control and charge control circuit7, the load20, the AC fixing heaters29and30, the heating-unit-temperature detecting circuits33and34, and the AC-fixing-heater control circuit39are the same as those in the first embodiment. Thus, explanations of the structures and the functions are omitted here

The first opening and closing circuit40opens and closes the connection between the output of the step-down chopper circuit50and the capacitor bank9. The second opening and closing circuit41connects the output of the step-down chopper circuit50and the input of the constant-voltage generating circuit13. The third opening and closing circuit42opens and closes the connection between the input of the constant-voltage generating circuit13and the capacitor bank9. It is possible to supply a voltage to the constant-voltage generating circuit13even at the time of charge by closing the second opening and closing circuit41. In charging the charge accumulating unit when it is unnecessary to supply electric power to the load, for example, at the time of the energy saving mode, it is possible to reduce electric power if the second opening and closing circuit41is opened. The first to the third opening and closing circuits according to this embodiment include FETS. It goes without saying that opening and closing circuit including IGBTs or the like may be used.

When a relay is used for the second opening and closing circuit41and the third opening and closing circuit42, it is possible to continuously supply electric power to the constant-voltage generating circuit13if a signal for opening the third opening and closing circuit42is outputted in a fixed time after a signal for turning on the second opening and closing circuit41is outputted. When the second opening and closing circuit41is turned off, it is possible to continuously supply electric power to the constant-voltage generating circuit13if a signal for opening the second opening and closing circuit41is outputted in a fixed time after a signal for turning on the third opening and closing circuit42is outputted.

Opening and closing of the first opening and closing circuit40is controlled by outputting a signal for turning on and off a FET40afrom the port6of the engine control unit10to a gate of the FET40a. Opening and closing of the second opening and closing circuit41is controlled by outputting a signal for turning on and off a FET41afrom the port4of the engine control unit10to a gate of the FET41a. Opening and closing of the third opening and closing circuit42is controlled by outputting a signal for turning on and off a FET42afrom the port5of the engine control unit10to a gate of the FET42a. The first opening and closing circuit40and the third opening and closing circuit42are set to be opened in a normal close state. Therefore, when the main power supply is off, discharge from the capacitor bank9is stopped.

Operation mode control processing according to this embodiment is the same as the processing of the flowcharts shown inFIGS. 6A to 6Dexplained in the first embodiment. Thus, only differences are explained below.

In this embodiment, instead of steps S628and S629, processing for outputting an opening signal to the first opening and closing circuit, outputting an opening signal to the second opening and closing circuit, and outputting an opening signal to the third opening and closing circuit is performed.

The opening-and-closing-circuit control processing P1in the flowcharts shown inFIGS. 6A to 6Dis replaced with opening-and-closing-circuit control processing P1shown inFIG. 15. The opening-and-closing-circuit control processing P2is replaced with opening-and-closing-circuit control processing P2shown inFIG. 16. The opening-and-closing-circuit control processing P3is replaced with opening-and-closing-circuit control processing P3shown inFIG. 17.

FIG. 15is a flowchart of a procedure of the opening-and-closing-circuit control processing P1performed by the engine control unit of the image forming apparatus. According to this processing, the constant-voltage generating circuit13generates a constant voltage using accumulated electric power of the capacitor bank9and supplies electric power to the load.

The CPU10atransmits a signal for using electric power of the charge accumulating unit to the CPU7aof the step-down-output control and charge control circuit7(step S1501). The CPU10aoutputs a closing signal to the first opening and closing circuit from the port6(step S1502) and outputs a closing signal to the third opening and closing circuit from the port5(step S1503). When a relay is used for the second and the third opening and closing circuits, the CPU10acounts time N with the timer counter (step S1504). The CPU10aoutputs an opening signal to the second opening and closing circuit from the port4(step S1505).

FIG. 16is a flowchart of a procedure of the opening-and-closing-circuit control processing P2performed by the engine control unit of the image forming apparatus. According to this processing, the constant-voltage generating circuit13generates a constant voltage using a voltage outputted from the commercial power supply and supplies electric power to the load.

The CPU10atransmits a load power supply signal to the CPU7aof the step-down-output control and charge control circuit7(step S1601). The CPU10aoutputs an opening signal to the first opening and closing circuit from the port6(step S1602) and outputs a closing signal to the second opening and closing circuit from the port4(step S1603). When a relay is used for the second and the third opening and closing circuits, the CPU10acounts time N with the timer counter (step S1604). The CPU10aoutputs an opening signal to the third opening and closing circuit from the port5(step S1605).

FIG. 17is a flowchart of a procedure of the opening-and-closing-circuit control processing P3performed by the engine control unit of the image forming apparatus. According to this processing, a voltage outputted from the commercial power supply is stepped down and the charge accumulating unit is charged by the step-down voltage.

The CPU10aoutputs a closing signal to the first opening and closing circuit from the port6(step S1701) and outputs a closing signal to the second opening and closing circuit from the port4(step S1702). The CPU10aoutputs an opening signal to the third opening and closing circuit from the port5(step S1703). The CPU10atransmits a charge permission signal to the CPU7aof the step-down-output control and charge control circuit7(step S1704).

As described above, in this embodiment, in addition to the effects of the first embodiment, it is possible to supply electric power to the load even at the time of charge by closing the second opening and closing circuit. When it is unnecessary to supply electric power to the load, for example, at the time of the energy saving mode, it is possible reduce electric power by opening the second opening and closing circuit.

In this embodiment, when the second opening and closing circuit41and the third opening and closing circuit42are closed, in discharging a voltage at the capacitor bank9(supplying the voltage to the constant-voltage generating circuit13via the third opening and closing circuit42), the step-down-output control and charge control circuit7outputs a PWM signal for stepping down the voltage to an input voltage, which allows the constant-voltage generating circuit13to generate a constant voltage, to the gate of the FET51of the step-down chopper circuit50. Consequently, the capacitor bank9starts discharge and the voltage is supplied from the capacitor bank9to the constant-voltage generating circuit13. When the voltage supplied from the capacitor bank9is stepped down to the input voltage, which allows the constant-voltage generating circuit13to generate a constant voltage, the voltage supplied to the constant-voltage generating circuit13is switched to the voltage outputted from the step-down chopper circuit50.

As in the first embodiment, an engine power supply unit of an image forming apparatus according to a third embodiment of the present invention steps down a voltage outputted from the commercial power supply to charge a charge accumulating unit and changes a voltage outputted from the commercial power supply and a voltage outputted from the charge accumulating unit to constant voltages with a constant-voltage generating circuit to supply the voltages to the load. The third embodiment is different from the first embodiment in that a first opening and closing circuit is used instead of the first switching circuit and a second opening and closing circuit is used instead of the second switching circuit.

Concerning an example of a structure of an engine power supply unit300to which the present invention is applied, differences from the first embodiment are explained. Explanations of components identical with those in the first embodiment are omitted.FIG. 18is a circuit diagram of a circuit configuration of an engine power supply unit of a printer according to the third embodiment.FIG. 19is a detailed circuit diagram of a detailed circuit configuration of the engine power supply unit of the printer according to the third embodiment.

The engine power supply unit300of the printer according to this embodiment includes the filter1, the full-wave rectifying circuit2, the step-down chopper circuit50, the step-down-voltage detecting circuit19, the capacitor bank9, the charge-voltage detecting circuit16, the constant-voltage generating circuit13, the charge-current detecting circuit12, the engine control unit10, the step-down-output control and charge control circuit7, the load20, the AC fixing heaters29and30, the heating-unit-temperature detecting circuits33and34, the AC-fixing-heater control circuit39, the first opening and closing circuit40, and a second opening and closing circuit43.

Structures and functions of the filter1, the full-wave rectifying circuit2, the step-down chopper circuit50, the step-down-voltage detecting circuit19, the capacitor bank9, the charge-voltage detecting circuit16, the constant-voltage generating circuit13, the charge-current detecting circuit12, the engine control unit10, the step-down-output control and charge control circuit7, the load20, the AC fixing heaters29and30, the heating-unit-temperature detecting circuits33and34, and the AC-fixing-heater control circuit39are the same as those in the first embodiment. Thus, explanations of the structures and the functions are omitted here

The first opening and closing circuit40opens and closes the connection between the output of the step-down chopper circuit50and the capacitor bank9. The second opening and closing circuit43connects the input of the constant-voltage generating circuit13and the capacitor bank9. As a characteristic of the circuits according to this embodiment, a voltage is always supplied to the constant-voltage generating circuit13via a diode. When electric power is discharged from the capacitor bank9, a voltage is not supplied from the capacitor bank9to the constant-voltage generating circuit13if a voltage at the step-down chopper circuit50is set lower than a voltage at the capacitor bank9. The first and the second opening and closing circuits according to this embodiment include FETs. It goes without saying that opening and closing circuit including relays, IGBTs, or the like may be used.

Opening and closing of the first opening and closing circuit40is controlled by outputting a signal for turning on and off the FET40afrom the port6of the engine control unit10to the gate of the FET40aof the first opening and closing circuit40. Opening and closing of the second opening and closing circuit43is controlled by outputting a signal for turning on and off a FET43afrom the port5of the engine control unit10to the gate of the FET43a. The first opening and closing circuit40and the second opening and closing circuit43are set to be opened in the normal close state. Therefore, when the main power supply is off, discharge from the capacitor bank9is stopped.

FIGS. 20A and 20Bare flowcharts of a procedure of operation mode control processing performed by the engine control unit of the image forming apparatus. The operation mode control processing is partially the same as the processing of the flowcharts shown inFIGS. 6A to 6Dexplained in the first embodiment. Thus, only differences are explained below. Since processing before step S2001is the same as that at steps S601to S609inFIG. 6A, the explanation with reference toFIG. 6Ais referred to. An explanation of the processing is omitted here.

When the CPU10aof the engine control unit10judges at step S609inFIG. 6Athat the heating unit has the reload temperature, the fixing device comes into the standby state, electric power at the normal time set in advance is supplied to the fixing heaters, and normal temperature control is carried out (step S2001).

The CPU10ajudges whether the fixing device is in the standby state again (step S2002). When it is judged that the fixing device is in the standby state (“Yes” at step S2002), the CPU10ajudges whether a charge voltage is lower than 35 volts, i.e., whether the capacitor cells are in the full-charge state (step S2003). When it is judged that the charge voltage is lower than 35 volts, i.e., the capacitor cells are not in the full-charge state (“Yes” at step S2003), the CPU10aperforms the opening-and-closing-circuit control processing P3(step S2004). Consequently, the capacitor bank9is charged. Thereafter, the CPU10areturns to step S2001. When it is judged that the charge voltage is not lower than 35 volts, i.e., the capacitor cells are in the full-charge state (“No” at step S2003), the CPU10aperforms the opening-and-closing-circuit control processing P2(step S2005). Consequently, electric power inputted from the commercial power supply is supplied to the load via the constant-voltage generating circuit13. Thereafter, the CPU10areturns to step S2001.

When it is judged at step S2002that the fixing device is not in the standby state (“No” at step S2002), the CPU10ajudges whether the image forming apparatus is performing a copy operation (step S2006). When it is judged that the image forming apparatus is performing the copy operation (“Yes” at step S2006), the CPU10aperforms the opening-and-closing-circuit control processing P2(step S2007). Consequently, electric power inputted from the commercial power supply is supplied to the load via the constant-voltage generating circuit13. The load performs an image forming operation and normal electric power is supplied to the AC fixing heaters29and30(step S2008).

The CPU10ajudges whether a job has been finished (step S2009). When it is judged that the job has been finished (“Yes” at step S2009), the CPU10acarries out processing of the energy saving mode described later. When it is judged that the job has not been finished (“No” at step S2009), the CPU10aacquires, from the power use table T1, the number of copies N and an accumulated electric power use time M corresponding to a present sheet size with which use power is equal to or larger than normal electric power (step S2010).

The CPU10ajudges whether a present number of copies is N (step S2011). When it is judged that the present number of copies is not N (“No” at step S2011), the CPU10areturns to step S2008and the image forming operation is continued. When it is judged that the present number of copies is N (“Yes” at step S2011), to prevent the temperature of the heating unit from falling to be lower than a fixed image guarantee temperature, the CPU10aperforms the opening-and-closing-circuit control processing P1(step S2012). Consequently, the supply of electric power from the commercial power supply is stopped. Moreover, electric power accumulated in the capacitor bank9is supplied to the constant-voltage generating circuit13. It is possible to supply excess electric power to the heating unit of the fixing device. As a result, it is possible to supply maximum electric power of the heater rating to the AC fixing heaters29and30.

The CPU10acontinues the state in which the maximum electric power is supplied to the AC fixing heaters29and30and continues the copy operation (step S2013). The temperature fall in the heating unit of the fixing device occurs because heat of a fixing pressure roller moves to a sheet when sheet supply is started. Therefore, when this pressure roller is warmed, the temperature fall is solved. The CPU10acounts the accumulated electric power use time M, which is time until the pressure roller is warmed, with the timer (step S2014). When it is judged that a timer count is not M (“No” at step S2014), the CPU10areturns to step S2013. The maximum electric power of the heater rating is supplied to the fixing heaters until the accumulated electric power use time M elapses.

When it is judged that the timer count is M (“Yes” at step S2014), the CPU10aperforms the opening-and-closing-circuit control processing P2(step S2015). Consequently, the electric power inputted from the commercial power supply is supplied to the load. The load continuously performs the image forming operation and the CPU10asupplies normal electric power to the fixing heaters (step S2016). The CPU10ajudges whether sheets of a number that should be discharged in one job have been discharged (step S2017). When it is judged that the sheets of the number that should be discharged in one job have not been discharged (“No” at step S2017), the CPU10areturns to step S2016and continues the image forming operation. When it is judged that the sheets of the number that should be discharged in one job have been discharged (“Yes” at step S2017), the CPU10aacquires, from the power use table T2, post-processing that requires supply of electric power (step S2018).

The CPU10ajudges whether supply of electric power is necessary for the post-processing to be carried out (step S2019). When it is judged that supply of electric power is necessary for the post-processing (“Yes” at step S2019), the CPU10aperforms the opening-and-closing-circuit control processing P1(step S2020). Consequently, electric power accumulated in the capacitor bank9is supplied to the constant-voltage generating circuit13. It is possible to increase an output of a DC power supply. For example, supply of electric power is performed when a binding operation of staple processing is performed as the post-processing. A post-processing peripheral apparatus supplied with the electric power carries out a post-processing operation (step S2021). Thereafter, the CPU10areturns to step S2001. When it is judged that supply of electric power is not necessary for the post-processing (“No” at step S2019), since the copy operation has been finished, the CPU10areturns to step S2001.

When it is judged at step S2006that the image forming apparatus is not performing the copy operation (“No” at step S2006) or when it is judged at step S2009that the job has not been finished (“No” at step S2009), a procedure of the processing is substantially the same as that of steps S625to S628of the flowcharts inFIG. 6D. Thus, the explanation with reference toFIG. 6Dis referred to. An explanation of the procedure is omitted here and only differences are explained below.

In this embodiment, processing for transmitting a step-down output stop signal is performed instead of steps S628and S629.

The opening-and-closing-circuit control processing P1in the flowcharts shown inFIGS. 6A to 6Dis replaced with opening-and-closing-circuit control processing P1shown inFIG. 21. The opening-and-closing-circuit control processing P2is replaced with opening-and-closing-circuit control processing P2shown inFIG. 22. The opening-and-closing-circuit control processing P3is replaced with opening-and-closing-circuit control processing P3shown inFIG. 23.

FIG. 21is a flowchart of a procedure of the opening-and-closing-circuit control processing P1performed by the engine control unit of the image forming apparatus. According to this processing, the constant-voltage generating circuit13generates a constant voltage using accumulated electric power of the capacitor bank9and supplies electric power to the load.

The CPU10atransmits a signal for using electric power of the charge accumulating unit to the CPU7aof the step-down-output control and charge control circuit7(step S2101). The CPU10aoutputs an opening signal to the first opening and closing circuit from the port6(step S2102) and outputs a closing signal to the second opening and closing circuit from the port5(step S2103).

FIG. 22is a flowchart of a procedure of the opening-and-closing-circuit control processing P2performed by the engine control unit of the image forming apparatus. According to this processing, the constant-voltage generating circuit13generates a constant voltage using a voltage outputted from the commercial power supply and supplies electric power to the load.

The CPU10atransmits a load power supply signal to the CPU7aof the step-down-output control and charge control circuit7(step S2201). The CPU10aoutputs an opening signal to the first opening and closing circuit from the port6(step S2202). The CPU10aoutputs an opening signal to the second opening and closing circuit from the port5(step S2203).

FIG. 23is a flowchart of a procedure of the opening-and-closing-circuit control processing P3performed by the engine control unit of the image forming apparatus. According to this processing, a voltage outputted from the commercial power supply is stepped down and the charge accumulating unit is charged with the step-down voltage.

The CPU10aoutputs a closing signal to the first opening and closing circuit from the port6(step S2301) and outputs an opening signal to the second opening and closing circuit from the port5(step S2302). The CPU10atransmits a charge permission signal to the CPU7aof the step-down-output control and charge control circuit7(step S2303).

As described above, in this embodiment, it is possible to simplify the opening and closing circuits and electric power is always supplied to the load. Since an output of the step-down chopper circuit50is reduced at the time of discharge, it is possible to automatically switch the input of the constant-voltage generating circuit13to the step-down chopper circuit50side when a voltage at the capacitor bank9falls because of discharge. In other words, when a voltage at the capacitor bank9is discharged (supplied to the constant-voltage generating circuit13via the second opening and closing circuit43), the step-down-output control and charge control circuit7according to this embodiment outputs a PWM signal for lowering a voltage to an input voltage, which allows the constant-voltage generating circuit13to generate a rated voltage, to the gate of the FET51of the step-down chopper circuit50. Consequently, when the capacitor bank9starts discharge and a voltage falls to the input voltage, which allows the constant-voltage generating circuit13to generate a rated voltage, the input of the constant-voltage generating circuit13automatically switches to the step-down chopper circuit50side.

An engine power supply unit of an image forming apparatus according to a fourth embodiment of the present invention charges a charge accumulating unit with a voltage outputted from the commercial power supply using a charging circuit and changes a voltage outputted from the commercial power supply and a voltage outputted from the charge accumulating unit to constant voltages with a constant-voltage generating circuit to supply the voltages to load. The fourth embodiment is different from the first embodiment in that a step-down circuit is not provided and the charge accumulating unit is charged by the charging circuit.

Concerning an example of a structure of an engine power supply unit400to which the present invention is applied, differences from the first embodiment are explained. Explanations of components identical with those in the first embodiment are omitted.FIG. 24is a circuit diagram of a circuit configuration of an engine power supply unit of a printer according to the fourth embodiment.FIG. 25is a detailed circuit diagram of a detailed circuit configuration of the engine power supply unit of the printer according to the fourth embodiment.

The engine power supply unit400of the printer according to this embodiment includes the filter1, the full-wave rectifying circuit2, a voltage detecting circuit70, a charging circuit60, the capacitor bank9, the charge-voltage detecting circuit16, the constant-voltage generating circuit13, the charge-current detecting circuit12, the engine control unit10, the step-down-output control and charge control circuit7, the load20, the AC fixing heaters29and30, the heating-unit-temperature detecting circuits33and34, the AC-fixing-heater control circuit39, a first opening and closing circuit66, and a second opening and closing circuit67.

Structures and functions of the filter1, the full-wave rectifying circuit2, the capacitor bank9, the charge-voltage detecting circuit16, the constant-voltage generating circuit13, the charge-current detecting circuit12, the engine control unit10, the step-down-output control and charge control circuit7, the load20, the AC fixing heaters29and30, the heating-unit-temperature detecting circuits33and34, and the AC-fixing-heater control circuit39are the same as those in the first embodiment. Thus, explanations of the structures and the functions are omitted here

The charging circuit60charges the capacitor bank9. The charging circuit60includes, as shown inFIG. 25, the charge-voltage detecting circuit16and the step-down-output control and charge control circuit7.

The charge circuit60is connected to input a DC voltage outputted from the full-wave rectifying circuit2to a primary coil61aof a high-frequency transformer61arranged in parallel with the smoothing capacitor C2. A FET64as switching means is connected to the primary coil61ain series. In a switching circuit including the FET64, when the FET64is switched (on and off) by a PWM signal outputted from the PWM-signal generating circuit7eof the step-down-output control and charge control circuit7, a switching current flows to the primary coil61a.

A switching voltage is induced in a secondary coil61bof the transformer61by the switching current on the primary side. If a conduction period of this switching frequency is changed, it is possible to control an output voltage. Diodes62and65are connected to the secondary coil61bof the transformer61as a rectifying circuit. The switching voltage is rectified by the rectifying circuit, smoothed by a choke coil63and the capacitor C1, and converted into a DC output. This DC output is supplied to the capacitor bank9via a diode D1. The smoothed DC voltage is supplied to the constant-voltage generating circuit13(a DC/DC converter) via the first opening and closing circuit66(a FET66a). This charge voltage is monitored by the step-down-output control and charge control circuit7and controlled by changing an ON duty of a PWM signal with the PWM-signal generating circuit7e.

The charge control circuit7detects a charge voltage at the capacitor bank9, a charge current, and an operation of a bypass circuit and applies constant current charge or constant power charge to the capacitor bank9. The charge control circuit7generates a PWM signal for applying constant current charge and constant power charge to the capacitor bank9. The charge control circuit7includes the CPU7a, the SIC7b, the A/D converter7c, the charge-current detecting circuit7d, the PWM-signal generating circuit7e, a ROM, a RAM, a timer, an interrupt control circuit, and an input/output port.

The charge control circuit7detects an inter-terminal voltage at the capacitor bank9according to an output of the charge-voltage detecting circuit16. When the inter-terminal voltage at the capacitor bank9is lower than a value set in advance, the step-down-output control and charge control circuit7detects inter-terminal voltages at the resistor R1connected to the capacitor bank9in series one by one. To perform constant current charge, the step-down-output control and charge control circuit7outputs a PWM signal set in advance in association with the inter-terminal voltage to a gate of the FET64. The PWM signal for performing constant current charge may be obtained using a table created in advance based on a relation between the inter-terminal voltage at the resistor R1and the ON duty of the PWM signal. Alternatively, the PWM signal may be calculated by an arithmetic operation.

The charge control circuit7may control the PWM signal with reference to only a charge current to obtain a charge current set in advance. When the capacitor bank9is not charged, to prevent a large rush current from flowing to the capacitor bank9, the step-down-output control and charge control circuit7may output the PWM signal to set the charge voltage low and gradually increase the charge voltage. When the inter-terminal voltage at the capacitor bank9is equal to or higher than the value set in advance, to perform constant power charge, the step-down-output control and charge control circuit7detects charge currents of the capacitor bank9and inter-terminal voltages at the capacitor bank9one by one. The charge control circuit7outputs a PWM signal for performing constant power charge set in advance based on the charge currents and the charge voltages detected to the gate of the FET64. The PWM signal is determined by detecting a charge current of the capacitor bank9and an inter-terminal voltage at the capacitor bank9and calculating a PWM signal for performing constant power charge set in advance based on the charge current and the charge voltage detected.

When the step-down-output control and charge control circuit7detects any one of the single-cell full-charge signals5, the step-down-output control and charge control circuit7outputs the PWM signal for performing constant current charge set in advance to the gate of the FET64again. When the step-down-output control and charge control circuit7detects full-charge signals6of all the capacitor cells, the step-down-output control and charge control circuit7outputs a signal for stopping the charge operation to the gate of the FET64.

In the capacitor bank9according to this embodiment, thirty-six capacitor cells (electric double layer capacitor cells, each of which has 2.5 volts when fully charged, are connected in series. Therefore, when the sixteen capacitor cells are fully charged, a voltage at 90 volts is accumulated. The accumulated electric power of the capacitor bank9is supplied to the constant-voltage generating circuit13via the second opening and closing circuit67.

The first opening and closing circuit66and the second opening and closing circuit67include FETs. The CPU10aperforms ON/OFF control for the FET66aaccording to a signal from the port4. The first opening and closing circuit66(the FET66a) is closed when a signal for turning on the FET66ais outputted and is opened when a signal for turning off the FET66ais outputted. ON/OFF and close or open of the second opening and closing circuit67(a FET67a) are controlled according to a signal outputted from the port5of the CPU10a.

When electric power is unnecessary, for example, at the time of standby or at the time of the energy saving mode, to charge the capacitor bank9, the CPU10aoutputs a signal for turning off the FET67afrom the port5and outputs a signal for turning off the FET66aor a signal for turning on the FET66afrom the port4. When the FET66ais turned ON, electric power is also supplied to the load side.

When electric power exceeds an AC power rating of the commercial power supply or when flicker occurs because of sudden fluctuation in a load on the image forming apparatus side, to use accumulated electric power in the capacitor bank9, the CPU10aoutputs a signal for turning on the FET67afrom the port5and outputs a signal for turning OFF the FET66afrom the port4.

To stop discharge at the normal time other than charge or discharge, the CPU10aoutputs a signal for turning off the FET67afrom the port5and outputs a signal for turning on the FET66afrom the port4. Consequently, the commercial power supply is connected to the input of the constant-voltage generating circuit13.

After the image forming operation is finished, since the image forming apparatus enters the energy saving mode when a fixed time elapses, the CPU10aoutputs a signal for stopping a part of power output to the DC/DC converter14from the port2. When the energy saving release SW24(a platen open SW, an original detection SW of an ADF, etc.) is turned on, the energy saving mode is released and the DC/DC converter14returns to the normal operation. The CPU10aalso has a function of detecting fall of the commercial power supply by detecting a DC voltage at the commercial power supply, supplying accumulated electric power from the capacitor bank9by opening the first opening and closing circuit66and closing the second opening and closing circuit67, and supplementing AC power with the electric power.

FIGS. 26A to 26Dare flowcharts of a procedure of operation mode control processing performed by the engine control unit of the image forming apparatus.

When DC power is supplied according to power-on of the main power supply or release of the energy saving mode, the CPU10aof the engine control unit10performs initial setting related to peripheral circuits of the engine control unit10and memories (step S2601). The CPU10ajudges, from a detection result of the charge-voltage detecting circuit16, whether a charge voltage is 90 volts, i.e., whether the capacitor cells are in the full-charge state (step S2602). When it is judged that the capacitor cells are fully charged (“Yes” at step S2602), the CPU10aperforms the opening-and-closing-circuit control processing P1(step S2603). Consequently, it is possible to stop supply of electric power from the commercial power supply and supply electric power accumulated in the capacitor bank9to the constant-voltage generating circuit13. As a result, excess electric power is supplied to the heating unit of the fixing device (step S2604). When it is judged that the capacitor cells are not fully charged (“No” at step S2602), the CPU10aproceeds to step S2604.

The CPU10ajudges from a result of detection by the charge-voltage detecting circuit16whether the charge voltage is equal to or higher than 60 volts (step S2605). When it is judged that the charge voltage is equal to or higher than 60 volts (“Yes” at step S2605), the CPU10ajudges that it is possible to use accumulated electric power and judges whether a heating unit temperature is equal to or higher than temperature set in advance (e.g., 175° C.) (step S2606). When it is judged that the heating unit temperature has not reached the temperature set in advance (“No” at step S2606), the CPU10areturns to step S2604and continues to supply the maximum electric power of the heater rating to the AC fixing heaters29and30.

When it is judged that the heating unit temperature is equal to or higher than the temperature set in advance (“Yes” at step S2606) or when it is judged that the charge voltage at the capacitor bank9is lower than 60 volts (“No” at step S2605), the CPU10aperforms the opening-and-closing-circuit control processing P2(step S2607). Consequently, electric power is supplied from the commercial power supply to the load.

The CPU10asupplies electric power at the normal time set in advance to the AC fixing heaters29and30of the fixing device (step S2608). The CPU10ajudges whether the heating unit has a reload temperature (e.g., 180° C.) (step S2609). When it is judged that the heating unit does not have the reload temperature (“No” at step S2609), the CPU10areturns to step S2608. The supply of electric power at the normal time set in advance to the AC fixing heaters29and30is continued. When it is judged that the heating unit has the reload temperature (“Yes” at step S2609), the fixing device comes into the standby state and the supply of electric power at the normal time set in advance is continued (step S2601).

The CPU10ajudges whether the fixing device is in the standby state again (step S2611). When it is judged that the fixing device is in the standby state (“Yes” at step S2611), the CPU10ajudges whether a charge voltage is lower than 90 volts, i.e., whether the capacitor cells are in the full-charge state (step S2612). When it is judged that the charge voltage is lower than 90 volts, i.e., the capacitor cells are not in the full-charge state (“Yes” at step S2612), the CPU10aperforms the opening-and-closing-circuit control processing P3(step S2613). Consequently, the capacitor bank9is charged. Thereafter, the CPU10areturns to step S2610. When it is judged that the charge voltage is not lower than 90 volts, i.e., the capacitor cells are fully charged (“No” at step S2612), the CPU10aperforms the opening-and-closing-circuit control processing P2(step S2614). Consequently, electric power inputted from the commercial power supply is supplied to the load via the constant-voltage generating circuit13. Thereafter, the CPU1areturns to step S2610.

When it is judged at step S2611that the fixing device is not in the standby state (“No” at step S2611), the CPU10ajudges whether the image forming apparatus is performing a copy operation (step S2615). When it is judged that the image forming apparatus is performing the copy operation (“Yes” at step S2615), the CPU10aperforms the opening-and-closing-circuit control processing P2(step S2616). Consequently, electric power inputted from the commercial power supply is supplied to the load via the constant-voltage generating circuit13. The load performs an image forming operation and normal electric power is supplied to the AC fixing heaters29and30(step S2617).

The CPU10ajudges whether a job has been finished (step S2618). When it is judged that the job has been finished (“Yes” at step S2618), the CPU10acarries out processing of the energy saving mode described later. When it is judged that the job has not been finished (“No” at step S2618), the CPU10aacquires, from the power use table T1, the number of copies N and an accumulated electric power use time M corresponding to a present sheet size with which use power is equal to or larger than normal electric power (step S2619).

The CPU10ajudges whether a present number of copies is N (step S2620). When it is judged that the present number of copies is not N (“No” at step S2620), the CPU10areturns to step S2617and the image forming operation is continued. When it is judged that the present number of copies is N (“Yes” at step S2620), to prevent the temperature of the heating unit from falling to be lower than a fixed image guarantee temperature, the CPU10aperforms the opening-and-closing-circuit control processing P1(step S2621). Consequently, the supply of electric power from the commercial power supply is stopped. Moreover, electric power accumulated in the capacitor bank9is supplied to the constant-voltage generating circuit13. It is possible to supply excess electric power to the heating unit of the fixing device. As a result, it is possible to supply maximum electric power of the heater rating to the AC fixing heaters29and30.

The CPU10acontinues the state in which the maximum electric power is supplied to the AC fixing heaters29and30and continues the copy operation (step S2622). The temperature fall in the heating unit of the fixing device occurs because heat of a fixing pressure roller moves to a sheet when sheet supply is started. Therefore, when this pressure roller is warmed, the temperature fall is solved. The CPU10acounts the accumulated electric power use time M, which is time until the pressure roller is warmed, with the timer (step S2623). When it is judged that a timer count is not M (“No” at step S2623), the CPU10areturns to step S2622. The maximum electric power of the heater rating is supplied to the fixing heaters until the accumulated electric power use time M elapses.

When it is judged that the timer count is M (“Yes” at step S2623), the CPU10aperforms the opening-and-closing-circuit control processing P2(step S2624). Consequently, the electric power inputted from the commercial power supply is supplied to the load. The load continuously performs the image forming operation and the CPU10asupplies normal electric power to the fixing heaters (step S2625). The CPU10ajudges whether sheets of a number that should be discharged in one job have been discharged (step S2626). When it is judged that the sheets of the number that should be discharged in one job have not been discharged (“No” at step S2626), the CPU10areturns to step S2625and continues the image forming operation. When it is judged that the sheets of the number that should be discharged in one job have been discharged (“Yes” at step S2626), the CPU10aacquires, from the power use table T2, post-processing that requires supply of electric power (step S2627).

The CPU10ajudges whether supply of electric power is necessary for the post-processing to be carried out (step S2628). When it is judged that supply of electric power is necessary for the post-processing (“Yes” at step S2628), the CPU10aperforms the opening-and-closing-circuit control processing P1(step S2629). Consequently, electric power accumulated in the capacitor bank9is supplied to the constant-voltage generating circuit13. It is possible to increase an output of a DC power supply. For example, electric power is supplied when a binding operation of staple processing is performed as the post-processing. A post-processing peripheral apparatus supplied with the electric power carries out a post-processing operation (step S2630). Thereafter, the CPU10areturns to step S2610. When it is judged that supply of electric power is not necessary for the post-processing (“No” at step S2628), since the copy operation has been finished, the CPU10areturns to step S2610.

When it is judged at step S2615that the image forming apparatus is not performing the copy operation (“No” at step S2615) or when it is judged at step S2618that the job has been finished (“Yes” at step S2618), the CPU10ajudges whether the image forming apparatus is in the energy saving mode (step S2631). When it is judge that the image forming apparatus is not in the energy saving mode (“No” at step S2631), the CPU10areturns to step S2610. When it is judged that the image forming apparatus is in the energy saving mode (“Yes” at step S2631), the CPU10ajudges whether a charge voltage is lower than 35 volts, i.e., whether the capacitor cells are in the full-charge state (step S2632). When it is judged that the charge voltage is lower than 35 volts, i.e., the capacitor cells are not in the full-charge state (“Yes” at step S2632), to charge the capacitor bank9, the CPU10aperforms the opening-and-closing-circuit control processing P3(step S2633) and returns to step S2631. Although not shown in this flowchart, when this charge operation is finished, the image forming apparatus control unit also shifts to the energy saving mode. When it is judged that the charge voltage is not lower than 35 volts, i.e., the capacitor cells are in the full-charge state (“No” at step S2634), the CPU10areturns to step S2631.

FIG. 27is a flowchart of a procedure of the opening-and-closing-circuit control processing P1performed by the engine control unit of the image forming apparatus. According to this processing, the constant-voltage generating circuit13performs constant voltage output control using the accumulated electric power of the capacitor bank9.

The CPU10atransmits a signal for using electric power of the charge accumulating unit (step S2701). The CPU10aoutputs a signal for opening the first opening and closing circuit (step S2702) and outputs a signal for closing the second opening and closing circuit (step S2703).

FIG. 28is a flowchart of a procedure of the opening-and-closing-circuit control processing P2performed by the engine control unit of the image forming apparatus. According to this processing, electric power is supplied to the load from the commercial power supply.

The CPU10atransmits a signal for supplying electric power to the load (step S2801). The CPU10aoutputs a signal for closing the first opening and closing circuit (step S2802) and outputs a signal for opening the second opening and closing circuit (step S2803).

FIG. 29is a flowchart of a procedure of the opening-and-closing-circuit control processing P3performed by the engine control unit of the image forming apparatus. According to this processing, the capacitor bank9is charged.

The CPU10aoutputs a signal for closing the first opening and closing circuit (step S2901) and outputs a signal for opening the second opening and closing circuit (step S2902). The CPU10atransmits a charge permission signal (step S2903).

FIGS. 30A and 30Bare flowcharts of a procedure of charge processing performed by the step-down-output control and charge control circuit of the image forming apparatus. According to this processing, the capacitor bank9is charged.

The charge control circuit7judges whether a charge permission signal is transmitted from the CPU10aof the engine control unit10(step S3001). When it is judged that the charge permission signal is not transmitted (“No” at step S3001), the processing is finished. When it is judged that the charge permission signal is transmitted (“Yes” at step S3001), the step-down-output control and charge control circuit7judges whether a charge voltage has reached 90 volts (step S3002). Specifically, the step-down-output control and charge control circuit7checks the charge voltage from a result of detection by the charge-voltage detecting circuit16and judges whether the capacitor cells are in the full-charge state. When it is judged that the charge voltage has reached 90 volts (“Yes” at step S3002), since it is unnecessary to charge the charge accumulating unit, the step-down-output control and charge control circuit7transmits a full-charge voltage signal to the CPU10aof the engine control unit10(step S3003) and finishes the processing.

When it is judged that the charge voltage has not reached 90 volts (“No” at step S3002), to perform a charge operation, the step-down-output control and charge control circuit7transmits a charge operation signal to the CPU10aof the engine control unit10(step S3004). The charge control circuit7judges whether the charge voltage is equal to or lower than 24 volts (step S3005). When it is judged that the charge voltage is equal to or lower than 24 volts (“Yes” at step S3005), the step-down-output control and charge control circuit7detects a charge current of the charge accumulating unit, i.e., the capacitor bank9(step S3006). To perform constant current charge, the step-down-output control and charge control circuit7outputs a PWM signal corresponding to the charge current to the gate of the FET64(step S3007). Returning to step S3005, the step-down-output control and charge control circuit7judges whether the charge voltage is equal to or lower than 24 volts. When it is judged that the charge voltage is equal to or lower than 24 volts, the step-down-output control and charge control circuit7repeats the charge operation.

When it is judged at step S3005that the charge voltage is not equal to or lower than 24 volts (“No” at step S3005), the step-down-output control and charge control circuit7detects a charge current and a charge voltage at the charge accumulating unit, i.e., the capacitor bank9(step S3008). To perform constant power charge, the step-down-output control and charge control circuit7outputs a PWM signal corresponding to the charge current and the charge voltage detected to the gate of the FET64(step S3009). The charge control circuit7judges whether there is any one of the single-cell full-charge signals (step S3010). When it is judged that there is no single-cell full-charge signal (“No” at step S3010), the CPU10areturns to step S3008.

When it is judged that there is any one of the single-cell full-charge signal (“Yes” at step S3010), the step-down-output control and charge control circuit7carries out constant current charge (step S3011). The charge control circuit7judges whether there is an all-cell full-charge signal (step S3012). When it is judged that there is the all-cell full-charge signal (“Yes” at step S3012), to stop the charge operation, the step-down-output control and charge control circuit7outputs a PWM signal to the gate of the FET64(step S3013). The charge control circuit7transmits the all-cell full-charge signal to the CPU10a(step S3014) and finishes the processing. When it is judged that there is no all-cell full-charge signal (“No” at step S3012), the CPU10areturns to step S3011and performs constant current charge.

In the circuit configuration according to this embodiment, it is possible to supply electric power to the load at the time of charge. It is also possible to isolate a power supply to the load when it is desired to reduce electric power as at the time of the energy saving mode. It is possible to reduce the number of capacitor cells in use connected in series by expanding a control input voltage range of a constant voltage power supply.

An engine power supply unit of an image forming apparatus according to a fifth embodiment of the present invention charges a charge accumulating unit with a voltage outputted from the commercial power supply using a charging circuit and changes a voltage outputted from the commercial power supply and a voltage outputted from the charge accumulating unit to constant voltages with a constant-voltage generating circuit to supply the voltages to load. The fifth embodiment is different from the fourth embodiment in that an opening and closing circuit is provided between a step-down circuit and a capacitor bank.

Concerning an example of a structure of an engine power supply unit500to which the present invention is applied, differences from the fourth embodiment are explained. Explanations of components identical with those in the fourth embodiment are omitted.FIG. 31is a circuit diagram of a circuit configuration of an engine power supply unit of a printer according to the fifth embodiment.FIG. 32is a detailed circuit diagram of a detailed circuit configuration of the engine power supply unit of the printer according to the fifth embodiment.

The engine power supply unit500of the printer according to this embodiment includes the filter1, the full-wave rectifying circuit2, the voltage detecting circuit70, a charging circuit60, the capacitor bank9, the charge-voltage detecting circuit16, the constant-voltage generating circuit13, the charge-current detecting circuit12, the engine control unit10, the load20, the AC fixing heaters29and30, the heating-unit-temperature detecting circuits33and34, the AC-fixing-heater control circuit39, a first opening and closing circuit76, a second opening and closing circuit77, and a third opening and closing circuit78.

Structures and functions of the filter1, the full-wave rectifying circuit2, the capacitor bank9, the charge-voltage detecting circuit16, the constant-voltage generating circuit13, the charge-current detecting circuit12, the engine control unit10, the load20, the AC fixing heaters29and30, the heating-unit-temperature detecting circuits33and34, and the AC-fixing-heater control circuit39are the same as those in the first and the fourth embodiments. Thus, explanations of the structures and the functions are omitted. The fifth embodiment is different from the fourth embodiment in that the first opening and closing circuit76, the second opening and closing circuit77, and the third opening and closing circuit78are provided instead of the first opening and closing circuit66and the second opening and closing circuit67.

The first opening and closing circuit76opens and closes the connection between the commercial power supply and the charging circuit60. The second opening and closing circuit77connects the commercial power supply and constant-voltage power supply unit. The third opening and closing circuit78opens and closes the connection between the capacitor bank9and the constant-voltage generating circuit13. The constant-voltage generating circuit13uses an output of the second opening and closing circuit or the third opening and closing circuit as an input and generates a constant voltage.

When the capacitor bank9is charged, the CPU10acloses the first opening and closing circuit76(turns on a FET76a), closes the second opening and closing circuit77(turns off a FET77a) or closes the second opening and closing circuit77(turns on the FET77a), and opens the third opening and closing circuit78(turns off a FET78a). By closing the second opening and closing circuit77in this way, it is possible to supply a voltage to the constant-voltage generating circuit13even at the time of charge. In charging the charge accumulating unit when it is unnecessary to supply electric power to the load, for example, at the time of the energy saving mode, it is possible to reduce electric power by opening the second opening and closing circuit77.

When electric power of the capacitor bank9is used, the CPU10aopens the first opening and closing circuit76(turns off the FET76a), opens the second opening and closing circuit77(turns off the FET77a), and closes the third opening and closing circuit78(turns on the FET78a).

When electric power is supplied from the commercial power supply to the constant-voltage generating circuit13, the CPU10aopens the first opening and closing circuit76(turns off the FET76a), closes the second opening and closing circuit77(turns on the FET77a), and opens the third opening and closing circuit78(turns off the FET78a). When the third opening and closing circuit78is opened, electric power is continuously supplied to the constant-voltage generating circuit13if the second opening and closing circuit77is closed and then the third opening and closing circuit78is opened. When the second opening and closing circuit77is opened, electric power is continuously supplied to the constant-voltage generating circuit13if the third opening and closing circuit78is closed and then the second opening and closing circuit77is opened.

FIGS. 33A and 33Bare flowcharts of a procedure of operation mode control processing performed by the engine control unit of the image forming apparatus.

The procedure of the operation mode control processing according to this embodiment is the same as a part of the flowcharts shown inFIGS. 26A to 26D. Thus, only differences are explained. Since processing before step S3301is the same as the processing at steps S2601to S2609inFIG. 26A, the explanation with reference toFIG. 26Ais referred to. An explanation of the processing is omitted here.

When the CPU10aof the engine control unit10judges at step S2609inFIG. 26Athat the heating unit has the reload temperature, the fixing device comes into the standby state. Electric power at the normal time set in advance is supplied to the fixing heaters and normal temperature control is carried out (step S3301).

The CPU10ajudges whether the fixing device is in the standby state again (step S3302). When it is judged that the fixing device is in the standby state (“Yes” at step S3302), the CPU10ajudges whether a charge voltage is lower than 90 volts, i.e., the capacitor cells are in the full-charge state (step S3303). When it is judged that the charge voltage is lower than 90 volts, i.e., the capacitor cells are not in the full-charge state (“Yes” at step S3303), the CPU10aperforms the opening-and-closing-circuit control processing P3(step S3304) and returns to step S3301. Consequently, the capacitor bank9is charged. When it is judged that the charge voltage is not lower than 90 volts, i.e., the capacitor cells are in the full-charge state (“No” at step S3303), the CPU10aperforms the opening-and-closing-circuit control processing P2(step S3305) and returns to step S3301. Consequently, electric power is supplied to the load from the commercial power supply.

When it is judged at step S3302that the fixing device is not in the standby state (“No” at step S3302), the CPU10asets an operation mode or an operation condition for using accumulated electric power with reference to the power use tables T1and T2defining use of accumulated electric power for each operation mode and image forming operation process (step S3306). For example, the CPU10aacquires, from the power use tables T1and T2, setting of the number of copies with which the temperature of the heating unit falls according to the number of continuous copies, a timer count of time when the temperature of the heating unit recovers when maximum power is supplied to the fixing heaters, i.e., accumulated electric power of the capacitor bank9is used, and post-processing that requires supply of electric power and sets the setting of the number of copies, the timer count, and the post-processing.

The CPU10ajudges whether the image forming apparatus is performing a copy operation (step S3307). When it is judged that the image forming apparatus is performing a copy operation (“Yes” at step S3307), the CPU10ajudges whether there is the setting of the number of copies acquired from the power use tables T1and T2(step S3308). When it is judged that there is the setting of the number of copies (“Yes” at step S3308), to supply electric power to the load from the commercial power supply, the CPU10aperforms plural copy processing (step S3309). Since the plural copy processing is the same as that of the flowchart inFIG. 7in the first embodiment,FIG. 7and the explanation with reference toFIG. 7are referred to. An explanation of the plural copy processing is omitted here.

The CPU10aperforms the opening-and-closing-circuit control processing P2(step S3310). The load continuously performs the image forming operation and normal electric power is supplied to the fixing heaters (step S3311). The CPU10ajudges whether sheets of a number corresponding to one job have been discharged (step S3312). When it is judged that the sheets of the number corresponding to one job have not been discharged (“No” at step S3312), the CPU10areturns to step S3311. The load continues the image forming operation. When it is judged that the sheets of the number corresponding to one job have been discharged (“Yes” at step S3312), the CPU10ajudges whether supply of electric power is necessary for post-processing (step S3313).

When it is judged that supply of electric power is necessary for post-processing (“Yes” at step S3313), to increase an output of the DC power supply, the CPU10aperforms the opening-and-closing-circuit control processing P1(step S3314). Consequently, power accumulated in the capacitor bank9is supplied to the constant-voltage generating circuit13. A post-processing peripheral apparatus supplied with the electric power carries out a post-processing operation (step S3315). The CPU10areturns to step S3301. When it is judged that supply of electric power to the post-processing is unnecessary (“No” at step S3313), since the copy operation is finished, the CPU10areturns to step S3301.

When it is judged at step S3307that the image forming apparatus is not performing the copy operation (“No” at step S3307), since a procedure of the processing is the same as that at steps S2631to S2534of the flowchart inFIG. 26D, the explanation with reference toFIG. 26Dis referred to. An explanation of the processing is omitted here.

FIG. 34is a flowchart of a procedure of the opening-and-closing-circuit control processing P1performed by the engine control unit of the image forming apparatus. According to this processing, the constant-voltage generating circuit13performs constant voltage output control using accumulated electric power of the capacitor bank9.

The CPU10atransmits a signal for using electric power of the charge accumulating unit (step S3401). The CPU10aoutputs a signal for opening the first opening and closing circuit (step S3402). The CPU10aoutputs a signal for closing the third opening and closing circuit (step S3403). When a relay is used for the second and the third opening and closing circuits, the CPU10acounts time N with the timer counter (step S3404). The CPU10aoutputs a signal for opening the second opening and closing circuit (step S3405).

FIG. 35is a flowchart of a procedure of the opening-and-closing-circuit control processing P2performed by the engine control unit of the image forming apparatus. According to this processing, electric power is supplied to the load from the commercial power supply.

The CPU10atransmits a load power supply signal (step S3501). The CPU10aoutputs a signal for opening the first opening and closing circuit (step S3502) and outputs a signal for closing the second opening and closing circuit (step S3503). When a relay is used for the second and the third opening and closing circuits, the CPU10acounts the time N with the timer counter (step S3504). The CPU10aoutputs a signal for opening the third opening and closing circuit (step S3505).

FIG. 36is a flowchart of a procedure of the opening-and-closing-circuit control processing P3performed by the engine control unit of the image forming apparatus. According to this processing, the capacitor bank9is charged.

The CPU10aoutputs a signal for closing the first opening and closing circuit (step S3601) and outputs a signal for closing the second opening and closing circuit (step S3602). The CPU10aoutputs a signal for opening the third opening and closing circuit (step S3603) and transmits a charge permission signal (step S3604).

As described above, in addition to the effects of the fourth embodiments, in the circuit configuration according to this embodiment, when electric power is supplied to the load, it is possible to interrupt connection to the charge circuit by opening the first opening and closing circuit. In the case of a light load at the time of standby or the like, it is possible to supple electric power to the load even at the time of charge by closing the first opening and closing circuit and the second opening and closing circuit. When it is unnecessary to supply electric power to the load at the time of the energy saving mode or the like, it is possible to reduce electric power by opening the second opening and closing circuit.

The present invention has been explained using the first to the fifth embodiments. However, it is possible to apply various alterations or modifications to the embodiments. It is possible to freely combine the components and the functions explained in the first to the fifth embodiments.

The respective circuits described in the embodiments may be formed as a program stored in a storage medium. A control program executed in the printer according to the embodiments is stored in a ROM or the like in advance and provided.

The control program executed in the printer according to the embodiments may be recorded in a computer-readable recording medium such as a compact disk-read only memory (CD-ROM), a flexible disk (FD), a compact disk-recordable (CD-R), or a digital versatile disk (DVD) in an installable format or an executable format and provided.

The control program executed in the printer according to the embodiments may be stored on a computer connected to a network such as the Internet, downloaded through the network, and provided. The control program executed in the printer according to the embodiments may be provided or distributed through the network such as the Internet.

The control program executed in the printer according to the embodiments is formed as a module including the respective units (the engine control unit, etc.) described above. As actual hardware, when a CPU (a processor) reads out the control program from the ROM and executes the control program, the respective units are loaded on a main storage device and the engine control unit and the like are generated on the main storage device.

The power use tables T1and T2may be stored in a ROM in advance and may be constituted by any kind of storage medium generally used such as a hard disk (HD), an optical disk, or a memory card.

FIG. 37is a diagram for explaining an example of a schematic structure of the printer according to the embodiments. InFIG. 37, mechanical units of the image forming apparatus according to the first to the fifth embodiments are schematically shown. The printer as the image forming apparatus includes an intermediate transfer unit in the center thereof. The intermediate transfer unit includes an intermediate transfer belt110as an endless belt. The intermediate transfer belt110is, for example, a plural-layer belt in which an elastic layer is provided on a base layer formed of a less stretchable material such as canvas on fluoride fluorine resin with small stretch or a rubber material with large stretch. The elastic layer is obtained by forming a coat layer with high smoothness by coating, for example, fluorine resin on the surface of, for example, fluorine rubber or acrylonitrile-butadiene copolymer rubber.

The intermediate transfer belt110is wound around first to third support rollers114to116and driven to rotate clockwise. An intermediate-transfer-member cleaning unit117that removes a residual toner remaining on the intermediate transfer belt110after image transfer is provided on the left of a second support roller115.

Over the intermediate transfer belt110between the first support roller114and the second support roller115, there is an image forming device120including photosensitive member units140, charger units118, developing units, and cleaning units of colors black (K), yellow (Y), magenta (M), and cyan (C) along a moving direction of the intermediate transfer belt110. The image forming device120includes an IC tag and is detachably mounted on a printer body. Above the image forming device120, there is a writing unit121that irradiates a laser beam for image formation on respective photosensitive drums of the photosensitive units of the respective colors.

Below the intermediate transfer belt110, there is a secondary transfer unit122. In the secondary transfer unit122, a secondary transfer belt124as an endless belt is laid over between two rollers123. The secondary transfer unit122is arranged to push up the intermediate transfer belt110to press the intermediate transfer belt110against the third support roller116. The secondary transfer belt124transfers an image on the intermediate transfer belt110onto a sheet. Beside the secondary transfer unit122, there is a fixing unit125that fixes the transferred image on the sheet. A sheet having a toner image transferred thereon is fed to the fixing unit125. The fixing unit125is obtained by pressing a heating and pressing roller127against a fixing belt126as an endless belt. Below the secondary transfer unit122and the fixing unit125, there is a sheet reversing unit128that reverses a sheet just having an image formed on the front surface thereof to record an image on the rear surface thereof and feeds the sheet.

When a start switch of an operation unit (not shown) is pressed, an original on an original feeding stand130of an automatic document feeder (ADF)170is conveyed onto a contact glass132. When there is no original on the ADF, to read an original manually placed on the contact glass132, a scanner of an image reading unit171is driven and a first carriage123and a second carriage134are driven to perform reading and scanning. Light is emitted on the contact glass from a light source on the first carriage133. Reflected light from an original surface is reflected on a first mirror on the first carriage133, directed to the second carriage134, reflected on a mirror on the second carriage134, and focused on a charge coupled device (CCD)136as a reading sensor through a focusing lens135. Recording data of the respective colors K, Y, M, and C are generated based on an image signal obtained by the reading sensor136.

When the start switch is pressed, rotational drive of the intermediate transfer belt110is started and preparation for image formation of the respective units of the image forming device120is started. An image formation sequence for image formation of the respective colors is started. Exposure laser beams modulated based on the recording data of the respective colors are projected on the photosensitive drums for the respective colors. Toner images of the respective colors are superimposed and transferred onto the intermediate transfer belt110as one image. A sheet is fed to the secondary transfer unit122at such timing that, when the leading end of the toner image enters the secondary transfer unit122, the leading end thereof simultaneously enters the secondary transfer unit122. Consequently, the toner image on the intermediate transfer belt110is transferred onto the sheet. The sheet having the toner image transferred thereon is fed to the fixing unit125. The toner image is fixed on the sheet in the fixing unit125.

One of sheet feeding rollers142of a sheet feeding table172is selectively driven to rotate to deliver sheets from one of sheet feeding trays144provided in multiple stages in a sheet feeding unit143. One of the sheets is separated by a separating roller145, sent into a conveyance roller unit146, conveyed by a conveying roller147and guided to a conveying roller unit148in the printer100, and brought into contact with registration rollers149of the conveying roller unit148and stopped. Then, the sheet is delivered to the secondary transfer unit122at the timing described above. It is also possible to place sheets on a manual feed tray151and feed the sheet. When a user places the sheets on the manual feed tray151, the printer100drives to rotate the sheet feeding roller150to separate one of the sheets on the manual feed tray151and draw the sheet into a manual-feed sheet feeding path153and brings the sheet into contact with the registration rollers149to stop the sheet.

The sheet subjected to fixing processing in the fixing unit125and discharged is guided to a discharge roller156by a switching pawl155and stacked on a sheet discharge tray157. Alternatively, the sheet is guided to a sheet reversing unit128by the switching pawl155, reversed in the sheet reversing unit128, and guided to a transfer position again. After an image is recorded on the rear surface thereof, the sheet is discharged onto the sheet discharge tray157by the discharge roller156. On the other hand, a residual toner remaining on the intermediate transfer belt110after the image transfer is removed by the intermediate-transfer-member cleaning unit117. In this way, the printer prepares for the next image formation.

The registration rollers149are generally grounded for use. However, it is also possible to apply a bias voltage to the registration rollers149to remove paper powder of sheets. For example, the bias voltage is applied using a conductive rubber roller. The conductive rubber roller has a diameter of 18 millimeters. The surface of the conductive rubber roller is made of conductive NBR rubber with thickness of 1 millimeter. An electric resistance is about 109 Ωcm in a volume resistance of a rubber material. The paper surface after passing between the registration rollers149is charged slightly on a negative side. Thus, in the transfer from the intermediate transfer belt110to the sheet, a transfer condition may be changed from a transfer condition of the transfer performed without applying a voltage to the registration roller149. A voltage at about −800 volts is applied to a side to which a toner is transferred (the front side) of the intermediate transfer belt110. A voltage at about +200 volts is applied to the rear side by a transfer roller162.

FIG. 38is a longitudinal sectional side view of a schematic structure of the fixing device. As shown inFIG. 38, the fixing unit125includes a fixing roller129as a fixing member, a pressure roller127as a pressure member, and a pressing unit (not shown) that presses the pressure roller127against the fixing roller129with a fixed pressing force. The fixing roller129and the pressure roller127are driven to rotate by a driving mechanism (not shown).

The fixing device also includes a main heater29, an auxiliary heater30, and thermistors33aand34afor detecting surface temperature of the fixing roller129. The fixing heaters29and30are arranged inside the fixing roller129and heat the fixing roller129from the inside thereof to supply heat to the fixing roller129. The thermistors33aand34aare set in contact with the surface of the fixing roller129and detect surface temperature (fixing temperature) of the fixing roller129. The thermistor33ais arranged in a measurement area corresponding to the AC fixing heaters29. The thermistor34ais arranged in a measurement area corresponding to the auxiliary fixing heater30.

The AC fixing heaters29is turned on and heats the fixing roller129when the temperature of the fixing roller129has not reached a target temperature. The auxiliary fixing heater30also has a function of a supporting heater that supports warm-up of the fixing device using electric power of the charge accumulating unit, for example, at the time of warm-up from the time of power-on of the main power supply or at the time of an off mode for energy saving until it is possible to perform copying, i.e., at the time of warm-up of the fixing device. Therefore, the auxiliary fixing heater30is normally used at electric power slightly lower than rated electric power of heaters and used at the rated electric power when the temperature falls at the time of warm-up of the fixing device or at the time of continuous copying.

In such the fixing unit125, when a sheet bearing a toner image passes a nip section of the fixing roller129and the pressure roller127, the sheet is heated and pressed by the fixing roller129and the pressure roller127. Consequently, the toner image is fixed on the sheet.

FIG. 39is a schematic diagram of a post-processing apparatus. A branch section performs branch of sheets to a shift mode M1(upper sheet discharge), a shift mode M2(lower sheet discharge), a pre-stack mode, and a staple mode (lower sheet discharge) using an upper branch pawl180, a staple branch pawl182, and a pre-stack branch pawl183.

In the case of the staple mode for a plurality of documents, to reduce a standby time at the time of a staple operation, a first print of a second document is put on standby in a pre-stack tray184and, when a second print comes, sent to a staple tray186together with the second print.

An upper tray187and a lower tray188perform a side-shift operation for the trays at the time of a sort mode and lifting and lowering operations according to the number of prints to be discharged. In performing staple, sheets are gathered on the staple tray186, aligned by a roller and a jogger fence, and stapled by a stapler185. A punch unit181is driven by a punch motor and opens two punch holes in sheets.

FIG. 40is a schematic diagram of a stapler section. The staple tray186stacks sheets. The sheet stacked or a sheet bundle is subjected to stapling processing by the stapler185.

A power supply device according to a sixth embodiment of the present invention steps down a voltage outputted from the commercial power supply to charge a charge accumulating unit and changes a voltage outputted from the commercial power supply or a voltage outputted from the charge accumulating unit to constant voltages with a constant-voltage generating circuit to supply the voltages to load. The power supply device according to this embodiment is equivalent to the power supply unit in the engine power supply unit according to the first embodiment.

It is possible to mount the power supply device, to which the present invention is applied, on image forming apparatuses such as a copying machine other than the printer, a facsimile apparatus, and a multi function peripheral (MFP) in which a copying function, a printer function, and a facsimile function are combined.

FIG. 41is a circuit diagram of a circuit configuration of the power supply device according to the sixth embodiment.FIG. 42is a detailed circuit diagram of a detailed circuit configuration of the power supply device according to the sixth embodiment. In the figures, it is assumed that the power supply device shown inFIGS. 41 and 42are mounted on an engine unit of a printer.

A power supply device600according to this embodiment includes the filter1, the full-wave rectifying circuit2, the step-down chopper circuit50, the step-down-voltage detecting circuit19, the capacitor bank9, the charge-voltage detecting circuit16, the constant-voltage generating circuit13, the charge-current detecting circuit12, the step-down-output control and charge control circuit7, the first switching circuit55, and the second switching circuit56. An engine unit of a printer mounted with the power supply device600includes the engine control unit10, the load20, the AC fixing heaters29and30, the heating-unit-temperature detecting circuits33and34, and the AC-fixing-heater control circuit39.

Structures and functions of the filter1, the full-wave rectifying circuit2, the step-down chopper circuit50, the step-down-voltage detecting circuit19, the capacitor bank9, the charge-voltage detecting circuit16, the constant-voltage generating circuit13, the charge-current detecting circuit12, the step-down-output control and charge control circuit7, the first switching circuit55, and the second switching circuit56are substantially the same as those in the first embodiment. Thus, the above explanations are referred to and only differences are explained. The engine control unit10, the load20, the AC fixing heaters29and30, the heating-unit-temperature detecting circuits33and34, and the AC-fixing-heater control circuit39are the same as those in the first embodiment. Thus, only differences are explained below.

The step-down-output control and charge control circuit7detects a charge voltage at the capacitor bank9, a charge current, and an operation of a bypass circuit and applies constant current charge or constant power charge to the capacitor bank9. The step-down-output control and charge control circuit7has a function of generating a PWM signal for applying constant current charge and constant power charge to the capacitor bank9and a function of supplying a step-down voltage to the constant-voltage generating circuit13via the first switching circuit and the second switching circuit56. The step-down-output control and charge control circuit7includes the CPU7a, the SIC7b, the A/D converter7c, the charge-current detecting circuit7d, the PWM-signal generating circuit7e, a ROM, a RAM, a timer, an interrupt control circuit, and an input/output port7f. Since an operation of the step-down-output control and charge control circuit7is the same as that in the first embodiment, the above explanations are referred to and an explanation of the operation is omitted here.

In the step-down-output control and charge control circuit7, when a load power supply signal is outputted from the CPU10aof the engine control unit10to the CPU7a, a PWM signal set in advance is outputted from the PWM signal generating circuit7eto the gate of the FET51. In the step-down chopper circuit50, a step-down voltage is generated by the PWM signal and a voltage is supplied as an input to the constant-voltage generating circuit13via the first switching circuit55and the second switching circuit56. A PWM signal of a fixed duty ratio may be outputted to the step-down chopper circuit50. A step-down voltage may be detected by the step-down-voltage detecting circuit19and fed back to the step-down-output control and charge control circuit7to generate a fixed voltage. A voltage value to be stepped down may be outputted from the CPU10aof the engine control unit10to the CPU7aof the step-down-output control and charge control circuit7and determined. The step-down chopper circuit50may switch the primary coil50bof the high-frequency transformer50ashown inFIG. 3with the FET50d, rectify a voltage induced in the secondary coil50c, and generate a step-down voltage. The step-down chopper circuit50may generate a step-down voltage with the step-down chopper circuit described above.

The first switching circuit55includes the relay55a. The second switching circuit56includes the relay56a. It goes without saying that an opening and closing circuit including an FET, an IGBT, or the like instead of the relay may be used. The relays55aand56aare set to be connected to the commercial power supply (the step-down chopper circuit50) side in a normal close state (a state in which a coil is not conductive). Therefore, when a main power supply is off, discharge from the capacitor bank9is stopped.

Timing for switching the first switching circuit55and the second switching circuit56is outputted from the CPU10aof the engine control unit10via a communication interface between the SIC7bconnected to the CPU7aof the step-down-output control and charge control circuit7and a serial controller (SIC) connected to the CPU10aof the engine control unit10. When the switching timing is outputted from the CPU10a, the CPU7aof the step-down-output control and charge control circuit7outputs a signal for switching the relay55or the relay56to a drive circuit26for the relays55aand56afrom the input/output port7f.

When electric power is unnecessary at the time of standby, the energy saving mode, or the like, to charge the capacitor bank9, the CPU10atransmits a signal for energizing the relay55ato the step-down-output control and charge control circuit7via the serial controller (SIC)10d. The CPU10atransmits a signal for stopping the energization of the relay56ato the step-down-output control and charge control circuit7via the serial controller (SIC)10d.

When electric power exceeds an AC power rating of the commercial power supply or when flicker occurs because of sudden fluctuation in a load on the image forming apparatus side, to use accumulated electric power in the capacitor bank9, the CPU10aoutputs a signal for stopping the energization of the relay55ato the step-down-output control and charge control circuit7and outputs a signal for energizing the relay56ato the step-down-output control and charge control circuit7.

At the normal time other than charge or discharge, the CPU10aoutputs a signal for stopping the energization of the relay55ato the step-down-output control and charge control circuit7. The CPU10aoutputs a signal for stopping the energization of the relay56ato the step-down-output control and charge control circuit7. Consequently, the output of the step-down chopper circuit50is connected to the input of the constant-voltage generating circuit13.

After the image forming operation is finished, since the image forming apparatus enters the energy saving mode when a fixed time elapses, the CPU10aoutputs a signal for stopping a part of power output to the DC/DC converter14from the port2. When an energy saving release switch (SW)24(a platen open SW, an original detection SW of an ADF, etc.) returns to a normal operation and the energy saving mode is released.

FIG. 43is a detailed circuit diagram of capacitor cells and an equalizing circuit. In the circuit diagram shown inFIG. 43, bypass circuits17aare connected in parallel to the capacitor cells9a. Fourteen bypass circuit17aare connected in series to each of eighteen capacitor cells9a. The capacitor bank9is an electric double layer capacitor connected in series to store electric power.

The bypass circuit17ais connected in parallel between terminals of the capacitor cell9a. The bypass circuit17aincludes a shunt regulator X1, resistors R1to R5, a transistor Q1, and a diode D1. Detection of a terminal voltage at the capacitor cell9ais performed by a voltage dividing circuit including resisters R1and R2and the shunt regulator X1. When a divided voltage at the voltage dividing circuit including the resistors R1and R2is inputted to a control terminal of the shunt regulator X1and the terminal voltage at the capacitor cell9ais charged to a predetermined voltage, the shunt regulator X1is turned on.

When the shunt regulator X1is turned on, a base current flows to the transistor Q1through the resistor R3and the transistor Q1is turned on. When the transistor Q1is turned on, a charge current of the capacitor cell9ais bypassed in a current direction12by an electric current determined by the resistor R5. When the transistor Q1is turned on, the transistor Q2is turned on. An electric current flows to light-emitting diodes of photo-couplers TLP1and TLP2through resistors R7and R8.

Since a Bank Full terminal is connected in series to the other bypass circuit17a, all the capacitor cells9aare charged to a predetermined voltage. When all the bypass circuit17aoperate, an all-cell full-charge signal is outputted. According to this signal, the PWM signal generating circuit7eof the step-down-output control and charge control circuit7shown inFIG. 42stops the charge.

Cell Full terminals of the bypass circuit17aare connected in parallel. When the capacitor cell9aconnected to any one of the bypass circuit17ais charged to the predetermined voltage and the bypass circuit17aoperates, a cell full-charge signal is outputted. The cell full-charge signal is inputted to the step-down-output control and charge control circuit7shown inFIGS. 41 and 42. The step-down-output control and charge control circuit7performs a predetermined constant current charge operation according to the cell full-charge signal. The other bypass circuits17ahave the same functions and structures as the bypass circuit17adescribed above, explanations of the other bypass circuits17aare omitted here.

FIGS. 44A to 44Care flowcharts of a procedure of step-down output control performed by the power supply device and step-down-voltage control and charge control processing performed by the step-down-output control and charge control circuit. According to this processing, the capacitor bank9is charged. An output of the commercial power supply is stepped down by the step-down chopper circuit50.

The CPU7aof the step-down-output control and charge control circuit7judges whether a charge permission signal is transmitted from the CPU10aof the engine control unit10(step S4401). When it is judged that the charge permission signal is transmitted (“Yes” at step S4401), the CPU7ajudges whether a charge voltage has reached 35 volts (step S4402). Specifically, the CPU7achecks the charge voltage from a result of detection by the charge-voltage detecting circuit16and judges whether the capacitor cells are in the full-charge state. When it is judged that the charge voltage has reached 35 volts (“Yes” at step S4402), since it is necessary to charge the capacitor bank9, the CPU7atransmits a full-charge voltage signal to the CPU10aof the engine control unit10(step S4403) and finishes the processing.

When it is judged that the charge voltage has not reached 35 volts (“No” at step S4402), to perform a charge operation, the CPU7atransmits a charge operation signal to the CPU10aof the engine control unit10(step S4404). The CPU7ajudges whether the charge voltage is equal to or lower than 24 volts (step S4405). When it is judged that the charge voltage is equal to or lower than 24 volts (“Yes” at step S4405), the CPU7adetects a charge current of the charge accumulating unit, i.e., the capacitor bank9(step S4406). To perform constant current charge, the CPU7aoutputs a PWM signal corresponding to the charge current detected from the PWM-signal generating circuit7eto the gate of the FET51of the step-down chopper circuit50(step S4407). Returning to step S4405, the CPU7ajudges whether the charge voltage is equal to or lower than 24 volts. When it is judged that the charge voltage is equal to or lower than 24 volts, the CPU7arepeats the charge operation described above.

When it is judged at step S4405that the charge voltage is not equal to or lower than 24 volts (“No” at step S4405), the CPU7adetects a charge current and a charge voltage at the charge accumulating unit, i.e., the capacitor bank9(step S4408). To perform constant power charge, the CPU7aoutputs a PWM signal corresponding to the charge current and the charge voltage detected from the PWM-signal generating circuit7eto the gate of the FET51(step S4409). The CPU7ajudges whether there is any one of single-cell full-charge signals (step S4410). When it is judged that there is no single-cell full-charge signal (“No” at step S4410), the CPU7areturns to step s4408.

When there is any one of the single-cell full-charge signals (“Yes” at step s4410), the CPU7acarries out constant current charge (step S4411). The CPU7ajudges whether there is an all-cell full-charge signal (step S4412). When it is judged that the all-cell full-charge signal (“Yes” at step S4412), to stop the charge operation, the CPU7aoutputs a PWM signal to the gate of the FET51(step S4413). The CPU7atransmits the all-cell full-charge signal to the CPU10a(step S4414) and finishes the processing. When it is judged that there is no all-cell full-charge signal (“No” at step S4412), the CPU7areturns to step S4411and performs constant current charge.

When it is judged at step S4401that the charge permission signal is not transmitted (“No” at step4401), the CPU7ajudges whether there is an image forming operation signal, i.e., the image forming operation signal is outputted from the CPU10a(step S4415). When it is judged that there is the image forming operation signal (“Yes” at step s4415), the CPU7adetects a voltage outputted from the step-down chopper circuit50with the step-down-voltage detecting circuit19(step S4416). The CPU7ajudges whether the voltage outputted from the step-down chopper circuit50is 30 volts (step S4417). This step-down voltage is set in advance to be lower than a charge voltage at the capacitor bank9. When the respective capacitor cells are fully charged, a voltage at the capacitor bank9is higher than 30 volts.

When it is judged that the voltage outputted from the step-down chopper circuit50is not 30 volts (“No” at step S4417), the CPU7aoutputs a PWM signal corresponding to the step-down voltage detected from the PWM-signal generating circuit7eto set the step-down voltage to 30 volts (step S4418). As this PWM signal, a PWM signal associated with the step-down voltage detected may be set in a table in advance. A PWM signal may be generated by an analog circuit by comparing a comparative-signal generating circuit (a triangular wave) and an analog voltage set in advance (a voltage for outputting 30 volts).

When it is judged that the voltage outputted from the step-down chopper circuit50is 30 volts (“Yes” at step S4417), the CPU7areturns to step S4416. The CPU7arepeats such an operation to maintain the step-down voltage at 30 volts with the PWM-signal generating circuit7e.

When it is judged at step S4415that there is no image forming operation signal (“No” at step S4415), the CPU7ajudges whether there is a load power supply signal, i.e., whether the load power supply signal is outputted from the CPU10a(step S4419). When it is judged that there is no load power supply signal (“No” at step S4419), the CPU7aproceeds to step S4416. When it is judged that there is the load power supply signal (“Yes” at step S4419), the CPU7ajudges whether there is a power use signal for using electric power of the charge accumulating unit, i.e., whether the power use signal for using electric power of the charge accumulating unit is outputted from the CPU10a(step S4420). When it is judged that there is no power use signal for using electric power of the charge accumulating unit (“No” at step S4420), the CPU7afinishes the processing.

When it is judged that there is the power use signal for using electric power of the charge accumulating unit (“Yes” at step S4420), the CPU7adetects a voltage outputted from the step-down chopper circuit50with the step-down-voltage detecting circuit19(step S4421). The CPU7ajudges whether the voltage outputted from the step-down chopper circuit50is 28 volts (step S4422). This step-down voltage is a voltage set such that the capacitor bank9starts discharge and the voltage falls to a voltage equal to or lower than 28 volts, the output of the step-down chopper circuit50automatically changes to the input of the constant-voltage generating circuit13.

When it is judged that the voltage outputted from the step-down chopper circuit50is not 28 volts (“No” at step S4422), the CPU7aoutputs a PWM signal corresponding to the detected step-down voltage from the PWM-signal generating circuit7eto the gate of the FET51of the step-down chopper circuit50to set the step-down voltage to 28 volts (step S4423). As this PWM signal, a PWM signal associated with the step-down voltage detected may be set in a table in advance. A PWM signal may be generated by an analog circuit by comparing a comparative-signal generating circuit (a triangular wave) and an analog voltage set in advance (a voltage for outputting 28 volts). When it is judged that the voltage outputted from the step-down chopper circuit50is 28 volts (“Yes” at step S4422), the CPU7areturns to step S4421. The CPU7arepeats such an operation to maintain the step-down voltage at 28 volts with the PWM-signal generating circuit7e.

FIGS. 45A to 45Dare flowcharts of a procedure of operation mode control processing performed by the engine control unit of the image forming apparatus.

When DC power is supplied according to power-on of the main power supply or release of the energy saving mode, the CPU10aof the engine control unit10performs initial setting related to the CPU10aof the engine control unit10, the peripheral circuit of the CPU10a, and the memories (step S4501). The CPU10ajudges whether a fixing temperature is equal to or lower than the fixed temperature with the heating-unit-temperature detecting circuits33and34(step S4502). The set temperature is set to temperature at which time until the fixing device reaches a reload temperature (e.g., 180° C.) according to power-on of the main power supply or release of the energy saving mode is time set in advance. As the set temperature is higher, the reload time is shorter.

When it is judged that the fixing temperature is equal to or lower than the set temperature (“Yes” at step S4502), the CPU10ajudges from a result of detection by the charge-voltage detecting circuit16whether a charge voltage is equal to or higher than 30 volts (step S4503). When it is judged that the charge voltage is equal to or higher than 30 volts (“Yes” at step S4503), the CPU10aperforms the opening-and-closing-circuit control processing P1(step S4504). Consequently, it is possible to stop supply of electric power from the commercial power supply and supply electric power accumulated in the capacitor bank9to the constant-voltage generating circuit13. As a result, excess electric power is supplied to the heating unit of the fixing device and maximum electric power is supplied to the fixing heaters (step S4505). At the time of the normal operation, electric power is not supplied at 10% duty. Electric power may be supplied only at the time of warm-up of the fixing heater30as an auxiliary heater or at the time when a fixing temperature falls.

The CPU10ajudges from a result of detection by the charge-voltage detecting circuit16whether a charge voltage is equal to or higher than 28 volts (step S4506). When it is judged that the charge voltage is equal to or higher than 28 volts (“Yes” at step S4506), the CPU10ajudges that it is possible to use accumulated electric power and judges whether a heating unit temperature is equal to or higher than temperature set in advance (e.g., 175° C.) (step S4507). When it is judged that the heating unit temperature has not reached the temperature set in advance (“No” at step S4507), the CPU10areturns to step S4505and continues to supply maximum electric power of the heater rating of the AC fixing heaters29and30.

When it is judged that the heating unit temperature is equal to or higher than the temperature set in advance (“Yes” at step S4507), when it is judged at step S4502that the fixing temperature is not equal to or lower than the set temperature (“No” at step S4502), when it is judged at step S4503that the charge temperature is not equal to or higher than 30 volts (“No” at step S4503), or when it is judged at step S4506that the charge voltage at the capacitor bank9is not equal to or higher than 28 volts (“No” at step S4506), the CPU10aperforms the opening-and-closing-circuit control processing P2(step S4508). Consequently, electric power is supplied from the commercial power supply (the step-down chopper circuit50) to the load.

The CPU10asupplies electric power at the normal time set in advance to the AC fixing heaters29and30of the fixing device (step S4509). The CPU10ajudges whether the heating unit has a reload temperature (e.g., 180° C.) (step S4510). When it is judged that the heating unit does not have the reload temperature (“No” at step S4510), the CPU10areturns to step S45009and the supply of electric power at the normal time set in advance to the AC fixing heaters29and30is continued. When it is judged that the heating unit has the reload temperature (“Yes” at step S4510), the fixing device comes into the standby state, the electric power at the normal time set in advance is supplied to the fixing heaters, and normal temperature control is carried out (step S4511).

The CPU10ajudges whether the fixing device is in the standby state again (step S4512). When it is judged that the fixing device is in the standby state (“Yes” at step S4512), the CPU10ajudges whether a charge voltage is lower than 35 volts (step S4513). When it is judged that the charge voltage is lower than 35 volts (“Yes” at step S4513), the CPU10aperforms the opening-and-closing-circuit control processing P3(step S4514) and returns to step S4511. Consequently, the capacitor bank9is charged. When it is judged that the charge voltage is not lower than 35 volts (“No” at step S4513), the CPU10aperforms the opening-and-closing-circuit control processing P2(step S4515) and returns to step S4511. Consequently, electric power is supplied from the commercial power supply (the step-down chopper circuit50) to the load.

When it is judged at step S4512that the fixing device is not in the standby state (“No” at step S4512), the CPU10asets an operation mode or an operation condition for using accumulated electric power with reference to the power use tables T1and T2defining use of accumulated electric power for each operation mode and image forming operation process (step S4516). For example, the CPU10aacquires, from the power use tables T1and T2, setting of the number of copies with which the temperature of the heating unit falls according to the number of continuous copies, a timer count of time when the temperature of the heating unit recovers when maximum power is supplied to the fixing heaters, i.e., accumulated electric power of the capacitor bank9is used, and post-processing that requires supply of electric power and sets the setting of the number of copies, the timer count, and the post-processing.

The CPU10ajudges whether the image forming apparatus is performing a copy operation (step S4517). When it is judged that the image forming apparatus is performing a copy operation (“Yes” at step S4517), the CPU10ajudges whether there is the setting of the number of copies acquired from the power use tables T1and T2(step S4518). When it is judged that there is the setting of the number of copies (“Yes” at step S4518), the CPU10aperforms plural copy processing (step S4519). Details of the plural copy processing are described later.

The CPU10aperforms the opening-and-closing-circuit control processing P2(step S4520). Consequently, electric power is supplied from the commercial power supply (the step-down chopper circuit50) to the load. The load continuously performs the image forming operation and normal electric power is supplied to the fixing heaters (step S4521). The CPU10ajudges whether sheets of a number corresponding to one job have been discharged (step S4522). When it is judged that the sheets of the number corresponding to one job have not been discharged (“No” at step S4522), the CPU10areturns to step S4521. The load continues the image forming operation. When it is judged that the sheets of the number corresponding to one job have been discharged (“Yes” at step S4522), the CPU10ajudges whether supply of electric power is necessary for post-processing (step S4523).

When it is judged that supply of electric power is necessary for post-processing (“Yes” at step S4523), to increase an output of the DC power supply, the CPU10aperforms the opening-and-closing-circuit control processing P1(step S4524). Consequently, power accumulated in the capacitor bank9is supplied to the constant-voltage generating circuit13. A post-processing peripheral apparatus supplied with the electric power carries out a post-processing operation (step S4525). The CPU10areturns to step S4511. When it is judged that supply of electric power to the post-processing is unnecessary (“No” at step S4523), since the copy operation is finished, the CPU10areturns to step S4511).

When it is judged at step S4517that the image forming apparatus is not performing the copy operation (“No” at step S4517), the CPU10ajudges whether the image forming apparatus is in the energy saving mode (step S4526). When it is judged that the image forming apparatus is not in the energy saving mode (“No” at step S4526), the CPU10areturns to step S4511. When it is judged that the image forming apparatus is in the energy saving mode (“Yes” at step S4526), the CPU10ajudges whether a charge voltage is lower than 35 volts (step S4527). When it is judged that the charge voltage is lower than 35 volts (“Yes” at step S4527), to charge the capacitor bank9, the CPU10aperforms the opening-and-closing-circuit control processing P3(step S4528) and returns to step S4526. Although not shown in this flowchart, when this charge operation is finished, the image forming apparatus control unit also shifts to the energy saving mode. When it is judged that the charge voltage is not lower than 35 volts (“No” at step S4527), the CPU10aswitches the first switching circuit to the commercial power supply side (step S4529), switches the second switching circuit to the commercial power supply side (step S4530), and returns to step S4526.

FIG. 46is a flowchart of a procedure of plural-copy control processing performed by the engine control unit of the printer.

First, the CPU10aof the engine control unit10performs the opening-and-closing-circuit control processing P2(step S4601). Consequently, electric power is supplied from the commercial power supply (the step-down chopper circuit50) to the load. The load carry out an image forming operation and normal electric power is supplied to the AC fixing heaters29and30(step S4602). The CPU10ajudges whether copying for the number of copies N acquired from the power use tables has been carried out (step S4603). When it is judged that copying for the number of copies N has not been carried out (“No” at step S4603), the CPU10areturns to step S4602. The load repeats the image forming operation. When it is judged that copying for the number of copies N has been carried out (“Yes” at step S4603), the CPU10aperforms the opening-and-closing-circuit control processing P1(step S4604). Consequently, the supply of electric power from the commercial power supply is stopped and electric power accumulated in the capacitor bank9is supplied to the constant-voltage generating circuit13. As a result, excess electric power is supplied to the heating unit of the fixing device. Thus, it is possible to supply the maximum power of the heater rating to the AC fixing heaters29and30. It is possible to prevent the temperature of the heating unit from falling to be lower than a fixed image guarantee temperature.

The CPU10acontinues the state in which the maximum power is supplied to the AC fixing heaters29and30and continues the image forming operation (step S4605). The CPU10ajudges whether the timer counter is M (step S4606). When it is judged that the timer counter is not M (“No” at step S4606), the CPU10areturns to step S4605. When it is judged that the timer counter is M (“Yes” at step S4606), the CPU10aleaves the processing.

The temperature fall of the heating unit of the fixing device occurs because heat of a fixing pressure roller moves to a sheet when sheet supply is started. Therefore, when this pressure roller is warmed, the temperature fall is solved. The time M until the pressure roller is warmed is acquired from the power use table T2and set as the timer count. Thus, it is possible to supply the maximum power of the heater rating to the fixing heaters until the time M comes.

FIG. 47is a flowchart of a procedure of the opening-and-closing-circuit control processing P1performed by the engine control unit of the image forming apparatus. According to this processing, electric power is supplied from the capacitor bank9. The constant-voltage generating circuit13outputs a constant voltage and supplies electric power to the load.

The CPU10atransmits a signal for using electric power of the charge accumulating unit to the CPU7aof the step-down-output control and charge control circuit7(step S4701). The CPU1atransmits a signal for switching the first switching circuit to the commercial power supply side to the CPU7aof the step-down-output control and charge control circuit7(step S4702) and transmits a signal for switching the second switching circuit to the charge accumulating unit side to the CPU7aof the step-down-output control and charge control circuit7(step S4703).

FIG. 48is a flowchart of a procedure of the opening-and-closing-circuit control processing P2performed by the engine control unit of the image forming apparatus. According to this processing, electric power is supplied from the commercial power supply (the step-down chopper circuit50) to the load.

The CPU10atransmits a signal for supplying electric power to the load to the CPU7aof the step-down-output control and charge control circuit7(step S4801). The CPU10atransmits a signal for switching the first switching circuit to the commercial power supply side to the CPU7aof the step-down-output control and charge control circuit7(step S4802) and transmits a signal for switching the second switching circuit to the charge accumulating unit side to the CPU7aof the step-down-output control and charge control circuit7(step S4803).

FIG. 49is a flowchart of a procedure of the opening-and-closing-circuit control processing P3performed by the engine control unit of the image forming apparatus. According to this processing, the capacitor bank9is charged.

The CPU10atransmits a signal for switching the first switching circuit to the charge accumulating unit side to the CPU7aof the step-down-output control and charge control circuit7(step S4901) and transmits a signal for switching the second switching circuit to the commercial power supply side to the CPU7aof the step-down-output control and charge control circuit7(step S4902). The CPU10atransmits a charge permission signal to the CPU7aof the step-down-output control and charge control circuit7(step S4903).

In this way, in the power supply device600according to this embodiment, constant voltage is generated by the constant-voltage generating circuit13from an output of the capacitor bank9charged by the commercial power supply or an output of the commercial power supply and the constant voltage generated is supplied to the load. Thus, it is possible to realize a plurality of functions, which are realized by a plurality of circuits in the past, with one constant-voltage generating circuit13and simplify a circuit configuration of the engine power supply unit of the printer. This makes it possible to reduce a warm-up time of the fixing device using the commercial power supply for general offices in Japan without applying special work related to a power supply and simplify a circuit configuration of the power supply device including the charge accumulating unit. Since the circuit configuration of the power supply device including the charge accumulating unit is simplified, it is possible to reduce manufacturing cost for the image forming apparatus. Since a complicated structure is not adopted for the circuit configuration of the power supply device, it is possible to realize improvement of a quality of the apparatus and improvement of easiness of maintenance.

Since a voltage at the commercial power supply is stepped down and the capacitor bank9is charged with the voltage stepped down, it is possible to reduce the number of capacitor cells connected in series. It is possible to accumulate an accumulated charge amount (equal to or higher than DC 30 volts) acceptable as a voltage at the fixing device (a halogen heater).

By using a normal-close relay for the switching circuit, in a state in which the main power supply is off, it is possible to supply an output of the step-down chopper circuit50to the constant-voltage generating circuit13. Thus, a circuit configuration for supplying an output of the commercial power supply (the step-down chopper circuit50) or an output of the capacitor bank9is simplified.

FIG. 50is a circuit diagram of a circuit configuration of a power supply device according to another embodiment. In a power supply device700shown inFIG. 50, drive circuit for the relays55aand56aof the power supply device600according to the sixth embodiment is provided in an image forming apparatus and an interface for directly controlling the first and the second switching circuits55and56on the image forming apparatus side is provided.

As in the sixth embodiment, a power supply device according to a seventh embodiment of the present invention steps down a voltage outputted from the commercial power supply to charge a charge accumulating unit and changes a voltage outputted from the commercial power supply and a voltage outputted from the charge accumulating unit to constant voltages with a constant-voltage generating circuit to supply the voltages to load. The seventh embodiment is different from the sixth embodiment in that a first opening and closing circuit is used instead of the first switching circuit and a second opening and closing circuit and a third opening and closing circuit are used instead of the second switching circuit.

FIG. 51is a circuit diagram of a circuit configuration of the power supply device according to the seventh embodiment.FIG. 52is a detailed circuit diagram of a detailed circuit configuration of the power supply device according to the seventh embodiment. The power supply device shown inFIGS. 51 and 52is mounted on an engine unit of a printer.

A power supply device800according to this embodiment includes the filter1, the full-wave rectifying circuit2, the step-down chopper circuit50, the step-down-voltage detecting circuit19, the capacitor bank9, the charge-voltage detecting circuit16, the constant-voltage generating circuit13, the charge-current detecting circuit12, the step-down-output control and charge control circuit7, the first opening and closing circuit40, the second opening and closing circuit41, and the third opening and closing circuit42. An engine unit of a printer mounted with the power supply device800includes the engine control unit10, the load20, the AC fixing heaters29and30, the heating-unit-temperature detecting circuits33and34, and the AC-fixing-heater control circuit39.

Structures and functions of the filter1, the full-wave rectifying circuit2, the step-down chopper circuit50, the step-down-voltage detecting circuit19, the capacitor bank9, the charge-voltage detecting circuit16, the constant-voltage generating circuit13, the charge-current detecting circuit12, the step-down-output control and charge control circuit7, the first opening and closing circuit40, the second opening and closing circuit41, and the third opening and closing circuit42are substantially the same as those in the sixth embodiment. Thus, the above explanations are referred to and only differences are explained. The engine control unit10, the load20, the AC fixing heaters29and30, the heating-unit-temperature detecting circuits33and34, and the AC-fixing-heater control circuit39are the same as those in the sixth embodiment. Thus, only differences are explained below.

When a voltage at the capacitor bank9is discharged, i.e., when the voltage is supplied to the constant-voltage generating circuit13via the third opening and closing circuit42, the step-down-output control and charge control circuit7outputs a PWM signal for lowering the voltage to an input voltage, which allows the constant-voltage generating circuit13to generate a constant voltage, to the gate of the FET51. Consequently, the capacitor bank9starts discharge. When the voltage inputted to the constant-voltage generating circuit13falls to the voltage, which allows the constant-voltage generating circuit13to generate a constant voltage, the input of the constant-voltage generating circuit13is automatically switched to the step-down chopper circuit50side.

The first opening and closing circuit40opens and closes the connection between the output of the step-down chopper circuit50and the capacitor bank9. The second opening and closing circuit41connects the output of the step-down chopper circuit50and the input of the constant-voltage generating circuit13. The third opening and closing circuit42opens and closes the connection between the input of the constant-voltage generating circuit13and the capacitor bank9. It is possible to supply a voltage to the constant-voltage generating circuit13even at the time of charge by closing the second opening and closing circuit41. In charging the charge accumulating unit when it is unnecessary to supply electric power to the load, for example, at the time of the energy saving mode, it is possible to reduce electric power if the second opening and closing circuit41is opened.

When a relay is used for the second opening and closing circuit41and the third opening and closing circuit42, it is possible to continuously supply electric power to the constant-voltage generating circuit13if a signal for opening the third opening and closing circuit42is outputted in a fixed time after a signal for turning on the second opening and closing circuit41is outputted. When the second opening and closing circuit41is turned off, a signal for opening the second opening and closing circuit41only has to be outputted in a fixed time after a signal for turning on the third opening and closing circuit42is outputted.

The serial controller (SIC)10dof the engine control unit10controls opening and closing of the first opening and closing circuit40by outputting a signal for turning on and off the gate of the FET40aof the first opening and closing circuit40to the step-down-output control and charge control circuit7. The serial controller (SIC)10dof the engine control unit10controls opening and closing of the second opening and closing circuit41by outputting a signal for turning on and off the gate of the FET41ato the step-down-output control and charge control circuit7. The serial controller (SIC)10dof the engine control unit10controls opening and closing of the third opening and closing circuit42by outputting a signal for turning on and off the gate of the FET42to the step-down-output control and charge control circuit7. The opening and closing operations of the opening and closing circuits are described later.

Charge control processing and operation mode control processing by the power supply device800constituted as described above are substantially the same as those in the sixth embodiment. Thus,FIGS. 44A to 46and the explanations of the figure are referred to. Only differences from the sixth embodiment are explained.

The opening-and-closing-circuit control processing P1in the flowcharts shown inFIGS. 45A to 45Dis replaced with opening-and-closing-circuit control processing P1shown inFIG. 53. The opening-and-closing-circuit control processing P2in the flowcharts shown inFIGS. 45A to 45Dis replaced with opening-and-closing-circuit control processing P2shown inFIG. 54. The opening-and-closing-circuit control processing P3in the flowcharts shown inFIGS. 45A to 45Dis replaced with opening-and-closing-circuit control processing P3shown inFIG. 55.

FIG. 53is a flowchart of a procedure of the opening-and-closing-circuit control processing P1performed by the engine control unit of the image forming apparatus. According to this processing, the constant-voltage generating circuit13generates a constant voltage using accumulated electric power of the capacitor bank9and supplies electric power to the load.

The CPU10atransmits a signal for using electric power of the charge accumulating unit to the CPU7aof the step-down-output control and charge control circuit7(step S5301). The CPU10atransmits an opening signal for the first opening and closing circuit to the CPU7aof the step-down-output control and charge control circuit7(step S5302) and transmits a closing signal for the third opening and closing circuit to the CPU7aof the step-down-output control and charge control circuit7(step S5303). When a relay is used for the second and the third opening and closing circuits, the CPU10acounts time N with the timer counter (step S5304). The CPU10atransmits an opening signal for the second opening and closing circuit to the CPU7aof the step-down-output control and charge control circuit7(step S5305).

FIG. 54is a flowchart of a procedure of the opening-and-closing-circuit control processing P2performed by the engine control unit of the image forming apparatus. According to this processing, the constant-voltage generating circuit13generates a constant voltage using a voltage outputted from the commercial power supply and supplies electric power to the load.

The CPU10atransmits a load power supply signal to the CPU7aof the step-down-output control and charge control circuit7(step S5401). The CPU10atransmits an opening signal for the first opening and closing circuit to the CPU7aof the step-down-output control and charge control circuit7(step S5402) and outputs a closing signal for the second opening and closing circuit to the CPU7aof the step-down-output control and charge control circuit7(step S5403). When a relay is used for the second and the third opening and closing circuits, the CPU10acounts time N with the timer counter (step S5404). The CPU10aoutputs an opening signal for the third opening and closing circuit to the CPU7aof the step-down-output control and charge control circuit7(step S5405).

FIG. 55is a flowchart of a procedure of the opening-and-closing-circuit control processing P3performed by the engine control unit of the image forming apparatus. According to this processing, a voltage outputted from the commercial power supply is stepped down and the charge accumulating unit is charged by the step-down voltage.

The CPU10aoutputs a closing signal for the first opening and closing circuit to the CPU7aof the step-down-output control and charge control circuit7(step S5501) and outputs a closing signal for the second opening and closing circuit to the CPU7aof the step-down-output control and charge control circuit7(step S5502). The CPU10aoutputs an opening signal for the third opening and closing circuit to the CPU7aof the step-down-output control and charge control circuit7(step S5303). The CPU10atransmits a charge permission signal to the CPU7aof the step-down-output control and charge control circuit7(step S5504).

As described above, in the power supply device800according to the seventh embodiment, in addition to the effects described above, it is possible to supply electric power to the load even at the time of charge by closing the second opening and closing circuit. Thus, even at the time of charge, it is possible to connect load in which fluctuation to some degree of a power supply voltage does not cause a problem. When it is unnecessary to supply electric power to the load, for example, at the time of the energy saving mode, it is possible reduce electric power by opening the second opening and closing circuit. It is possible to prevent interruption of electric power supplied to the load by opening the third opening and closing circuit after closing the second opening and closing circuit or opening the second opening and closing circuit after closing the second opening and closing circuit.

As in the sixth embodiment, a power supply device according to an eighth embodiment of the present invention steps down a voltage outputted from the commercial power supply to charge a charge accumulating unit and changes a voltage outputted from the commercial power supply and a voltage outputted from the charge accumulating unit to constant voltages with a constant-voltage generating circuit to supply the voltages to load. The eighth embodiment is different from the sixth embodiment in that a first opening and closing circuit is used instead of the first switching circuit and a second opening and closing circuit is used instead of the second switching circuit.

FIG. 56is a circuit diagram of a circuit configuration of the power supply device according to the eighth embodiment.FIG. 57is a detailed circuit diagram of a detailed circuit configuration of the power supply device according to the eighth embodiment. The power supply device shown inFIGS. 56 and 57is mounted on an engine unit of a printer.

A power supply device900according to this embodiment includes the filter1, the full-wave rectifying circuit2, the step-down chopper circuit50, the step-down-voltage detecting circuit19, the capacitor bank9, the charge-voltage detecting circuit16, the constant-voltage generating circuit13, the charge-current detecting circuit12, the step-down-output control and charge control circuit7, the first opening and closing circuit40and the second opening and closing circuit43. An engine unit of a printer mounted with the power supply device900includes the engine control unit10, the load20, the AC fixing heaters29and30, the heating-unit-temperature detecting circuits33and34, and the AC-fixing-heater control circuit39.

Structures and functions of the filter1, the full-wave rectifying circuit2, the step-down chopper circuit50, the step-down-voltage detecting circuit19, the capacitor bank9, the charge-voltage detecting circuit16, the constant-voltage generating circuit13, the charge-current detecting circuit12, the step-down-output control and charge control circuit7, the first opening and closing circuit40, and the second opening and closing circuit43are substantially the same as those in the sixth embodiment. Thus, the above explanations are referred to and only differences are explained. The engine control unit10, the load20, the AC fixing heaters29and30, the heating-unit-temperature detecting circuits33and34, and the AC-fixing-heater control circuit39are the same as those in the sixth embodiment. Thus, only differences are explained below.

As in the embodiments described above, the first opening and closing circuit40opens and closes the connection between the output of the step-down chopper circuit50and the capacitor bank9. The second opening and closing circuit41connects the output of the step-down chopper circuit50to the input of the constant-voltage generating circuit13via the diode44and opens and closes the connection between the input of the constant-voltage generating circuit13and the capacitor bank9. These circuits always supplies voltages to the constant-voltage generating circuit13via the diode. Thus, when electric power is discharged from the capacitor bank9, if a voltage at the step-down chopper circuit50is set lower than a voltage at the capacitor bank9, a voltage is not supplied from the capacitor bank9to the constant-voltage generating circuit13.

The serial controller (SIC)10dof the engine control unit10controls opening and closing of the first opening and closing circuit40by outputting a signal for turning on and off the gate of the FET40aof the first opening and closing circuit40to the step-down-output control and charge control circuit7. The serial controller (SIC)10dof the engine control unit10controls opening and closing of the second opening and closing circuit43by outputting a signal for turning on and off the gate of the FET43ato the step-down-output control and charge control circuit7. Opening and closing operations of the opening and closing circuits are described later.

FIGS. 58A and 58Bare flowcharts of a procedure of operation mode control processing performed by the engine control unit of the image forming apparatus. Since the operation mode control processing is partially the same as that in the flowcharts shown inFIGS. 45A to 45Dexplained in the sixth embodiment, only differences are explained. Since the processing before step S5801is the same as that at steps S4501to S4510inFIG. 45A, the explanation with reference toFIG. 45is referred to and an explanation of the processing is omitted here.

When it is judged at step S4510inFIG. 45Athat the CPU10aof the engine control unit10has the reload temperature, the fixing device comes into the standby state, electric power at the normal time set in advance is supplied to the fixing heaters, and normal temperature control is carried out (step S5801).

The CPU10ajudges whether the fixing device is in the standby state again (step S5802). When it is judged that the fixing device is in the standby state (“Yes” at step S5802), the CPU10ajudges whether a charge voltage is lower than 35 volts (step S5803). When it is judged that the charge voltage is lower than 35 volts (“Yes” at step S5803), the CPU10aperforms the opening-and-closing-circuit control processing P3(step S5804). Consequently, the capacitor bank9is charged. Thereafter, the CPU10areturns to step S5801. When it is judged that the charge voltage is not lower than 35 volts (“No” at step S5803), the CPU10aperforms the opening-and-closing-circuit control processing P2(step S5805). Consequently, electric power inputted from the commercial power supply is supplied to the load via the constant-voltage generating circuit13. Thereafter, the CPU10areturns to step S5801.

When it is judged at step S5802that the fixing device is not in the standby state (“No” at step S5802), the CPU10ajudges whether the image forming apparatus is performing a copy operation (step S5806). When it is judged that the image forming apparatus is performing the copy operation (“Yes” at step S5806), the CPU10aperforms the opening-and-closing-circuit control processing P2(step S5807). Consequently, electric power inputted from the commercial power supply is supplied to the load via the constant-voltage generating circuit13. The load performs an image forming operation and normal electric power is supplied to the AC fixing heaters29and30(step S5808).

The CPU10ajudges whether a job has been finished (step S5809). When it is judged that the job has been finished (“Yes” at step S5809), the CPU10acarries out processing of the energy saving mode described later. When it is judged that the job has not been finished (“No” at step S5809), the CPU10aacquires, from the power use table T1, the number of copies N and an accumulated electric power use time M corresponding to a present sheet size with which use power is equal to or larger than normal electric power (step S5810).

The CPU10ajudges whether a present number of copies is N (step S5811). When it is judged that the present number of copies is not N (“No” at step S5811), the CPU10areturns to step S5808and the image forming operation is continued. When it is judged that the present number of copies is N (“Yes” at step S5811), to prevent the temperature of the heating unit from falling to be lower than a fixed image guarantee temperature, the CPU10aperforms the opening-and-closing-circuit control processing P1(step S5812). Consequently, the supply of electric power from the commercial power supply is stopped. Moreover, electric power accumulated in the capacitor bank9is supplied to the constant-voltage generating circuit13. It is possible to supply excess electric power to the heating unit of the fixing device. As a result, it is possible to supply maximum electric power of the heater rating to the AC fixing heaters29and30.

The CPU10acontinues the state in which the maximum electric power is supplied to the AC fixing heaters29and30and continues the copy operation (step S5813). The temperature fall in the heating unit of the fixing device occurs because heat of a fixing pressure roller moves to a sheet when sheet supply is started. Therefore, when this pressure roller is warmed, the temperature fall is solved. The CPU10acounts the accumulated electric power use time M, which is time until the pressure roller is warmed, with the timer (step S5814). When it is judged that a timer count is not M (“No” at step S5814), the CPU10areturns to step S5813. The maximum electric power of the heater rating is supplied to the fixing heaters until the accumulated electric power use time M elapses.

When it is judged that the timer count is M (“Yes” at step S5814), the CPU10aperforms the opening-and-closing-circuit control processing P2(step S5815). Consequently, the electric power inputted from the commercial power supply is supplied to the load. The load continuously performs the image forming operation and the CPU10asupplies normal electric power to the fixing heaters (step S5816). The CPU10ajudges whether sheets of a number that should be discharged in one job have been discharged (step S5817). When it is judged that the sheets of the number that should be discharged in one job have not been discharged (“No” at step S5817), the CPU10areturns to step S5816and continues the image forming operation. When it is judged that the sheets of the number that should be discharged in one job have been discharged (“Yes” at step S5817), the CPU10aacquires, from the power use table T2, post-processing that requires supply of electric power (step S5818).

The CPU10ajudges whether supply of electric power is necessary for the post-processing to be carried out (step S5819). When it is judged that supply of electric power is necessary for the post-processing (“Yes” at step S5819), the CPU10aperforms the opening-and-closing-circuit control processing P1(step S5820). Consequently, electric power accumulated in the capacitor bank9is supplied to the constant-voltage generating circuit13. It is possible to increase an output of a DC power supply. For example, supply of electric power is performed when a binding operation of staple processing is performed as the post-processing. A post-processing peripheral apparatus supplied with the electric power carries out a post-processing operation (step S5821). Thereafter, the CPU10areturns to step S5801. When it is judged that supply of electric power is not necessary for the post-processing (“No” at step S5819), since the copy operation has been finished, the CPU10areturns to step S5801.

When it is judged at step S5806that the image forming apparatus is not performing the copy operation (“No” at step S5806) or when it is judged at step S5809that the job has been finished (“Yes” at step S5809), the CPU10ajudges whether the image forming apparatus is in the energy saving mode and performs processing. A procedure of the processing is substantially the same as that of steps S4526to S4530of the flowcharts inFIG. 45D. Thus, the explanation with reference toFIG. 45Dis referred to. An explanation of the procedure is omitted here and only differences are explained below.

In this embodiment, processing for transmitting a step-down output stop signal to the CPU7aof the step-down-output control and charge control circuit7is performed instead of steps S4529and S4530.

The opening-and-closing-circuit control processing P1in the flowcharts shown inFIGS. 58A and 58Bis replaced with opening-and-closing-circuit control processing P1shown inFIG. 59. The opening-and-closing-circuit control processing P2is replaced with opening-and-closing-circuit control processing P2shown inFIG. 60. The opening-and-closing-circuit control processing P3is replaced with opening-and-closing-circuit control processing P3shown inFIG. 61.

FIG. 21is a flowchart of a procedure of the opening-and-closing-circuit control processing P1performed by the engine control unit of the image forming apparatus. According to this processing, the constant-voltage generating circuit13generates a constant voltage using accumulated electric power of the capacitor bank9and supplies electric power to the load.

The CPU10atransmits a signal for using electric power of the charge accumulating unit to the CPU7aof the step-down-output control and charge control circuit7(step S5901). The CPU10atransmits an opening signal for the first opening and closing circuit to the CPU7aof the step-down-output control and charge control circuit7(step S5902) and transmits a closing signal for the second opening and closing circuit to the CPU7aof the step-down-output control and charge control circuit7(step S5903).

FIG. 60is a flowchart of a procedure of the opening-and-closing-circuit control processing P2performed by the engine control unit of the image forming apparatus. According to this processing, the constant-voltage generating circuit13generates a constant voltage using a voltage outputted from the commercial power supply and supplies electric power to the load.

The CPU10atransmits a load power supply signal to the CPU7aof the step-down-output control and charge control circuit7(step S6001). The CPU10atransmits an opening signal for the first opening and closing circuit to the CPU7aof the step-down-output control and charge control circuit7(step S6002). The CPU10atransmits an opening signal for the second opening and closing circuit to the CPU7aof the step-down-output control and charge control circuit7(step S6003).

FIG. 61is a flowchart of a procedure of the opening-and-closing-circuit control processing P3performed by the engine control unit of the image forming apparatus. According to this processing, a voltage outputted from the commercial power supply is stepped down and the charge accumulating unit is charged with the step-down voltage.

The CPU10atransmits a closing signal for the first opening and closing circuit to the CPU7aof the step-down-output control and charge control circuit7(step S6101) and transmits an opening signal for the second opening and closing circuit to the CPU7aof the step-down-output control and charge control circuit7(step S6102). The CPU10atransmits a charge permission signal to the CPU7aof the step-down-output control and charge control circuit7(step S6103).

As described above, in the power supply device900according to this embodiment, in addition to the effects described above, opening and closing circuits are reduced by setting a voltage at the step-down circuit lower than a charge voltage at the capacitor bank9when the second opening and closing circuit is closed. When a voltage at the capacitor bank9falls because of discharge, the input of the constant-voltage generating circuit13is automatically switched to the step-down chopper circuit50side.

FIG. 62is a circuit diagram of a circuit configuration of a power supply device according to another embodiment.FIG. 63is a detailed circuit diagram of a detailed circuit configuration of the power supply device according to the another embodiment. The power supply device shown inFIGS. 62 and 63is mounted on an engine unit of a printer.

A power supply device1000shown inFIGS. 62 and 63charges a charge accumulating unit with a voltage outputted from the commercial power supply using a charging circuit and changes a voltage outputted from the commercial power supply and a voltage outputted from the charge accumulating unit to constant voltages with a constant-voltage generating circuit to supply the voltages to load. This embodiment is different from the sixth embodiment in that the step-down circuit is not provided, the charge accumulating unit is charged by a charge and control circuit, and opening and closing circuits are controlled.

In the same manner as the conventional power supply, the power supply device1000according to this embodiment supplies an output of the full-wave rectifying circuit2to the constant-voltage generating circuit13, divides the output of the full-wave rectifying circuit2, connects the output to the charging circuit60, and charges the capacitor bank9with the output. Thus, it is possible to easily add an auxiliary charge accumulating function to the structure of the conventional power supply. It is possible to reduce the number of capacitor cells in use by increasing a control input voltage range of the constant-voltage generating circuit13.

When a load is light at the time of standby or the like, it is possible to supply electric power to the load even at the time of charge by closing the first opening and closing circuit66. When it is unnecessary to supply electric power to the load at the time of the energy saving mode or the like, it is possible to reduce electric power by opening the opening and closing circuit.

In the power supply device1000according to this embodiment, by adopting a voltage transformer in the charging circuit60, an opening and closing circuit that connects the commercial power supply to a charging circuit is made unnecessary.

FIG. 64is a circuit diagram of a circuit configuration of the power supply device according to still another embodiment.FIG. 65is a detailed circuit diagram of a detailed circuit configuration of the power supply device according to the still another embodiment. The power supply device shown inFIGS. 64 and 65is mounted on an engine unit of a printer.

A power supply device1100shown inFIGS. 64 and 65has substantially the same structure as the power supply device1000. The power supply device1100is different from the power supply device1000in that the power supply device1100includes the first opening and closing circuit76, the second opening and closing circuit77, and the third opening and closing circuit78instead of the first opening and closing circuit66and the second opening and closing circuit67.

In the power supply device1100according to this embodiment, in addition to the effects described above, when a load is light at the time of standby or the like, it is possible to supply electric power to the load even at the time of charge by closing the first opening and closing circuit76and the second opening and closing circuit77. When it is unnecessary to supply electric power to the load at the time of the energy saving mode or the like, it is possible to reduce electric power by opening the opening and closing circuits.

In the power supply device1100according to this embodiment, although the opening and closing circuits that connect the commercial power supply to the charging circuit60are necessary, it is possible to simplify a circuit configuration of a charging circuit by using a step-down chopper circuit.

According to the embodiments, the step-down unit steps down a voltage outputted from the commercial power supply, the step-down/charge control unit controls a step-down voltage, the charge accumulating unit is charged based on the step-down voltage outputted, the constant-voltage generating unit generates a constant voltage based on the output of the charge accumulating unit or the output of the step-down unit, and the voltage-supply control unit supplies the constant voltage to the load that performs an image forming operation. This makes it possible to supply a voltage from the charge accumulating unit charged by the commercial power supply to the load. Therefore, there is an effect that it is possible to reduce a warm-up time of the load, which performs an image forming operation, using the commercial power supply generally used in offices in Japan. Further, it is possible to generate a constant voltage with one constant-voltage generating unit based on a voltage outputted the charge accumulating unit or a voltage outputted from the commercial power supply. Therefore, there is an effect that it is possible to simplify structures of an image forming apparatus and a power supply device including a power supply unit. Moreover, since it is possible to simplify the structures of the image forming apparatus and the power supply device, there is an effect that it is possible to reduce manufacturing cost for the image forming apparatus and the power supply device.