Patent Publication Number: US-8971750-B2

Title: Image forming apparatus for discharging electric charge charged to a capacitor and discharge device for discharging electric charge charged to a capacitor

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an apparatus that controls capacitor discharge. 
     2. Description of the Related Art 
     In an image forming apparatus as an example of an apparatus including a substrate equipped with a capacitor, when the substrate is inserted or withdrawn for the purpose of maintenance, the substrate to be inserted or withdrawn needs to be prevented from being destroyed due to a hot swap caused by electric charge charged to the capacitor. To this end, some methods are discussed relating to the discharge of the capacitor. 
     For example, Japanese Patent Application Laid-Open No. 61-032400 discusses a flash lamp for emitting light by discharge of electric charge charged to a capacitor, a power-off detection circuit for detecting that a power source is turned off, and a power source for the flash lamp that causes the capacitor to forcibly discharge when the power-off state is detected. 
     Japanese Patent Application Laid-Open No. 07-333751 discusses an image forming apparatus including a protective cover and an emergency discharge circuit including a switch for detecting an installed condition of the protective cover, wherein, when removal of the cover is detected, electric charge stored in the capacitor is discharged. 
     Recently, power-saving has been promoted more and more. For example, a printer that performs a standby operation with a standby power of 1.0 W is discussed. The printer capable of performing the standby operation with such low power consumption is provided with an all-all-night power source. The all-night power source is provided, for example, for detecting an access to the printer from the external device even when a power source of the apparatus main body is set to an OFF state by a user operation. Accordingly, the power source of the printer can be automatically returned from the OFF state at any time the user desires to use the printer. 
     The all-night power source is described below in more detail. The all-night power source is normally equipped with a capacitor in order to generate a smoothed power source output and performs the above described standby operation while continuously charging the capacitor (i.e., while storing electric charge to the capacitor). For example, in a case where the image forming apparatus is placed in the standby state with low power consumption such as 1.0 W, it is desirable that the power to be consumed in charging the capacitor is minimized as much as possible. In this regard, to minimize discharge of the capacitor as much as possible, a measure for interrupting the discharge path is provided in the circuit. This is because, if a large current is discharged, the circuit operates to charge the corresponding amount of current, resulting in inviting an increase of the standby power. 
     As described above, not only the low power consumption of the printer in the standby operation but also improved usability, e.g., automatic return of the printer from the standby operation, has been also required lately. To the contrary, in the method that the electric charge of the capacitor is automatically and immediately discharged as it is discussed in Japanese Patent Application Laid-Open No. 61-032400 and Japanese Patent Application Laid-Open No. 07-333751, easier maintenance can be realized but the improved usability cannot be realized to a satisfactory level. 
     On the other hand, as described above, when the substrate is inserted or withdrawn for the purpose of maintenance, to prevent the substrate to be inserted or withdrawn from being destroyed due to the hot swap caused by the electric charge charged to the capacitor, it is necessary to discharge the capacitor. However, in the printer equipped with the all-night power source including the above described capacitor, the electric charge of the capacitor cannot be discharged immediately and automatically. Therefore, a service person is forced to wait for completion of the discharge of the electric charge of the capacitor for a long time. 
     A solution for the above issue can be found in providing the printer with a circuit that can detect disconnection of a power source cable from an alternating current (AC) inlet and can change the capacitor to automatic discharge of the electric charge. However, the above solution requires a new automatic detection circuit for detecting the disconnection of the power source cable from the AC inlet. As a result thereof, the solution invites an increased cost. For example, while the printer is in a standby state with the standby power of 1.0 W, it is necessary to operate the automatic detection circuit using a zero crossing detection. Accordingly, an operation power to be used in a photocoupler or the like increases. Alternatively, in order to save data in a case of power outage or power shutoff, a configuration can be assumed that reads and writes a memory by using the electric charge charged to the capacitor. However, in the case of the above assumption, if the electric charge of the capacitor is discharged immediately in a manner as discussed in Japanese Patent Application Laid-Open No. 61-032400 and Japanese Patent Application Laid-Open No. 07-333751, a possible problem is created in an operation of the printer. 
     Such a problem is created not only for the image forming apparatus as described in the above example but is commonly created to all the apparatus equipped with the capacitor. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to an apparatus capable of reducing power consumption and of swiftly performing discharge of a capacitor while saving a cost thereof. 
     According to an aspect of the present invention, an image forming apparatus includes a power source configured to convert an input alternating current (AC) voltage to output thus converted voltage, a capacitor configured to be connected to somewhere between an output of the power source and a ground to smoothen the output voltage from the power source, an operating unit configured to instruct an operation different from an ON and OFF operation of the power source, a switch configured to switch a state between a state that the power source is connected to a load and a state that the power source is disconnected from the load, and a control unit configured to detect an operation of the operating unit, wherein a power supply state to the image forming apparatus can be switched between a first power supply state in which power is supplied to the load and to the control unit and a second power supply state in which power consumption is less than that in the first power supply state, the power source is disconnected from the load by the switch to stop supplying power to the load, power is supplied to the switch, and power is supplied to the control unit, and wherein, when the image forming apparatus operates in the first power supply state, if the operation is detected by the control unit, an operation according to the detected operation is performed and, when the image forming apparatus operates in the second power supply state, if the operation is detected by the control unit, the power source is brought into connection with the load via the switch so as to increase a discharge current of the capacitor. 
     According to another aspect of the present invention, a discharge device that is connected to somewhere between an output of a power source that converts an input alternating current (AC) voltage and outputs thus converted voltage and a ground and is configured to discharge a capacitor for smoothing an output from the power source includes an operating unit configured to instruct an operation different from an ON and OFF operation of the power source, a switch configured to switch a state between a state that the power source is connected to a load and a state that the power source is disconnected from the load, and a control unit configured to detect an operation of the operating unit, wherein a power supply state to the discharge device can be switched between a first power supply state in which power is supplied to the load and to the control unit and a second power supply state in which power consumption is less than that in the first power supply state, the power source is disconnected from the load by the switch to stop supplying power to the load, power is supplied to the switch, and power is supplied to the control unit, and wherein, when the discharge device operates in the first power supply state, if the operation is detected by the control unit, an operation according to the detected operation is performed and, when the discharge device operates in the second power supply state, if the operation is detected by the control unit, the power source is brought into connection with the load via the switch so as to increase a discharge current of the capacitor. According to another aspect of the present invention, an image forming apparatus includes a power source configured to convert an input alternating current (AC) voltage to output thus converted voltage, a capacitor configured to smoothen the output voltage from the power source, an operating unit configured to instruct an operation of the image forming apparatus, a switch configured to switch a state between a state that the power source is connected to a load and a state that the power source is disconnected from the load, and a control unit configured to detect an operation of the operating unit, wherein a power supply state to the image forming apparatus can be switched between a first power supply state in which power is supplied to the load and to the control unit and a second power supply state in which power consumption is less than that in the first power supply state, the power source is disconnected from the load by the switch to stop supplying power to the load and power is supplied to the control unit, and wherein, when the image forming apparatus operates in the first power supply state, if the operation is detected by the control unit, an operation according to the detected operation is performed and, when the image forming apparatus operates in the second power supply state, if the operation is detected by the control unit, the power source is brought into connection with the load via the switch. According to another aspect of the present invention, A discharge device that is configured to discharge a capacitor for smoothing an output from the power source, the discharge device includes a switch configured to switch a state between a state that the power source is connected to a load and a state that the power source is disconnected from the load, a detecting unit configured to detect an operation of an apparatus that is connected to the power source, wherein a power supply state to the discharge device can be switched between a first power supply state in which power is supplied to the load and to the detecting unit and a second power supply state in which power consumption is less than that in the first power supply state, the power source is disconnected from the load by the switch to stop supplying power to the load and power is supplied to the control unit, and wherein, when the discharge device operates in the first power supply state, if the operation is detected by the control unit, an operation according to the detected operation is performed and, when the discharge device operates in the second power supply state, if the operation is detected by the control unit, the power source is brought into connection with the load via the switch. 
     Further features and aspects of the present invention will become apparent from the following detailed description of exemplary embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate exemplary embodiments, features, and aspects of the invention and, together with the description, serve to explain the principles of the invention. 
         FIG. 1  is a schematic diagram illustrating a cross sectional configuration of an image forming apparatus. 
         FIG. 2  is a block diagram illustrating a circuit configuration in the image forming apparatus. 
         FIG. 3  illustrates a circuit configuration of a power unit. 
         FIG. 4  is a flow chart illustrating control of capacitor discharge. 
         FIG. 5  is a timing chart in the control of the capacitor discharge. 
         FIGS. 6A and 6B  illustrate a time-sequential voltage waveform of the capacitor when the power source cable is disconnected in a power OFF state. 
         FIG. 7  is another flow chart of the control of the capacitor discharge. 
         FIG. 8  is another timing chart in the control of the capacitor discharge. 
         FIG. 9  is a block diagram illustrating a circuit configuration in another image forming apparatus. 
         FIG. 10  is a schematic diagram of an operation panel. 
         FIG. 11  illustrates a circuit configuration of a power unit. 
         FIG. 12  is further another flow chart of the control of the capacitor discharge. 
         FIG. 13  is further another timing chart in the control of the capacitor discharge. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     Various exemplary embodiments, features, and aspects of the invention will be described in detail below with reference to the drawings. 
       FIG. 1  is a schematic diagram illustrating an entire configuration of an image forming apparatus according to a first exemplary embodiment of the present invention.  FIG. 1  illustrates a main body of an image forming apparatus  100 . A toner cartridge  101  is detachably mounted to the image forming apparatus  100 . A photosensitive member  102  is an image bearing member. A semiconductor laser  103  is a light source. A polygonal mirror  105  is rotated by a scanner motor  104 . In an optical path of the laser beam  106 , a light beam emitted from the semiconductor laser  103  is polarized by the polygonal mirror  105  to scan over the photosensitive member  102 . A light receiving sensor  107  receives the light beam polarized by the polygonal mirror  105 . A charging roller  108  uniformly charges over the photosensitive member  102 . A developing roller  109  develops an electrostatic latent image formed on the photosensitive member  102  with a toner. A transfer roller  110  transfers a toner image developed by the developing roller  109  to a predetermined recording sheet. 
     A fixing device  111  includes a fixing heater  112  for heat-fusing the toner transferred to the recording sheet, and a fixing film  124  and a pressure roller  125 , which fix the toner on the recording sheet thereto by applying heat and pressure while conveying the recording sheet. A sheet cassette  113  stores sheets. A sheet feed roller  114  feeds out a sheet from the sheet cassette  113  with a single rotation to a conveyance path. A feeding roller  115  and a retard roller  116  are paired to separate sheets piece by piece in a case where the sheet feed roller  114  picks up a bundle of sheets. The feeding roller  115  and the retard roller  116  subsequently feed out the sheets separately to the conveyance path. An intermediate roller pair  117  conveys the sheet fed from the sheet cassette  113  to the image forming unit. A pre-transferring roller pair  118  sends thus conveyed sheet to the photosensitive member  102 . 
     A top sensor  119  synchronizes writing (i.e., recording/printing) an image to the photosensitive member  102  with a sheet conveyance with respect to the fed sheet as well as measures a length of the fed sheet in a sheet conveyance direction. A fixing sensor  120  detects presence or absence of the sheet after the toner image is fixed thereto. A conveyance roller pair  121  discharges the sheet after fixation to a paper discharge conveyance path. A discharge roller pair  122  discharges the sheet to a discharge tray  123  on which discharged sheets are stacked. A commercial power supply (i.e., commercial alternating power supply)  150  outputs an alternating current (AC) voltage. A power unit  208  connected to the commercial power supply (i.e., commercial alternating power supply)  150  via a power source cable  151  converts the AC voltage into almost direct current (DC) voltage and supplies power to be consumed by the above described image forming operation at the converted voltage to each unit of the apparatus. 
       FIG. 2  is a block diagram illustrating a circuit configuration in the image forming apparatus  100 . In  FIG. 2 , a printer controller  201  renders image code data transmitted from an external device such as a host computer (not illustrated) to bit data necessary for printing of the printer as well as reads out printer internal information to display it. An engine controller  202  controls a printing operation of each unit of the printer engine according to an instruction of the printer controller  201  as well as informs the printer internal information to the printer controller  201 . The engine controller  202  includes a central processing unit (CPU) and an application specific integrated (ASIC) circuit. 
     A high voltage control unit  203  performs high voltage output control with respect to each of the charge, the development, the transfer, and the like according to an instruction of the engine controller  202 . An optical system control unit  204  controls driving and stopping of the scanner motor  104  and lighting of the laser beam according to an instruction of the engine controller  202 . A fixing device control unit  205  performs driving and stopping of energization to the fixing heater  112  according to an instruction of the engine controller  202 . A sensor input unit  206  notifies the engine controller  202  of detection results of the light receiving sensor  107 , the top sensor  119 , the fixing sensor  120 , and the like. 
     A sheet conveyance control unit  207  performs driving and stopping of the motors, rollers, and the like for conveying the recording sheet according to an instruction of the engine controller  202 . The sheet conveyance control unit  207  controls driving and stopping of each of the sheet feed roller  114 , the pair of the feed roller  115  and the retard roller  116 , the pre-transferring roller pair  118 , the photosensitive member  102 , the fixing film  124 , the pressure roller  125 , the conveyance roller pair  121 , and the discharge roller pair  122 . A power unit  208  supplies power to the engine controller  202 , the printer controller  201 , and each control unit. 
     The power unit  208  generates a DC voltage when the power source cable  151  is connected to the power unit  208  to input an alternating current (AC). The power unit  208  is equipped with an all-night power source that continues a power supply of a second power of a supply amount smaller than that of a first power, so that an automatic return operation can be performed even in a case where a power OFF operation of the printer is performed by a user. The power OFF here does not mean a state that the power supply is completely interrupted but means a state that a minimum power supply required for the automatic return to a power ON state can be made. 
     The power ON is a state that more power is supplied than the power supplied in a power OFF state and corresponds to a state where print data is received from an external device to be ready to form an image. The power ON state corresponds to a print standby state. In the power ON state, power is also supplied to the engine controller  202  and the printer controller  201 . Further, in the power ON state, an operating clock frequency of the CPU  306  is set higher than that in the power OFF state. 
     The printer controller  201  has such a configuration that an operator who works on maintenance can easily detach the printer controller  201  for the purpose of an improved workability. The operator disconnects the power source cable  151 , then attaches or detaches the printer controller  201 . 
       FIG. 3  illustrates a circuit configuration of the engine controller  202 , the printer controller  201 , and the power unit  208  in the image forming apparatus  100 . The engine controller  202  includes the CPU  306 . 
     When AC is input into the power unit  208 , an alternate current (AC)/direct current (DC) converter  301  converts an AC current to a DC current and generates a DC voltage (i.e., voltage after conversion). Although it is not illustrated in  FIG. 3 , a capacitor is provided in the AC/DC converter  301  for smoothing an output voltage. Thus generated DC voltage is divided by a voltage divided resistance (not illustrated) and fedback to control the divided voltage to be a predetermined voltage. 
     The CPU  306  can switch the output voltage according to switching of the voltage divided resistance. The voltage divided resistance outputs a voltage +V 1  (i.e., voltage after conversion) in a case of the voltage divided resistance  1 , whereas outputs a voltage +V 2  (i.e., voltage after conversion) in a case of the voltage divided resistance  2 . A relationship between the voltage +V 1  and the voltage +V 2  is +V 1 &gt;+V 2 . The voltage +V 1  input from the AC/DC converter  301  is also supplied to a laser drive substrate (not illustrated) provided with the semiconductor laser  103  via a V 1  supply load switch (not illustrated) in addition to the DC/DC converter  305 . 
     The DC/DC converter  305  is a step-down type DC/DC converter which outputs the voltage +V 2  when the voltage +V 1  is input. The voltage +V 2  generated by the DC/DC converter  305  is supplied to the engine controller  202  and the printer controller  201 . The CPU  306 , the capacitor  304 , current-limiting resistors  307 ,  308 , and  310 , a switch (SW)  302  for performing a test print, and a SW  303  for allowing the user to switch the printer state between the power ON state and the power OFF state are connected to the voltage +V 2  within the engine controller  202 , respectively. 
     Also, a light-emitting diode (LED)  311  (i.e., display unit visible from the outside of a device as a load) which emits light when the printer is in the power ON state in order to inform that the printer is in the power ON state is also connected to the voltage +V 2  within the engine controller  202 . A transistor (Tr)  309  (i.e., switching unit), which is a drive transistor, for changing a connection state between the LED  311  and the power source, in other words, for turning ON (i.e., a state that the power source is connected to the load) and OFF (i.e., a state that the power source is disconnected from the load) the LED  311  is also connected to the voltage +V 2  within the engine controller  202 . Here, the capacitor  304  is connected to somewhere between the DC/DC converter  305  and a ground to take a roll of smoothing an output voltage output from the DC/DC converter  305 . An output voltage after being smoothen is supplied to the apparatus main body. 
     A field effect transistor (FET)  312  (i.e., switching unit) is a load switch for turning ON (i.e., a state that the power source is connected to the load) and OFF (i.e., a state that the power source is disconnected from the load) the power supply from the voltage +V 2  to a sensor  206  (i.e., load). The sensor  206  includes a plurality of sensors such as photo-interrupters. The sensor  206  consumes power constantly while it is supplied with power. The voltage +V 2  supplies power to other units (not illustrated) via a V 2  supply load switch (not illustrated). The V 1  supply load switch and the V 2  supply load switch are switched between ON and OFF according to an instruction from the CPU  306 . 
     The SW  302  and SW  303  are momentary switches. Pressing of the switch allows the electrodes within the switch to contact with each other to establish conduction therebetween. Release of the pressing of the switch allows the electrodes within the switch to disconnect from each other to keep a non-conduction state therebetween. The CPU  306  operates in a state that the CPU  306  can detect a pressed state of each momentary switch in both of a power ON state and a power OFF state. In other words, the CPU  306  is supplied with power so as to be able to operate in both of the power ON state and the power OFF state. 
     A printer controller  201  is configured such that a substrate can be detached from the printer by unscrewing a substrate fixing screw (not illustrated) arranged on a surface of the printer. The SW  302  is a switch (SW) for performing a test print through which a printing operation is confirmed during maintenance of the printer. The SW  302  corresponds to an operating unit for performing an operation other than an ON/OFF operation of the power source. Normally, the operating unit corresponding to the SW  302  is installed inside an outer cover of a back surface of the printer so as not to allow the user to operate it. A dedicated hole is provided in the outer cover of the back surface at a position facing to the SW  302 . The service person can press the SW  302  with a dedicated tool without removing the outer cover of the printer. 
     The printer controller  201  has a function for detecting an access (e.g., input of a print job) from an external device such as a host computer in the power OFF state of the apparatus main body. The printer controller  201  notifies the CPU  306  that an access from the external device is detected. The CPU  306  operates so as to be detectable of the notification indicating the access from the external device even in the power OFF state. 
     When the power source cable  151  is connected and an AC input is started, the printer is brought into the power OFF state. In the power OFF state of the printer, the CPU  306  comes into a low power consumption mode in which an operating clock frequency of the CPU  306  is lowered as well as the LED  311  is turned off. In addition, to minimize the power consumption, the FET  312  is turned OFF by the CPU  306 , so that the power supply to the sensor  206  is turned OFF. The CPU  306  causes the V 1  supply load switch and the V 2  supply load switch to turn OFF and the power supply to the other units (not illustrated) is turned OFF. The voltage divided resistance of the AC/DC converter  301  is switched to the voltage divided resistance  2  by the CPU  306  and an output voltage of the AC/DC converter  301  comes to be the voltage +V 2 . 
     The DC/DC converter  305  performs feedback such that the output voltage becomes the voltage +V 2 . Therefore, when the voltage +V 2  equivalent to the output voltage is input, current to be used in the feedback becomes smaller and thus only little current is consumed. 
     When an operation button corresponding to the SW  303  is pressed, the printer becomes the power ON state from the power OFF state. In the power ON state, the CPU  306  returns to a normal operating clock frequency to cause the LED  311  (i.e., load) to light up. According to an instruction from the CPU  306 , the voltage divided resistance of the AC/DC converter  301  is switched to the voltage divided resistance  1  and an output voltage of the AC/DC converter  301  becomes the voltage +V 1 . The CPU  306  starts supplying power to the sensor  206  by turning the FET  312  ON as well as starts supplying power to the other units by turning the V 1  supply load switch and the V 2  supply load switch ON. When the SW  302  is pressed in the power ON state, the CPU  306  starts the print operation to print a test print image. The test print here is performed for the purpose that the service person confirms whether the printer can normally form a toner image by, for example, forming a black vertical line over an entire page of an A4 size sheet. As a matter of course, what is formed in the test print is changed according to a purpose of use thereof. The test print is not limited to what is exemplified here. 
       FIG. 4  is a flow chart illustrating control of the capacitor discharge in the present exemplary embodiment. The flow chart in  FIG. 4  is performed during a print standby state. At the time, power required in forming a toner image is not supplied to the members directly related to a toner image formation, e.g., the fixing device  111 . A load connected to the power source in the flow chart of  FIG. 4  is a load to which power is supplied also during the print standby state. 
     In step S 401 , the CPU  306  determines whether the printer is currently in the power ON state or in the power OFF state. If the printer is in the power ON state (i.e., in a first power supply state), as described above, power is supplied at least to the CPU  306  that detects states of pressing the SW  303  and the SW  302 . In other words, the CPU  306  functions as a detection unit for detecting an operation input to the operating unit. Power is supplied also at least to the sensor  206  and the LED  311  as loads other than the CPU  306 . Power may be supplied also to a laser drive substrate (not illustrated). 
     If the printer is in the power OFF state (i.e., in a second power supply state), power to the loads, e.g., the sensor  206  and the LED  311 , to which power is supplied in the power ON state is interrupted. In other words, a connection between the loads and the power source is interrupted by a switch, e.g., the FET  312 . Further in the power OFF state, power is supplied only to the CPU  306 , which detects an operation to the operating unit, an operation of switch ON or OFF of the power source, and an access from an external device, and the switching units. As a matter of course, power consumed in the power OFF state is less than power consumed in the power ON state. 
     If the CPU  306  determines that the printer is in the power ON state (NO in step S 401 ), then in step S 407 , the CPU  306  detects whether the SW  302  (i.e., operating unit) is turned ON. 
     If the CPU  306  detects that the SW  302  is turned ON (YES in step S 407 ), then in step S 408 , the CPU  306  controls the image forming unit to print a test print image in response to the pressing of the SW  302 . Then, the processing returns to step S 401 . If the SW  302  is not pressed, namely is OFF, (NO in step S 407 ), the processing returns to step S 401 . 
     In step S 401 , if the CPU  306  determines that the printer is in the power OFF state (YES in step S 401 ), then in step S 402 , the CPU  306  detects whether the SW  302  is turned ON. If the CPU  306  detects that the SW  302  is turned ON (YES in step S 402 ), in step S 403 , the CPU  306  turns the Tr  309  (i.e., switching unit) ON to cause the LED  311  (i.e., load) to light up. 
     In step S 404 , the CPU  306  turns the FET  312  (i.e., switching unit) ON to connect the sensor  206  (i.e., load). A time period during which the Tr  309  and the FET  321  are continuously kept ON is equal to or more than a time period during which at least the discharge of the capacitor  304  is completed under a condition that the AC input voltage from the commercial power supply (i.e., commercial alternating power supply)  150  is interrupted. 
     On the other hand, if the CPU  306  detects that the SW  302  is OFF (NO in step S 402 ), then in step S 405 , the CPU  306  turns the Tr  309  (i.e., switching unit) OFF to bring the LED  311  (i.e., load) into disconnection with the power source. The CPU  306  causes the LED  311  (i.e., load) to be turned off, thereby disconnecting the LED  311  from the power source. In step S 406 , the CPU  306  turns the FET  312  (i.e., switching unit) OFF to cut off the connection between the sensor  206  and the power source. Then, the processing returns to step S 401 . If the CPU  306  detects that the SW  302  is OFF (NO in step S 402 ) and the LED  311  has already been turned off and the FET  312  is OFF, the state is maintained as it is. Then, the processing returns to step S 401 . 
     A description is made as to the control of the capacitor discharge in the present exemplary embodiment.  FIG. 5  illustrates a timing chart in the control of the capacitor discharge.  FIG. 5  corresponds also to the flow chart in  FIG. 4 . 
     When the CPU  306  detects that the SW  302  is pressed and thus an input signal from the SW  302  changes from High level to Low level, the CPU  306  turns the FET  312  (i.e., switching unit) ON. The CPU  306  also turns the Tr  309  (i.e., switching unit) ON to cause the LED  311  to light up. The sensor  206  (i.e., load) connected via the FET  312  consumes a predetermined amount of current while the sensor  206  is supplied with power. The LED  311  (i.e., load) also consumes current. Consequently, while the SW  302  is kept pressed, an amount of current to be consumed can be increased by an amount of current consumed by the sensor  206  and the LED  311 . 
       FIG. 6A  illustrates a relationship between a time started from a point at which the power source cable  151  is disconnected in the power OFF state and a voltage waveform of the capacitor  304 . Since the power consumption is small in the power OFF state, an amount of discharging the electric charge having been charged in the capacitor  304  is small. Therefore, a voltage of the capacitor  304  can be kept for 60 seconds even after the AC input is interrupted. 
     On the other hand,  FIG. 6B  illustrates a relationship between a time starting from a point at which the power source cable  151  is disconnected when the SW  302  is kept pressed in the power OFF state and a voltage waveform of the capacitor  304 . While the SW  302  is pressed in the power OFF state, control of the capacitor discharge is performed, and consumption current increases. As a result thereof, the discharge current of the capacitor  304  becomes larger. A time period during which the voltage of the capacitor  304  is kept becomes 3 seconds, i.e., the discharge of the capacitor  304  can be completed in a short time. As a result thereof, a waiting time of a service person can be remarkably shortened. When the control of the capacitor discharge is completed in a state that the AC input is interrupted, the voltage held by the capacitor  304  and the voltage of the all-night power source become 0 V, respectively, as well as the CPU  306  is turned OFF. 
     Further in the control of the capacitor discharge, the LED  311  that is supplied with power from the all-night power source is lighted while the capacitor  304  connected to the all-night power source maintains its voltage. When the power source cable  151  is disconnected and the discharge of the capacitor  304  is completed, the voltage of the all-night power source becomes 0 V and thus the LED  311  is turned off. Therefore, for example, when an operator such as the service person performs the control of the capacitor discharge, the service person can visually confirm the completion of the discharge of the capacitor  304 . 
     In the present exemplary embodiment, when the control of the capacitor discharge is performed, a single switching unit is controlled, however the present invention is not limited thereto. The number of switching units connected to the all-night power source may be plural. In addition, the LED of the power source switch is lighted while the control of the capacitor discharge is performed in order to allow the operator to confirm the completion of the discharge of the capacitor  304 . However, the present invention is not limited thereto. Another display unit such as the other LED and a liquid crystal may be used so as to allow the operator to visually confirm the discharge of the capacitor  304 . Alternatively, the all-night power source may be connected to a speaker as a load to output sound. 
     As described above, according to the present exemplary embodiment, provided is the printer that has a usability and consumes lower power and that can promptly discharge electric charge of the capacitor while saving a cost thereof. More specifically, by causing the CPU  306  to determine the power supply state of the printer, the switch for conventionally performing the test print when the power is ON is used as a switch for performing the control of the capacitor discharge in the power OFF state. Further in the control of the capacitor discharge, connection to the existing load enables the discharge of the capacitor without requiring an additional circuit. Accordingly, the substrate can be securely prevented from being destroyed by the hot swap. 
     Since an operator performs the control of the capacitor discharge by operating the switch, discharge of the capacitor connected to the all-night power source can be performed at any time the operator desires. Lighting of the LED such as a power source switch LED that can be visually confirmed by the operator while performing the control of the capacitor discharge enables the operator to confirm the completion of the discharge of the capacitor  304 . Accordingly, the substrate can be securely prevented from being destroyed by the hot swap. 
     An image forming apparatus according to a second exemplary embodiment is described below. The discharge of the capacitor is performed while the SW  302  is kept pressed in the first exemplary embodiment, whereas the discharge of the capacitor is performed for a predetermined time period when the pressing of the SW  302  is detected in the present exemplary embodiment. A description is made as to such control that information is provided by the LED in a case where the discharge is not completed even if the discharge of the capacitor  304  is performed for the predetermined time period. The configurations illustrated in  FIG. 1  (i.e., schematic diagram of the configuration),  FIG. 2  (i.e., block diagram of the circuit),  FIG. 3  (i.e., circuit configuration of the engine controller, the printer controller, and the power unit), and  FIGS. 6A and 6B  (i.e., relationships between a voltage held by the capacitor and time thereof) according to the present exemplary embodiment are similar to those of the first exemplary embodiment, so that descriptions thereof are omitted here. 
       FIG. 7  is a flow chart illustrating control of the capacitor discharge according to the present exemplary embodiment. Processing different from that in  FIG. 4  is mainly described here. The flow chart in  FIG. 7  is also performed when the printer is placed in a print standby state. Thus, power to be required in forming a toner image is not supplied to members, e.g., fixing device  111 , directly related to a toner image formation. To the contrary, the load connected to the power source in the flow chart of  FIG. 7  is a load to which power is supplied even when the printer is placed in the print standby state. 
     In step S 401 , the CPU  306  determines whether the printer is currently in the power ON state or in the power OFF state. If the CPU  306  determines that the printer is in the power OFF state (YES in step S 401 ), in step S 701 , the CPU  306  detects whether the SW  302  is pressed for a time period equal to or more than a time Ta. 
     When the CPU  306  detects that the SW  302  is pressed for the time period equal to or more than the time Ta (YES in step S 701 ), in step S 702 , the CPU  306  turns the Tr  309  (i.e., switching unit) ON to cause the LED  311  (i.e., load) to be lighted for a period of a time Tb. In step S 703 , the CPU  306  turns the FET  312  (i.e., switching unit) ON for a period of the time Tb to connect the sensor  206  (i.e., load). A time period during which the Tr  309  and the FET  321  are continuously kept ON is equal to or more than a time period during which at least the discharge of the capacitor  304  is completed under a condition that the AC input voltage from the commercial power supply (i.e., commercial alternating power supply)  150  is interrupted. 
     In step S 704 , the Tr  309  is turned ON and OFF to cause the LED  311  to blink for a time period Tc after the time Tb has passed. According to the processing in step S 704 , the LED  311  can be displayed in a display form different from the display form of the LED  311  (i.e., display unit) corresponding to that in step S 703 . Accordingly, a failure in disconnecting the power source cable  151  can be informed to the operator. 
       FIG. 8  is a timing chart illustrating the control of the capacitor discharge in the present exemplary embodiment. The time period Ta in  FIG. 8  is a time period that the CPU  306  requires in detecting the SW  302  being pressed. The time period Tb is set to be a time long enough for discharging the electric charge of the capacitor when the control of the capacitor discharge is performed after the AC input is interrupted and is to be longer than the time period Ta. The time period Tc is set to 10 seconds. 
     If the CPU  306  detects that the SW  302  is pressed and that the printer is in the power OFF state, the CPU  306  performs the following control of the capacitor discharge. When the CPU  306  detects that the input signal from the SW  302  changes from High level to Low level and that a time period during which the Low level continues is equal to or more than the time period Ta, the CPU  306  turns the FET  312  ON for the time period Tb as a predetermined time period. The CPU  306  further turns the Tr  309  ON and also causes the LED  311  to be lighted for the time period Tb. After the time period Tb has passed, the CPU  306  causes the Tr  309  and the LED  311  to blink for the time period Tc. 
     According to the above described control, the operator can end the discharge control of the capacitor with a single pressing of the SW  302 , i.e., can save a step of continuously pressing the SW  302 . The time period Tb is the time long enough for discharging the electric charge of the capacitor. In addition, the SW  302  can be used as an informing unit for informing that the AC input is performed when the power source cable  151  is failed to be disconnected by causing the LED  311  to blink after the time period Tb has passed. 
     As described above, according to the present invention, the operator can end the control of the capacitor discharge with a single pressing of the SW  302 . In other words, the operator can save the time and effort to continuously press the SW  302 . As a result thereof, the substrate can be securely prevented from being destroyed by the hot swap. 
     In addition, by blinking the LED  311  after the control of the capacitor discharge is performed, the operator can be notified of the failure in disconnecting the power source cable  151  if the power source cable  151  is failed to be disconnected. 
     An image forming apparatus according to a third exemplary embodiment is described below. In the present exemplary embodiment, a method in which an operating unit and a display unit different from those used in the first exemplary embodiment and the second exemplary embodiment are used is described. The configurations illustrated in  FIG. 1  (i.e., schematic diagram of the configuration) and  FIGS. 6A and 6B  (i.e., relationships between a voltage held by the capacitor and time thereof) according to the present exemplary embodiment are similar to those of the first exemplary embodiment, so that descriptions thereof are omitted here. 
       FIG. 9  is a block diagram illustrating a circuit configuration in the image forming apparatus  100 . An operation panel  209  is newly added thereto. Configurations other than the operation panel  209  are similar to those of the first exemplary embodiment, so that descriptions thereof are omitted here. The operation panel  209  includes a liquid crystal display, various types of switches, LEDs, and the like and is used for informing a printer state to the user, changing various printer settings via a user operation, and the like. 
       FIG. 10  is a schematic diagram illustrating the operation panel  209  according to the present exemplary embodiment. Although an operation button corresponding to the SW  303  described in the first exemplary embodiment is not illustrated in the operation panel  209  in  FIG. 10 , an operation button corresponding to the SW  303  is actually provided thereon. A momentary switch corresponding to the SW  303  is provided in a power supply circuit diagram in  FIG. 11 . 
     The operation panel  209  includes a liquid crystal display  501  as a display unit, LEDs  502  and  503  (i.e., loads), and key switches  504  through  508  (i.e., operating unit for performing an operation other than the ON/OFF operation of the power source). The liquid crystal display  501 , the LEDs  502  and  503 , and the key switches  504  through  508  are controlled by the CPU  306 , respectively. The key switches  504  through  508  are momentary switches. Pressing of each key switch causes the electrodes within the switch to contact with each other to allow energization therebetween only while the switch is pressed, whereas causes the electrodes within the switch to detach from each other to keep non-energization state when the pressing of the switch is stopped. 
     The liquid crystal display  501  on which graphics indicating character information and apparatus conditions can be displayed can display the apparatus conditions, remaining amounts of consumables, and various settings. The LEDs  502  and  503  can indicate an operating state of the printer to the user by being lighted, turned off, or blinked. 
     The LED  502  is a Ready LED  502  that lights for indicating a state that the laser beam printer (LBP) is ready for printing, and the LED  503  is an Attention LED  503  that blinks for indicating a state that the LBP is not ready for printing, respectively. The Ready LED  502  blinks while the LBP is in a sleep mode in order to indicate the user that the LBP is in the sleep mode. 
     The key switch  504  is a numeric keypad for inputting numerals related to various settings. The key switch  505  is a selection key for selecting movement in up, down, and left. The key switch  506  is a stop key for temporarily stopping a printing operation. For example, the stop key  506  is pressed during image formation, a printer controller control unit issues an instruction to stop the printing operation to each unit of the apparatus in operation so as to stop the image formation. The key switch  507  is a menu key for displaying setting menus of the image forming apparatus  100 . The key switch  508  is a determination key for entering a selected item. 
       FIG. 11  illustrates a circuit configuration of the engine controller  202 , the printer controller  201 , the power unit  208 , and the operation panel unit  209  in the image forming apparatus  100 . The liquid crystal display  501  and the key switches  504  through  508  (not illustrated in  FIG. 11 ) in the operation panel unit  209  are controlled and detected by the CPU  306 , respectively. Current-limiting resistors  516  and  517  of the operation panel unit  209  are resistances for limiting a current flow in a case where the key switches  507  and  508  are pressed, respectively. Turning ON and OFF of the LED  502  (i.e., load) and the LED  503  (i.e., load) is controlled by a Tr  512  (i.e., switching unit) and a Tr  514  (i.e., switching unit), respectively. The other configurations are similar to those of the first exemplary embodiment, so that descriptions thereof are omitted here. 
     Control of the capacitor discharge in the present exemplary embodiment is described below. In the first exemplary embodiment, a test print button is used to perform the control of the capacitor discharge, whereas, in the present exemplary embodiment, the control of the capacitor discharge is performed according to an operation with the operation panel  209  illustrated in  FIG. 10 . 
       FIG. 12  is a flow chart illustrating the control of the capacitor discharge in the present exemplary embodiment. In step S 1201 , the CPU  306  determines whether the printer is currently in the power ON state or in the power OFF state. If the CPU  306  determines that the printer is not in the power OFF state but in the power ON state (NO in step S 1201 ), in step S 1207 , the CPU  306  invalidates a concurrent operation of the SW  507  and the SW  508 . Then, the processing returns to step S 1201 . 
     On the other hand, in a case where the CPU  306  determines that the printer is in the power OFF state (YES in step S 1201 ), in step S 1202 , the CPU  306  detects whether the SW  507  and the SW  508  are concurrently turned ON, i.e., detects a predetermined pressing instruction provided to a plurality of operation buttons. 
     If the CPU  306  detects that the SW  507  and the SW  508  are concurrently turned ON (YES in step S 1202 ), in step S 1203 , the CPU  306  turns both of the Tr  512  (i.e., switching unit) and the Tr  514  (i.e., switching unit) ON to cause the LED  502  (i.e., load) and the LED  503  (i.e., load) to be lighted. 
     Then in step S 1204 , the CPU  306  turns the FET  312  (i.e., switching unit) ON to connect the sensor  206  (i.e., load) to the power source. 
     If the CPU  306  detects that either one or both of the SW  507  and the SW  508  is/are turned OFF (NO in step S 1202 ), in step S 1205 , the CPU  306  turns the Tr  512  and the Tr  514  OFF to cause the LED  502  and the LED  503  to be turned off. In step S 1206 , the CPU  306  turns the FET  312  OFF to cut off the connection of the sensor  206 . Then, the processing returns to step S 1201 . When the CPU  306  detects that either one or both of the SW  507  and the SW  508  is/are in the OFF state (NO in step S 1202 ), and if the LED  502  and the LED  503  have already been turned off and the FET  312  is in the OFF state, the CPU  306  maintains the state as it is. Then, the processing returns to step S 1201 . 
       FIG. 13  illustrates a timing chart in the control of the capacitor discharge in the present exemplary embodiment. The CPU  306  keeps operating regardless of the power OFF state or the power ON state of the printer, so that the CPU  306  can determine whether the printer is in the power OFF state or in the power ON state. When the CPU  306  detects that both of the SW  507  and the SW  508  are concurrently pressed and that the printer is in the power OFF state, the CPU  306  performs the below described control of the capacitor discharge. 
     When the CPU  306  detects that input signals from both of the SW  507  and the SW  508  are Low level, the CPU  306  turns the FET  312  ON. Further, the CPU  306  turns both of the Tr  512  and the Tr  514  ON to cause the LED  502  and the LED  503  to be lighted. In a case where the printer is in the power OFF state and either one of the SW  507  or the SW  508  is pressed, the CPU  306  does not perform the control of the capacitor discharge. 
     The test print button according to the first exemplary embodiment is often provided on a portion where a user cannot press with his/her finger and therefore a dedicated tool for pressing the test print button is sometimes required. However, the above described control eliminates the necessity of the dedicated tool and thus improves the user friendliness. In addition, the capacitor discharge is performed only when the user presses a plurality of key switches, at the same time, which are not generally operated by the user, so that the control of the capacitor discharge is seldom performed by the user. Accordingly, unnecessary increase of power consumption can be avoided. 
     In the present exemplary embodiment, concurrent pressing of two key switches on the operation panel causes the control of the capacitor discharge to be performed. However, the present invention is not limited to this configuration. Alternatively, pressing of a single key switch or concurrent pressing of more than two key switches on the operation panel may cause the control of the capacitor discharge to be performed. 
     As described above, according to the present invention, when the operator desires to perform the control of the capacitor discharge, the operator can complete the discharge of the capacitor without requiring the dedicated tool. 
     In the above described exemplary embodiments, the image forming apparatus is exemplified. However, the configurations and the operations of the above described exemplary embodiments are applicable not only to the image forming apparatus but also to any apparatus including the capacitor that smoothen the output from the power source. 
     While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all modifications, equivalent structures, and functions. 
     This application claims priority from Japanese Patent Application No. 2011-132533 filed Jun. 14, 2011, which is hereby incorporated by reference herein in its entirety.