Power conversion device and image forming device

Abstract

The present application provides a power conversion device and an image forming device that reduce losses. The power conversion device includes a PFC circuit, a DCDC converter, a PFC control circuit, a DCDC converter control circuit, and a power supply circuit. The PFC circuit includes an inductor and a first switching element, which converts an input pulsating voltage into a DC voltage and outputs it. The DCDC converter includes an insulating transformer and a second switching element, which outputs the output voltage of the PFC circuit input to the primary side of the insulating transformer from the secondary side of the insulating transformer as an arbitrary DC voltage. The PFC control circuit controls the first switching element. The DCDC converter control circuit controls the second switching element. When the PFC circuit is started and the DCDC converter is not started, the power supply circuit uses the voltage generated in the first auxiliary winding coupled with the inductor magnetic field to provide a DC voltage to the PFC control circuit, and when the DCDC converter is started, uses the voltage generated in the second auxiliary winding coupled with the insulating transformer magnetic field to provide a DC voltage to the PFC control circuit.

Description

Technical Field

[0001] Embodiments of the present invention relate to a power conversion device and an image forming apparatus. Background Art

[0002] There is a power conversion circuit including a power factor correction circuit (PFC circuit) that converts an input pulsating voltage into a DC voltage and a DCDC converter that converts an output voltage of the PFC circuit into an arbitrary DC voltage insulated from an AC power supply. The DCDC converter is, for example, an inductor-inductor-capacitor circuit (LLC circuit). This power conversion circuit includes a PFC control circuit that controls the PFC circuit and an LLC control circuit that controls the LLC circuit.

[0003] The PFC control circuit obtains a DC voltage for operation from a power supply circuit, which includes a winding, a smoothing diode, and a capacitor that are magnetically coupled to an inductor in the PFC circuit. In addition, the LLC control circuit obtains a DC voltage for operation from a power supply circuit, which includes a winding, a smoothing diode, and a capacitor that are magnetically coupled to a transformer (e.g., an isolation transformer) in the LLC circuit.

[0004] While the current generated by the pulsating voltage flows through the inductor of the PFC circuit, the alternating current generated by the alternating voltage flows through the transformer of the LLC circuit. Therefore, there is a problem that the power supply circuit that supplies the DC voltage to the PFC control circuit has a larger loss (poor conversion efficiency) than the power supply circuit that supplies the DC voltage to the LLC control circuit. Summary of the invention

[0005] An object of the present invention is to provide a power conversion device and an image forming device capable of reducing loss.

[0006] A power conversion device according to one embodiment includes a PFC circuit, a DCDC converter, a PFC control circuit, a DCDC converter control circuit, and a power supply circuit. The PFC circuit includes an inductor and a first switching element, which converts an input pulsating voltage into a DC voltage and outputs the converted voltage. The DCDC converter includes an isolation transformer and a second switching element, which outputs an output voltage of the PFC circuit input to the primary side of the isolation transformer from the secondary side of the isolation transformer as an arbitrary DC voltage. The PFC control circuit controls the first switching element. The DCDC converter control circuit controls the second switching element. When the PFC circuit is activated and the DCDC converter is not activated, the power supply circuit supplies a DC voltage to the PFC control circuit using a voltage generated in a first auxiliary winding coupled to the inductor magnetic field, and when the DCDC converter is activated, the power supply circuit supplies a DC voltage to the PFC control circuit using a voltage generated in a second auxiliary winding coupled to the isolation transformer magnetic field.

[0007] An image forming apparatus according to one embodiment includes: an image forming unit that forms an image on a printing medium; a PFC circuit having an inductor and a first switching element, the PFC circuit converting an input pulsating voltage into a DC voltage and outputting the converted DC voltage; a DCDC converter having an isolation transformer and a second switching element, the DCDC converter outputting an output voltage of the PFC circuit input to the primary side of the isolation transformer from the secondary side of the isolation transformer as an arbitrary DC voltage to the image forming unit; a PFC control circuit that controls the first switching element; a DCDC converter control circuit that controls the second switching element; and a power supply circuit that supplies a DC voltage to the PFC control circuit using a voltage generated in a first auxiliary winding that is magnetically coupled to the inductor when the PFC circuit is activated and the DCDC converter is not activated, and supplies a DC voltage to the PFC control circuit using a voltage generated in a second auxiliary winding that is magnetically coupled to the isolation transformer when the DCDC converter is activated. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 This is a diagram for explaining an example of the configuration of an image forming apparatus according to an embodiment.

[0009] Figure 2 It is a diagram for explaining an example of the configuration of the power conversion circuit according to the first embodiment.

[0010] Figure 3 It is a diagram for explaining an example of the operation of the power conversion circuit according to the first embodiment.

[0011] Figure 4 It is a diagram for explaining an example of the configuration of a power conversion circuit according to the second embodiment.

[0012] Figure 5 It is a diagram for explaining an example of the operation of the power conversion circuit according to the second embodiment.

[0013] Figure 6 It is a diagram for explaining another configuration example of the power conversion circuit according to the second embodiment.

[0014] Description of Reference Numerals

[0015] 1...image forming device, 11...power supply unit, 12...system controller, 13...display unit, 14...operation interface, 15...scanner, 16...transport motor, 17...processing unit, 18...exposure device, 19...fixer, 21...filter circuit, 22...power conversion circuit, 22A...power conversion circuit, 31...processor, 32...memory, 41...rectifier circuit, 42...PFC circuit, 43...LLC circuit, 44...PFC control circuit, 45...LLC control circuit, 46...first power supply circuit, 46A...first power supply circuit, 47...second power supply circuit, 47A...second power supply circuit, 51... .voltage detection circuit, C1...smoothing capacitor, C2...resonance capacitor, C3...smoothing capacitor, C4...smoothing capacitor, C5...smoothing capacitor, D1...diode, D2...diode, D3...diode, D4...diode, D5...diode, D6...diode, D7...diode, L1...inductor, L2...inductor, L3...winding, L4...winding, L5...winding, N1...auxiliary winding, N2...auxiliary winding, Q1...switching element, Q2...switching element, Q3...switching element, SW1...switching element, SW2...switching circuit, T1...insulation transformer, PC1...photocoupler. DETAILED DESCRIPTION

[0016] The following describes embodiments with reference to the drawings.

[0017] Figure 1 This is an explanatory diagram for explaining an example of the configuration of an image forming apparatus 1 according to one embodiment. The image forming apparatus 1 is, for example, a multifunction peripheral (MFP) that performs various processes such as image formation while conveying a recording medium such as a print medium. The image forming apparatus 1 is, for example, a solid scanning printer (e.g., an LED printer) that scans an LED array and performs various processes such as image formation while conveying a recording medium such as a print medium.

[0018] For example, the image forming apparatus 1 has a configuration for receiving toner from a toner cartridge and forming an image on a printing medium using the received toner. The toner may be a monochrome toner or a color toner such as cyan, magenta, yellow, and black. In addition, the toner may be a decolorizing toner that is decolorized when heated.

[0019] like Figure 1As shown, the image forming apparatus 1 includes a power supply unit 11 , a system controller 12 , a display unit 13 , an operation interface 14 , a scanner 15 , a conveying motor 16 , a processing unit 17 , an exposure device 18 , and a fixing device 19 .

[0020] The power supply unit 11 converts AC power supplied from the AC power supply AC into DC power, and supplies the DC power to the system controller 12, the display unit 13, the operation interface 14, the scanner 15, the conveying motor 16, the processing unit 17, the exposure device 18, and the fixing device 19. The power supply unit 11 includes a filter circuit 21 and a power conversion circuit (power conversion device) 22.

[0021] The filter circuit 21 is a circuit for removing noise leaking from the power conversion circuit 22 to the AC power supply AC. The filter circuit 21 is, for example, an EMC filter. The filter circuit 21 outputs an AC voltage of a commercial frequency 50 Hz or 60 Hz component input from an input terminal from an output terminal, and supplies it to the power conversion circuit 22. The filter circuit 21 shields the high-frequency noise generated in the power conversion circuit 22 from being transmitted to the output terminal. Thus, the filter circuit 21 prevents the high-frequency noise generated in the power conversion circuit 22 from being transmitted to the AC power supply AC via the input terminal.

[0022] The power conversion circuit 22 is a circuit that converts AC power supplied from the AC power source AC via the filter circuit 21 into DC power and outputs the DC power. The detailed configuration of the power conversion circuit 22 will be described later.

[0023] The system controller 12 controls the image forming apparatus 1. The system controller 12 includes, for example, a processor 31 and a memory 32.

[0024] The processor 31 is a computing element that performs arithmetic processing. The processor 31 is, for example, a CPU. The processor 31 performs various processes based on data such as programs stored in the memory 32. The processor 31 functions as a control unit capable of performing various operations by executing the programs stored in the memory 32.

[0025] The memory 32 is a storage medium that stores programs and data used by the programs. In addition, the memory 32 also functions as a working memory. That is, the memory 32 temporarily stores data being processed by the processor 31 and programs executed by the processor 31.

[0026] The processor 31 performs various information processing by executing the program stored in the memory 32. For example, the processor 31 generates a control signal for controlling the operation of the power supply unit 11, the scanner 15, the conveying motor 16, the processing unit 17, the exposure device 18, and the fixing device 19. The processor 31 controls the operation of the power supply unit 11, the scanner 15, the conveying motor 16, the processing unit 17, the exposure device 18, and the fixing device 19 through the control signal.

[0027] The display unit 13 includes a display that displays a screen based on a video signal input from a display control unit such as the system controller 12 or a graphic controller (not shown). For example, a screen for various settings of the image forming apparatus 1 is displayed on the display unit 13 .

[0028] The operation interface 14 is connected to an operation member not shown in the figure. The operation interface 14 provides an operation signal corresponding to the operation of the operation member to the system controller 12. The operation member is, for example, a touch sensor, a numeric keypad, a power key, a paper feed key, various function keys or a keyboard. The touch sensor acquires information indicating a position designated in a certain area. The touch sensor is integrally formed with the display unit 13 as a touch panel, and thus inputs a signal indicating a position touched on the screen displayed on the display unit 13 to the system controller 12.

[0029] The scanner 15 includes an image sensor, lighting, and optical elements. The image sensor is a photographic element with pixels arranged in a line that convert light into an electrical signal (image signal). The image sensor is composed of, for example, a charge coupled device (CCD), a complementary metal oxide semiconductor (CMOS), or other photographic elements. The lighting irradiates light to the object to be read. The optical element images the light from the object to be read on the pixels of the image sensor. Thus, the scanner 15 acquires an image of the object to be read.

[0030] The conveying motor 16 drives a conveying mechanism for conveying a print medium used in printing by the image forming apparatus 1. The conveying mechanism is composed of a plurality of rollers and a plurality of guides (not shown). The plurality of rollers are rotated by the conveying motor 16. The conveying motor 16 rotates the shaft based on the control of the system controller 12, thereby rotating the rollers linked to the rotation of the shaft. The plurality of rollers moves the print medium by rotating. The plurality of guides control the conveying direction of the print medium.

[0031] The process unit 17 is configured to form a toner image. For example, the process unit 17 is provided for each toner. A toner cartridge is connected to the process unit 17. The process unit 17 also includes a photosensitive drum, a charger, and a developer.

[0032] The photosensitive drum is a photosensitive body having a cylindrical drum and a photosensitive layer formed on the outer peripheral surface of the drum. The charger charges the surface of the photosensitive drum uniformly. The developer is a device that makes the toner adhere to the photosensitive drum.

[0033] The exposure device 18 includes a plurality of light emitting elements. The exposure device 18 forms a latent image on the photosensitive drum by irradiating light from the light emitting elements to the charged photosensitive drum. The light emitting element is, for example, a light emitting diode (LED). One light emitting element is configured to irradiate light to a point on the photosensitive drum. The plurality of light emitting elements are arranged in a direction parallel to the rotation axis of the photosensitive drum, i.e., in a main scanning direction.

[0034] The exposure device 18 irradiates light onto the photosensitive drum through a plurality of light emitting elements arranged in the main scanning direction, thereby forming a latent image of one line on the photosensitive drum. Furthermore, the exposure device 18 forms a plurality of latent images by continuously irradiating light onto the rotating photosensitive drum.

[0035] In the above structure, when light is irradiated from the exposure device 18 onto the charged surface of the photosensitive drum, an electrostatic latent image is formed. The developer attaches toner to the latent image formed on the surface of the photosensitive drum, thereby forming a toner image on the surface of the photosensitive drum.

[0036] The toner image formed on the surface of the photosensitive drum is transferred to the surface of the printing medium by a transfer mechanism (not shown) including a transfer belt and a transfer roller, etc. That is, the process unit 17, the exposure device 18 and the transfer mechanism constitute an image forming section that forms a toner image on the printing medium.

[0037] The fixer 19 fixes the toner image on the printing medium to which the toner image is transferred. The fixer 19 has a heater, a heating member heated by the heater, and a pressurizing member that applies pressure to the printing medium together with the heating member. The heater of the fixer 19 generates heat by the power supplied from the power supply unit 11, and heats the heating member. The heater of the fixer 19 is, for example, a halogen heater or an IH heater. The pressurizing member applies pressure to the heating member by using stress applied from a tension member not shown in the figure. By applying pressure from the pressurizing member to the heating member, a clamping portion (fixing clamping portion) in which the pressurizing member and the heating member are in close contact is formed. The pressurizing member is rotated by a motor not shown in the figure. The pressurizing member moves the printing medium that has entered the fixing clamping portion by rotating, and presses the printing medium to the heating member.

[0038] With the above configuration, the pressing member and the heating member apply heat and pressure to the print medium passing through the fixing nip. The toner on the print medium is melted by the heat provided by the heating member, and is applied to the surface of the print medium by the pressure provided by the heating member and the pressure member. Thus, the toner image is fixed on the print medium passing through the fixing nip.

[0039] (First Embodiment)

[0040] Next, the detailed configuration of the power conversion circuit 22 of the power supply unit 11 according to the first embodiment will be described.

[0041] Figure 2 It is a diagram for explaining a configuration example of the power conversion circuit 22 .

[0042] The alternating current power source AC is connected to the power conversion circuit 22 via the filter circuit 21. The power conversion circuit 22 converts the alternating current voltage of the alternating current power source AC at a high frequency, and supplies an arbitrary direct current voltage to each load of the image forming apparatus 1.

[0043] The power conversion circuit 22 includes a rectifier circuit 41, a PFC circuit 42, an LLC circuit 43, a PFC control circuit 44, an LLC control circuit 45, a first power supply circuit 46, and a second power supply circuit 47. That is, the power conversion circuit 22 is a two-stage power supply circuit.

[0044] The rectifier circuit 41 performs full-wave rectification on the AC voltage input from the AC power source AC via the filter circuit 21, and supplies the DC voltage to the subsequent circuit. That is, the rectifier circuit 41 converts the AC voltage into a DC voltage (pulsating voltage), and supplies it to the PFC circuit 42. The rectifier circuit 41 is, for example, a full-wave rectifier circuit (rectifier) ​​composed of a plurality of diodes.

[0045] The PFC circuit 42 is connected to the output terminal of the rectifier circuit 41. The PFC circuit 42 includes an inductor L1, a switching element Q1, a diode D1, and a smoothing capacitor C1.

[0046] The inductor L1 is connected between one output terminal of the rectifying circuit 41 and the anode of the diode D1. In addition, the cathode of the diode D1 is connected to the high potential side terminal of the smoothing capacitor C1.

[0047] The switching element Q1 is an element that is turned on and off under the control of the PFC control circuit 44. The switching element Q1 is turned on and off according to the gate signal G1 provided from the PFC control circuit 44. The switching element Q1 is a FET composed of a wide bandgap semiconductor such as SiC, GaN, gallium oxide, or diamond. In addition, the switching element Q1 may also be a MOSFET composed of silicon. The drain of the switching element Q1 is connected to the anode of the inductor L1 and the diode D1. The source of the switching element Q1 is connected to the low potential side terminal of the smoothing capacitor C1.

[0048] According to the above configuration, the PFC circuit 42 boosts the output voltage of the rectifier circuit 41 by turning the switch element Q1 on and off, and charges the smoothing capacitor C1. That is, the smoothing capacitor C1 supplies the boosted output voltage of the rectifier circuit 41 to the LLC circuit 43, which is the subsequent circuit.

[0049] The LLC circuit 43 is connected to the subsequent stage of the PFC circuit 42. The LLC circuit 43 is a DCDC conversion circuit (DCDC converter) that provides a DC voltage required by a load from a DC voltage provided from the PFC circuit 42. The LLC circuit 43 includes a switching element Q2, a switching element Q3, an inductor L2, a resonant capacitor C2, a winding L3, a winding L4, a winding L5, a diode D2, a diode D3, and a smoothing capacitor C3. In addition, the diode D2 and the diode D3 may also be configured by a MOSFET in a synchronous rectification manner.

[0050] The switching element Q2 and the switching element Q3 are elements that are turned on and off under the control of the LLC control circuit 45. The switching element Q2 and the switching element Q3 are, for example, silicon MOSFETs. The switching element Q2 is a high-side switch that is turned on and off according to the gate signal G2 provided from the LLC control circuit 45. The switching element Q3 is a low-side switch that is turned on and off according to the gate signal G3 provided from the LLC control circuit 45.

[0051] The drain terminal of the switching element Q2 is connected to one output terminal of the PFC circuit 42 (the high potential side terminal of the smoothing capacitor C1). The source terminal of the switching element Q3 is connected to the other output terminal of the PFC circuit 42 (the low potential side terminal of the smoothing capacitor C1), and the drain terminal is connected to the source terminal of the switching element Q2. In addition, the inductor L2, the resonant capacitor C2, and the winding L3 are connected in series between the connection point of the switching element Q2 and the switching element Q3 and the source terminal of the switching element Q3.

[0052] The winding L3, the winding L4 and the winding L5 constitute the insulating transformer T1. The winding L3 is the primary side of the insulating transformer T1, and the winding L4 and the winding L5 are the secondary side of the insulating transformer T1. The winding L4 and the winding L5 are insulated from the winding L3 and excited by the magnetic field generated in the winding L3. The winding L4 and the winding L5 are connected to each other. The insulating transformer T1 is configured, for example, so that the turn ratio of the winding L3 to the winding L4 is equal to the turn ratio of the winding L3 to the winding L5. The connection point of the winding L4 and the winding L5 is connected to the low potential side terminal of the smoothing capacitor C3.

[0053] The anode of the diode D2 is connected to the winding L4, and the cathode is connected to the high potential side terminal of the smoothing capacitor C3. The anode of the diode D3 is connected to the winding L5, and the cathode is connected to the high potential side terminal of the smoothing capacitor C3.

[0054] According to the above-mentioned configuration, the switching element Q2 and the switching element Q3 are alternately turned on and off, and an alternating voltage is applied to the winding L3 through the resonant action of the inductor L2 and the resonant capacitor C2. As a result, an alternating current equivalent to that of the inductor L2 flows through the winding L3. As a result, a magnetic field that changes according to the alternating current is generated in the insulating transformer T1. The change in the magnetic field (change in magnetic flux) generated in the insulating transformer T1 generates an induced voltage in the winding L4 and the winding L5. The induced voltage causes an alternating current to flow through the windings L4 and L5. Specifically, the positive half-wave portion of the alternating current flows through the winding L4, and the negative half-wave portion of the alternating current flows through the winding L5. That is, currents of half waves and opposite phases flow through the windings L4 and L5, respectively. The current generated in the winding L4 is rectified by the diode D2, and the smoothing capacitor C3 is charged. The current generated in the winding L5 is rectified by the diode D3, and the smoothing capacitor C3 is charged. Thus, DC power (DC voltage DCV) is supplied to the load connected to the smoothing capacitor C3.

[0055] The PFC control circuit 44 generates a gate signal G1 for turning on and off the switching element Q1 of the PFC circuit 42, and inputs the gate signal G1 to the gate of the switching element Q1. The PFC control circuit 44 switches the switching element Q1 so that the input current approaches a sine wave, for example.

[0056] The LLC control circuit 45 generates a gate signal G2 for turning on and off the switch element Q2 of the LLC circuit 43, and inputs it to the gate of the switch element Q2. In addition, the LLC control circuit 45 generates a gate signal G3 for turning on and off the switch element Q3 of the LLC circuit 43, and inputs it to the gate of the switch element Q3. The LLC control circuit 45 turns the switch element Q2 and the switch element Q3 on and off alternately. As a result, an alternating voltage is applied to the winding L3 through the resonant action of the inductor L2 and the resonant capacitor C2 of the LLC circuit 43. As a result, an alternating current flows through the winding L3, generating a magnetic field.

[0057] The first power supply circuit 46 and the second power supply circuit 47 are power supply circuits for supplying a DC voltage to the PFC control circuit 44 and the LLC control circuit 45. The first power supply circuit 46 supplies a DC voltage PFCVcc, which is a voltage for operating the PFC control circuit 44, to the PFC control circuit 44 based on a magnetic field generated in the inductor L1 of the PFC circuit 42. The first power supply circuit 46 includes an auxiliary winding N1, a diode D4, a smoothing capacitor C4, and a diode D5.

[0058] The auxiliary winding N1 is magnetically coupled to the inductor L1 of the PFC circuit 42. A current generated by a pulsating voltage applied from the rectifier circuit 41 flows through the inductor L1. The auxiliary winding N1 is excited according to the magnetic field generated by the current flowing through the inductor L1, and generates power.

[0059] The diode D4 has an anode connected to the auxiliary winding N1 and a cathode connected to the high potential side terminal of the smoothing capacitor C4 .

[0060] The smoothing capacitor C4 is connected in parallel to the auxiliary winding N1 via a diode D4. The smoothing capacitor C4 is charged by a current generated by a voltage generated in the auxiliary winding N1 and rectified by the diode D4. In addition, the smoothing capacitor C4 is connected in parallel to a power supply input terminal of the PFC control circuit 44 via a diode D5.

[0061] The diode D5 has an anode connected to the high potential side terminal of the smoothing capacitor C4 , and a cathode connected to the power supply input terminal of the PFC control circuit 44 .

[0062] According to the above configuration, the first power supply circuit 46 receives power from the PFC circuit 42 via the auxiliary winding N1 , rectifies and smoothes the received power, and generates a DC voltage PFCVcc. The first power supply circuit 46 supplies the DC voltage PFCVcc to the power input terminal of the PFC control circuit 44 .

[0063] The second power supply circuit 47 supplies the LLC control circuit 45 with a DC voltage LLCVcc, which is a voltage for operating the LLC control circuit 45, based on a magnetic field generated in the isolation transformer T1 of the LLC circuit 43, and also supplies the DC voltage LLCVcc to the PFC control circuit 44. The second power supply circuit 47 includes an auxiliary winding N2, a diode D6, a smoothing capacitor C5, and a diode D7.

[0064] The auxiliary winding N2 is a winding that is magnetically coupled to the isolation transformer T1 of the LLC circuit 43. The alternating current generated by the switching elements Q2 and Q3 as described above flows through the winding L3 of the isolation transformer T1. The auxiliary winding N2 is excited according to the magnetic field generated in the isolation transformer T1 to generate power.

[0065] The diode D6 has an anode connected to the auxiliary winding N2 and a cathode connected to the high potential side terminal of the smoothing capacitor C5 .

[0066] The smoothing capacitor C5 is connected in parallel with the auxiliary winding N2 via the diode D6. The smoothing capacitor C5 is charged by a current generated by the voltage generated in the auxiliary winding N2 and rectified by the diode D6. In addition, the smoothing capacitor C5 is connected in parallel with the power supply input terminal of the LLC control circuit 45.

[0067] According to the above configuration, the second power supply circuit 47 receives power from the LLC circuit 43 via the auxiliary winding N2 , rectifies and smoothes the received power, and generates a DC voltage LLCVcc. The second power supply circuit 47 supplies the DC voltage LLCVcc to the power input terminal of the LLC control circuit 45 .

[0068] The anode of the diode D7 is connected to the high potential side terminal of the smoothing capacitor C5, and the cathode is connected to the power input terminal of the PFC control circuit 44. That is, the smoothing capacitor C5 is also connected in parallel to the power input terminal of the PFC control circuit 44 via the diode D7.

[0069] According to the above configuration, the second power supply circuit 47 also provides the DC voltage LLCVcc to the power input terminal of the PFC control circuit 44. It should be noted that when the DC voltage PFCVcc> the DC voltage LLCVcc, the DC voltage LLCVcc from the second power supply circuit 47 is not provided to the PFC control circuit 44, and when the DC voltage PFCVcc< the DC voltage LLCVcc, the DC voltage LLCVcc from the second power supply circuit 47 is provided to the PFC control circuit 44.

[0070] Next, the operation of the power conversion circuit 22 will be described.

[0071] Figure 3 It is an explanatory diagram for explaining the operation of the power conversion circuit 22 . Figure 3 The example shows the relationship between the AC voltage provided from the AC power supply AC via the filter circuit 21, the pulsating voltage provided from the rectifier circuit 41, the DC voltage PFCVcc from the first power supply circuit 46, the DC voltage DCV as the output of the power conversion circuit 22, the DC voltage LLCVcc from the second power supply circuit 47, and the voltage provided to the PFC control circuit 44.

[0072] Assume that the AC voltage is not supplied at timing t0 and starts to be supplied at timing t1. In this case, the AC voltage is converted into a pulsating voltage by the rectifier circuit 41 and supplied to the PFC circuit 42, and the inductor L1 of the PFC circuit 42 is turned on.

[0073] When the inductor L1 is turned on, a voltage is generated in the auxiliary winding N1 of the first power supply circuit 46 by the magnetic field generated in the inductor L1. The generated voltage is rectified and smoothed by the diode D4 and the smoothing capacitor C4, and becomes a DC voltage PFCVcc at timing t2, and is supplied to the PFC control circuit 44 via the diode D5. Therefore, at timing t2, the voltage supplied to the PFC control circuit 44 is the DC voltage PFCVcc. It should be noted that at this time point, the LLC circuit 43 has not yet started.

[0074] Next, when the PFC control circuit 44 starts and a high voltage is applied to the smoothing capacitor C1, the LLC circuit 43 starts at timing t3. When the LLC circuit 43 starts, power is supplied from the primary side to the secondary side of the isolation transformer T1, and the DC voltage DCV is output from the power conversion circuit 22.

[0075] Simultaneously with the output of the DC voltage DCV from the power conversion circuit 22, a voltage is generated in the auxiliary winding N2 of the second power supply circuit 47 by the magnetic field generated in the isolation transformer T1. The generated voltage is rectified and smoothed by the diode D6 and the smoothing capacitor C5, becomes a DC voltage LLCVcc at timing t3, and is supplied to the LLC control circuit 45, starting a steady-state operation.

[0076] In addition, when the DC voltage LLCVcc>the DC voltage PFCVcc, the DC voltage LLCVcc from the second power supply circuit 47 is also supplied to the PFC control circuit 44. Therefore, at the timing t3, the voltage supplied to the PFC control circuit 44 increases from the DC voltage PFCVcc to the DC voltage LLCVcc. It should be noted that the DC voltage LLCVcc from the second power supply circuit 47 is cut off by the diode D5 so as to avoid being applied to the first power supply circuit 46. In addition, during the steady-state operation after the timing t3 in which the DC voltage LLCVcc is supplied from the second power supply circuit 47 to the PFC control circuit 44, the DC voltage PFCVcc of the first power supply circuit 46 is not supplied to the outside from the closed circuit of the auxiliary winding N1, the smoothing capacitor C4, and the diode D4.

[0077] The DC voltage PFCVcc from the first power supply circuit 46 is determined by the pulsating voltage applied to the inductor L1 and the turns ratio of the auxiliary winding N1 to the inductor L1. The DC voltage LLCVcc from the second power supply circuit 47 is determined by the alternating voltage applied to the winding L3 of the isolation transformer T1 and the turns ratio of the auxiliary winding N2 to the winding L3. Therefore, the pulsating voltage applied to the inductor L1, the turns ratio of the auxiliary winding N1 to the inductor L1, the alternating voltage applied to the winding L3 of the isolation transformer T1, and the turns ratio of the auxiliary winding N2 to the winding L3 are set so that the DC voltage LLCVcc>the DC voltage PFCVcc.

[0078] As described above, while the current generated by the pulsating voltage flows through the inductor L1 of the PFC circuit 42, the alternating current generated by the alternating voltage flows through the isolation transformer T1 of the LLC circuit 43. Therefore, the loss of the first power supply circuit 46 that supplies the DC voltage PFCVcc to the PFC control circuit 44 is greater than the loss of the second power supply circuit 47 that supplies the DC voltage LLCVcc to the LLC control circuit 45 (the conversion efficiency is poor).

[0079] For this reason, in the power supply circuit of the power conversion circuit 22 of the first embodiment, when the PFC circuit 42 is activated and the LLC circuit 43 is not activated, a DC voltage is supplied to the PFC control circuit 44 by a voltage generated in the first auxiliary winding N1 magnetically coupled to the inductor L1, and when the LLC circuit 43 is activated, a DC voltage is supplied to the PFC control circuit 44 by a voltage generated in the second auxiliary winding N2 magnetically coupled to the insulation transformer T1. Therefore, the second power supply circuit 47 is designed so that the DC voltage LLCVcc> the DC voltage PFCVcc in steady-state operation. Thus, the second power supply circuit 47 supplies the DC voltage LLCVcc to the PFC control circuit 44 and the LLC control circuit 45 in steady-state operation. In addition, the first power supply circuit 46 does not output the DC voltage PFCVcc in steady-state operation. As a result, the loss in the power conversion circuit 22 can be reduced.

[0080] Furthermore, the first power supply circuit 46 includes a diode D5 whose cathode is connected to the PFC control circuit 44. This can prevent the DC voltage LLCVcc from the second power supply circuit 47 from being applied to the smoothing capacitor C4.

[0081] Furthermore, the second power supply circuit 47 includes a diode D7 whose cathode is connected to the PFC control circuit 44. This can prevent the DC voltage PFCVcc from the first power supply circuit 46 from being applied to the smoothing capacitor C5.

[0082] For example, it is assumed that when PFCVcc=15(V) and LLCVcc=17(V), a current of 50(mA) flows through each of the PFC control circuit 44 and the LLC control circuit 45. In addition, it is assumed that at this time, the conversion efficiency of generating the DC voltage PFCVcc from the auxiliary winding N1 is 50%, and the conversion efficiency of generating the DC voltage LLCVcc from the auxiliary winding N2 is 80%. The power consumption in this case is calculated.

[0083] (1) When the PFC control circuit 44 is driven with PFCVcc=15(V) and the LLC control circuit 45 is driven with LLCVcc=17(V), the power consumption in the PFC control circuit 44 (W)=15(V)×50(mA) / 0.5=1.5(W), the power consumption in the LLC control circuit 45 (W)=17(V)×50(mA) / 0.8=1.0625(W), the total power consumption (W)=1.5(W)+1.0625(W)=2.5625(W)

[0084] (2) When the PFC control circuit 44 and the LLC control circuit 45 are driven with LLCVcc=17(V), the power consumption in the PFC control circuit 44 (W)=17(V)×50(mA) / 0.8=1.0625(W), the power consumption in the LLC control circuit 45 (W)=17(V)×50(mA) / 0.8=1.0625(W), and the total power consumption (W)=1.0625(W)+1.0625(W)=2.125(W).

[0085] As described above, a power consumption difference of 2.5625 (W) - 2.125 (W) = 0.4375 (W) can be achieved between (1) and (2).

[0086] (Second Embodiment)

[0087] Next, a detailed configuration of a power conversion circuit 22A according to the second embodiment will be described.

[0088] Figure 4 2 is a diagram for explaining an example of the configuration of the power conversion circuit 22A. The configuration of the first power supply circuit 46 and the second power supply circuit 47 of the power conversion circuit 22A is different from that of the first embodiment. The first power supply circuit 46 and the second power supply circuit 47 in the second embodiment are referred to as the first power supply circuit 46A and the second power supply circuit 47A, respectively. In addition, for the description of the same configuration as the first embodiment, the same reference numerals are marked and the description is omitted.

[0089] The first power supply circuit 46A includes an auxiliary winding N1 , a diode D4 , a smoothing capacitor C4 , and a switching element SW1 .

[0090] The switch element SW1 is an element that connects the smoothing capacitor C4 and the PFC control circuit 44 when turned on, and disconnects the smoothing capacitor C4 and the PFC control circuit 44 when turned off. The switch element SW1 is turned on and off under the control of the second power supply circuit 47A. The switch element SW1 is a normally-on switch that is turned on when the control signal from the second power supply circuit 47A is at an L level, and is turned off when the control signal from the second power supply circuit 47A is at an H level. The switch element SW1 is composed of, for example, a relay switch, but may be composed of any switch.

[0091] The second power supply circuit 47A includes an auxiliary winding N2 , a diode D6 , a diode D7 , a smoothing capacitor C5 , and a voltage detection circuit 51 .

[0092] The voltage detection circuit 51 is a circuit that detects the voltage of the smoothing capacitor C5 and outputs the detection result to the first power supply circuit 46A as a control signal for switching the switch element SW1 on and off. When the voltage of the smoothing capacitor C5 is equal to or higher than a preset threshold, the voltage detection circuit 51 outputs an H-level signal to the switch element SW1. In addition, when the voltage of the smoothing capacitor C5 is lower than a preset threshold, the voltage detection circuit 51 outputs an L-level signal to the switch element SW1.

[0093] Figure 5 2 is an explanatory diagram for explaining the operation of the power conversion circuit 22A. Figure 5 In the example, the relationship between the AC voltage provided from the AC power supply AC via the filter circuit 21, the pulsating voltage provided from the rectifier circuit 41, the DC voltage PFCVcc from the first power supply circuit 46A, the DC voltage DCV as the output of the power conversion circuit 22, the DC voltage LLCVcc from the second power supply circuit 47A, the on and off of the switching element SW1, and the voltage provided to the PFC control circuit 44 is shown.

[0094] Assume that the AC voltage is not supplied at timing t0 and the AC voltage starts to be supplied at timing t1. In this case, the AC voltage is converted into a pulsating voltage by the rectifier circuit 41 and supplied to the PFC circuit 42, and the inductor L1 of the PFC circuit 42 is turned on.

[0095] When the inductor L1 is turned on, a voltage is generated in the auxiliary winding N1 of the first power supply circuit 46A by the magnetic field generated in the inductor L1. The generated voltage is rectified and smoothed by the diode D4 and the smoothing capacitor C4, and becomes the DC voltage PFCVcc at the timing t2. At this point in time, since the LLC circuit 43 is not operating, the smoothing capacitor C5 of the second power supply circuit 47A is not charged. Therefore, the control signal from the voltage detection circuit 51 is at the L level, and the switch element SW1 is turned on. Therefore, the DC voltage PFCVcc from the smoothing capacitor C4 is provided to the PFC control circuit 44 via the switch element SW1. Therefore, at the timing t2, the voltage provided to the PFC control circuit 44 is the DC voltage PFCVcc.

[0096] Next, when the PFC control circuit 44 is activated and a high voltage is applied to the smoothing capacitor C1, the LLC circuit 43 is activated at timing t3. When the LLC circuit 43 is activated, power is supplied from the primary side to the secondary side of the isolation transformer T1, and the DC voltage DCV is output from the power conversion circuit 22.

[0097] At the same time as the DC voltage DCV is output from the power conversion circuit 22, a voltage is generated in the auxiliary winding N2 of the second power supply circuit 47A by the magnetic field generated in the isolation transformer T1. The generated voltage is rectified and smoothed by the diode D6 and the smoothing capacitor C5, and becomes the DC voltage LLCVcc at the timing t3. The DC voltage LLCVcc from the smoothing capacitor C5 is provided to the LLC control circuit 45. In addition, the DC voltage LLCVcc from the smoothing capacitor C5 is provided to the PFC control circuit 44 via the diode D7.

[0098] Furthermore, the voltage of the smoothing capacitor C5 is detected by the voltage detection circuit 51, and the control signal from the voltage detection circuit 51 becomes H level. As a result, the switch element SW1 is turned off. Therefore, at timing t3, the first power supply circuit 46A is not supplied with power to the PFC control circuit 44. However, as described above, since the DC voltage LLCVcc is supplied to the PFC control circuit 44 from the second power supply circuit 47A, the voltage supplied to the PFC control circuit 44 is maintained.

[0099] As described above, the power conversion circuit 22A of the second embodiment cuts off the power supply from the first power supply circuit 46A having a lower conversion efficiency than the second power conversion circuit 22A by the switch element SW1 during steady-state operation with the LLC circuit 43 activated. With this configuration, the loss in the power conversion circuit 22 can be reduced as in the first embodiment.

[0100] Figure 6 It is an explanatory diagram for explaining a modification example of the switching element SW1.

[0101] exist Figure 6 In the example of FIG. 1 , the first power conversion circuit 22A includes a switch circuit SW2 instead of the switch element SW1 , and the switch circuit SW2 includes a photocoupler PC1 and a field effect transistor FET.

[0102] The switch circuit SW2 is connected between the smoothing capacitor C4 and the PFC control circuit 44 , and switches between a state in which the smoothing capacitor C4 and the PFC control circuit 44 are connected and a state in which the smoothing capacitor C4 and the PFC control circuit 44 are disconnected.

[0103] The field effect transistor FET of the switch circuit SW2 is, for example, a normally open switch. The source of the field effect transistor FET is connected to the high potential side terminal of the smoothing capacitor C4, and the drain of the field effect transistor FET is connected to the PFC control circuit 44. That is, the field effect transistor FET connects the smoothing capacitor C4 and the PFC control circuit 44 when in the on state, and disconnects the smoothing capacitor C4 and the PFC control circuit 44 when in the off state.

[0104] The emitter-collector of the phototransistor PT of the photocoupler PC1 is connected between the source-gate of the field effect transistor FET. Specifically, the collector of the phototransistor PT of the photocoupler PC1 is connected to the high potential side terminal of the smoothing capacitor C4, and the emitter is connected to the gate of the field effect transistor FET.

[0105] In addition, the anode and cathode of the light emitting diode LED of the photocoupler PC1 are connected to the current path through which the current flows by the voltage generated in the second auxiliary winding N2. Specifically, the anode of the light emitting diode LED of the photocoupler PC1 is connected to the high potential side terminal of the smoothing capacitor C5, and the cathode is connected to the low potential side terminal. That is, the light emitting diode LED of the photocoupler PC1 is connected in parallel with the smoothing capacitor C5 of the second power supply circuit 47A. The light emitting diode LED of the photocoupler PC1 emits light by the current flowing when the voltage from the smoothing capacitor C5 exceeds the voltage at which the light emitting diode LED can be turned on.

[0106] According to the above configuration, the field effect transistor FET is kept in the on state until the light emitting diode LED of the photocoupler PC1 emits light, thereby maintaining the state where the smoothing capacitor C4 and the PFC control circuit 44 are connected.

[0107] When the LLC circuit 43 is started and enters a steady-state operation, the light-emitting diode LED of the photocoupler PC1 emits light. When the light-emitting diode LED emits light, the emitter-collector of the phototransistor PT of the photocoupler PC1 is turned on, and the gate-source voltage of the field effect transistor FET becomes less than the threshold of the FET drive voltage. Therefore, the field effect transistor FET becomes an off state. As a result, the smoothing capacitor C4 and the PFC control circuit 44 are cut off. As a result, the DC voltage PFCVcc is not supplied from the first power supply circuit 46A to the PFC control circuit 44, and the DC voltage LLCVcc is supplied from the second power supply circuit 47A to the PFC control circuit 44. As a result, the loss in the power conversion circuit 22 can be reduced as in the first embodiment.

[0108] Although several embodiments are described, these embodiments are only presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other ways, and various omissions, substitutions, and changes can be made without departing from the scope of the purpose of the invention. These embodiments and their variations are included in the scope and purpose of the invention, and are also included in the invention described in the claims and their equivalents.

Claims

1. A power conversion device comprising: A PFC circuit having an inductor and a first switching element, wherein the PFC circuit converts an input pulsating voltage into a DC voltage and outputs the DC voltage; A DCDC converter having an isolation transformer and a second switching element, the DCDC converter outputting an output voltage of the PFC circuit input to the primary side of the isolation transformer from the secondary side of the isolation transformer as an arbitrary DC voltage; A PFC control circuit, controlling the first switch element; A DCDC converter control circuit controls the second switch element; as well as a power supply circuit, wherein when the PFC circuit is started and the DCDC converter is not started, the power supply circuit uses a voltage generated in a first auxiliary winding coupled with a magnetic field of the inductor to provide a DC voltage to the PFC control circuit; and when the DCDC converter is started, the power supply circuit uses a voltage generated in a second auxiliary winding coupled with a magnetic field of the isolation transformer to provide a DC voltage to the PFC control circuit. The power supply circuit comprises: a first power supply circuit, generating a first DC voltage by using a voltage generated in the first auxiliary winding, and providing the first DC voltage to the PFC control circuit via a first diode, wherein a cathode of the first diode is connected to the PFC control circuit; as well as The second power supply circuit generates a second DC voltage higher than the first DC voltage using the voltage generated in the second auxiliary winding, and provides the second DC voltage to the PFC control circuit via a second diode, wherein a cathode of the second diode is connected to the PFC control circuit.

2. A power conversion device comprising: A PFC circuit having an inductor and a first switching element, wherein the PFC circuit converts an input pulsating voltage into a DC voltage and outputs the DC voltage; A DCDC converter having an isolation transformer and a second switching element, the DCDC converter outputting an output voltage of the PFC circuit input to the primary side of the isolation transformer from the secondary side of the isolation transformer as an arbitrary DC voltage; A PFC control circuit, controlling the first switch element; A DCDC converter control circuit controls the second switch element; as well as a power supply circuit, wherein when the PFC circuit is started and the DCDC converter is not started, the power supply circuit uses a voltage generated in a first auxiliary winding coupled with a magnetic field of the inductor to provide a DC voltage to the PFC control circuit; and when the DCDC converter is started, the power supply circuit uses a voltage generated in a second auxiliary winding coupled with a magnetic field of the isolation transformer to provide a DC voltage to the PFC control circuit. The power supply circuit comprises: a first power supply circuit, providing a DC voltage to the PFC control circuit using the voltage generated in the first auxiliary winding via a normally open switch that is turned off according to the voltage generated in the second auxiliary winding; as well as The second power supply circuit uses the voltage generated in the second auxiliary winding to provide a DC voltage to the PFC control circuit.

3. The power conversion device according to claim 2, characterized in that: The normally open switch has: a field effect transistor, a drain of the field effect transistor being connected to the PFC control circuit; and A photocoupler having an emitter-collector connected between the source-gate of the field effect transistor and an anode and a cathode connected to a current path through which current flows due to a voltage generated in the second auxiliary winding.

4. An image forming device comprising: The power conversion device according to any one of claims 1 to 3; and The image forming unit forms an image on a printing medium.

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