Abstract:
There is provided a power supply unit, comprising: a converter transformer; a first low voltage generation unit to generate a first voltage on a secondary side of the converter transformer and output the first voltage; a first controller that controls an activation state of a primary side of the converter transformer based on the first voltage; an inactivation unit to inactivate operation of the first controller based on the first voltage to let the first low voltage generation unit to suspend output of the first voltage; a high voltage supply unit to output a high voltage higher than the first voltage by using the first voltage; a detection unit to detect an anomalous state concerning output of the high voltage of the high voltage supply unit. The high voltage supply unit inactivates the operation of the first controller through the inactivation unit when the anomalous state is detected.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]    This application claims priority under 35 U.S.C. §119 from Japanese Patent Application No. 2008-222045, filed on Aug. 29, 2008. The entire subject matter of the application is incorporated herein by reference. 
       BACKGROUND  
       [0002]    1. Technical Field 
         [0003]    Aspects of the present invention relate to a power supply unit and an image forming device having the power supply unit. 
         [0004]    2. Related Art 
         [0005]    In general, a power supply unit is provided in an image forming device to supply voltages to components in the image forming device. Japanese Patent Provisional Publication No. 2001-086742A discloses a technique in which a voltage is outputted on a secondary side of a converter transformer, and switching control is performed for controlling an activation state of a primary side of the converter transformer based on an output voltage on the primary side of the converter transformer. 
         [0006]    Regarding an image forming device having a cover through which a user can access a high voltage generation circuit provided in the image forming device to generate a high voltage, a technique where high voltage output is cut off with an interlock switch when the cover is opened has been proposed. 
       SUMMARY  
       [0007]    However, use of such an interlock switch hampers downsizing of the power supply unit. In addition, even if the interlock switch is employed, the high voltage is kept to be outputted until the cover is opened even when anomalous high voltage output occurs. In this case, internal components to which high voltages are supplied might be damaged. 
         [0008]    Aspects of the present invention are advantageous in that at least one of a power supply unit and an image forming device having the same configured such that when anomalous high voltage output occurs, high voltage output can be stopped while suppressing deterioration of components due to an anomalous state of the high voltage output, without increasing the size of the power supply unit is provided. 
         [0009]    According to an aspect of the invention, there is provided a power supply unit, comprising: a first converter transformer; a first low voltage generation unit configured to generate a first voltage on a secondary side of the first converter transformer and output the first voltage; a first controller that controls an activation state of a primary side of the first converter transformer, on the primary side of the first converter transformer, based on the first voltage; an inactivation unit configured to inactivate operation of the first controller based on the first voltage to let the first low voltage generation unit to suspend output of the first voltage; a high voltage supply unit configured to output a high voltage higher than the first voltage by using the first voltage; an anomalous state detection unit configured to detect an anomalous state concerning output of the high voltage of the high voltage supply unit. In this configuration, the high voltage supply unit inactivates the operation of the first controller through the inactivation unit when the anomalous state is detected by the anomalous state detection unit. 
         [0010]    Such a configuration makes it possible to stop output of the high voltage in accordance with detection of the anomalous state without increasing the size and cost of the power supply unit. 
         [0011]    According to another aspect of the invention, there is provided an image forming device, comprising: the above described power supply unit; and an image formation unit configured to form an image by using the high voltage supplied by the power supply unit. 
         [0012]    Such a configuration makes it possible to stop output of the high voltage in accordance with detection of the anomalous state without increasing the size and cost of the power supply unit. 
         [0013]    It is noted that various connections are set forth between elements in the following description. It is noted that these connections in general and unless specified otherwise, may be direct or indirect and that this specification is not intended to be limiting in this respect. Aspects of the invention may be implemented in computer software as programs storable on computer-readable media including but not limited to RAMs, ROMs, flash memory, EEPROMs, CD-media, DVD-media, temporary storage, hard disk drives, floppy drives, permanent storage, and the like. 
     
    
     
       BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS  
         [0014]      FIG. 1  is a cross section illustrating a general configuration of a laser printer according to a first embodiment. 
           [0015]      FIG. 2  is a circuit diagram f a power supply unit provided in the laser printer. 
           [0016]      FIG. 3  is a flowchart illustrating a high voltage output anomaly detection process according to the first embodiment. 
           [0017]      FIG. 4  is a variation of the high voltage output anomaly detection process shown in  FIG. 3 . 
           [0018]      FIG. 5  is a circuit diagram of a power supply unit according to a second embodiment. 
           [0019]      FIG. 6  is a flowchart illustrating a high voltage output anomaly detection process according to the second embodiment. 
           [0020]      FIG. 7  is a flowchart illustrating a high voltage output anomaly detection process according to another embodiment. 
       
    
    
     DETAILED DESCRIPTION  
       [0021]    Hereafter, embodiments according to the invention will be described with reference to the accompanying drawings. 
       First Embodiment 
       [0022]      FIG. 1  is a cross section illustrating a general configuration of a laser printer  10  according to a first embodiment. 
         [0023]    The laser printer  10  is a so-called direct tandem type color laser printer. That is, the laser printer  10  includes four development rollers  31 K,  31 C,  31 M and  31 Y respectively corresponding to four colors of black, cyan, magenta and yellow, and four photosensitive drums  32 K,  32 C,  32 M and  32 Y respectively corresponding to four colors of black, cyan, magenta and yellow. In the following, the right side on  FIG. 1  is defined as a front side of the laser printer  1 . It should be noted that various types of image forming devices, such as a monochrome laser printer, an LED printer and a multifunction peripheral having facsimile and copy functions, can be employed as a device to which the feature of an embodiment is applied. 
         [0024]    The laser printer  10  (hereafter, simply referred to as a printer  10 ) has a box-shaped body casing  11 . In the body casing  11 , a paper supply unit  21 , a paper carrying unit  23  configured to carry a sheet of paper  3  as an example of a recording medium, an image formation unit  25  configured to form an image through an electrophotographic process, and a scanning unit  27  are arranged to be stacked in this order from the bottom side. Further, the printer  10  includes an electric circuit  20  which supplies various signals to the components in the printer  10 . The electric circuit  20  includes a power supply unit  40  which is explained in detail below. 
         [0025]    The development rollers  31 K- 31 Y (hereafter, frequently referred to as development rollers  31  collectively), the photosensitive drums  32 K- 32 Y (hereafter, frequently referred to as photosensitive drums  32  collectively), chargers  33 K- 33 Y (hereafter, frequently referred to as chargers  33  collectively), transfer rollers  34 K- 34 Y (hereafter, frequently referred to as transfer rollers  34  collectively) and a fixing unit  35  are included in the image formation unit  25 . The fixing unit  35  includes a heat roller  35 A having a heat source, and a pressure roller  35 B which presses the sheet of paper  3  against the heat roller  35 A so that a toner image transferred to the sheet of paper  3  is fixed by heat on the sheet of paper  3 . 
         [0026]    The front side of the body casing  11  is formed to be an access opening for accessing to the image formation unit  25  where a front cover  15  is provided to be rotatable. That is, the front cover  15  is opened by a user operation. The front cover  15  serves to open or close the access opening. An open/close sensor  22  is provided near to the front cover  15 . The open/close sensor  22  generates a detection signal corresponding to an opened state or a closed state of the front cover  15 , and supplies the detection signal to the electric circuit  20 . 
         [0027]    The scanning unit  27  is provided with a polygonal mirror (not shown) and four laser diodes corresponding to the four colors. Each laser beam (L 1 , L 2 , L 3 , L 4 ) emitted by the laser diode is deflected by the polygonal mirror, and is further deflected by an optical component (e.g., a reflection mirror provided on an optical path) to be incident on a surface of the corresponding photosensitive drum  32  ( 32 K- 32 Y). With this configuration, an electrostatic latent image is formed on each photosensitive drum  32 . Thereafter, an image is formed on the sheet of paper  3  being carried on a paper carrying path through a development process, a transfer process and a fixing process. The sheet of paper after image formation is then ejected on an output tray provided on an upper wall  11 A of the body casing  11 . 
         [0028]    A configuration of a power supply unit  40  according to the first embodiment will now be described.  FIG. 2  is a circuit diagram f the power supply unit  40 . It should be noted that the power supply unit  40  can be applied to various types of devices. As shown in  FIG. 2 , the power supply unit  40  includes a rectifying unit  50 , a low voltage power supply unit  60  and a high voltage power supply unit  70 . The rectifying unit  50  includes a rectifying circuit  51  and a smoothing capacitor C 1 . The rectifying unit  50  rectifies an altering current (e.g. AC 100V). 
         [0029]    The low voltage power supply unit  60  is a so-called RCC (Ringing Choke Converter), and includes a converter transformer T 1 , a switching transistor Q 1 , a primary side control circuit  61 , an overcurrent detection circuit  62 , an overvoltage detection circuit  63 , an output voltage control circuit  64  and a photocoupler PC 1 . 
         [0030]    The low voltage power supply unit  60  includes a diode D 1  and a capacitor C 2  on a secondary side of the converter transformer T 1 . The diode D 1  and the capacitor C 2  serve to rectify the voltage of the secondary side of the converter transformer T 1  to generate DC 24V, and to supply DC 24V to a circuit (e.g., the high voltage power supply unit  70 ) that needs a high voltage. 
         [0031]    The lower voltage power supply unit  60  includes a diode D 2 , a capacitor C 3  and a DC-DC converter  66  connected to an intermediate tap of the secondary winding of the converter transformer T 1 . The diode D 2  and the capacitor C 3  serve to rectify the voltage of the intermediate tap of the secondary side of the converter transformer T 1  to generate a predetermined DC voltage. The DC-DC converter  66  converts the predetermined DC voltage into a certain voltage (DC 3.3V in this embodiment), and supplies DC 3.3V to a circuit (e.g., an LCD monitor  24  provided on the body casing  11 ) operating in a direct current of a low voltage. 
         [0032]    The overcurrent detection circuit  62  may include an error amplifier and a comparator. The overcurrent detection unit  62  detects current by a voltage difference of both terminals of a current detection resistance R 1 , and when the voltage difference exceeds a predetermined value, the overcurrent detection unit  62  supplies current to a diode of the photocoupler PC 1  via the resistance R 4  and the diode D 3 . Accordingly, a transistor of the photocoupler PC 1  turns to ON, and the primary side control circuit  61  moves to a suspended state, and the low voltage power supply unit  60  shuts down. 
         [0033]    The overvoltage detection circuit  63  includes a zener diode connected to an output line. When the output DC voltage exceeds a predetermined voltage (e.g., a zener voltage), the overvoltage detection circuit  63  supplies a predetermined current to a diode of the photocoupler PC 1  via the resistance R 5  and the diode D 4  to shut down the low voltage power supply unit  60  as in the case of the overcurrent detection circuit  62 . 
         [0034]    The output voltage control circuit  64  includes an error amplifier and an insulating element (e.g., a photocoupler). The output voltage control circuit  64  detects the output voltage through dividing resistances R 2  and R 3 . The error amplifier amplifies a difference between the output voltage (i.e., the divided voltage) and a reference value, and supplies the amplified signal to the photocoupler. In this case, the output voltage control circuit  64  controls the primary side control circuit  61  via the photocoupler so that the output voltage (i.e., the divided voltage) becomes equal to the reference value of the error amplifier. Further, in this case, the primary side control circuit  61  controls the activation state of the primary side of the converter transformer T 1  based on the current of a transistor of a photocoupler of the output voltage control circuit  64 . 
         [0035]    The high voltage power supply unit  70  includes a CPU  71 , a voltage boosting circuit  72  and a high voltage detection circuit  73 . The high voltage power supply unit  70  receives DC 24V from the low voltage power supply unit  60 , and generates a high voltage (e.g., a charge voltage to be applied to the charger  33 , a development bias to be applied to the development roller  31  and a transfer bias to be applied to the transfer roller  34 ) to be supplied to the image formation unit  25  base on DC 24V. It should be noted that in  FIG. 2  only a partial configuration outputting a charge voltage Vchg to be applied to the charger  33  is illustrated for the sake of simplicity. 
         [0036]    The high voltage supply unit  70  has a high voltage output ON mode in which a regular high voltage is outputted and a high voltage output OFF mode in which high voltage output is cut off. 
         [0037]    The voltage boosting circuit  72  may include an RCC (Ringing Choke Converter) having a converter transformer, and outputs a high voltage, such as a charge voltage Vchg of 5 kV to 8 kV. The high voltage detection circuit  73  includes dividing resistances R 7  and R 8 , and generates a high voltage detection signal Vdv by dividing the high voltage output. Although not shown in  FIG. 2 , a plurality of high voltage detection circuits  73  are respectively provided for a plurality of voltage boosting circuits  72 . 
         [0038]    The CPU  71  controls the voltage boosting circuit  72 , for example, by a PWM (Pulse Width Modulation) signal, based on a high voltage (i.e., a divided voltage) detected by the high voltage detection circuit  73 . Furthermore, the CPU  71  receives a mode switch signal MS for turning on or off the high voltage output, and turns on or off the high voltage output in accordance with the mode switch signal MS. That is, the CPU  71  turns on or off the PWM signal in accordance with the mode switch signal MS. 
         [0039]    Although not shown in  FIG. 2 , the CPU  71  includes a plurality of PWM signal generators generating a plurality of PWM signals for the plurality of voltage boosting circuits  72 , and an A-D conversion unit including a plurality of A-D converters for converting high voltage detection signals Vdv respectively supplied from a plurality of high voltage detection circuits  73  into digital signals. The CPU  71  is connected with a ROM  74  storing various types of programs to be executed by the CPU  71 , and an NVRAM  75  storing various types of data, such as results of processes by the CPU  71 . 
         [0040]    Hereafter, control for detecting high voltage anomaly is explained.  FIG. 3  is a flowchart illustrating a high voltage output anomaly detection process. The high voltage output anomaly detection process is executed under control of the CPU  71  in accordance with a program stored in the ROM  74 . 
         [0041]    In step S 100 , the CPU  71  receives a mode switch signal MS for cutting off the high voltage output, for example, when a print command has not been received for a predetermined time period. Then, the CPU  71  moves to the high voltage output OFF mode where generation of the high voltage is stopped. At this moment, the PWM signal generator in the CPU  71  is inactivated, and the PWM signal generator stops to generate the PWM signal. In this case, the voltage boosting circuit  72  is also inactivated to stop generation of the high voltage. At this moment, the CPU  71  detects the high voltage output based on the high voltage detection signal Vdv. 
         [0042]    Next, in step S 120 , the CPU  71  judges whether output of a high voltage higher than or equal to a predetermined voltage (which may be set at 0V) is detected in accordance with the high voltage detection signal Vdv. If the CPU  71  judges that the high voltage output higher than or equal to the predetermined voltage is not detected (S 120 : NO), the high voltage output anomaly detection process terminates. 
         [0043]    On the other hand, if the CPU  71  judges that the high voltage output higher than or equal to the predetermined voltage is detected (S 120 : YES), control proceeds to step S 130 . In step S 130 , the CPU  71  judges that an anomalous state concerning output of a high voltage occurs because a high voltage is outputted regardless of the high voltage output OFF mode, and executes a backup process for saving current statuses. For example, the backup process includes a process where information indicating which of high voltages is in an anomalous state is stored in the NVRAM  75 , and a process where the information is printed on the sheet of paper  3  through the image formation unit  25 . 
         [0044]    In step S 140 , error information indicating the anomalous state of the high voltage output is displayed on the LCD monitor  24  which serves as an indication unit. The LCD monitor  24  is driven by DC 3.3V. It should be noted that various types of indication units, such as a buzzer, may be employed for indicating error information. 
         [0045]    Next, in step S 150 , the CPU  71  judges whether the front cover  15  is in the opened state. The CPU  71  waits until the front cover  15  moves to the opened state (S 150 : NO). When the CPU  71  judges that the front cover  15  is in the opened state (S 150 : YES), the CPU  71  generates a power supply shutdown signal SS, and supplies the power supply shutdown signal SS to the photocoupler PC 1  via the resistance R 6  and the diode D 5 . In response to the power supply shutdown signal SS, the primary side control circuit  61  is inactivated, and the lower voltage power supply unit  60  and the high voltage power supply unit  70  are suspended. 
         [0046]    Hereafter, advantages of the first embodiment are explained. When high voltage output is detected in the high voltage OFF mode where the high voltage output is cut off, the CPU  71  inactivates the primary side control circuit  61  with the power supply shutdown signal SS. In this case, the CPU  71  inactivates the primary side control circuit  61  by simply using the photocoupler PC 1 . Therefore, according to the first embodiment, an interlock switch is not needed. As a result, it becomes possible to stop high voltage output when the anomalous state of the high voltage output is detected without increasing the size of the power supply unit  40  and without increasing cost. In addition, it becomes possible to suppress deterioration of a component (e.g., the photosensitive drum  32  of the image formation unit  25 ) to which a high voltage is supplied. It should be noted that such anomalous state of the high voltage output is caused, for example, by a faulty operation of the PWM signal generator or abnormal oscillation of the voltage boosting circuit  72 . 
         [0047]    According to the first embodiment, it is possible to continue to inform a user of the anomalous state of the high voltage output through the LCD monitor  24  as long as possible until the front cover  15  is opened. It is also possible to prevent the user from carelessly touch a high voltage. 
         [0048]    As described above, the information concerning the anomalous state of the high voltage output is stored in the NVRAM  75 , or is printed out. Therefore, maintenance work for the anomalous state of the high voltage output can be performed more effectively. 
         [0049]    Typically, the charge voltage Vchg applied to the charger  33  has the maximum energy of high voltages to be applied to the components in the image formation unit  25 . Therefore, the highest priority for preventing the user to touch the high voltage should be assigned to the charge voltage Vchg. Therefore, as shown in step S 145  in  FIG. 4 , the CPU  71  may judge whether the high voltage is the charge voltage Vchg. In this case, the CPU  71  may execute step S 150  and step S 160  for the power supply shutdown process only when output of the charge voltage Vchg is in the anomalous state. In this case, the above described advantages can be realized more effectively when the anomalous state of the charge voltage Vchg occurs. 
       Second Embodiment  
       [0050]    Hereafter, a second embodiment is described with reference to  FIGS. 5 and 6 . Since the feature of the second embodiment corresponds to a variation of the power supply unit of the first embodiment, in the following the explanations focus on the feature of the second embodiment. Therefore, in the following, the same reference numbers as those of the first embodiment are also referred to for the explanation of the second embodiment. 
         [0051]      FIG. 5  is a circuit diagram of a power supply unit  40 A according to the second embodiment. As shown in  FIG. 5 , the power supply unit  40 A includes two low voltage power supply units  60 A and  60 B. The low voltage power supply unit  60 B generates DC 3.3.V. Therefore, in this embodiment, the low voltage power supply unit  60 A is configured such that the diode D 2  and the capacitor C 3  and the DC-DC converter  66  are omitted from the low voltage power supply unit  60  of the first embodiment. 
         [0052]    Similarly to the low voltage power supply unit  60 A, the low voltage power supply unit  60 B is an RCC (Ringing Choke Converter), and includes a converter transformer T 2 , a switching transistor Q 2 , a primary side control circuit  61 A, a diode D 6 , a capacitor C 4 , a overcurrent detection circuit  62 A, an output voltage control circuit  64 A, and a photocoupler PC 2 . That is, the low voltage power supply unit  60 B is different from the low voltage power supply unit  60 A in that the low voltage power supply unit  60 B is not provided with a overvoltage detection circuit and does not receive the power supply shutdown signal SS. 
         [0053]    In this configuration, when a high voltage larger than or equal to a predetermined voltage is detected in the high voltage output OFF mode, the CPU  71  operates to inactivate only the primary side control circuit  61  of the low voltage power supply unit  60 A without inactivating the primary side control circuit  61 A of the low voltage power supply unit  60 B. That is, when anomalous high voltage is detected, output of DC  24 V is stopped, while DC 3.3V is outputted continuously. 
         [0054]    For this reason, in the high voltage output anomaly detection process shown in  FIG. 6  according to the second embodiment, ajudgment step for judging whether the front cover  15  is opened in S 150  in  FIG. 3  is omitted. That is, according to the second embodiment, the low voltage power supply unit  60 A is inactivated regardless of whether the front cover  15  is opened or closed. 
         [0055]    As a result, it becomes possible to stop the anomalous high voltage output in an early stage and securely, and to inform the user of the anomalous high voltage output through the LCD monitor  24  by using DC 3.3V even if the high voltage output has been stopped. In addition, since the anomalous high voltage output is stopped in an early stage, it becomes possible to suppress deterioration of the component (e.g., the photosensitive drum  32 ) to which a high voltage is applied in comparison with the case where the primary side control circuit  61  of the low voltage power supply unit  60 A is inactivated after the opened state of the front cover  15  is detected. That is, according to the second embodiment, it becomes possible to suppress deterioration of the photosensitive drum  32  due to anomalous high voltage output in compassion with the configuration of the first embodiment. 
         [0056]    It should be noted that the resistances R 7 , R 8 , R 9  and R 10  in the low voltage power supply unit  60 B respectively correspond to the resistances R 1 , R 2 , R 3  and R 4  in the low voltage power supply unit  60 A, and the diode D 7  in the low voltage power supply unit  60 B corresponds to the diode D 3  in the low voltage power supply unit  60 A. 
         [0057]    Although the present invention has been described in considerable detail with reference to certain preferred embodiments thereof, other embodiments are possible. 
         [0058]    (1) In the above described embodiments, the anomalous high voltage output is detected in the high voltage output OFF mode in which output of a high voltage is stopped. However, the present invention is not limited to such an example. The anomalous high voltage output may be detected regardless of the ON/OFF state of the high voltage output mode.  FIG. 7  illustrates a high voltage output anomaly detection process of such a case. As shown in  FIG. 7 , in this case, step S 100  in  FIG. 3  is omitted, and in step S 121  the CPU judges whether an anomalous high voltage is detected in accordance with the high voltage detection signal Vdv in place of step S 120  in  FIG. 3 . In this case, it is also possible to stop the high voltage output when the anomalous high voltage output is detected without increasing the size of the power supply unit and without increasing cost. Furthermore, it is possible to suppress deterioration of the component due to the anomalous high voltage. 
         [0059]    It should be noted that “anomalous high voltage” includes a state where at least one of the high voltages including the charge voltage, the development bias and the transfer bias is outside a predetermined voltage range. That is, “anomalous high voltage” is not limited to the case where the high voltage output exceeds the predetermined range. Factors causing the anomalous high voltage include a faulty operation of the voltage boosting circuit, and an abnormal state concerning the generation of the PWM signal (e.g., a faulty operation of the PWM signal generator or the A-D converter). 
         [0060]    (2) In the above described embodiments, the image forming device is configured to have an open/close cover, a detector for detecting the opened or closed state of the cover, and an indication unit. However, the present invention is not limited to such an example. For example, these components may be provided in the power supply unit itself. 
         [0061]    (3) In the above described embodiments, the power supply unit ( 40 ,  40 A) is provided in the image forming device. However, the present invention is not limited to such an example. For example, the power supply unit according to the embodiment can also be applied to various types of devices which require a high voltage. 
         [0062]    (4) In the above described embodiments, detection of the anomalous high voltage output is conducted in accordance with the high voltage detection signal Vdv. However, the present invention is not limited to such an example. For example, when high voltage output is controlled by constant current control, the anomalous state in high voltage generation may be detected in accordance with current detection on the side of the high voltage output in place of the voltage detection. That is, the feature of each of the above described embodiments may be applied to the case where the high voltage output is controlled by constant current control in addition to the case where the high voltage output is controlled by constant voltage control.