Power supply circuit and image forming apparatus

Abstract

To save power.SOLUTION: An image forming apparatus 1 is provided with: a power rectification unit 48 that rectifies and smooths AC voltage to convert it into DC voltage; a transformer 49 that converts the voltage value of the DC voltage output from the power rectification unit 48 and supplies the voltage to a control unit 32; a constant voltage control unit 52 that outputs a feedback signal according to a result of comparison between a reference voltage Vk and the output voltage from the transformer 49; an oscillation control unit 53 that outputs a switching driving signal based on the feedback signal; a switching unit 50 that controls the DC voltage output from the power rectification unit 48 by switching based on the switching driving signal, and applies the voltage to the transformer 49; a voltage setting switching circuit 58 that changes the reference voltage Vk by using a Powersave signal output from the control unit 32; and the control unit 32 that outputs, to a power supply circuit 47, the Powersave signal for controlling the voltage value of the DC voltage supplied from the transformer 49.SELECTED DRAWING: Figure 6

Description

Technical Field

[0001] The present invention relates to a power supply circuit and an image forming apparatus, and is suitable for application to, for example, an electrophotographic image forming apparatus.

Background Art

[0002] Conventionally, in an image forming apparatus, there is one that eliminates waste of unnecessary power and reduces power consumption by providing output voltage switching means for switching an output voltage in a low consumption mode (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In such an image forming apparatus, further power saving is desired.

[0005] The present invention has been made in consideration of the above points, and intends to propose a power supply circuit and an image forming apparatus capable of power saving.

Means for Solving the Problems

[0006] To solve these problems, the power supply circuit of the present invention includes a power supply that receives AC voltage from a commercial power source and a control unit that receives DC voltage from the power supply. The power supply includes a power supply rectifier unit that rectifies and smooths the AC voltage to convert it into DC voltage, a transformer that converts the voltage value of the DC voltage output from the power supply rectifier unit and supplies it to the control unit, a constant voltage control unit that outputs a feedback signal according to the result of comparing a reference voltage with the output voltage of the transformer, an oscillation control unit that outputs a switching drive signal based on the feedback signal, a switching unit that controls the DC voltage output from the power supply rectifier unit by switching based on the switching drive signal and applies it to the transformer, and a voltage setting switching unit that changes the reference voltage according to a control signal output from the control unit. The control unit is The control unit has multiple power cut-off switches, provided for each of the multiple operating voltage ranges of external devices connected to the control unit, which switch between cutting off and supplying the voltage to the external devices. When transitioning to a power-saving state, the power cut-off switches corresponding to the operating voltage range of the external devices connected to the control unit are kept ON, thereby maintaining the supply of voltage to the external devices connected to the control unit. At the same time, the power cut-off switches corresponding to the operating voltage range of external devices not connected to the control unit are turned OFF, thereby cutting off the supply of voltage to external devices not connected to the control unit. Simultaneously, a control signal is output to the power supply that controls the voltage value of the DC voltage supplied from the transformer to a voltage value corresponding to the operating voltage range in which the power cut-off switches are kept ON. I did that.

[0007] Furthermore, the image forming apparatus of the present invention includes a power supply that receives AC voltage from a commercial power supply, a control unit that receives DC voltage from the power supply, and an image forming unit that forms an image on a medium. The power supply includes a power supply rectifier unit that rectifies and smooths the AC voltage to convert it into DC voltage, a transformer that converts the voltage value of the DC voltage output from the power supply rectifier unit and supplies it to the control unit, a constant voltage control unit that outputs a feedback signal according to the result of comparing a reference voltage with the output voltage of the transformer, an oscillation control unit that outputs a switching drive signal based on the feedback signal, a switching unit that controls the DC voltage output from the power supply rectifier unit by switching based on the switching drive signal and applies it to the transformer, and a voltage setting switching unit that changes the reference voltage according to a control signal output from the control unit. The control unit is The control unit has multiple power cut-off switches, provided for each of the multiple operating voltage ranges of external devices connected to the control unit, which switch between cutting off and supplying the voltage to the external devices. When transitioning to a power-saving state, the power cut-off switches corresponding to the operating voltage range of the external devices connected to the control unit are kept ON, thereby maintaining the supply of voltage to the external devices connected to the control unit. At the same time, the power cut-off switches corresponding to the operating voltage range of external devices not connected to the control unit are turned OFF, thereby cutting off the supply of voltage to external devices not connected to the control unit. Simultaneously, a control signal is output to the power supply that controls the voltage value of the DC voltage supplied from the transformer to a voltage value corresponding to the operating voltage range in which the power cut-off switches are kept ON. I did that.

[0008] The present invention enables a power-saving state when no external device to be powered is connected, by maintaining a voltage lower than the voltage supplied to the external device. [Effects of the Invention]

[0009] According to the present invention, a power supply circuit and an image forming apparatus that can reduce power consumption can be realized. [Brief explanation of the drawing]

[0010] [Figure 1] This is a perspective view showing the external configuration of an image forming apparatus. [Figure 2] This is a left side view showing the internal configuration of an image forming apparatus. [Figure 3] This is a block diagram showing the control configuration of an image forming apparatus. [Figure 4] This is a block diagram showing the configuration of a power supply circuit. [Figure 5] This is a circuit diagram showing the configuration of the constant voltage control unit and the oscillation control unit. [Figure 6] This is a block diagram showing the configuration of the control unit. [Figure 7] This is a time chart showing the operation of the control unit. [Modes for carrying out the invention]

[0011] The embodiments for carrying out the invention (hereinafter referred to as embodiments) will be described below with reference to the drawings. [1. Configuration of the image forming apparatus] As shown in Figures 1 and 2, the image forming apparatus 1 is a so-called direct tandem color printer and has a roughly box-shaped apparatus housing 2. In the following description of the image forming apparatus 1, the side of the image forming apparatus 1 that the user faces in front of the apparatus housing 2 will be referred to as the front, the opposite side as the rear, the left and right sides as viewed from the user facing the front, and the upper and lower sides will be defined and explained accordingly. The image forming apparatus 1 is comprehensively controlled by the control unit 32 (Figure 3).

[0012] A paper feeding section 4 is provided on the lower side of the device housing 2. The paper feeding section 4 consists of a paper feed cassette 5, a paper feed roller 6, and a registration roller 7, etc. By rotating the paper feed roller 6, the paper S is discharged from the paper feed cassette 5, and its movement is detected by a paper feed sensor and transported to the registration roller 7.

[0013] Furthermore, the device housing 2 is provided with an image forming unit 11 for forming a printed image by printing the color image to be printed on the surface of the paper S. The image forming unit 11 has four image forming units 3 (image forming units 3K, 3Y, 3M, and 3C) arranged in order from the front (upstream) to the rear (downstream). These units develop electrostatic latent images representing the different color components of the printed image—black (K), yellow (Y), magenta (M), and cyan (C)—using toner to form a toner image corresponding to the print job. The image forming units 3K, 3Y, 3M, and 3C are similarly configured except that they use different colored toners for developing the electrostatic latent images, and are detachably mounted in order from the front to the rear at the upper end of the device housing 2. The image forming units 3K, 3Y, 3M, and 3C rotate the photosensitive drum 12 while the LED (Light Emitting Diode) head 13 exposes the surface of the photosensitive drum 12 to form an electrostatic latent image representing predetermined color components of the printed image, and then develop this electrostatic latent image using toner to form a toner image. When the cover 8 located on the top of the device housing 2 is closed, the LED head 13 comes into contact with the developing device 14 and exposes the charged surface of the photosensitive drum 12 based on the print data to form an electrostatic latent image.

[0014] Furthermore, the image forming unit 11 has a transfer unit 10 positioned below the image forming unit 3K and below the image forming unit 3C, which transfers the toner image formed by the image forming units 3K, 3Y, 3M, and 3C onto the surface of the paper S. The transfer unit 10 has a drive roller 15 and a tension roller 16 rotatably mounted diagonally below the rear of the image forming unit 3C and diagonally below the front of the image forming unit 3K, respectively. The transfer unit 10 also has an endless transport belt 9 stretched from the drive roller 15 to the tension roller 16, which electrostatically attracts and transports the paper S for toner image transfer. The transport belt 9 is transported along the belt travel direction Db by the rotational drive of the drive roller 15.

[0015] The image forming units 3K, 3Y, 3M, and 3C are identically configured except that the color of the toner used for developing the electrostatic latent image is different. Therefore, hereinafter, the image forming units 3K, 3Y, 3M, and 3C will be collectively described as the image forming unit 3. The image forming unit 3 includes a developing device 14 and a toner cartridge 17. The developing device 14 has a case formed in a substantially J shape, and is provided with a supply roller 18, a developing roller 19, a photosensitive drum 12, a charging roller 20, and a cleaning unit 21. The supply roller 18 supplies the toner stored in the toner cartridge 17 to the developing roller 19 side. The charging roller 20 uniformly charges the surface of the photosensitive drum 12. The developing roller 19 charges the toner and electrostatically attaches it to the electrostatic latent image formed on the photosensitive drum 12 to form a toner image with a certain layer thickness. The cleaning unit 21 removes the toner remaining on the surface of the photosensitive drum 12 after transfer. The photosensitive drum 12 carries the electrostatic latent image and also carries the toner image obtained by developing the electrostatic latent image with toner.

[0016] Also, inside the conveyance belt 9 in the transfer unit 10, four transfer rollers 22 corresponding to the four photosensitive drums 12 are provided so as to be arranged in order from the front side to the rear side and rotatable. Thereby, when forming a printed image, the transfer unit 10 sandwiches the paper S conveyed by the conveyance belt 9 between the upper part of the surface of the transfer roller 22 and the lower part of the surface of the corresponding four photosensitive drums 12 in order, and transfers the toner images on the surfaces of the four photosensitive drums 12 to the surface of the paper S by applying a transfer bias voltage to the transfer roller 22.

[0017] In this configuration, the image forming unit 3 supplies toner from the toner cartridge 17 to the developing unit 14. Subsequently, the image forming unit 3 rotates the photosensitive drum 12 and uniformly charges the surface of the photosensitive drum 12 with the charging roller 20, and exposes the surface of the photosensitive drum 12 with the LED head 13 based on the print data to form an electrostatic latent image. Next, the image forming unit 3 applies a development bias voltage to the developing roller 19, thereby electrostatically depositing the toner supplied by the supply roller 18 onto the electrostatic latent image formed on the photosensitive drum 12 to form a toner image. Furthermore, the image forming unit 3 sandwiches the paper S, which is being transported by the transport belt 9, between the transfer roller 22 and the photosensitive drum 12, transferring the toner image on the surface of the photosensitive drum 12 to the surface of the paper S. In this way, the transfer unit 10 transfers toner images for all four colors to the surface of the paper S and hands over the paper S with the transferred toner image to the fixing unit 23.

[0018] In the image forming unit 11, a fixing unit 23 is positioned behind the transfer unit 10 to fix the toner image to the surface of the paper S. The fixing unit 23 has a paper passage formed approximately in the center of the fixing unit housing 24 for passing the paper S, and is provided with fixing rollers 25. These fixing rollers 25 consist of a heating roller 26 rotatably mounted on the upper side of the paper passage and a pressure roller 27 rotatably mounted on the lower side of the paper passage. Thus, when forming a printed image, the fixing unit 23 takes the paper S, on which the toner image has been transferred from the transfer unit 10, into the paper passage and sandwiches it between the heating roller 26 and the pressure roller 27, which are rotating in opposite directions. The fixing unit 23 then heats and pressurizes the paper S between the heating roller 26 and the pressure roller 27, which are rotating in opposite directions, thereby fixing the toner image to the surface of the paper S. The fixing unit 23 fixes the toner images for four colors to the surface of the paper S to form a printed image, and then passes the paper S with the printed image to the upper discharge unit 30 or the lower duplex printing unit 29 via a switching plate 28.

[0019] In such a configuration, the image forming apparatus 1 conveys the paper S stored in the paper feed cassette 5 to the image forming unit 11 by the paper feed unit 4. While conveying the paper S by the conveyance belt 9, the image forming unit 11 transfers toner onto the paper S by the developing device 14 of the image forming unit 3. The paper S is conveyed to the fixing unit 23 by the conveyance belt 9. When the paper S passes through, the fixing unit 23 fixes the toner placed on the paper S to the paper S by high temperature. The conveyance direction of the paper S is switched by the switching plate 28, and after being conveyed to the discharge unit section 30, it is discharged to the paper delivery unit 31 or conveyed to the duplex printing unit 29. The paper S conveyed to the duplex printing unit 29 is conveyed back to the image forming unit 11 again for image formation on the opposite side of the paper, and after passing through the fixing unit 23 again, it is discharged to the paper delivery unit 31.

[0020] [2. Control Configuration of Image Forming Apparatus] As shown in FIG. 3, the control unit 32 is composed of a logic circuit unit (logical circuit unit) 34 and a drive circuit unit 33. The logic circuit unit 34 is mainly composed of a CPU (Central Processing Unit) 35, a RAM (Random Access Memory) 36, and a ROM (Read Only Memory) 37. The CPU 35 is connected to various sensors 38 and an operation board 39, and a drive circuit 40 of the drive circuit unit 33 is connected thereto, and outputs a signal for drive control to the drive circuit 40. The ROM 37 stores various programs such as a control program (software) related to the image forming operation in the image forming unit 11 (FIG. 2). The CPU 35 reads out the necessary programs from the ROM 37 and comprehensively controls the operations of the paper feed unit 4 and the image forming unit 11 to execute the image forming operation. The RAM 36 is used as a work area when the CPU 35 executes the control program. The DC voltage used in this logic circuit unit 34 is 5 [V].

[0021] The drive system circuit section 33 mainly consists of a drive circuit 40 and actuators 41 that operate based on the drive signals output from the drive circuit 40. The actuators 41 consist of a paper feed motor 42, a transport motor 43, a belt motor 44, a fixing motor 45, and a developing drive motor 46, etc. These actuators 41 drive each component described in Figure 2. The DC voltage used for driving in this drive system circuit section 33 is 24[V].

[0022] The DC voltage Vin supplied to the logic circuit section 34 of the control unit 32 configured in this way, and the drive DC voltage 24V supplied to the drive circuit section 33, are supplied from the power supply circuit 47 (Figure 4), which will be described later.

[0023] The control unit 32 is equipped with a timing means such as a timer for measuring the passage of time. After the initial operation when the power is turned on or after the image forming operation is completed, the control unit 32 transitions the image forming apparatus 1 from the standby state to a sleep state after a predetermined amount of time has elapsed. Furthermore, when the control unit 32 receives an operation instruction such as a print instruction from a higher-level device or operator while in the standby state or sleep state, it transitions the image forming apparatus 1 to the operating state.

[0024] In operation, the logic circuit section 34 is supplied with a supply voltage Vin (DC voltage 5[V]) from the power supply circuit 47, and the drive circuit section 33 is supplied with a drive DC voltage of 24[V] from the power supply circuit 47. On the other hand, in standby or sleep mode, the logic circuit section 34 is supplied with a supply voltage Vin (DC voltage of 5[V] or less) from the power supply circuit 47, but the drive circuit section 33 is not supplied with a drive DC voltage of 24[V] from the power supply circuit 47.

[0025] Here, "operating state" refers to the state in which the image forming apparatus 1 is operating after receiving operation instructions such as print instructions from a higher-level device or operator. "Standby state" refers to the state in which the image forming apparatus 1 is not performing any operations such as printing, and is waiting in a state where it can immediately print if it receives operation instructions such as print data. Furthermore, "sleep state" refers to a state in which a predetermined amount of time has elapsed since the image forming apparatus 1 transitioned to the standby state, and preparatory operations are required before it can perform printing operations after receiving operation instructions such as print data. This state is functionally more dormant than the standby state.

[0026] [3. Power Supply Circuit Configuration] As shown in Figure 4, the power supply circuit 47 is composed of a power rectifier unit 48, a switching unit 50, a secondary rectifier unit 51, a constant voltage control unit 52, and an oscillation control unit 53.

[0027] The power supply rectifier unit 48 rectifies and smooths the AC voltage, which is the commercial power input from an external source. The switching unit 50 switches the DC voltage output from the power supply rectifier unit 48 by switching operation and supplies it to the primary side (input winding side) of the transformer 49. The secondary rectifier unit 51 rectifies the square wave induced on the secondary side (output winding side) of the transformer 49 and outputs a DC voltage to the control unit 32, which is the load device.

[0028] The constant voltage control unit 52 compares the reference voltage Vk with the output voltage of the secondary rectifier unit 51 and outputs a control signal (feedback signal) to the oscillation control unit 53 according to the result of the comparison. The constant voltage control unit 52 is also connected to the Powersave signal output from the control unit 32 for switching between voltage setting and phase compensation.

[0029] The oscillation control unit 53 outputs a switching drive signal to the switching unit 50 according to the control signal output from the constant voltage control unit 52, that is, the amount of feedback of the output voltage of the secondary rectifier unit 51.

[0030] The switching unit 50 changes the voltage applied to the primary side of the transformer 49 by changing the operating time for switching the DC voltage output from the power supply rectifier unit 48 based on the switching drive signal output from the oscillation control unit 53.

[0031] Furthermore, the power supply circuit 47 is a flyback type circuit, and since it is a power supply that supplies multiple voltage outputs, multiple flyback circuits are connected to the power supply rectifier unit 48 and the control unit 32. The DC voltage output of each of these flyback circuits is supplied to the logic circuit unit 34 and the drive circuit unit 33 of the control unit 32, respectively. In the following description, the explanation of the 24[V] drive DC voltage supplied to the drive circuit unit 33 will be omitted.

[0032] [4. Configuration of the constant voltage control unit and the oscillation control unit] As shown in Figure 5, the constant voltage control unit 52 mainly consists of a shunt regulator 54 which serves as the reference voltage Vk, and a voltage setting switching circuit 58 which generates a detection voltage Vref from the output voltage of the secondary rectifier 51. The detection voltage Vref generated by the resistive voltage division by the voltage setting switching circuit 58 is input to the reference terminal of the shunt regulator 54 as a comparison voltage.

[0033] The shunt regulator 54 is connected to a capacitor 61 and a resistor 62 for phase compensation to ensure the stability and responsiveness of the control element 59. A limiting resistor 63 is connected in series with the shunt regulator 54 via the photocoupler 64 to limit the current flowing to the photodiode 64a of the photocoupler 64.

[0034] The oscillation control unit 53 mainly consists of the phototransistor 64b of the photocoupler 64 and a control element 59 for converting the output of the phototransistor 64b into a gate signal for the switching unit 50. The output of the control element 59 is connected to the FET (Field Effect Transistor) 60 of the switching unit 50 via a limiting resistor 65. Here, the oscillation control unit 53 is an element that controls the on / off time interval of the switching unit 50 to obtain a stable output voltage.

[0035] When current is supplied to the photodiode 64a of the photocoupler 64, light causes current to flow to the base of the phototransistor 64b, and then current flows from the collector terminal to the emitter terminal, turning the photocoupler 64 on. In this way, the photocoupler 64 is switched on / off by the supply of current to the photodiode 64a. At this time, the photodiode 64a and the phototransistor 64b are electrically isolated from each other. A limiting resistor 68 is connected in series with the photocoupler 64 to limit the current flowing to the phototransistor 64b. Capacitors 66 and 67 and a resistor 69 are also provided in the oscillation control unit 53 to ensure the stability of the operation of the control element 59.

[0036] Furthermore, the voltage setting switching circuit 58 consists of voltage divider resistors 55A and 55B, voltage divider resistors 56A and 56B that smooth the PWM signal and adjust the detection voltage Vref mentioned above, and a smoothing capacitor 57. The Powersave signal, which is a PWM (Pulse Width Modulation), is input to this voltage setting switching circuit 58 from the control unit 32 (Figure 4). PWM is a pulse signal that repeatedly switches between a Low level of 0[V] and a High level of open output with a constant duty cycle.

[0037] When the image forming apparatus 1 is started up, if the Powersave signal remains open output, no current flows through the voltage divider resistor 56B. Therefore, the detected voltage Vref is determined by the voltage divider resistors 56A, 55A, and 55B, and the detected voltage Vref is at its highest state. In this state, the supply voltage Vin to the control unit 32 is set to output a voltage value of 5[V]. On the other hand, if the PWM remains at a low level, the detected voltage Vref is determined by the voltage divider resistors 56A, 55A, 55B, and 56B, and the detected voltage Vref is at its lowest state. In this state, the supply voltage Vin to the control unit 32 is set to output 3.3[V].

[0038] This voltage setting switching circuit 58 allows the control unit 32 to gradually decrease the detected voltage Vref by reducing the proportion of the PWM High level in the Powersave signal (i.e., Duty). Therefore, by changing the PWM Duty, the control unit 32 can change the supply voltage Vin to which it is powered from 3.3[V] to 5[V]. The pulse period of the PWM signal should preferably be a period (10[kHz] or higher) that can sufficiently smooth the detected voltage Vref in order to reduce the ripple voltage generated in the supply voltage Vin.

[0039] [5. Configuration of the control unit] As shown in Figure 6, the control unit 32 has power supply zones 70A, 70B, 70C, and 70D, which are wiring to which power is supplied. These power supply zones 70A, 70B, 70C, and 70D are electrically separated from each other by switches SW1, SW2, and SW3. Hereafter, power supply zones 70A, 70B, 70C, and 70D will be collectively referred to as power supply zone 70.

[0040] [5-1. Configuration of Power Zone 70A] The voltage detection element IC1, switch SW1, and sub-CPU 72A are connected to power zone 70A. The supply voltage Vin, supplied from the power supply circuit 47, is supplied to the voltage detection element IC1, switch SW1, and sub-CPU 72A. The power supply voltage range for this power zone 70A is set to 3.3[V] to 5.25[V].

[0041] The voltage detection element IC1 is a reset IC connected to the sub-CPU 72A. It detects the voltage state of power supply zone 70A and notifies the sub-CPU 72A of the detection result. Specifically, the voltage detection element IC1 notifies a High level if the voltage of power supply zone 70A exceeds 3.3[V], and a Low level if it falls below 3.3[V].

[0042] Switch SW1, which acts as the first power cut-off switch, is connected to the sub-CPU 72A and is controlled by the sub-CPU 72A according to the state of the voltage detection element IC2 to supply or cut off power from power zone 70A to power zone 70B.

[0043] The sub-CPU 72A is configured, for example, by a microcontroller, and performs limited sub-control to the main CPU 72B, which performs the main control, during a power-saving sleep state. The sub-CPU 72A has an operating voltage range of 3.3[V] to 5.25[V], and operates when at least 3.3[V] is supplied. The sub-CPU 72A can also turn switch SW1 ON / OFF by sending an output signal to switch SW1. Furthermore, the sub-CPU 72A is connected to the main CPU 72B, which is the main CPU of the image forming apparatus 1, and transmits a Powersave signal to the constant voltage control unit 52 of the power supply circuit 47 (Figure 4) in response to notifications from voltage detection element IC1 and voltage detection element IC2.

[0044] [5-2. Configuration of Power Zone 70B] Power supply zone 70B is connected downstream of switch SW1, and the voltage detection element IC2, switch SW2, and DC-DC converter 74 are connected to it. The power supply voltage range for this power supply zone 70B is set to 3.8[V] to 5.25[V].

[0045] The voltage detection element IC2 is a reset IC connected to the sub-CPU 72A. It detects the voltage state of the power supply zone 70B and notifies the sub-CPU 72A of the detection result. Specifically, the voltage detection element IC2 notifies a High level when the voltage of the power supply zone 70B exceeds 3.8[V], and a Low level when it falls below 3.8[V].

[0046] Switch SW2, which acts as a second power cut-off switch, is connected to the main CPU 72B and is controlled by the main CPU 72B according to the state of the voltage detection element IC3 to supply or cut off power from power zone 70B to power zone 70C.

[0047] The DC-DC converter 74 supplies a stable 3.3V power to the main CPU 72B by stepping down a voltage of 3.8V or higher (for example, 5V) to a 3.3V voltage.

[0048] [5-3. Configuration of Power Zone 70C] Power supply zone 70C is connected downstream of switch SW2, and the voltage detection element IC3 and switch SW3 are connected to it. The power supply voltage range of this power supply zone 70C is set to 4.5[V] to 5.25[V]. An expansion tray 84 can also be connected to power supply zone 70C. When the expansion tray 84 is connected to power supply zone 70C, it receives power from power supply zone 70C and becomes operational.

[0049] The voltage detection element IC3 is a reset IC connected to the main CPU 72B. It detects the voltage state of the power supply zone 70C and notifies the main CPU 72B of the detection result. Specifically, the voltage detection element IC3 notifies a High level if the voltage of the power supply zone 70C exceeds 4.5[V], and a Low level if it falls below 4.5[V].

[0050] Switch SW3 is connected to the main CPU 72B and, under the control of the main CPU 72B, supplies or cuts off power from power zone 70C to power zone 70D.

[0051] The main CPU 72B is configured, for example, by a microcontroller and is the main CPU of the image forming apparatus 1. This sub-CPU 72 has an operating voltage range of 3.3 ± 0.5 [V] and operates when 3.3 [V] is supplied. The main CPU 72B can turn switches SW2 and SW3 ON / OFF by sending output signals to switches SW2 and SW3.

[0052] The expansion tray 84 has an operating voltage range of 4.5[V] to 5.25[V] and operates when at least 4.5[V] is supplied. When the expansion tray 84 is powered from the power supply zone 70C, communication takes place between the expansion tray 84 and the main CPU 72B via a communication signal line (not shown). When communication with the expansion tray 84 is established, the main CPU 72B can detect that the expansion tray 84 is mounted on the image forming apparatus 1.

[0053] [5-4. Configuration of Power Zone 70D] The power supply zone 70D is connected downstream of the switch SW3. The power supply voltage range of this power supply zone 70D is set to 4.75[V] to 5.25[V]. The power supply zone 70D is equipped with a USB Host 80, to which an external USB device (not shown) can be connected. This USB device operates by receiving power from the image forming apparatus 1 and communicating via USB (Universal Serial Bus). The USB device has an operating voltage range of 4.75[V] to 5.25[V] and will operate when a voltage of at least 4.75[V] is supplied. When this USB device is connected to the USB Host 80, power is supplied from the power supply zone 70D, and it becomes operational. When the USB device is powered from the power supply zone 70D, communication takes place between the USB device and the main CPU 72B via a communication signal line (not shown). When communication with the USB device is established, the main CPU 72B can detect that an external device is connected to the USB Host 80.

[0054] Furthermore, a WLAN (Wireless Local Area Network) unit 82, which is an optional wireless LAN unit powered by the image forming apparatus 1, can be connected to the power zone 70D. The WLAN unit 82 has an operating voltage range of 4.75[V] to 5.25[V], and will operate when a voltage of at least 4.75[V] is supplied. When the WLAN unit 82 is connected to the power zone 70D, it is powered from the power zone 70D and becomes operational. When the WLAN unit 82 is powered from the power zone 70D, communication takes place between the WLAN unit 82 and the main CPU 72B via a communication signal line (not shown). When communication with the WLAN unit 82 is established, the main CPU 72B can detect that the WLAN unit 82 is connected to the power zone 70D.

[0055] Furthermore, USB Device 86 and LAN Unit 88, which operate by receiving power from a Host PC (not shown) and are not powered by the image forming apparatus 1, are not connected to any power zone 70.

[0056] In the following, the voltage detection elements IC1, IC2, and IC3 will be collectively referred to as the voltage detection element IC, and the switches SW1, SW2, and SW3 will be collectively referred to as the power cut-off switches SW.

[0057] [6. Operation of the power supply circuit] In this configuration, the operation of the power supply circuit 47 will be explained using Figures 4 and 5. In the power supply circuit 47, the AC voltage (AC input) input from the outside is rectified and smoothed by the power supply rectifier unit 48 and output as a DC voltage to the switching unit 50. The switching unit 50 is turned on / off by the control of the constant voltage control unit 52 and the oscillation control unit 53, and switches the output voltage of the power supply rectifier unit 48 to supply to the primary side of the transformer 49.

[0058] The square wave induced on the secondary side of the transformer 49 is rectified and smoothed as a DC voltage by the secondary rectifier 51 and output. In this embodiment, the supply voltage Vin output from the secondary rectifier 51 is 5[V], and this supply voltage Vin is supplied to the control unit 32. The output voltage of the secondary rectifier 51 is also applied to the constant voltage control unit 52.

[0059] The constant voltage control unit 52 compares the reference voltage Vk of the shunt regulator 54 with the detected voltage Vref determined by the voltage setting switching circuit 58 in order to maintain a constant voltage at all times. If the output voltage of the secondary rectifier unit 51 is higher or lower than the reference voltage Vk, it outputs a feedback signal to the oscillation control unit 53 to adjust the on / off operation time of the switching unit 50.

[0060] In this manner, the constant voltage control unit 52 outputs a feedback signal to the oscillation control unit 53 so that the output voltage of the secondary rectifier unit 51 becomes the reference voltage Vk. The oscillation control unit 53 controls the on / off time of the switching operation of the switching unit 50 based on the feedback signal, thereby keeping the output voltage of the secondary rectifier unit 51 at a constant voltage.

[0061] [7. Operation of the power supply circuit] Figure 7 shows a time chart of the operation of the control unit 32 of the image forming apparatus 1 in this embodiment. First, the image forming apparatus 1 starts up at timing T1. At this time, the sub-CPU 72A and the main CPU 72B are powered by a supply voltage Vin of 5[V] from the power supply circuit 47 and start up simultaneously. When the image forming apparatus 1 starts up with power supplied to the power supply circuit 47, the Powersave signal output from the sub-CPU 72A is an open output, so the PWM Duty is at 100[%], and the power supply circuit 47 starts supplying a supply voltage of 5[V] as Vin to the control unit 32. Since the image forming apparatus 1 wants to start printing as soon as possible after startup, it does not enter a sleep state, but maintains the supply voltage Vin at its maximum voltage of 5[V] output by setting the PWM Duty to 100[%].

[0062] When the printing operation is completed and a predetermined time has elapsed or a command to transition to sleep mode is received, the image forming apparatus 1 begins preparing to transition to sleep mode. When the transition to sleep mode begins, the image forming apparatus 1 first stops supplying 24[V] to the drive system circuit 33.

[0063] Next, the main CPU 72B checks whether the USB Host 80 and WLAN unit 82, which operate within the power supply voltage range of 4.75[V] to 5.25[V] set for power supply zone 70D, are connected to power supply zone 70D as expansion devices. If the main CPU 72B detects that the USB Host 80 and WLAN unit 82 are connected to power supply zone 70D as expansion devices, it enters sleep mode with switch SW3 still ON. Therefore, when the image forming apparatus 1 enters sleep mode with the expansion device connected to power supply zone 70D, the expansion device continues to receive power from power supply zone 70D. This allows the expansion device to operate even in sleep mode.

[0064] On the other hand, if the main CPU 72B cannot detect that the USB Host 80 or WLAN unit 82 are connected as additional devices, it determines that it does not need to supply power to the USB Host 80 or WLAN unit 82 and turns off switch SW3 at timing T2. When the main CPU 72B turns off switch SW3, the power supply to the power supply zone 70D downstream of switch SW3 is cut off. As a result, the image forming apparatus 1 can reduce the supply voltage Vin to the required 4.5[V] in the power supply zone 70C, which is set to a power supply voltage range of 4.5[V] to 5.25[V].

[0065] In this case, after the main CPU 72B turns the switch SW3 OFF, it instructs the sub-CPU 72A to gradually decrease the PWM Duty of the Powersave signal. Here, decreasing the PWM Duty means increasing the amount of time the Powersave signal is at 0[V] per unit time. As the PWM Duty gradually decreases, the supply voltage Vin gradually decreases. When the supply voltage Vin gradually decreases and the voltage detection element IC3 detects 4.5[V] at timing T3, the voltage detection element IC3 notifies the main CPU 72B that the supply voltage Vin has decreased to the predetermined voltage of 4.5[V]. Upon receiving notification from the voltage detection element IC3, the main CPU 72B instructs the sub-CPU 72A to maintain the PWM Duty.

[0066] Next, the main CPU 72B checks whether the expansion tray 84, which can be driven within the power supply voltage range of 4.5[V] to 5.25[V] set in the power supply zone 70C, is connected to the power supply zone 70C. If the main CPU 72B detects that the expansion tray 84 is connected to the power supply zone 70C, it enters sleep mode with switch SW2 still ON. Therefore, when the image forming apparatus 1 enters sleep mode with the expansion tray 84 connected to the power supply zone 70C, the expansion tray 84 continues to receive power from the power supply zone 70C. As a result, the expansion tray 84 remains operational even in sleep mode.

[0067] On the other hand, if the main CPU 72B cannot detect that the expansion tray 84 is connected, it determines that it does not need to supply power to the expansion tray 84 and turns off switch SW2 at timing T4. When the main CPU 72B turns off switch SW2, the power supply to the power supply zone 70C downstream of switch SW2 is cut off. As a result, the image forming apparatus 1 can reduce the supply voltage Vin to the required 3.8[V] in the power supply zone 70B, which is set to a power supply voltage range of 3.8[V] to 5.25[V].

[0068] In this case, after turning off switch SW2, the main CPU 72B instructs the sub-CPU 72A to gradually further decrease the PWM Duty of the Powersave signal. When the supply voltage Vin drops further and the voltage detection element IC2 detects 3.8[V] at timing T5, the voltage detection element IC2 notifies the main CPU 72B that the supply voltage Vin has dropped to the predetermined voltage of 3.8[V]. Upon receiving notification from the voltage detection element IC2, the main CPU 72B instructs the sub-CPU 72A to maintain the PWM Duty.

[0069] Here, the main CPU 72B operates at 3.3[V], and in order to operate the main CPU 72B based on a supply voltage Vin of 3.8[V] to 5[V], the DC-DC converter 74 steps down the supply voltage Vin to generate 3.3[V] and supplies it to the main CPU 72B. Generally, since the DC-DC converter 74 steps down the input voltage and outputs it, the input voltage must be at least the forward voltage of the switching diode built into the converter IC higher than the output voltage of the DC-DC converter 74. Therefore, the power supply zone 70B requires a voltage higher than the voltage required to generate the 3.3[V] for the main CPU 72B. For this reason, in this embodiment, the power supply voltage range required for the power supply zone 70B is set to 3.8[V] to 5.25[V].

[0070] Next, the main CPU 72B checks whether it can shut off its own power supply. In order to transition to the off mode, which is the mode that reduces power consumption the most for the image forming apparatus 1, by shutting off switch SW1 and shutting off the power supply to the main CPU 72B, the image forming apparatus 1 must stop all but a limited minimum of functions, such as monitoring the power switch. This requires that processes such as backing up temporary information that was stored on RAM 36 (Figure 3) to ROM 37 be completed. Once the transition process to off mode is complete, the main CPU 72B instructs the sub-CPU 72A to turn off switch SW1.

[0071] When the sub-CPU 72A turns off switch SW1 at timing T6, the power supply to the power supply zone 70B downstream of switch SW1 is cut off. As a result, the image forming apparatus 1 can reduce the supply voltage Vin to the required 3.3[V] in power supply zone 70A, which is set to a power supply voltage range of 3.3[V] to 5.25[V].

[0072] In this case, after switching switch SW1 OFF, the sub-CPU 72A gradually further reduces the PWM Duty of the Powersave signal to 0%. When the supply voltage Vin drops further and the voltage detection element IC1 detects 3.3V at timing T7, the voltage detection element IC1 notifies the sub-CPU 72A that the supply voltage Vin has dropped to the predetermined voltage of 3.3V. At this point, the PWM Duty becomes 0%.

[0073] Sub-CPU 72A monitors the power ON status of the image forming apparatus 1 and remains in off mode until the image forming apparatus 1 restarts and powers on. When sub-CPU 72A detects that the image forming apparatus 1 has restarted by acquiring a change in the power ON signal (not shown), sub-CPU 72A turns on switch SW1 at timing T8. When sub-CPU 72A turns on switch SW1, power supply to the power zone 70B downstream of switch SW1 begins.

[0074] After switching SW1 ON, the sub-CPU 72A gradually increases the PWM Duty of the Powersave signal. Instead of setting the PWM Duty to 100% immediately, the sub-CPU 72A gradually increases the PWM Duty of the Powersave signal. As the PWM Duty gradually increases, the supply voltage Vin also gradually increases. When the supply voltage Vin gradually increases and the voltage detection element IC2 detects 3.8V at timing T9, the voltage detection element IC1 notifies the sub-CPU 72A that the supply voltage Vin has risen to the predetermined voltage of 3.8V. Upon receiving notification from the voltage detection element IC1, the sub-CPU 72A maintains the PWM Duty and begins communicating with the main CPU 72B to confirm that the main CPU 72B has started up.

[0075] When communication with the sub-CPU 72A becomes possible, the main CPU 72B turns on switch SW2 at timing T10. When the main CPU 72B turns on switch SW2, power supply to the power zone 70C downstream of switch SW2 begins.

[0076] After the main CPU 72B turns on switch SW2, it instructs the sub-CPU 72A to gradually increase the PWM Duty of the Powersave signal. When the supply voltage Vin rises further and the voltage detection element IC2 detects 4.5[V] at timing T11, the voltage detection element IC2 notifies the sub-CPU 72A that the supply voltage Vin has risen to the predetermined voltage of 4.5[V]. Upon receiving notification from the voltage detection element IC2, the sub-CPU 72A maintains the PWM Duty.

[0077] Next, the main CPU 72B checks if the expansion tray 84, which can be operated within the power supply voltage range of 4.5[V] to 5.25[V] set for power supply zone 70C, is connected to power supply zone 70C.

[0078] Next, at timing T12, the main CPU 72B turns on switch SW3. When the main CPU 72B turns on switch SW3, power supply to the power zone 70D downstream of switch SW3 begins.

[0079] After the main CPU 72B turns on switch SW3, it instructs the sub-CPU 72A to gradually increase the PWM Duty of the Powersave signal to 100%. When the supply voltage Vin rises further and the voltage detection element IC3 detects 5.0V at timing T13, the voltage detection element IC3 notifies the main CPU 72B that the supply voltage Vin has risen to the predetermined voltage of 5.0V. At this point, the PWM Duty becomes 100%. Upon receiving notification from the voltage detection element IC3, the main CPU 72B instructs the sub-CPU 72A to maintain the PWM Duty.

[0080] Next, the main CPU 72B checks whether the USB Host 80 and WLAN unit 82, which operate within the power supply voltage range of 4.75[V] to 5.25[V] set for power supply zone 70D, are connected to power supply zone 70D as additional devices.

[0081] Subsequently, if the main CPU 72B cannot detect that the USB Host 80 or WLAN unit 82 are connected as expansion devices, it determines that it does not need to supply power to the USB Host 80 or WLAN unit 82 and turns off switch SW3. When the main CPU 72B turns off switch SW3, the power supply to the power zone 70D downstream of switch SW3 is cut off. As a result, when an expansion device is connected to the power zone 70D, the main CPU 72B will not be able to recognize the expansion device simply by plugging it in like a plug-and-play device, but power consumption in sleep mode can be reduced.

[0082] Furthermore, if the main CPU 72B cannot detect that the USB Host 80 or WLAN unit 82 are connected as expansion devices, and also cannot detect that the expansion tray 84 is connected, the main CPU 72B determines that it does not need to supply power to the USB Host 80, WLAN unit 82, or expansion tray 84, and turns off switch SW2 in addition to switch SW3. When the main CPU 72B turns off switch SW2, the power supply to power zones 70C and 70D downstream of switch SW2 is cut off. As a result, when the expansion tray 84 or expansion device is connected to power zone 70C or 70D, the main CPU 72B will not be able to recognize the expansion tray 84 or expansion device simply by plugging it in like a plug-and-play device, but power consumption in sleep mode can be reduced.

[0083] [8. Effects, etc.] Here, the standby voltage, which is the output voltage from the power supply in the power-saving sleep state, is generally set to 5V, the same as that used by USB devices connected to the image forming apparatus, in order to minimize losses during voltage reduction. This 5V output is widely used because it is used by USB interfaces, but in order to further reduce the power consumption of the ICs inside the image forming apparatus, including the CPU, in the sleep state, it is further stepped down from 5V to 3.3V using a DC-DC converter or similar device. For the image forming apparatus alone, a standby voltage of 3.3V is sufficient if only the CPU is present in the sleep state, but if the standby voltage is stepped down to 3.3V, for example, a wireless LAN unit connected to the image forming apparatus and operating on the USB bus power of 5V will no longer be able to meet the operating voltage range. Therefore, the wireless LAN unit will not operate in the sleep state, and even if the wireless LAN unit is operated in the sleep state, the image forming apparatus will not wake up from sleep. As a result, the wireless LAN unit, which is an external device connected to the image forming apparatus, ceases to function as a factor in waking the image forming apparatus from sleep state. Therefore, in image forming machines to which USB devices are connected, even when no external devices are connected, the operating voltage of 5[V] was maintained as the standby voltage in sleep mode, thus requiring further power saving.

[0084] In response to this, when transitioning to sleep mode, the image forming apparatus 1 checks whether external devices such as the USB Host 80, WLAN unit 82, and expansion tray 84 are connected. If none are connected, it determines that there is no need to supply power to these external devices in sleep mode. Subsequently, the image forming apparatus 1 turns off switches SW2 and SW3 to cut off power supply to external devices in sleep mode, sets the PWM Duty of the Powersave signal supplied from the control unit 32 to the voltage setting switching circuit 58 of the constant voltage control unit 52 to 0%, and steps down the voltage value of the supply voltage Vin supplied from the power supply circuit 47 to the control unit 32 from 5V to 3.3V.

[0085] Therefore, when the image forming apparatus 1 transitions to sleep mode without any additional devices such as the USB Host 80 or WLAN unit 82, or external devices such as the expansion tray 84 connected, it can cut off power to the external devices and reduce the supply voltage Vin from 5[V] to 3.3[V]. As a result, the image forming apparatus 1 can reduce power consumption in sleep mode compared to when the supply voltage Vin is maintained at 5[V] in sleep mode.

[0086] On the other hand, when the image forming apparatus 1 transitions to sleep mode, if additional devices such as the USB Host 80 or WLAN unit 82 are connected, switch SW3 remains ON and the supply voltage Vin is maintained at 5[V], so that a supply voltage of 5[V] Vin continues to be supplied to these additional devices during sleep mode. As a result, even in sleep mode, the connected additional devices remain operational, and operations on these additional devices can trigger a return from sleep mode to standby mode or operating mode.

[0087] On the other hand, when the image forming apparatus 1 transitions to sleep mode, if additional devices such as the USB Host 80 and WLAN unit 82 are not connected, but the expansion tray 84 is connected, switch SW3 is turned OFF while switch SW2 remains ON, the supply voltage Vin is stepped down to 4.5[V], and although power supply to the additional devices is cut off in sleep mode, a supply voltage of 4.5[V] Vin is continuously supplied to the expansion tray 84.

[0088] Therefore, even in sleep mode, the image forming apparatus 1 can keep the connected expansion tray 84 operational, and can return from sleep mode to standby mode or operating mode by operation on the expansion tray 84. In addition, the image forming apparatus 1 can cut off power supply to unconnected expansion equipment and reduce the supply voltage Vin from 5[V] to 4.5[V], thereby reducing power consumption in sleep mode compared to when the supply voltage Vin is maintained at 5[V] in sleep mode.

[0089] In this way, the image forming apparatus 1 can selectively reduce the supply voltage Vin according to the connection status of external devices, so as to which external device, when operated, will cause the apparatus to wake up from sleep mode (i.e., the connection option that triggers the wake-up). Therefore, the image forming apparatus 1 can selectively set the supply voltage Vin according to the connected external device, and can reduce power consumption in sleep mode in a more precise and selective manner.

[0090] Furthermore, when the image forming apparatus 1 transitions to sleep mode, it does not abruptly reduce the supply voltage Vin from 5[V] to 3.3[V], but gradually reduces the supply voltage Vin while switching the switch SW to turn it OFF. Similarly, when the image forming apparatus 1 wakes up from sleep mode, it does not abruptly increase the supply voltage Vin from 3.3[V] to 5[V], but gradually increases the supply voltage Vin while switching the switch SW to turn it ON. As a result, the image forming apparatus 1 can easily identify the location of a fault in each power supply zone 70.

[0091] Furthermore, when the image forming apparatus 1 wakes up from sleep mode, it turns on switches SW1, SW2, and SW3 at the minimum necessary supply voltage Vin within the operating voltage range of the equipment downstream of the switches SW. This suppresses inrush current compared to applying 5[V] all at once.

[0092] Here, it is conceivable to pre-generate four types of voltages—5V, 4.5V, 3.8V, and 3.3V—to supply from the transformer 49 to the control unit 32, and then sequentially cut off the supply of 5V, 4.5V, and 3.8V voltages to the control unit 32 when the image forming apparatus 1 transitions to a sleep state. However, in that case, the circuit configuration becomes more complex and larger.

[0093] In contrast, the image forming apparatus 1 generates only one type of voltage, 5V (excluding 24V), which is supplied from the transformer 49 to the control unit 32. When transitioning to sleep mode, it controls the PWM Duty of the Powersave signal to sequentially decrease the supply voltage Vin from 5V to 4.5V, 3.8V, and 3.3V. Thus, the image forming apparatus 1 can generate multiple supply voltages Vin based on the voltage that is 5V when the PWM Duty is 100%, while preventing the circuit configuration from becoming complex and large, and selectively decreasing the supply voltage Vin.

[0094] With the above configuration, the image forming apparatus 1 includes a power supply circuit 47 that is supplied with AC voltage from a commercial power source, a control unit 32 that is supplied with a DC voltage, Vin, from the power supply circuit 47, and an image forming unit 11 that forms an image on a medium. The power supply circuit 47 includes a power supply rectifier unit 48 that rectifies and smooths the AC voltage to convert it into a DC voltage, a transformer 49 that converts the voltage value of the DC voltage output from the power supply rectifier unit 48 and supplies it to the control unit 32, a constant voltage control unit 52 that outputs a feedback signal according to the result of comparing a reference voltage Vk with the output voltage of the transformer 49, an oscillation control unit 53 that outputs a switching drive signal based on the feedback signal, a switching unit 50 that controls the DC voltage output from the power supply rectifier unit 48 by switching based on the switching drive signal and applies it to the transformer 49, and a voltage setting switching circuit 58 that changes the reference voltage Vk by a Powersave signal as a control signal output from the control unit 32. The control unit 32 is configured to output a Powersave signal to the power supply circuit 47 that controls the voltage value of the DC voltage supplied from the transformer 49.

[0095] As a result, the image forming apparatus 1 can enter a sleep state while maintaining a voltage lower than the voltage supplied to an external device when no external device to be powered is connected during the sleep state.

[0096] [9. Other Embodiments] In the above-described embodiment, the image forming apparatus 1 is equipped with a voltage detection element IC1 in the control unit 32 and connected to the power supply zone 70A, so that the power supply voltage (i.e., supply voltage Vin) of the sub-CPU 72A does not fall below the operating voltage range (3.3[V]) of the sub-CPU 72A. The present invention is not limited to this, and the image forming apparatus 1 does not need to be equipped with a voltage detection element IC1 in the control unit 32 if, when the PWM Duty of the Powersave signal is at its smallest, which is 0[%], the supply voltage Vin does not fall below the operating voltage range (3.3[V]) of the sub-CPU 72A and the operating voltage range of the power supply voltage of the sub-CPU 72A is satisfied.

[0097] Furthermore, since there is a linear relationship between the supply voltage Vin and the PWM Duty of the Powersave signal, the image forming apparatus 1 may calculate the PWM Duty of the Powersave signal when the supply voltage Vin is 3.3[V] based on the fact that the supply voltage Vin detected by the voltage detection element IC2 is 5[V] when the PWM Duty of the Powersave signal is 100[%] and the PWM Duty of the Powersave signal when the supply voltage Vin detected by the voltage detection element IC2 is, for example, 3.8[V], and then set the PWM Duty of the Powersave signal when the supply voltage Vin is 3.3[V]. In this case as well, the image forming apparatus 1 does not need to mount the voltage detection element IC1 on the control unit 32.

[0098] Furthermore, in the embodiment described above, the case in which the image forming apparatus 1 is configured with reset ICs for the voltage detection elements IC1, IC2, and IC3 has been described. The present invention is not limited to this, and the image forming apparatus 1 may be configured with various other elements such as Zener diodes for the voltage detection elements, as long as it is possible to detect a predetermined voltage with a predetermined detection accuracy.

[0099] Furthermore, in the above-described embodiment, the image forming apparatus 1 is described in the case where, at timing T1 (Figure 7), a supply voltage Vin of 5[V] from the power supply circuit 47 is supplied to the sub-CPU 72A and the main CPU 72B and they are started simultaneously. The present invention is not limited to this, but if the image forming apparatus 1 is always in off mode immediately after the AC cable is plugged in, even when the image forming apparatus 1 is started at timing T1 (Figure 7), the supply voltage Vin can be gradually increased in the same procedure as the recovery procedure from off mode shown at timing T8, thereby suppressing inrush current.

[0100] Furthermore, in the embodiment described above, the case in which the image forming apparatus 1 uses a PWM signal for the Powersave signal has been described. The present invention is not limited to this, and the image forming apparatus 1 may use any other signal, such as an analog signal, as long as it can control the supply voltage Vin by controlling the switching unit 50 to change the voltage applied to the primary side of the transformer 49. However, if the Powersave signal is an analog signal, for example, the High level of the Powersave signal will change according to the supply voltage Vin, which complicates the control. Therefore, if the Powersave signal is a PWM signal that alternates between a Low level of 0[V] and a High level that is an open output, the image forming apparatus 1 can be easily controlled.

[0101] Furthermore, in the embodiment described above, the case in which the image forming apparatus 1 turns off switch SW3 when it cannot detect that the USB Host 80 or WLAN unit 82 are connected as expansion devices after restarting from sleep mode was mentioned. The present invention is not limited to this, and the image forming apparatus 1 may also turn on switch SW3 only when the user checks the connection of expansion devices via a menu or the like. In this case, although power consumption increases slightly compared to the case in which switch SW3 is always OFF when no expansion devices are connected, power consumption can be reduced compared to the case in which switch SW3 is always ON when no expansion devices are connected, and the main CPU 72B can recognize the expansion devices connected to power zone 70D. The same applies to the control of switches SW2 and SW3 when it is not possible to detect that the USB Host 80 or WLAN unit 82 are connected as expansion devices, and it is also not possible to detect that the expansion tray 84 is connected.

[0102] Furthermore, the image forming apparatus 1 may turn switch SW3 ON at any time interval (for example, once every minute). In this case, although power consumption increases slightly compared to the case where switch SW3 is always OFF when no additional equipment is connected, power consumption can be reduced compared to the case where switch SW3 is always ON when no additional equipment is connected, and the main CPU 72B can recognize the additional equipment connected to power zone 70D. The same applies to the control of switches SW2 and SW3 when it is not possible to detect that the USB Host 80 or WLAN unit 82 are connected as additional equipment, and it is also not possible to detect that the expansion tray 84 is connected.

[0103] Furthermore, in the embodiment described above, the image forming apparatus 1 is provided with three voltage detection elements IC1, IC2, and IC3 and three switches SW1, SW2, and SW3 in the control unit 32. The present invention is not limited to this, and the image forming apparatus 1 may be provided with various other numbers of voltage detection elements IC and switches SW in the control unit 32 depending on the voltage value of the supply voltage Vin detected by the control unit 32. In that case, for example, an additional voltage detection element IC may be connected in parallel with voltage detection element IC3, and if, for example, the operating voltage range of the expansion tray 84 is higher than that of the main CPU 72B, the PWM duty cycle may be set based on that voltage.

[0104] Furthermore, in the embodiment described above, the image forming apparatus 1, when it cannot detect that external devices such as the USB Host 80, WLAN unit 82, or expansion tray 84 are connected to the control unit 32, reduces the supply voltage Vin to 3.3[V], the lowest voltage value within the operating voltage range of the sub-CPU 72A, which is 3.3[V] to 5.25[V]. The present invention is not limited to this, and the supply voltage Vin may be reduced to various other voltage values ​​within the operating voltage range, such as reducing the supply voltage Vin to 3.4[V], which is higher than the lowest limit of 3.3[V] within the operating voltage range. In that case, although the power consumption in sleep mode will increase compared to when the supply voltage Vin is reduced to 3.3[V], the power consumption in sleep mode can be reduced compared to when the supply voltage Vin is kept at 5[V]. The same applies when the supply voltage Vin is reduced to 3.8[V] and when it is reduced to 4.5[V].

[0105] Furthermore, the above-described embodiment described the case in which the present invention is applied to an image forming apparatus 1. The present invention is not limited to this, and may also be applied to various devices that have a power-saving state, such as facsimile machines, MFPs (Multifunction Printers), and copiers.

[0106] Furthermore, the present invention is not limited to the embodiments described above and other embodiments. That is, the scope of the present invention extends to embodiments that arbitrarily combine some or all of the embodiments described above and other embodiments. In addition, the scope of the present invention also extends when a part of the configuration described in any embodiment among the embodiments described above and other embodiments is extracted and substituted or adapted for a part of the configuration of any embodiment among the embodiments described above and other embodiments, or when the extracted part of the configuration is added to any embodiment.

[0107] Furthermore, in the embodiment described above, the image forming apparatus 1 is configured by a power supply circuit 47 as a power source, a control unit 32 as a control unit, and an image forming unit 11 as an image forming unit, and the power source has a power supply rectifier unit 48 as a power supply rectifier unit, a transformer 49 as a transformer, a constant voltage control unit 52 as a constant voltage control unit, an oscillation control unit 53 as an oscillation control unit, a switching unit 50 as a switching unit, and a voltage setting switching circuit 58 as a voltage setting switching unit.The present invention is not limited to this, and the image forming apparatus may be configured by a power source, a control unit, and an image forming unit with various other configurations, and the power source may have a power supply rectifier unit, a transformer, a constant voltage control unit, an oscillation control unit, a switching unit, and a voltage setting switching unit with various other configurations. [Industrial applicability]

[0108] This invention can be used in various devices that have a power-saving state. [Explanation of Symbols]

[0109] 1...Image forming apparatus, 2...Apparatus housing, 3...Image forming unit, 4...Paper feeding section, 5...Paper feeding cassette, 6...Paper feeding roller, 7...Registration roller, 8...Cover, 9...Conveyor belt, 10...Transfer section, 11...Image forming section, 12...Photosensitive drum, 13...LED head, 14...Developing apparatus, 15...Drive roller, 16...Tension roller, 17...Toner cartridge, 18...Supply roller, 19...Developing roller, 20...Charging roller, 21...Cleaning 22... Transfer roller, 23... Fixing unit, 24... Fixing unit housing, 25... Fixing roller, 26... Heating roller, 27... Pressure roller, 28... Switching plate, 29... Duplex printing unit, 30... Discharge unit, 31... Paper transfer unit, S... Paper, 32... Control unit, 33... Drive system circuit, 34... Logic system circuit, 35... CPU, 36... RAM, 37... ROM, 38... Various sensors, 39... Operation board, 40... Drive circuit, 41... Actuator 42...Eta components, 43...Paper feed motor, 44...Transport motor, 45...Fusing motor, 46...Developer drive motor, 47...Power supply circuit, 48...Power rectifier section, 49...Transformer, 50...Switching section, 51...Secondary rectifier section, 52...Constant voltage control section, 53...Oscillation control section, 54...Shunt regulator, 55A, 55B, 56A, 56B...Voltage divider resistors, 57...Smoothing capacitors, 58...Voltage setting switching circuit, 59...Control elements, 60 ...FET, 61...Capacitor, 62...Resistor, 63...Limiting resistor, 64...Photocoupler, 64a...Photodiode, 64b...Phototransistor, 65, 68...Limiting resistor, 66, 67...Capacitor, 69...Resistor, 70A, 70B, 70C, 70D...Power supply zone, IC1, IC2, IC3...Voltage detection element, SW1, SW2, SW3...Switch, 72A...Sub-CPU, 72B...Main CPU, 74...DC-DC converter, 80...USB Host, 82...WLAN unit, 84...Expansion tray, 86...USB Device, 88...LAN unit, Vin...Supply voltage, Vk...Reference voltage, Vref...Detection voltage.

Claims

1. A power supply that receives AC voltage from the commercial power supply, A control unit supplied with a DC voltage from the aforementioned power supply and Equipped with, The aforementioned power supply is A power supply rectifier unit that rectifies and smooths the AC voltage to convert it into a DC voltage, A transformer that converts the voltage value of the DC voltage output from the power supply rectifier and supplies it to the control unit, A constant voltage control unit that outputs a feedback signal corresponding to the result of comparing a reference voltage with the output voltage of the transformer, An oscillator control unit that outputs a switching drive signal based on the feedback signal, A switching unit controls the DC voltage output from the power supply rectifier unit by switching based on the switching drive signal and applies it to the transformer. A voltage setting switching unit changes the reference voltage based on a control signal output from the control unit. It has, The control unit, Multiple power cut-off switches are provided for each of the multiple operating voltage ranges of the external device connected to the control unit, and switch between cutting off and supplying the voltage supplied to the external device. It has, When transitioning to a power-saving state, the power cut-off switch corresponding to the operating voltage range of the external device connected to the control unit is kept ON, thereby maintaining the supply of the supply voltage to the external device connected to the control unit. At the same time, the power cut-off switch corresponding to the operating voltage range of the external device not connected to the control unit is turned OFF, thereby cutting off the supply of the supply voltage to the external device not connected to the control unit. Simultaneously, a control signal is output to the power supply that controls the voltage value of the DC voltage supplied from the transformer to a voltage value corresponding to the operating voltage range that maintains the ON state of the power cut-off switch. A power supply circuit characterized by the following features.

2. The control unit, The control signal is output to the power supply to control the voltage value of the DC voltage supplied from the transformer to the lowest voltage value within the operating voltage range that maintains the ON state of the power cut-off switch. The power supply circuit according to feature 1.

3. The control unit, The external device is connected to the main CPU, which controls the power cut-off switch and, in the power-saving state, the supply voltage is cut off and the CPU ceases to operate. In the aforementioned power-saving state, the sub-CPU operates by supplying a supply voltage lower than the supply voltage value when the external device is connected to the main CPU, and controls the power cut-off switch to cut off the supply of the supply voltage to the main CPU when transitioning to the power-saving state. The power supply circuit according to claim 1, characterized by having the following features.

4. The control unit, Voltage detection elements are provided for each of the aforementioned operating voltage ranges to detect the supply voltage. It further possesses, When transitioning to the power-saving state, the second power cut-off switch, which is the power cut-off switch, is turned OFF to cut off the supply of the supply voltage downstream of the second power cut-off switch, and then the control signal that gradually reduces the supply voltage is output to the power supply. When the voltage detection element detects that the supply voltage has dropped to a predetermined operating voltage, the first power cut-off switch, which is the power cut-off switch upstream of the second power cut-off switch, is turned OFF to cut off the supply of the supply voltage downstream of the first power cut-off switch, and then the control signal that gradually reduces the supply voltage is output to the power supply. The power supply circuit according to feature 1.

5. The control unit, Voltage detection elements are provided for each of the aforementioned operating voltage ranges to detect the supply voltage. It further possesses, When recovering from the power-saving state, the first power cut-off switch is turned ON to supply the supply voltage to the second power cut-off switch, which is downstream of the first power cut-off switch, and then a control signal is output to the power supply to gradually increase the supply voltage. When the voltage detection element detects that the supply voltage has risen to a predetermined operating voltage, the second power cut-off switch is turned ON to start supplying the supply voltage downstream of the second power cut-off switch, and then a control signal is output to the power supply to further gradually increase the supply voltage. The power supply circuit according to feature 1.

6. The aforementioned control signal is a PWM signal, The control unit controls the voltage value of the DC voltage supplied from the transformer by changing the duty cycle of the PWM signal. The power supply circuit according to feature 1.

7. A power supply that receives AC voltage from the commercial power supply, A control unit that receives a DC voltage from the aforementioned power supply, Image forming unit that forms an image on the medium and Equipped with, The aforementioned power supply is A power supply rectifier unit that rectifies and smooths the AC voltage to convert it into a DC voltage, A transformer that converts the voltage value of the DC voltage output from the power supply rectifier and supplies it to the control unit, A constant voltage control unit that outputs a feedback signal corresponding to the result of comparing a reference voltage with the output voltage of the transformer, An oscillator control unit that outputs a switching drive signal based on the feedback signal, A switching unit controls the DC voltage output from the power supply rectifier unit by switching based on the switching drive signal and applies it to the transformer. A voltage setting switching unit changes the reference voltage based on a control signal output from the control unit. It has, The control unit, Multiple power cut-off switches are provided for each of the multiple operating voltage ranges of the external device connected to the control unit, and switch between cutting off and supplying the voltage supplied to the external device. It has, When transitioning to a power-saving state, the power cut-off switch corresponding to the operating voltage range of the external device connected to the control unit is kept ON, thereby maintaining the supply of the supply voltage to the external device connected to the control unit. At the same time, the power cut-off switch corresponding to the operating voltage range of the external device not connected to the control unit is turned OFF, thereby cutting off the supply of the supply voltage to the external device not connected to the control unit. Simultaneously, a control signal is output to the power supply that controls the voltage value of the DC voltage supplied from the transformer to a voltage value corresponding to the operating voltage range that maintains the ON state of the power cut-off switch. An image forming apparatus characterized by the following:

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