Power circuit, and image processing apparatus

Abstract

To provide a power circuit that, even when AC voltage is interrupted, causes a voltage discharged from a capacitor to reliably take a bypass so as to prevent the voltage from being input to a control IC, and prevent a malfunction of the control IC, and an image processing apparatus comprising the power circuit.SOLUTION: A bypass circuit 60 is a circuit that is connected to an AC / DC converter 40 and causes a voltage discharged from a capacitor C2 due to interruption of AC voltage of an image forming apparatus 10 to take a bypass from a power line L3 without supplying the voltage to a terminal t8. As shown in Figure 4, the bypass circuit 60 comprises a capacitor C3 (example of third capacitor of the present invention), a rectification circuit 61 (example of second rectifier of the present invention), and a photocoupler 64. The bypass circuit 60 further comprises a MOSFET 65.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a power supply circuit that converts AC voltage into DC voltage, and to an image processing apparatus that includes this power supply circuit. [Background technology]

[0002] Image forming devices such as copiers, printers, and facsimiles have a power supply circuit that supplies DC voltage to load devices such as a control unit, an operation display unit, and a motor that supplies the driving force required for image forming operations. The power supply circuit has an AC / DC converter that rectifies AC voltage input from the indoor wiring of the facility where the image forming device is installed, to generate and output DC voltage (see Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-217309 Summary of the Invention [Problem to be solved by the invention]

[0004] A power supply circuit, such as an AC / DC converter that converts AC voltage to DC voltage, is provided with multiple capacitors. For example, the power supply circuit may be provided with a boost capacitor used to boost the voltage, a smoothing capacitor that smooths the rectified voltage, and a bypass capacitor that removes noise. The power supply circuit may also be provided with a control IC that switches a predetermined switching unit to output the converted DC voltage from the switching unit. The control IC has a voltage input terminal to which the unrectified AC voltage is input.

[0005] In a power supply circuit configured in this manner, if the plug socket of the image forming device is unplugged and the AC voltage input is cut off, the voltage discharged from the capacitor that stores the charge will flow back and be input to the voltage input terminal of the control IC, causing the control IC to temporarily restart and malfunction, which may result in the control unit of the image processing device or other load devices malfunctioning.

[0006] An object of the present invention is to provide a power supply circuit that can reliably divert the voltage discharged from a capacitor so that it does not enter a control IC even when AC voltage is interrupted, thereby preventing malfunction of the control IC, and an image processing device equipped with this power supply circuit. [Means for solving the problem]

[0007] A power supply circuit according to one aspect of the present invention is a power supply circuit that converts AC voltage into DC voltage, and includes: a control IC having at least a voltage input terminal connected to at least an AC power supply line and a first output terminal that outputs a predetermined DC voltage based on a voltage input to the voltage input terminal; a first capacitor provided on the secondary side of a first rectifier that rectifies the AC voltage; and a second capacitor that is connected in series with the first capacitor and has a positive electrode connected to the negative electrode of the first capacitor and the voltage input terminal, wherein a bypass circuit is connected to the power supply circuit for bypassing a voltage discharged from the second capacitor when the AC voltage is interrupted from a connection leading to the voltage input terminal, the bypass circuit including: a third capacitor having a positive electrode connected to the AC power supply line; a second rectifier that rectifies the AC voltage input via the third capacitor when the AC voltage is applied; and a photocoupler to which the DC voltage rectified by the second rectifier is input, The light emitting diode operates upon receiving the DC voltage, and a phototransistor having a collector terminal connected to the positive electrode of the second capacitor and an emitter terminal connected to the ground potential.

[0008] An image processing device according to another aspect of the present invention includes the power supply circuit and an image processing unit operated by the DC voltage output from the power supply circuit. [Effects of the Invention]

[0009] According to the present invention, even if the AC voltage is interrupted, the voltage discharged from the capacitor can be reliably diverted so as not to be input to the control IC, thereby preventing malfunction of the control IC. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a diagram showing the configuration of an image forming apparatus according to an embodiment of the present invention. [Figure 2] FIG. 2 is a diagram showing the configuration of a power supply unit according to an embodiment of the present invention. [Figure 3] FIG. 3 is a circuit diagram showing the configuration of the AC / DC converter of the power supply unit. [Figure 4] FIG. 4 is a circuit diagram showing a bypass circuit included in the AC / DC converter. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings. Note that the following embodiment is an example of the present invention, and does not limit the technical scope of the present invention.

[0012] [Image forming apparatus 10] The configuration of an image forming apparatus 10 according to one embodiment of the present invention will be described with reference to Figure 1. Note that in this embodiment, the image forming apparatus 10 will be described as an example of an image processing apparatus of the present invention, but the image processing apparatus of the present invention may also be an image processing apparatus such as a printer, a facsimile machine, a copier, a scanner, or a multifunction machine having each of these functions.

[0013] 1, image forming apparatus 10 includes image reading section 11 (image processing section), image forming section 12 (image processing section), operation display section 13, paper feed section 14, communication section 15, and main control section 20 that controls these sections. Each of these components is provided in a housing of image forming apparatus 10. Image forming apparatus 10 also includes power supply unit 30 (an example of a power supply device) that supplies power required for image reading section 11, image forming section 12, operation display section 13, paper feed section 14, communication section 15, main control section 20, etc. In FIG. 1, power lines are indicated by solid lines, and signal lines are indicated by dashed lines.

[0014] The image reading unit 11, image forming unit 12, operation and display unit 13, paper feed unit 14, communication unit 15, and main control unit 20 each have a drive unit that consumes power to operate, and are loads in the image forming apparatus 10. Examples of the drive unit include a motor, a liquid crystal display, a light source, a sensor, and a CPU 21. The power supply unit 30 generates and supplies voltages of the required voltage levels to each of these drive units.

[0015] The image reading unit 11 is a so-called scanner equipped with a contact glass, a reading unit, a mirror, an optical lens, a CCD, and the like. The image reading unit 11 executes an image reading process to read image data from a document set at a predetermined position. Specifically, the document is placed on the contact glass, and then an image reading instruction is input from the operation display unit 13. The reading unit is then moved in the sub-scanning direction by a built-in drive motor. During this movement, light is continuously irradiated onto the document in succession by one line of light from the light source of the reading unit. The reflected light from the document is then guided to the CCD via the mirror and the optical lens, and light intensity data corresponding to the amount of light received by the CCD is output to the main control unit 20. The main control unit 20 generates image data of the document based on the optical data.

[0016] Image forming unit 12 performs an image formation process (printing process) based on electrophotography. Specifically, image forming unit 12 performs the image formation process based on image data read by image reading unit 11 or print data (print job) input via communication unit 15 from an external information processing device such as a personal computer. Image forming unit 12 includes a photosensitive drum, a charging device, a developing device, a transfer device, a fixing device, a laser scanner unit, a paper conveying device, and the like. When the print data is input, the charging device uniformly charges the photosensitive drum to a predetermined potential. Next, the laser scanner unit irradiates the surface of the photosensitive drum with light based on the image data included in the print job. This forms an electrostatic latent image on the surface of the photosensitive drum. The electrostatic latent image on the photosensitive drum is then developed into a toner image by the developing device. The toner image formed on the photosensitive drum is then transferred to a print sheet (sheet member) by the transfer device and then fixed to the print sheet by the fixing device. In this embodiment, an electrophotographic image forming unit 12 will be described as an example, but the image forming unit 12 is not limited to an electrophotographic image forming unit, and may be an inkjet recording unit, or may be any other recording or printing unit.

[0017] The operation and display unit 13 includes an operation unit such as a push button switch and a display unit such as a liquid crystal panel. The operation and display unit 13 is equipped with a panel control unit including a liquid crystal driver. The panel control unit recognizes signals input from the operation unit. The panel control unit also executes display processing of various data on the display unit.

[0018] The paper feed unit 14 stores printing paper on which an image is formed in the image forming unit 12. The paper feed unit 14 also includes a feeding mechanism (not shown), which feeds the printing paper stored in the paper feed unit 14 toward the image forming unit 12. The feeding mechanism is made up of a pickup roller that picks up printing paper from the paper storage unit, a feeding roller that sends the printing paper toward the image forming unit 12, and the like. The pickup roller and the feeding roller are driven to rotate by a drive motor. When the motor is driven to rotate, the feeding roller feeds the printing paper.

[0019] The communication unit 15 is a communication interface that connects the image forming apparatus 10 to a predetermined communication network and accepts input of print data and the like transmitted from the outside via the communication network. Specifically, the communication unit 15 is a communication interface card or the like that complies with the IEEE802.3 standard. The print data sent to the image forming apparatus 10 from the outside is input via the communication unit 15.

[0020] The main control unit 20 comprehensively controls the image forming apparatus 10. The main control unit 20 is configured as a control board on which a microcomputer is mounted, the main components of which include a CPU 21, a storage unit such as a ROM, a RAM, and a flash memory, and electronic devices such as an oscillator.

[0021] 1, the main control unit 20 is connected to each load unit such as the image reading unit 11 and the image forming unit 12 via an internal bus 26 so that they can communicate with each other. The main control unit 20 performs overall control of the image forming apparatus 10 by having the CPU 21 execute the program stored in the ROM.

[0022] The power supply unit 30 supplies power to each component, such as the image reading unit 11, the image forming unit 12, the operation display unit 13, the paper feed unit 14, the communication unit 15, and the main control unit 20. The power supply unit 30 is connected to each component by a power line.

[0023] The power supply unit 30 includes a power supply control unit 31 and a power supply voltage supply unit 32 .

[0024] Power supply voltage supply unit 32 rectifies, for example, AC 100V or AC 200V, which is a commercial power supply, and converts it into a DC reference voltage of DC 24V. Power supply voltage supply unit 32 also performs switching control of the reference voltage to convert it into a voltage appropriate for each component, such as image reading unit 11, image forming unit 12, operation display unit 13, paper feed unit 14, communication unit 15, and main control unit 20, and then supplies it to each component.

[0025] The power supply control unit 31 controls the supply of power output to each component from the power supply voltage supply unit 32. The power supply control unit 31 is configured as a control board on which a microcomputer including a CPU, ROM, RAM, etc. as main components is mounted. Specifically, the power supply control unit 31 is a power supply IC called a Power Management IC (PMIC).

[0026] As shown in FIG. 2, the power supply voltage supply unit 32 includes an AC / DC converter 40 (an example of a power supply circuit of the present invention) and a DC / DC converter 50.

[0027] The AC / DC converter 40 rectifies AC voltage of AC 100V or AC 200V, which is a commercial power supply, and converts it into the predetermined DC reference voltage (for example, DC 24V), which is output to each component of the image forming apparatus 10.

[0028] The DC / DC converter 50 further steps down the voltage on the secondary side of the AC / DC converter 40, that is, the reference voltage. The DC / DC converter 50 generates, for example, DC 5V and outputs it to the main control unit 20.

[0029] [AC / DC Converter 40] The configuration of AC / DC converter 40 will be described below with reference to Fig. 3. As shown in Fig. 3, AC / DC converter 40 includes a filter 401, a rectifier circuit 41 (an example of a first rectifier of the present invention), a capacitor C1 (an example of a first capacitor of the present invention), a capacitor C2 (an example of a second capacitor of the present invention), a switching element 43 (an example of a switching unit of the present invention), a control IC 44 (an example of a control IC of the present invention), a high-frequency transformer 45, and a rectifying and smoothing circuit 46.

[0030] The rectifier circuit 41 rectifies an AC voltage (for example, AC 100V) input from an external commercial power source and converts it into a DC voltage. The rectifier circuit 41 is a diode bridge circuit consisting of four diodes, and rectifies the AC component of the AC voltage into a unidirectional pulsating current. The rectifier circuit 41 may be a half-wave rectifier circuit using one diode, or a full-wave rectifier circuit using two diodes.

[0031] Capacitors C1 and C2 are provided on the secondary side of the rectifier circuit 41. Capacitors C1 and C2, together with the rectifier circuit 41, form a voltage doubler rectifier circuit that doubles the voltage. Capacitors C1 and C2 are, for example, electrolytic capacitors, film capacitors, ceramic capacitors, or supercapacitors.

[0032] The positive electrode C1(+) of the capacitor C1 is connected to the positive electrode of the diode 41A of the rectifier circuit 41, and is connected to the power supply line L2 from the input terminal AC+ of the AC power supply 35 via the diode 41A. The capacitor C2 is connected in series with the capacitor C1, and specifically, the positive electrode C2(+) of the capacitor C2 is connected to the negative electrode C1(-) of the capacitor C1. The positive electrode C2(+) of the capacitor C2 is connected to the power supply line L3 from the input terminal AC- of the AC power supply 35. The negative electrode C2(-) of the capacitor C2 is connected to the negative electrode of the diode 41B of the rectifier circuit 41, and is connected to the power supply line L2 from the input terminal AC+ of the AC power supply 35 via the diode 41B. The negative electrode of the capacitor C2 is connected to ground potential (GND). This realizes the voltage doubler rectifier circuit.

[0033] In the rectifier circuit 41, the current flow path switches each time the input voltage input from the AC power supply 35 (see FIG. 3) switches between positive and negative. That is, when the input voltage is positive, the input voltage input from the input terminal AC+ of the AC power supply 35 passes through a diode 41A in the rectifier circuit 41 and is supplied to the positive electrode C1(+) of the capacitor C1, thereby charging the capacitor C1. On the other hand, when the input voltage is negative, the input voltage input from the input terminal AC- of the AC power supply 35 is supplied to the positive electrode C2(+) of the capacitor C2, thereby charging the capacitor C2. As described above, since the capacitors C1 and C2 are connected in series, the DC voltage across the capacitors C1 and C2 is supplied to the transformer 45.

[0034] The positive electrode C2(+) of the capacitor C2 is also connected to a terminal t8 (a terminal for inputting voltage) of a control IC 44 (described later) via a diode D2. That is, the power supply line L3 is connected to the terminal t8 of the control IC 44 via the diode D2. The capacitor C2 is connected between the power supply line L3 and the ground potential (GND), and also serves as a so-called bypass capacitor that drops noise generated on the power supply line L3 to the ground potential and stabilizes the voltage of the power supply line L3.

[0035] The transformer 45 is a voltage converter that steps down the DC voltage rectified by the rectifier circuit 41 at a predetermined transformation ratio.

[0036] When a control signal (frequency signal) of a predetermined frequency is input, the switching element 43 switches the power supply line L1 on the high-voltage side (primary side) of the transformer 45 in accordance with the frequency of the control signal. As a result, a pulsed (rectangular wave) voltage signal (rectangular wave voltage signal) corresponding to the reference voltage is generated by the switching element 43. In other words, the switching element 43 converts the DC voltage smoothed by the capacitor C1 into the pulsed voltage signal. The switching element 43 is a switching element such as a FET, and specifically, is an N-channel power MOSFET. Note that while a power MOSFET is exemplified as the switching element 43, it is possible to use, for example, a normal MOSFET or a normal FET (field effect transistor) instead, or a power transistor or a normal transistor.

[0037] The transformer 45 steps down the pulse-shaped (rectangular wave) voltage signal corresponding to the reference voltage. The secondary voltage signal stepped down by the transformer 45 is rectified and further smoothed by a rectifying and smoothing circuit 46, thereby being converted into the DC reference voltage (e.g., DC 24 V). In the rectifying and smoothing circuit 46, the voltage is rectified by two diodes 46A and 46B and a coil 46C, and smoothed by an electrolytic capacitor 46D.

[0038] The control IC 44 outputs the control signal to the gate terminal of the switching element 43. Specifically, the control IC 44 is a PWM control IC known as a PWM controller. The control IC 44 appropriately changes the duty ratio of the control signal. This controls the switching of the switching element 43 so that the voltage signal of a predetermined frequency is output. Specifically, the control IC 44 controls the on / off of the switching element 43. As a result, the DC power supply line L1 smoothed by the capacitor C1 is intermittently opened and closed, and the pulsed voltage signal is applied from the switching element 43 to the primary side of the transformer 45.

[0039] The control IC 44 has eight terminals t1 to t8. The terminal t1 is a terminal for detecting an auxiliary voltage. The terminal t2 is a terminal for inputting a voltage to be fed back. The terminal t3 is a terminal for detecting a current, and the source terminal of the switching element 43 is connected to the terminal t3. The terminal t4 is a GND terminal connected to a ground potential. The terminal t5 (an example of a second output terminal of the present invention) is a terminal for outputting the control signal input to the gate terminal of the switching element 43. The terminal t6 (an example of a first output terminal of the present invention) is a terminal for outputting a DC power supply voltage (Vcc). The terminal t7 is an unused, unconnected terminal. The terminal t8 (an example of a voltage input terminal of the present invention) is a terminal to which the AC power supply line L2 is connected via a diode D1 and a voltage dividing resistor R1. The positive electrode C2(+) of the capacitor C2 is connected to the terminal t8 via a diode D2.

[0040] The control IC 44 is an IC with an undervoltage malfunction prevention function known as UVLO (Under Voltage Lock Out). The UVLO function protects the control IC 44 by halting operation before it goes into an abnormal state when the input voltage at terminal t8 drops below the operating voltage range. Specifically, when the input voltage at terminal t8 drops below a set voltage, the internal circuit stops operating. While operation is suspended due to the UVLO function, voltage output from terminal t6 is suspended, and output of the control signal from terminal t5 is also suspended. On the other hand, when the input voltage at terminal t8 rises above a predetermined release voltage, the suspended state is released and operation resumes.

[0041] In the AC / DC converter 40 configured as described above, if the plug socket of the image forming apparatus 10 is unplugged and the AC voltage input is interrupted, the voltage discharged from the capacitor C2, which stores the electric charge, may leak into the terminal t8 (voltage input terminal) of the control IC 44. When the AC voltage is interrupted, the input voltage at the terminal t8 drops below the set voltage at which the UVLO function activates, and the operation of the control IC 44 should normally be stopped. However, if the voltage discharged from the capacitor C2 leaks into the terminal t8 of the control IC 44 after the AC voltage is interrupted and a voltage equal to or greater than the release voltage is input to the terminal t8 of the control IC 44, the control IC may temporarily restart, causing the control IC 44 to malfunction, or the DC power supply voltage (Vcc) may be erroneously output from the terminal t6, potentially causing the main control unit 20 of the image forming apparatus 10 or other load devices to malfunction.

[0042] In response to this, a bypass circuit 60 (see FIG. 4) configured as described below is connected to the AC / DC converter 40 of this embodiment. Therefore, even if the input of AC voltage to the image forming apparatus 10 is interrupted, the voltage discharged from the capacitor C2 can be reliably diverted so as not to be input to the control IC, thereby preventing malfunction of the control IC 44.

[0043] [Bypass circuit 60] The configuration of the bypass circuit 60 will be described below with reference to Fig. 4. The bypass circuit 60 is connected to the AC / DC converter 40, and is a circuit that bypasses the voltage discharged from the capacitor C2 when the AC voltage of the image forming apparatus 10 is interrupted from being supplied to the terminal t8, and bypasses the voltage from the power supply line L3 to the bypass circuit 60 side. As shown in Fig. 4, the bypass circuit 60 includes a capacitor C3 (an example of the third capacitor of the present invention), a rectifier circuit 61 (an example of the second rectifier of the present invention), and a photocoupler 64. The bypass circuit 60 also includes a MOSFET 65.

[0044] The positive electrode of the capacitor C3 is connected to the positive electrode D1(+) of the diode D1. That is, the positive electrode of the capacitor C3 is connected to the AC power supply line L2. The negative electrode of the capacitor C3 is connected to the rectifier circuit 61 via a predetermined internal resistance. The capacitor C3 is capable of supplying AC voltage to the rectifier circuit 61, and may be, for example, an electrolytic capacitor, a film capacitor, a ceramic capacitor, or a supercapacitor.

[0045] When image forming apparatus 10 is supplied with an AC voltage (e.g., AC 100 V) from AC power supply 35 (see FIG. 3), rectifier circuit 61 rectifies the AC voltage input via capacitor C3 and converts it into a DC voltage. That is, rectifier circuit 61 rectifies the AC voltage from capacitor C3 into a DC voltage. Rectifier circuit 61 is a rectifier circuit made up of two diodes 61A and 61B, and rectifies the AC component of the AC voltage from capacitor C3 into a unidirectional pulsating current. The rectified DC voltage is smoothed by smoothing capacitor 62 and then input to photocoupler 64.

[0046] The DC voltage rectified by the rectifier circuit 61 is applied between terminals p1 and p2 of the photocoupler 64. The photocoupler 64 has a light-emitting diode 64A that emits light upon receiving the DC voltage, and a phototransistor 64B that operates in response to the light emitted by the light-emitting diode 64A.

[0047] The positive electrode of the light-emitting diode 64A is connected to the terminal p1, and the negative electrode of the light-emitting diode 64A is connected to the terminal p2.

[0048] The phototransistor 64B is a switching element that establishes conduction between the collector terminal p4 and the emitter terminal p3 when it receives light emitted from the light-emitting diode 64A. The collector terminal p4 of the phototransistor 64B is connected to the positive electrode C2(+) of the capacitor C2 of the AC / DC converter 40, and the emitter terminal p3 is connected to the ground potential (GND) of the AC / DC converter 40.

[0049] The MOSFET 65 is a switching element that turns on or off the connection L4 between the terminal t5 of the control IC 44 and the ground potential (GND). Specifically, the MOSFET 65 is an N-channel field-effect transistor. The gate terminal of the MOSFET 65 is connected to the collector terminal p4 of the phototransistor 64B and the positive electrode C2(+) of the capacitor C2, the source terminal is connected to the ground potential, and the drain terminal is connected to the terminal t5 of the control IC 44 via an internal resistor. When a predetermined voltage is applied to the gate terminal of the MOSFET 65 and the gate voltage becomes high, the drain terminal and the source terminal become conductive, and the terminal t5 of the control IC 44 becomes ground potential.

[0050] In the AC / DC converter 40 and bypass circuit 60 configured as described above, when an AC voltage (e.g., AC 100V) is supplied to the image forming apparatus 10, a voltage is applied to the light-emitting diode 64A of the photocoupler 64. As a result, light is emitted from the light-emitting diode 64A, turning on the phototransistor 64B, which causes the gate terminal of the MOSFET 65 to drop to the ground potential. In this state, the MOSFET 65 does not operate, so the AC / DC converter 40 operates stably and converts the AC voltage into a DC voltage.

[0051] On the other hand, when the AC voltage of the image forming apparatus 10 is cut off, AC voltage is no longer applied to the bypass circuit 60, the light-emitting diode 64A stops emitting light, and the phototransistor 64B stops and turns off. As a result, the voltage discharged from the capacitor C2 is applied to the gate terminal of the MOSFET 65. This causes conduction between the drain terminal and the source terminal of the MOSFET 65, and the terminal t5 of the control IC 44 becomes ground potential. This promotes the discharge of the capacitor C2, and the voltage at the terminal t8 of the control IC 44 does not rise to the release voltage. As a result, malfunction of the control IC 44 is prevented.

[0052] In the above embodiment, the bypass circuit 60 is connected to the AC / DC converter 40, but the AC / DC converter 40 may include the bypass circuit 60, for example.

[0053] [Notes on the Invention] The following is a summary of the invention extracted from the above-described embodiment. Note that the configurations and processing functions described in the following supplementary notes can be selected and combined as desired.

[0054] <Appendix 1> A power supply circuit for converting AC voltage into DC voltage, a control IC having at least a voltage input terminal connected to at least an AC power supply line and a first output terminal (Vcc) that outputs a predetermined DC voltage based on a voltage input to the voltage input terminal; a first capacitor provided on a secondary side of a first rectifier that rectifies the AC voltage; a second capacitor connected in series with the first capacitor, the positive electrode of which is connected to the negative electrode of the first capacitor and the voltage input terminal; a bypass circuit is connected to the power supply circuit, which bypasses the voltage discharged from the second capacitor due to a power interruption from a connection leading to the voltage input terminal; The bypass circuit is a third capacitor having a positive electrode connected to the AC power supply line; a second rectifier that rectifies the AC voltage input via the third capacitor when the AC voltage is applied; a photocoupler to which the DC voltage rectified by the second rectifier is input, The photocoupler is a light-emitting diode that operates by receiving the DC voltage; a phototransistor having a collector terminal connected to the positive electrode of the second capacitor and an emitter terminal connected to ground potential;

[0055] <Appendix 2> the bypass circuit further includes an N-channel MOSFET; 2. The power supply circuit according to claim 1, wherein the MOSFET has a gate terminal connected to the positive electrode of the second capacitor, a drain terminal connected to a second output terminal of the control IC, and a source terminal connected to a ground potential.

[0056] <Appendix 3> The control IC is 3. The power supply circuit according to claim 1, which is a PWM control IC that generates a predetermined rectangular wave voltage signal by causing a predetermined switching unit to perform a switching operation.

[0057] <Appendix 4> a power supply circuit according to any one of Supplementary Notes 1 to 3; an image processing unit that is operated by the DC voltage output from the power supply circuit. [Explanation of symbols]

[0058] 10: Image forming device 30: Power supply unit 31: Power supply control unit 32: Power supply voltage supply unit 40: AC / DC converter 41: Rectifier circuit 43: Switching element 44: Control IC 45: Trance 46: Rectifier smoothing circuit 50: DC / DC converter 60: Bypass circuit 61: Rectifier circuit 64: Photocoupler C1: Capacitor C2: Capacitor C3: Capacitor D1: Diode D2: Diode

Claims

1. A power supply circuit for converting AC voltage into DC voltage, a control IC having at least a voltage input terminal connected to at least an AC power supply line and a first output terminal that outputs a predetermined DC voltage based on a voltage input to the voltage input terminal; a first capacitor provided on a secondary side of a first rectifier that rectifies the AC voltage; a second capacitor connected in series with the first capacitor, the positive electrode of which is connected to the negative electrode of the first capacitor and the voltage input terminal; a bypass circuit is connected to the power supply circuit, which bypasses the voltage discharged from the second capacitor due to a power interruption from a connection leading to the voltage input terminal; The bypass circuit is a third capacitor having a positive electrode connected to the AC power supply line; a second rectifier that rectifies the AC voltage input via the third capacitor when the AC voltage is applied; a photocoupler to which the DC voltage rectified by the second rectifier is input, The photocoupler is a light-emitting diode that operates by receiving the DC voltage; a phototransistor having a collector terminal connected to the positive electrode of the second capacitor and an emitter terminal connected to ground potential;

2. the bypass circuit further includes an N-channel MOSFET; 2. The power supply circuit according to claim 1, wherein the MOSFET has a gate terminal connected to a positive electrode of the second capacitor, a drain terminal connected to a second output terminal of the control IC, and a source terminal connected to a ground potential.

3. The control IC includes:

3. The power supply circuit according to claim 1, wherein the power supply circuit is a PWM control IC that generates a predetermined rectangular wave voltage signal by causing a predetermined switching unit to perform a switching operation.

4. a power supply circuit according to claim 1 or 2; an image processing unit that is operated by the DC voltage output from the power supply circuit.

Images