Patent Publication Number: US-9417593-B2

Title: Image forming apparatus configured to switch between supplying and shutting-off of power to a portion of the image forming apparatus

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an image forming apparatus including a detection unit that detects an overcurrent. 
     2. Description of the Related Art 
     An image processing apparatus (image forming apparatus) which stops supplying power to a printer unit to reduce standby power consumption during standby in which a printing function is not executed (Japanese Patent Application Laid-Open No. 2001-109546), is known. The image processing apparatus discussed in Japanese Patent Application Laid-Open No. 2001-109546 includes a slave CPU, to which a first power supply unit supplies power regardless of a state (an on/off state) of a power switch operated by a user. The image processing apparatus also includes a master CPU, to which a second power supply unit supplies power when the power switch is on. In addition to the master CPU, the second power supply unit also supplies power to a copy function control unit that controls a copy function of the image processing apparatus. 
     This image processing apparatus discussed in Japanese Patent Application Laid-Open No. 2001-109546 enables the master CPU to execute turn-off processing, such as data saving processing, when the user turns off the power switch. When the turn-off processing is finished, the master CPU instructs the slave CPU to turn off power to the image processing apparatus. The slave CPU, which has received the instruction, turns off a switch arranged between the commercial power and the second power supply unit. This stops power supply from the grid power to the second power supply unit, stopping power supply to the master CPU and the copy function control unit. 
     A short circuit, which may be caused by reasons such as a failure of an electronic component to which the second power supply unit supplies power, would lead to passage of an excessive current if the second power supply unit maintains the output voltage. A solution typically provided for such an excessive current passing from the second power supply unit is a mechanism (a protective circuit) to shut off the passage of current from the second power supply unit. The image processing apparatus discussed in Japanese Patent Application Laid-Open No. 2001-109546 shuts off power supply from the second power supply unit by such a protective circuit in a case of a short circuit of an electronic component in the copy function control unit due to reasons such as a failure. This shuts off power supply to the master CPU, to which the second power supply unit supplies power. In other words, this image processing apparatus discussed in Japanese Patent Application Laid-Open No. 2001-109546 shuts off the power supply to the master CPU immediately when an overcurrent flows due to reasons such as a short circuit in an electronic component of a device to which the second power supply unit supplies power. Thus, in this image processing apparatus discussed in Japanese Patent Application Laid-Open No. 2001-109546, power supply to the master CPU is stopped without the master CPU performing the turn-off processing described above. As a result, data prior to the occurrence of the short circuit may be erased without being saved. 
     SUMMARY OF THE INVENTION 
     According to an aspect of the present invention, an image forming apparatus is capable of stopping power supply from a second power supply unit when an overcurrent flows from the second power supply unit, and preventing the image forming apparatus from losing data by a control unit, to which power is supplied from a first power supply unit, executing finish processing. 
     According to an exemplary embodiment of the invention, an image forming apparatus includes a first power supply unit configured to output first output power, a first device to which the first output power is supplied from the first power supply unit, a second power supply unit configured to output second output power, a second device to which the second output power is supplied from the second power supply unit, a detection unit configured to detect an overcurrent of the second power supply unit, a power source control unit to which the first output power is supplied from the first power supply unit, and configured to switch between supplying and shutting-off of the second output power to the second device, and a control unit to which the first output power is supplied from the first power supply unit, and configured to control an operation of the power source control unit, wherein, when the detection unit detects an overcurrent of the second output power, the power source control unit shuts off the second output power from the second power supply unit to the second device, and the control unit executes finish processing for the first device. 
     Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an image forming apparatus according to a first exemplary embodiment. 
         FIG. 2  is a block diagram illustrating a controller of the image forming apparatus. 
         FIG. 3  is a power supply circuit diagram of the image forming apparatus. 
         FIG. 4  is a power state transition diagram of the image forming apparatus. 
         FIG. 5  is a diagram illustrating a state of each unit at different power states. 
         FIG. 6  is a flowchart illustrating processing executed by a power source control unit. 
         FIG. 7  is a flowchart illustrating shutdown processing executed by a CPU of the controller. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     Exemplary embodiments of the invention will now be described with reference to the drawings. 
     &lt;Overall Configuration of Image Forming Apparatus&gt; 
       FIG. 1  is a diagram illustrating an external appearance of an image forming apparatus according to a first exemplary embodiment of the present invention. 
     As illustrated in  FIG. 1 , an image forming apparatus  10  includes an operation unit  12 , which is a user interface (UI), a scanner unit  13 , which is an image input device, and a printer unit  14 , which is an image output device. 
     The operation unit  12  includes various buttons  121  to be operated by a user and a display unit  122  to display an image. The display unit  122  displays screens, such as a status screen to display a status of the image forming apparatus  10  and a setting screen for the user to input information needed to execute a copy function and a fax function. The buttons  121  include a button  121   a  to allow inputting of the number of print copies and the like, a start button  121   b  to start copying, fax transmission, or the like, and a power-saving button  121   c  to cause the image forming apparatus  10  to transition to a low power state (a first sleep state to be described below). 
     The scanner unit  13  is a device to scan an image formed on an original to acquire image data. Light radiated to the image on the document is reflected to a charge-coupled device (CCD) to convert information of the image into electric signals. These electric signals are converted into luminance signals of R, G, and B colors to be output to a controller  11  (described below). 
     Originals to be scanned by the scanner unit  13  are set in a tray  202  of a document feeder  201 . When the user inputs an instruction to start scanning through the operation unit  12 , the scanner unit  13  causes the document feeder  201  to feed the documents one at a time from the tray  202  for scanning. Note that the scanner unit  13  may move a carriage including a light source and a CCD sensor to scan a document placed on a glass surface (not illustrated), in place of the automatic feeding by the document feeder  201 . 
     The printer unit  14  is a device to form an image on a sheet using input image data. Although the printer unit  14  according to the present exemplary embodiment forms an image through an electrophotographic process using a photosensitive drum or a photosensitive belt, the invention is not limited thereto. The printer unit  14  may be, for example, of the inkjet type, which ejects ink through a small nozzle array for printing on a sheet. 
     The image forming apparatus  10  also includes a plurality of sheet cassettes  203 ,  204 , and  205  to store sheets, on which images are formed by the printer unit  14 . The image forming apparatus  10  further includes a plurality of sheet cassette discharge trays  206 , onto which sheets with images formed thereon by the printer unit  14  are discharged. 
     &lt;Controller  11  of Image Forming Apparatus  10 &gt; 
     With reference to  FIG. 2 , the controller  11 , which controls overall operations of the image forming apparatus  10 , will now be described in detail. 
     As illustrated in  FIG. 2 , the controller  11  is electrically connected to the scanner unit  13 , the printer unit  14 , and the operation unit  12 . The controller  11  includes a central processing unit (CPU)  301 , a random-access memory (RAM)  302 , a read-only memory (ROM)  303 , an operation unit interface (I/F)  305 , a local area network (LAN) controller  306 , and a power source control unit  401 . The CPU  301 , the RAM  302 , the ROM  303 , the operation unit I/F  305 , the LAN controller  306 , and the power source control unit  401  are connected to a system bus  307 . The controller  11  also includes a hard disk drive (HDD)  304 , an image processing unit  309 , a scanner image processing unit  310 , and a printer image processing unit  312 . The HDD  304 , the image processing unit  309 , the scanner image processing unit  310 , and the printer image processing unit  312  are connected to an image bus  308 . 
     The CPU  301  collectively controls access to various devices connected thereto based on a control program and the like stored in the ROM  303 . The CPU  301  also controls various types of processing executed by the controller  11 . 
     The RAM  302  is a system work memory used by the CPU  301  to operate. The RAM  302  is also a memory to store image data temporarily. The RAM  302  includes a static random-access memory (SRAM) capable of retaining the stored contents when power is off, and a dynamic random-access memory (DRAM) in which the stored contents are erased when power is off. The ROM  303  stores an apparatus boot program. The HDD  304  stores system software and image data. 
     The operation unit I/F  305  is an interface to connect the system bus  307  and the operation unit  12 . The operation unit I/F  305  receives from the system bus  307  image data to be displayed on the operation unit  12 , and outputs the data to the operation unit  12 . The operation unit I/F  305  also outputs to the system bus  307  information input from the operation unit  12 . 
     The LAN controller  306  controls the input and output of information between the image forming apparatus  10  and an external apparatus  20  connected to a LAN  60 . 
     The power source control unit  401  controls power supply to each unit of the image forming apparatus  10 . The power source control unit  401  will be described in detail below. 
     The image bus  308  is a transmission path through which image data is transmitted and received, and is made up of a peripheral component interconnect (PCI) bus, an IEEE1394 bus, or the like. 
     The image processing unit  309  performs image processing, such as reading image data stored in the RAM  302 , enlarging and reducing a size of an image of Joint Photographic Experts Group (JPEG), Joint Bi-level Image Experts Group (JBIG), etc., and adjusting colors. The scanner image processing unit  310  corrects, processes, and edits image data received via the scanner I/F  311  from the scanner unit  13 . The scanner image processing unit  310  determines whether the received image data is of a color document or a black and white document and whether the data is of a text document or a photographic document. The scanner image processing unit  310  then adds a result of the determination to the image data. Such additional information is referred to as attribute data. The printer image processing unit  312  refers to the attribute data attached to the image data to perform image processing on the image data. The image data that has been subjected to the image processing is output via a printer I/F  313  to the printer unit  14 . 
     The scanner unit  13  includes a scanner control unit  331  and a scanner drive unit  332 . The scanner drive unit  332 , which is a physically driving device, includes a sheet conveyance motor to convey a document set in the tray  202  to a reading position of the scanner unit  13 . The scanner control unit  331  controls the operation of the scanner drive unit  332 . The scanner control unit  331  receives through communication with the CPU  301  setting information set by the user to perform scanning processing, and controls the operation of the scanner drive unit  332  according to the setting information. 
     The printer unit  14  includes a printer control unit  341  and a printer drive unit  342 . The printer drive unit  342 , which is a physically driving device, includes a fixing device and a sheet conveyance motor (not illustrated). The printer control unit  341  controls the operation of the printer drive unit  342 . The printer control unit  341  receives through communication with the CPU  301  setting information set by the user to perform printing processing, and controls the operation of the printer drive unit  342  according to the setting information. 
     &lt;Power Source Unit  40  of Image Forming Apparatus  10 &gt; 
       FIG. 3  is a power supply circuit diagram for the image forming apparatus  10 . Electric power generated by the power source unit  40  is supplied to each unit of the image forming apparatus  10  described above. The power source unit  40  includes a first power supply unit  410 , a second power supply unit  411 , a third power supply unit  412 , a first power monitor unit  413 , a second power monitor unit  414 , and a third power monitor unit  415 . 
     The first power supply unit  410  converts alternating-current (AC) power, which is supplied through a plug P, into direct-current (DC) power (first output power) (e.g., of 5.1 V). This DC power is supplied to devices of a first power supply system (i.e., the power source control unit  401 , the CPU  301 , the RAM  302 , the ROM  303 , the HDD  304 , the LAN controller  306 , and the buttons  121  of the operation unit  12 ). The second power supply unit  411  converts the AC power, which is supplied through the plug P, to DC power (second output power) (e.g., of 12 V). This DC power is supplied to devices of a second power supply system (i.e., the display unit  122  of the operation unit  12 , the image processing unit  309 , the scanner image processing unit  310 , the printer image processing unit  312 , the printer control unit  341  of the printer unit  14 , and the scanner control unit  331  of the scanner unit  13 ). The third power supply unit  412  converts the AC power, which is supplied through the plug P, to DC power (e.g., of 24 V) and supplies power to devices of a third power supply system (i.e., the printer drive unit  342  and the scanner drive unit  332 ). 
     The first power monitor unit  413  monitors the output voltage of the first power supply unit  410 . Upon detecting that the applied output voltage of the first power supply unit  410  exceeds a threshold, the first power monitor unit  413  outputs a power-good signal A, as a result of the monitoring, to the power source control unit  401 . 
     The second power monitor unit  414  monitors the output voltage of the second power supply unit  411 . Upon detecting that the applied output voltage of the second power supply unit  411  exceeds a threshold, the second power monitor unit  414  outputs a power-good signal B, as a result of the monitoring, to the power source control unit  401 . The third power monitor unit  415  monitors the output voltage of the third power supply unit  412 . Upon detecting that the applied output voltage of the third power supply unit  412  exceeds a threshold, the third power monitor unit  415  outputs a power-good signal C, as a result of the monitoring, to the power source control unit  401 . 
     A power switch  416  is arranged between the first power supply unit  410  and the first power supply system devices (at the primary side of the first power supply unit  410 ). The switch is turned on/off through operation by the user. A signal D indicative of a state (on or off) of the power switch  416  is input to the power source control unit  401 . A switch  417 , constituted by a field-effect transistor (FET), is provided in parallel with the power switch  416 . This switch  417  is turned from on to off, or from off to on, through a control signal E output from the power source control unit  401 . The power switch  416  is provided with a solenoid (not illustrated). Voltage is applied to this solenoid in response to a control signal K output from the power source control unit  401  to turn off the power switch  416 . 
     A relay switch  418  is provided between the plug P and the second power supply unit  411  (at the primary side of the second power supply unit  411 ). A relay switch  419  is provided between the plug P and the third power supply unit  412  (at the primary side of the third power supply unit  412 ). The relay switches  418  and  419  are turned from on to off, or from off to on, through a control signal F output from the power source control unit  401 . 
     A switch  420  is provided between the power switch  416  and the buttons  121  of the operation unit  12 , and the LAN controller  306 . The switch  420  is turned from on to off, or from off to on, through a control signal G output from the power source control unit  401 . Furthermore, a switch  421  (switching unit) is provided between the power switch  416  and the CPU  301 , the ROM  303 , and the HDD  304 . The switch  421  is turned from on to off, or from off to on, through a control signal H output from the power source control unit  401 . 
     &lt;Power State of Image Forming Apparatus  10 &gt; 
       FIG. 4  is a power state transition diagram of the image forming apparatus  10 .  FIG. 5  is a diagram of the on/off states of the devices in different power states of the image forming apparatus  10 . With reference to  FIGS. 4 and 5 , the power states of the image forming apparatus  10  will now be described. The image forming apparatus  10  may take a power-off state, a second sleep state, the first sleep state, or a standby state. 
     In the power-off state, power is not supplied to each unit of the image forming apparatus  10 . The switches  416  to  421  illustrated in  FIG. 3  are off in the power-off state. The power-off state may be a hibernation state. In the hibernation state, the switches  416  to  421  are off similarly to the power-off state. For the hibernation state, a state of the image forming apparatus  10  before the transition to the hibernation state is stored in the HDD  304 . This enables the image forming apparatus  10 , when resuming from the hibernation state, to resume quickly by using information stored in the HDD  304 . 
     In the second sleep state, power is not supplied to each unit of the image forming apparatus  10  except the power source control unit  401 , the RAM  302 , the LAN controller  306 , and the buttons  121  of the operation unit  12 . In the second sleep state, power is supplied from the first power supply unit  410  to the power source control unit  401 , the RAM  302 , the LAN controller  306 , and the buttons  121  of the operation unit  12 . In the second sleep state, the switches  416 ,  417  and  420  illustrated in  FIG. 3  are on, while the remaining switches  418 ,  419 , and  421  are off. The second sleep state allows the operation through the buttons  121  of the operation unit  12  by the user to be accepted. The second sleep state also allows the LAN controller  306  to receive a packet transmitted from the external apparatus  20 . In the second sleep state, the LAN controller  306 , in place of the CPU  301  of the controller  11 , returns a response to some specific packets transmitted from the external apparatus  20 . Such a function of the LAN controller  306  is referred to as a proxy response. The proxy response performed by the LAN controller  306  allows a response to be provided to the specific packets transmitted from the external apparatus  20  in the second sleep state (without resuming from the sleep). 
     The first sleep state is a state for responding to inquiry and the like from the network  60  with activating not all the devices in the controller  11 . When a packet (e.g., inquiry from the network  60 ) to which the LAN controller  306  cannot perform the proxy response is received from the external apparatus  20  in the second sleep state, the image forming apparatus  10  transitions from the second sleep state to the first sleep state. Power is supplied from the first power supply unit  410  to the CPU  301  and the HDD  304  in the first sleep state, and thus, the CPU  301  can return a response to the packet using information stored in the HDD  304 . In the first sleep state, power is supplied to the power source control unit  401 , the RAM  302 , the LAN controller  306 , the buttons  121  of the operation unit  12 , the CPU  301 , the ROM  303 , and the HDD  304 . In the first sleep state, power is not supplied to the second power supply system devices and the third power supply system devices. In the first sleep state, the switches  416 ,  417 ,  420 , and  421  illustrated in  FIG. 3  are on, while the switches  418  and  419  are off. 
     In the standby state, each function of the image forming apparatus  10 , such as the printing processing and the scanner processing, can be executed. When the power switch  416  is turned from off to on in the power-off state or in a suspend state, the image forming apparatus  10  transitions to the standby state. The image forming apparatus  10  also transitions to the standby state when a page description language (PDL) print job is received from the external apparatus  20  in the second sleep state. In the standby state, power is supplied to each of the controller  11 , the operation unit  12 , the printer unit  14 , and the scanner unit  13 . More specifically, the switches  416  to  421  illustrated in  FIG. 3  are on in the standby state. 
     The image forming apparatus  10  may be in another state other than the power-off state, the first sleep state, the second sleep state, and the standby state. More specifically, the image forming apparatus  10  may be in the suspend state. In the suspend state, power is not supplied to each unit of the image forming apparatus  10  except the power source control unit  401  and the RAM  302 . In the suspend state, the switch  417  illustrated in  FIG. 3  is on, while the other switches  416  and  418  to  421  are off. In the suspend state, a state of the image forming apparatus  10  before the transition to the suspend state is stored in the RAM  302 , to which power supply is maintained. This enables the image forming apparatus  10  to resume quickly by using the state of the image forming apparatus  10  stored in the RAM  302 . 
     With reference to  FIG. 4 , the power state transition of the image forming apparatus  10  will now be described. 
     When the power switch  416  is turned off in a state of the standby state, the image forming apparatus  10  transitions to the power-off state (see arrow ( 1 ) in  FIG. 4 ). 
     When the power switch  416  is turned on in the power-off state, the image forming apparatus  10  transitions to the standby state (see arrow ( 2 ) in  FIG. 4 ). 
     When a PDL print job is received from the external apparatus  20  in the first sleep state or the second sleep state, the image forming apparatus  10  transitions to the standby state (see arrow ( 3 ) in  FIG. 4 ). 
     When a packet to which the LAN controller  306  cannot perform the proxy response is received or when one of the buttons  121  of the operation unit  12  is pressed in the second sleep state, the image forming apparatus  10  transitions to the first sleep state (see arrow ( 4 ) in FIG.  4 ). 
     When a predetermined time has elapsed with the buttons  121  of the operation unit  12  not operated and a predetermined time has elapsed with no PDL print job received in the first sleep state, the image forming apparatus  10  transitions to the second sleep state (see arrow ( 5 ) in  FIG. 4 ). 
     When the power-saving button  121   c  of the operation unit  12  is pressed in the standby state, the image forming apparatus  10  transitions to the first sleep state (see arrow ( 6 ) in  FIG. 4 ). 
     The power source control unit  401  will now be described in detail. 
     The power source control unit  401  is a complex programmable logic device (CPLD). The power source control unit  401  controls the transition of the image forming apparatus  10  to the power states described above. The power source control unit  401  is supplied with power in the second sleep state and thus can detect a factor in resuming from the second sleep state (e.g., pressing of one of the buttons  121  of the operation unit  12 , and receiving of a packet to which the proxy response cannot be provided (a PDL print job,)). The factors in resuming from the second sleep state are not limited to the pressing of the buttons  121  and the receiving of a packet to which the proxy response cannot be performed. For example, the image forming apparatus  10 , if provided with a fax function, may resume from the second sleep state upon receipt of a fax. 
     The power source control unit  401  communicates with the CPU  301  to turn the switches  417  to  421  on or off in response to a command from the CPU  301 . 
     A wake signal J is input into the power source control unit  401  from the LAN controller  306 . Upon receipt of a packet to which the LAN controller  306  cannot perform the proxy response (including a PDL print job) through the network  60 , the LAN controller  306  outputs the wake signal J to the power source control unit  401 . Upon receipt of the wake signal J, the power source control unit  401  turns on the switch  421 . With the switch  421  on, the CPU  301  is activated to analyze the received packet. If the CPU  301  determines that a PDL print job is received, the CPU  301  causes the power source control unit  401  to output the control signal F to turn on the switches  418  and  419 . If the received packet is a packet that can be responded to using information stored in the HDD  304 , the power source control unit  401  does not output the control signal F. Thus, the switches  418  and  419  are not turned on. 
     A wake signal I is also input into the power source control unit  401  from the buttons  121  of the operation unit  12 . Upon pressing one of the buttons  121  of the operation unit  12  by the user, the operation unit  12  outputs the wake signal I to the power source control unit  401 . Upon receipt of the wake signal I, the power source control unit  401  turns on the switch  421 . The display unit  122  of the operation unit  12  may be turned on when one of the buttons  121  of the operation unit  12  is pressed by the user. 
     &lt;Operation of Power Source Control Unit  401 &gt; 
     With reference to  FIG. 6 , an operation executed by the power source control unit  401  will now be described. 
     If the power switch  416  is turned from on to off through the operation by the user (YES in step S 601 ), the signal D indicative of the state of the power switch  416  becomes Lo. In step S 602 , the power source control unit  401  notifies the CPU  301  that the power switch  416  is off in response to the signal D, which is being input into the power source control unit  401 , having become Lo. The CPU  301  executes shutdown processing in response to the notification. The shutdown processing executed by the CPU  301  will be described below. 
     In step S 603 , the power source control unit  401  determines whether the shutdown processing executed by the CPU  301  has been finished. Upon finishing of the shutdown processing, the CPU  301  transmits a shutdown finish notification to the power source control unit  401 . If the notification is received (YES in step S 603 ), the power source control unit  401  determines that the shutdown processing has been finished. If the shutdown processing has been finished, then in step S 604 , the power source control unit  401  stops outputting the control signal F to turn off the switches  418  and  419 . This causes the second power supply unit  411  to stop supplying power to the second power supply system devices, and the third power supply unit  412  to stop supplying power to the third power supply system devices. As a result, the second power monitor unit  414  stops outputting the power-good signal B, and the third power monitor unit  415  stops outputting the power-good signal C. With the output of the power-good signals B and C stopped, then in step S 605 , the power source control unit  401  stops outputting the control signal E to turn off the switch  417 . This causes the first power supply unit  410  to stop supplying power to the first power supply system devices. This results in stopping of power supply to each unit of the image forming apparatus  10 . 
     If the power source control unit  401  does not receive the shutdown finish notification from the CPU  301  after the elapse of a predetermined time since the power switch  416  has been turned off (YES in step S 606 ), the power source control unit  401  stops outputting the control signals F and E. This stops power supply to each unit of the image forming apparatus  10  even if the shutdown processing cannot be completed due to any reason including a freeze of the CPU  301 . 
     In step S 607 , the power source control unit  401  determines whether an overcurrent has been detected. If the second power monitor unit  414  has detected an overcurrent, the second power monitor unit  414  stops outputting the power-good signal B. If the third power monitor unit  415  has detected an overcurrent, the third power monitor unit  415  stops outputting the power-good signal C. The power source control unit  401  determines that an overcurrent has been detected if the output of the power-good signal B or the power-good signal C is stopped. If an overcurrent has been detected (YES in step S 607 ), then in step S 608 , the power source control unit  401  stops outputting the control signal F to turn off the switches  418  and  419 . In step S 609 , the power source control unit  401  makes an interrupt request to the CPU  301  to perform the shutdown processing. In step S 610 , the power source control unit  401  determines whether the shutdown processing executed by the CPU  301  has been finished. The power source control unit  401  determines that the shutdown processing has been finished if a shutdown finish notification has been received. If the shutdown processing has been finished (YES in step S 610 ), then in step S 611 , the power source control unit  401  stops outputting the control signals E and K. With the output of the control signal E stopped, the switch  417  is turned off. With the output of the control signal K, voltage is applied to the solenoid of the power switch  416 . This drives the solenoid to turn off the power switch  416 . This stops the power supply to the constituents of the image forming apparatus  10 . 
     If the power source control unit  401  does not receive the shutdown finish notification from the CPU  301  after the elapse of a predetermined time since the power switch  416  has been turned off (YES in step S 612 ), the power source control unit  401  stops outputting the control signals E and K. This stops the power supply to each unit of the image forming apparatus  10  even if the shutdown processing cannot be completed due to reasons including a freeze of the CPU  301 . 
     &lt;Operation of CPU  301 &gt; 
     With reference to  FIG. 7 , the shutdown processing performed by the CPU  301  will now be described. 
     The CPU  301  performs the shutdown processing, when the power switch  416  is turned from on to off, or when an overcurrent is detected. 
     If the power switch  416  is turned from on to off (YES in step S 701 ), then in step S 702 , the CPU  301  performs finish processing for the printer unit  14  and the scanner unit  13 . When the power switch  416  is turned from on to off, the power source control unit  401  notifies the CPU  301  that the power switch  416  has been turned off. In step S 701 , the CPU  301  determines that the power switch  416  is turned off according to the notification. If the power switch  416  is turned off, then in step S 702 , the CPU  301  finishes an application to control the printer unit  14  and an application to control the scanner unit  13 . In step S 703 , the CPU  301  performs the finish processing for the controller  11 . Upon finishing of the shutdown processing, then in step S 704 , the CPU  301  transmits a shutdown finish notification to the power source control unit  401 . 
     In a case where the power switch  416  is not turned off (NO in step S 701 ), if an overcurrent is detected and the power source control unit  401  makes an interrupt request for the shutdown (YES in step S 705 ), the CPU  301  executes the shutdown processing. In the present exemplary embodiment, the CPU  301  does not perform the finish processing for the printer unit  14  and the scanner unit  13 . With the occurrence of the overcurrent, the power source control unit  401  has shut off power supply to the printer unit  14  and the scanner unit  13 , and thus, the CPU  301  does not perform the finish processing for the printer unit  14  and the scanner unit  13 . In step S 706 , the CPU  301  executes the finish processing for the controller  11 . Upon finishing of the shutdown processing, then in step S 707 , the CPU  301  transmits a shutdown finish notification to the power source control unit  401 . 
     The CPU  301  may notify the user of the occurrence of the overcurrent before executing the shutdown processing in response to the interrupt request for the shutdown by the power source control unit  401 . 
     In the present exemplary embodiment described above, the CPU  301  is separated from the second power supply unit  411  and the third power supply unit  412 . Therefore, if the occurrence of an overcurrent at the second power supply unit  411  or the third power supply unit  412  turns off the switches  418  and  419 , the CPU  301  is supplied with power from the first power supply unit  410 . The CPU  301  is, therefore, capable of performing the shutdown processing for the controller  11 . As described above, even with the occurrence of an overcurrent, data saving processing can be performed before power supply to the CPU  301  is stopped in the present exemplary embodiment. 
     Additionally, in the exemplary embodiment, an occurrence of an overcurrent at the second power supply unit  411 , which generates 12 V, or the third power supply unit  412 , which generates 24 V, would lead to increased load to the second power supply system devices and the third power supply system devices. In the present exemplary embodiment, power supply to the second power supply unit  411  and the third power supply unit  412  is shut off immediately at the occurrence of the overcurrent. With this operation, load to be applied to the second power supply system devices and the third power supply system devices can be reduced. 
     In the present exemplary embodiment, the power supply system for the CPU  301  of the controller  11 , which executes the shutdown processing, is independent from the power supply systems for the printer unit  14  and the scanner unit  13 . This allows power supply to the second power supply system devices and the third power supply system devices to be shut off in response to an overcurrent occurrence thereof without shutting off power supply to the CPU  301  of the controller  11 . 
     &lt;Other Exemplary Embodiments&gt; 
     Although the invention has been described in detail based on preferred exemplary embodiments, the invention is not limited to these specific exemplary embodiments. The invention also includes various modifications to be made without departing from the spirit of the invention. Additionally, parts of the exemplary embodiments described above may be combined as appropriate. 
     In the above-described exemplary embodiments, an example has been described in which the power source control unit  401 , which is a hardware logic circuit, executes the steps illustrated in  FIG. 6 , but the invention is not limited thereto. The power source control unit  401  may be a processor, and may execute a program to carry out the steps in  FIG. 6 . 
     Although the exemplary embodiments described above include the second power monitor unit  414  and the third power monitor unit  415 , any one of the power monitor units may be provided. 
     Functions illustrated in the flowcharts described above in the exemplary embodiments may be implemented by a processing apparatus (a CPU or a processor) of a computer, a personal computer, or the like executing software (a program) acquired through a network or any of various types of storage media. 
     According to the exemplary embodiments described above, in a case where an overcurrent flows from the second power supply unit, the second power supply unit stops supplying power and a control unit supplied with power from the first power supply unit can execute the finish processing to prevent loss of data. 
     Other Embodiments 
     Embodiments of the present invention can also be realized by a computer of a system or apparatus that reads out and executes computer executable instructions recorded on a storage medium (e.g., non-transitory computer-readable storage medium) to perform the functions of one or more of the above-described embodiment(s) of the present invention, and by a method performed by the computer of the system or apparatus by, for example, reading out and executing the computer executable instructions from the storage medium to perform the functions of one or more of the above-described embodiment(s). The computer may comprise one or more of a central processing unit (CPU), micro processing unit (MPU), or other circuitry, and may include a network of separate computers or separate computer processors. The computer executable instructions may be provided to the computer, for example, from a network or the storage medium. The storage medium may include, for example, one or more of a hard disk, a random-access memory (RAM), a read only memory (ROM), a storage of distributed computing systems, an optical disk (such as a compact disc (CD), digital versatile disc (DVD), or Blu-ray Disc (BD)™), a flash memory device, a memory card, and the like. 
     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 such modifications and equivalent structures and functions. 
     This application claims the benefit of Japanese Patent Application No. 2013-136175 filed Jun. 28, 2013, which is hereby incorporated by reference herein in its entirety.