JP7149818B2 - Power conversion device and image forming device - Google Patents

Description

TECHNICAL FIELD Embodiments of the present invention relate to a power converter and an image forming apparatus.

A power conversion device that converts power is commonly used. A power converter supplies power from a primary side to a secondary side via a transformer. A power converter includes a switching IC (control circuit) on the primary side. The switching IC causes an alternating voltage to flow to the primary side of the transformer by switching the switching element. A switching IC operates by a voltage generated in an auxiliary winding magnetically coupled with a transformer. The power conversion device has a shunt regulator on the secondary side. The shunt regulator adjusts the output voltage output from the secondary side to the load based on the voltage of the reference voltage terminal. That is, the power converter adjusts the output voltage to a predetermined voltage using the shunt regulator.

The power converter switches the voltage dividing ratio of the shunt regulator by switching the resistor connected to the reference voltage terminal of the shunt regulator. Thereby, the power converter can switch the output voltage. When the output voltage is switched, the voltage across the auxiliary winding that supplies the switching IC also changes. For example, if the voltage supplied from the auxiliary winding is too high (above the rating), the switching IC will shut down due to the overvoltage protection function. Also, for example, if the voltage supplied from the auxiliary winding is too low, the switching IC will stop due to the low voltage detection function. Thus, there is a problem that the switching IC may not operate normally due to the switching of the output voltage.

JP 2016-144310 A

An object of the present invention is to provide a power converter and an image forming apparatus that operate stably.

A power converter according to an embodiment includes an isolation transformer, a DC power supply, a first switch, a control circuit, a rectifying/smoothing circuit, and a voltage adjusting circuit. The isolation transformer includes a primary winding, a secondary winding electromagnetically coupled to the primary winding, a first auxiliary winding, and a second auxiliary winding. A DC power supply outputs a DC voltage to the primary winding. A first switch switches connection between the DC power supply and the primary winding. A control circuit is connected to the first auxiliary winding and controls the first switch. A rectifying/smoothing circuit is connected to the secondary winding, rectifies and smoothes the current generated in the secondary winding, and outputs a DC voltage. A voltage adjustment circuit adjusts the output voltage of the rectifying/smoothing circuit, and according to the adjustment of the output voltage, connects the second auxiliary winding to the control circuit, and adjusts the rectifying voltage through the first resistor. A shunt regulator for adjusting the output voltage based on the voltage of a reference voltage terminal connected to the output terminal of the smoothing circuit and grounded via a second resistor; and a third resistor connected to the reference voltage terminal. a second switch connected between the third resistor and the output terminal of the rectifying/smoothing circuit; a third switch controlling the second switch; and a conductive path of the third switch. and a fourth switch for connecting the second auxiliary winding to the control circuit in response to the current of the second auxiliary winding.

FIG. 1 is a diagram for explaining an example of the configuration of an image forming apparatus according to one embodiment. FIG. 2 is a diagram for explaining an example of the configuration of the power converter according to one embodiment. FIG. 3 is a diagram for explaining another configuration example of the power converter according to one embodiment. FIG. 4 is a diagram for explaining an example of a product information processing apparatus including a power conversion device according to one embodiment.

Embodiments will be described below with reference to the drawings.
FIG. 1 is an explanatory diagram showing a configuration example of an image forming apparatus (electrophotographic apparatus) 2 including a power conversion circuit (power conversion apparatus) 1 according to one embodiment. In this embodiment, the power conversion circuit 1 is assumed to be incorporated in the image forming apparatus 2, but may be incorporated in any device.
The image forming apparatus 2 is, for example, a multifunction printer (MFP) that performs various processes such as image formation while conveying a recording medium such as a print medium. The image forming apparatus 2 forms a latent image (electrostatic latent image) on the photosensitive drum by charging the photosensitive drum and irradiating the photosensitive drum with light corresponding to image data for printing (print data). . The image forming apparatus 2 adheres toner (developer) to the latent image formed on the photosensitive drum to form a toner image on the photosensitive drum. The image forming apparatus 2 transfers the toner image on the photosensitive drum onto a printing medium, and applies high heat and pressure to the printing medium onto which the toner image has been transferred by means of a heater, thereby fixing the toner image onto the printing medium.

First, a configuration example of the image forming apparatus 2 will be described. As shown in FIG. 1, the image forming apparatus 2 includes a housing 11, a paper feed cassette 12, a paper discharge tray 13, a transport section 14, an image forming section 15, a fixing device 16, a system controller 17, and a power supply unit 18. Prepare.

The housing 11 is the main body of the image forming apparatus 2 . The housing 11 accommodates a paper feed cassette 12 , a paper discharge tray 13 , a transport section 14 , an image forming section 15 , a fixing device 16 , a system controller 17 and a power supply unit 18 .

The paper feed cassette 12 is a cassette that accommodates the print media P. As shown in FIG. The paper feed cassette 12 is configured to be able to supply the print medium P from the outside of the housing 11 . For example, the paper feed cassette 12 is configured to be able to be pulled out from the housing 11 .

The paper discharge tray 13 is a tray that supports the print medium P discharged from the image forming apparatus 2 .

The transport unit 14 is a mechanism that transports the print medium P within the image forming apparatus 2 . As shown in FIG. 1 , the transport section 14 includes a paper feed transport path 21 and a paper discharge transport path 22 .

The paper feed transport path 21 and the paper discharge transport path 22 are composed of a plurality of guides, a plurality of rollers, and a plurality of motors (not shown). The paper feed transport path 21 and the paper discharge transport path 22 are driven by a motor that operates under the control of the system controller 17 to rotate rollers that move the print medium P by rotating while sandwiching the print medium P. , transports the print medium P.

The paper feed transport path 21 is a transport path for supplying the print medium P accommodated in the paper feed cassette 12 to the image forming section 15 .

The discharge conveying path 22 is a conveying path through which the printing medium P on which an image is formed by the image forming section 15 and the toner image is fixed by the fixing device 16 is discharged from the housing 11 . The print medium P ejected by the paper ejection transport path 22 is ejected to the paper ejection tray 13 .

The image forming section 15 is configured to form an image on the print medium P under the control of the system controller 17 . As shown in FIG. 1 , the image forming section 15 includes a photoreceptor 31 , a charger 32 , an exposure device 33 , a developer 34 and a transfer mechanism 35 .

The photoreceptor 31 is a cylindrical photoreceptor drum. The photosensitive member 31 is rotated at a constant speed by a driving mechanism (not shown).

The charger 32 uniformly charges the surface of the photoreceptor 31 .

The exposure device 33 forms an electrostatic latent image on the charged photoreceptor 31 . The exposure unit 33 forms an electrostatic latent image on the surface of the photoreceptor 31 by irradiating the surface of the photoreceptor 31 with laser light using a light emitting element or the like based on print data.

The developing device 34 causes toner to adhere to the latent image on the photoreceptor 31 . Thereby, a toner image is formed on the surface of the photoreceptor 31 .

The transfer mechanism 35 transfers the toner image formed on the photoreceptor 31 to the print medium P. As shown in FIG. For example, the transfer mechanism 35 includes a primary transfer belt, a secondary transfer roller, a secondary transfer opposing roller, and the like. The primary transfer belt receives the toner image from the surface of photoreceptor 31 . The secondary transfer roller and the secondary transfer counter roller press the primary transfer belt against the print medium conveyed by the paper feed conveyance path 21 and convey the same. As a result, the toner image on the photoreceptor 31 is transferred to the print medium P. As shown in FIG.

The fixing device 16 is configured to fix the toner image transferred to the printing medium P onto the printing medium P. As shown in FIG. As shown in FIG. 1, the fuser 16 includes a heat roller and a press roller.

The heat roller is a heating member that applies heat to the print medium P. As shown in FIG. The heat roller is made of metal. The heat roller is formed, for example, in a hollow cylindrical shape. An induction coil to which a high-frequency current is supplied from the power supply unit 18 is provided near the heat roller. The induction coil is provided at a position capable of applying a magnetic field to at least the heat roller. An eddy current is generated in the heat roller by a magnetic field generated in the induction coil when a high-frequency current flows through the induction coil. As a result, heat is generated in the heat roller due to the resistance component inside the heat roller. Thereby, the heat roller is heated to a high temperature.

The press roller is a pressure member that presses the print medium P against the heat roller. The press roller is rotated by a motor (not shown). The press roller applies pressure to the heat roller by a pressure mechanism (not shown). In this manner, the press roller applies pressure to the heat roller to form a nip (fixing nip) where the heat roller and the press roller are brought into close contact with each other. The press roller applies heat and pressure to the print medium P to fix the toner image on the print medium P by passing the print medium P onto which the toner image has been transferred through the fixing nip.

A system controller 17 controls the image forming apparatus 2 . The system controller 17 includes, for example, a processor 41 and memory 42 .

The processor 41 is an arithmetic element that executes arithmetic processing. The processor 41 is, for example, a CPU. The processor 41 performs various processes based on data such as programs stored in the memory 42 . The processor 41 functions as a control unit that causes the image forming apparatus 2 to perform various operations by executing programs stored in the memory 42 . For example, the processor 41 controls the conveying section 14, the image forming section 15, the fixing device 16, and the power supply unit 18 by executing programs stored in the memory 42. FIG.

The memory 42 is a storage medium that stores programs and data used in the programs. The memory 42 also functions as a working memory. That is, the memory temporarily stores data being processed by the processor 41, programs executed by the processor 41, and the like.

In the above configuration, the processor 41 of the system controller 17 transfers the toner image onto the print medium P by controlling the transport section 14, the image forming section 15, the fixing device 16, and the power supply unit 18 based on the print data. to fix the toner image on the print medium P. Thus, an image is formed on the print medium P. FIG.

The processor 41 also switches the operating state of the image forming apparatus 2 . The operating state is, for example, a ready state in which an image can be formed on the print medium P, a sleep state in which input of a predetermined operation is waited, and the like. The ready state is a state in which high voltage is required. The sleep state is a state in which operation is possible at a lower voltage than in the ready state. The processor 41 switches between a ready state and a sleep state by controlling the power supply unit 18 . The processor 41 inputs a switching signal (sleep signal) for switching between the ready state and the sleep state to the power supply unit 18 .

The power supply unit 18 is configured to supply power to each component of the image forming apparatus 2 . FIG. 2 is an explanatory diagram for explaining the configuration of the power supply unit 18. As shown in FIG. As shown in FIG. 2 , the power supply unit 18 has a filter circuit 51 , a rectifier circuit 52 and a power conversion circuit 1 .

Filter circuit 51 is connected between commercial power supply AC and rectifier circuit 52 . The filter circuit 51 reduces noise entering from the commercial power supply AC and noise flowing out to the rectifier circuit 52 . The filter circuit 51 is composed of, for example, a capacitor.

The rectifier circuit 52 full-wave rectifies the AC voltage input from the commercial power supply AC via the filter circuit 51, and supplies the DC voltage to the subsequent circuit. That is, the rectifier circuit 52 converts the AC voltage into a DC voltage and supplies the DC voltage to the power conversion circuit 1 . The rectifier circuit 52 is, for example, a full-wave rectifier circuit (rectifier) composed of a plurality of diodes.

The filter circuit 51 is also connected to the fixing device 16 . As a result, a high-frequency current flows through the induction coil of the fixing device 16 due to the AC voltage.

The power conversion circuit 1 is a circuit that supplies a DC voltage of any voltage value to a load. The power conversion circuit 1 has a primary side to which power is supplied and a secondary side to output power.

First, the configuration of the primary side of the power conversion circuit 1 will be described. The power conversion circuit 1 includes a DC voltage source 61, an isolation transformer 62, and a switch circuit 63 as a configuration on the primary side. Moreover, the power conversion circuit 1 may be configured to further include a power factor correction circuit as a configuration on the primary side.

A DC voltage source 61 is a circuit that supplies a DC voltage to an insulating transformer 62 . The DC voltage source 61 has a smoothing capacitor C1. The smoothing capacitor C1 accumulates charges from the DC voltage (pulsated positive voltage) supplied from the rectifier circuit 52, and supplies the smoothed DC voltage to the circuit connected in parallel.

The isolation transformer 62 includes a primary side winding (primary winding) L1 that generates a magnetic field, and a secondary side that is insulated from the primary winding L1 and is excited by the magnetic field generated in the primary winding L1. winding (secondary winding) L2. The isolation transformer 62 further includes an auxiliary winding L3 and an auxiliary winding L4 that are excited by the magnetic field generated in the primary winding L1 and supply power to the switch circuit 63. As shown in FIG. That is, the secondary winding L2, the auxiliary winding L3, and the auxiliary winding L4 are electromagnetically coupled with the primary winding L1.

The switch circuit 63 is a circuit that controls on/off of the current flowing from the smoothing capacitor C1 to the primary winding L1 by switching. The switch circuit 63 includes a semiconductor switch S1, a control circuit 64, a diode D1, a diode D2, a smoothing capacitor C2, a photocoupler PC1, and a photocoupler PC2.

The semiconductor switch S1 is a semiconductor switch that switches between conductive states under the control of the control circuit 64 . Under the control of the control circuit 64, the semiconductor switch S1 turns on and off the current flowing from the smoothing capacitor C1 to the primary winding L1. The semiconductor switch S1 is, for example, an n-channel FET. The drain terminal of the semiconductor switch S1 is connected to the primary winding L1, the source terminal of the semiconductor switch S1 is connected to the low potential side of the smoothing capacitor C1, and the gate terminal of the semiconductor switch S1 is connected to the control circuit 64. It is The semiconductor switch S1 has a conductive state (ON state) in which the drain terminal and the source terminal are conductive and a non-conductive state (OFF state) in which the drain terminal and the source terminal are disconnected from each other from the control circuit 64 to the gate terminal. Switching is performed based on an input control signal.

The control circuit 64 is a control circuit that controls the semiconductor switch S1. The control circuit 64 has a terminal connected to the high potential side of the smoothing capacitor C2, a terminal connected to the low potential side of the smoothing capacitor C2, a terminal connected to the control terminal of the semiconductor switch S1, and a photocoupler PC1. With connected terminals. The control circuit 64 inputs a high-frequency pulse signal as a control signal to the semiconductor switch S1. The control circuit 64, for example, inputs a pulse signal to the gate terminal of the semiconductor switch S1. Thereby, the control circuit 64 switches the semiconductor switch S1 between the ON state and the OFF state at high speed. As a result, a high-frequency pulse is supplied to the primary winding L1 of the insulating transformer 62 by the potential of the smoothing capacitor C1, and a magnetic field is generated by the primary winding L1.

As described above, the switch circuit 63 functions as a flyback converter that converts the DC voltage into high frequency pulses. Note that the switch circuit 63 may be configured as a half-bridge converter or other converter circuit such as a full-bridge converter that supplies a high-frequency pulse to the primary winding L1 of the isolation transformer 62 according to the potential of the smoothing capacitor C1. good.

Diode D1 rectifies the current developed in auxiliary winding L3.

Diode D2 rectifies the current developed in auxiliary winding L4.

The smoothing capacitor C2 is connected in parallel with the auxiliary winding L3 and the auxiliary winding L4. Also, the smoothing capacitor C2 is connected in parallel with the control circuit 64 . That is, the smoothing capacitor C2 accumulates electric charges from the current generated in the auxiliary winding L3 and the current generated in the auxiliary winding L4, and supplies a smoothed DC voltage to the control circuit 64 connected in parallel. .

The photocoupler PC1 includes a light emitting diode LED1 and a phototransistor PT1. In the photocoupler PC1, current flows from the anode to the cathode of the light-emitting diode LED1, and when the light-emitting diode LED1 emits light, light enters the phototransistor PT1, and the collector terminal and the emitter terminal of the phototransistor PT1 are electrically connected.

A light-emitting diode LED1 of the photocoupler PC1 is provided on the secondary side of the power conversion circuit 1, and a phototransistor PT1 of the photocoupler PC1 is provided on the primary side of the power conversion circuit 1. FIG. A collector terminal of the phototransistor PT1 of the photocoupler PC1 is connected to the control circuit 64 . The emitter terminal of the phototransistor PT1 of the photocoupler PC1 is connected to the low potential side of the smoothing capacitor C1. The voltage between the collector terminal and the emitter terminal of the phototransistor PT1 of the photocoupler PC1 changes according to the light emission of the light emitting diode LED1.

The photocoupler PC2 includes a light emitting diode LED2 and a phototransistor PT2. In the photocoupler PC2, a current flows from the anode to the cathode of the light-emitting diode LED2, and when the light-emitting diode LED2 emits light, light is incident on the phototransistor PT2, and conduction is established between the collector terminal and the emitter terminal of the phototransistor PT2.

A light-emitting diode LED2 of the photocoupler PC2 is provided on the secondary side of the power conversion circuit 1, and a phototransistor PT2 of the photocoupler PC2 is provided on the primary side of the power conversion circuit 1. FIG. A collector terminal of the phototransistor PT2 of the photocoupler PC2 is connected to the cathode of the diode D2. The emitter terminal of the phototransistor PT2 of the photocoupler PC2 is connected to the high potential side of the smoothing capacitor C2. That is, the photocoupler PC2 electrically connects the auxiliary winding L4 and the high potential side of the smoothing capacitor C2 via the diode D2 according to the light emission of the light emitting diode LED2.

Next, the configuration of the secondary side of the power conversion circuit 1 will be described. The power conversion circuit 1 includes a secondary winding L2 of an isolation transformer 62, a rectifying/smoothing circuit 65, and a voltage adjusting circuit 66 as a secondary side configuration. The output terminal on the secondary side of the power conversion circuit 1 is connected to various loads of the image forming apparatus 2 (for example, the conveying section 14, the image forming section 15, the system controller 17, etc.).

Secondary winding L2 is excited in response to the magnetic field generated by primary winding L1 to generate power. A voltage corresponding to the ratio of the number of turns of the primary winding L1 and the secondary winding L2 is generated in the secondary winding L2.

The rectifying/smoothing circuit 65 is a circuit that rectifies and smoothes the power generated in the secondary winding L2. The rectifying/smoothing circuit 65 has a diode D3 and a smoothing capacitor C3.

The diode D3 has an anode connected to the secondary winding L2 and a cathode connected to the high potential side of the smoothing capacitor C3. Diode D3 rectifies the current generated in secondary winding L2 and supplies it to smoothing capacitor C3.

Smoothing capacitor C3 smoothes the positive voltage supplied from diode D3. The smoothing capacitor C3 supplies a DC voltage to the circuits connected in parallel. A high potential side of the smoothing capacitor C3 is connected to the output terminal of the power conversion circuit 1 . That is, a load is connected to the smoothing capacitor C3. The smoothing capacitor C3 supplies a smoothed DC voltage to the load.

The voltage adjustment circuit 66 is a circuit that adjusts the voltage of the output terminal of the power conversion circuit 1 . The voltage adjustment circuit 66 draws current from the smoothing capacitor C3 and supplies it to GND, thereby adjusting the voltage of the output terminal of the power conversion circuit 1 to a predetermined voltage. The voltage adjustment circuit 66 has, for example, a shunt regulator 67 . The voltage adjustment circuit 66 lowers the potential on the high potential side of the smoothing capacitor C3 according to the voltage division ratio of the shunt regulator 67 .

The voltage adjustment circuit 66 includes a resistor R1, a resistor R2, a resistor R3, a resistor R4, a resistor R5, a resistor R6, a diode D4, a light emitting diode LED1 of the photocoupler PC1, a light emitting diode LED2 of the photocoupler PC2,
It has a shunt regulator 67, a switch Q1 and a switch Q2.

The shunt regulator 67 is a circuit that adjusts the voltage of the output terminal of the power conversion circuit 1 and is a constant voltage regulator. The shunt regulator 67 has an input terminal, an output terminal, and a reference voltage terminal. The shunt regulator 67 also includes a transistor provided in parallel with the load, that is, between the high potential side of the smoothing capacitor C3 and GND, and an error amplifier. The shunt regulator 67 causes current to flow from the input terminal to the output terminal as the error amplifier controls the transistor based on the potential of the reference voltage terminal.

The input terminal of the shunt regulator 67 is the collector terminal of the transistor. The input terminal of the shunt regulator 67 is connected to the high potential side of the smoothing capacitor C3 via a series connection of the light emitting diode LED1 of the photocoupler PC1 and the resistor R1.

The output terminal of the shunt regulator 67 is the emitter terminal of the transistor. An output terminal of the shunt regulator 67 is connected to GND.

A reference voltage terminal of the shunt regulator 67 is an input terminal of the error amplifier. The output terminal of the error amplifier is connected to the base terminal of the transistor. A reference voltage terminal of the shunt regulator 67 is connected to the high potential side of the smoothing capacitor C3 via the resistor R2. A reference voltage terminal of the shunt regulator 67 is connected to GND via a resistor R3. Furthermore, the reference voltage terminal of the shunt regulator 67 is connected via a resistor R4 to the output terminal (emitter terminal) of the switch Q1, which will be described later.

The switches Q1 and Q2 are semiconductor switches such as npn transistors. Switch Q1 and switch Q2 may be n-type MOSFETs.

A base terminal (control terminal) of the switch Q1 is connected to a connection point between the resistors R5 and R6. The emitter terminal of switch Q1 is connected to the reference voltage terminal of shunt regulator 67 via resistor R4. A collector terminal of the switch Q1 is connected to the high potential side of the smoothing capacitor C3.

A base terminal (control terminal) of the switch Q2 is connected to the system controller 17 of the image forming apparatus 2 . The emitter terminal of switch Q2 is connected to GND. A collector terminal of the switch Q2 is connected to the high potential side of the smoothing capacitor C3 via a series connection of a resistor R5, a resistor R6, a diode D4, and the light emitting diode LED2 of the photocoupler PC2.

For example, the switch Q2 is turned on/off based on a signal from the system controller 17 of the image forming apparatus 2 . Specifically, the switch Q2 is turned on by the sleep signal input from the system controller 17. FIG. Also, the switch Q2 is turned off by a signal from the system controller 17 instructing to cancel sleep.

In the power conversion circuit 1 having the above configuration, the operating configuration changes depending on whether the switch Q2 is turned on or off. First, the operation of the power conversion circuit 1 when the switch Q2 is off will be described.

(State of each switch)
When switch Q2 is off, no current flows through the series connection of resistor R5, resistor R6, diode D4, and light emitting diode LED2 of optocoupler PC2. Therefore, the switch Q1 and the phototransistor PT2 of the photocoupler PC2 are also turned off.

(Operation of shunt regulator 67)
When the switch Q1 is off, the reference voltage terminal of the shunt regulator 67 is connected to the resistors R2 and R3. In this case, the voltage Vout1 adjusted by the shunt regulator 67 is output from the output terminal of the power conversion circuit 1 according to the reference voltage Vref which is the voltage of the reference voltage terminal of the shunt regulator 67 and the voltage division ratio of the resistors R2 and R3. be. The voltage Vout1 is Vout1=(1+R2/R3)×Vref.

The current drawn into the shunt regulator 67 turns on the phototransistor PT1 of the photocoupler PC1. As a result, on the primary side, current flows from the control circuit 64 to the low potential side of the smoothing capacitor C1 via the phototransistor PT1. The current value of the current flowing through the phototransistor PT1 varies depending on the current flowing through the light emitting diode LED1 of the photocoupler PC1, that is, the current drawn into the shunt regulator 67. FIG.

(Power supply from auxiliary winding)
On the primary side, electric charges are accumulated in the smoothing capacitor C2 due to the current generated in the auxiliary winding L3, and power is supplied to the control circuit 64. FIG. Since the phototransistor PT2 of the photocoupler PC2 connected between the auxiliary winding L4 and the smoothing capacitor C2 is off, power is not supplied from the auxiliary winding L4 to the smoothing capacitor C2. Assuming that the number of turns of the secondary winding L2 is N2 and the number of turns of the auxiliary winding L3 is N3, the voltage VCC1 applied to the control circuit 64 is VCC1=(N3/N2)×Vout1.

(Operation of control circuit 64)
The control circuit 64 controls the semiconductor switch S1 to supply a high-frequency pulse to the primary winding L1 of the insulating transformer 62 by the potential of the smoothing capacitor C1, thereby generating a magnetic field in the primary winding L1.

The control circuit 64 controls the on/off duty ratio of the pulse signal input to the semiconductor switch S1 based on the current flowing to the low potential side of the smoothing capacitor C1 via the phototransistor PT1 of the photocoupler PC1. As described above, the voltage between the emitter terminal and the collector terminal of the phototransistor PT1 of the photocoupler PC1 changes according to the light emission of the light emitting diode LED1. That is, the voltage between the emitter terminal and the collector terminal of the phototransistor PT1 of the photocoupler PC1 changes according to the current flowing from the rectifying/smoothing circuit 65 on the secondary side to the input terminal of the shunt regulator 67. FIG. The control circuit 64 controls the semiconductor switch S1 based on the current flowing through the phototransistor PT1 of the photocoupler PC1 to the low potential side of the smoothing capacitor C1 or the voltage between the collector terminal and the emitter terminal of the phototransistor PT1. Controls the on/off duty ratio of the input pulse signal.
Thereby, the control circuit 64 controls the strength of the magnetic field generated in the primary winding L1 of the isolation transformer 62 . This controls the power supplied to the secondary side.

Next, the operation of the power conversion circuit 1 when the switch Q2 is on will be described.
(State of each switch)
When switch Q2 is on, current flows through the series connection of resistor R5, resistor R6, diode D4, and light emitting diode LED2 of optocoupler PC2. Therefore, the switch Q1 is turned on. Also, since current flows through the light emitting diode LED2 of the photocoupler PC2, the phototransistor PT2 of the photocoupler PC2 is also turned on.

(Operation of shunt regulator 67)
When the switch Q1 is on, the resistors R2 and R4 are connected in parallel between the reference voltage terminal of the shunt regulator 67 and the high potential side of the smoothing capacitor C3. , and GND. In this case, the combined resistance of the resistor R2 and the resistor R4 is R0=R2×R4/(R2+R4). Therefore, the voltage Vout2 output from the output terminal of the power conversion circuit 1 is Vout2=(1+R0/R3)×Vref. Note that the combined resistance R0 has a smaller value than the resistance R2. Therefore, the voltage division ratio of the shunt regulator 67 changes, and the voltage Vout2 becomes smaller than the voltage Vout1 when the switch Q1 is off.

(Power supply from auxiliary winding)
On the primary side, since the phototransistor PT2 of the photocoupler PC2 connected between the auxiliary winding L4 and the smoothing capacitor C2 is turned on, power is supplied from the auxiliary winding L4 to the smoothing capacitor C2. state. That is, electric charges are accumulated in the smoothing capacitor C2 by the current generated in the auxiliary winding L3 and the auxiliary winding L4, and power is supplied to the control circuit 64. FIG.

Assuming that the number of turns of the auxiliary winding L4 is N4, the voltage VCC2 applied to the control circuit 64 is VCC2=[(N3+N4)/N2]×Vout2. That is, the auxiliary winding L4 adjusts the voltage VCC2 to a voltage higher than the voltage VCC1 compared to when the switch Q2 is off. Since VCC2>VCC1, the current generated in the auxiliary winding L3 and the auxiliary winding L4 flows in the order of the high potential side of the auxiliary winding L3, the auxiliary winding L4, the diode D2, the phototransistor PT2, and the smoothing capacitor C2. . Thus, when Vout1>Vout2, VCC1<VCC2.

In the power conversion circuit 1, the number of turns N3 of the auxiliary winding L3 is adjusted so that the voltage of VCC1 becomes an appropriate value when the switch Q2 is off, and the voltage of VCC2 is adjusted when the switch Q2 is on. The number of turns N4 of the auxiliary winding L4 is adjusted so that the voltage has an appropriate value. Thereby, the power conversion circuit 1 can supply the voltage required for operation to the control circuit 64 even when the output voltage is switched.

As described above, the power conversion circuit 1 is a circuit that supplies power from the primary side to the secondary side while the primary side and the secondary side are electrically insulated by the isolation transformer 62 . The power conversion circuit 1 includes a smoothing capacitor C1 functioning as a DC power supply, a semiconductor switch S1, and a control circuit 64 as a primary side configuration. The isolation transformer 62 includes a primary winding L1, a secondary winding L2 electromagnetically coupled to the primary winding L1, an auxiliary winding L3, and an auxiliary winding L4. The control circuit 64 causes the primary winding L1 to generate a magnetic field by on/off controlling a switch that switches the connection between the smoothing capacitor C1 and the primary winding L1. Auxiliary winding L3 is energized by the magnetic field generated by primary winding L1 and supplies power to control circuit 64 . Also, the auxiliary winding L4 is connected to the control circuit 64 via the collector and emitter of the photocoupler PC2.

The power conversion circuit 1 also includes a rectifying/smoothing circuit 65 and a shunt regulator 67 as a secondary side configuration. The rectifying/smoothing circuit 65 is connected to the secondary winding L2, rectifies and smoothes the current generated in the secondary winding L2, and outputs a DC voltage. The shunt regulator 67 adjusts the output voltage of the rectifying/smoothing circuit 65 based on the voltage of the reference voltage terminal connected to the output terminal of the rectifying/smoothing circuit 65 via the resistor R2 and grounded via the resistor R3.

The power conversion circuit 1 switches the switch Q<b>2 based on a signal supplied from the system controller 17 of the image forming apparatus 2 . The conductive path of the switch Q2 is connected to the anode and cathode of the photocoupler PC2. Also, the conductive path of the switch Q2 is connected to the control terminal of the switch Q1 that connects the resistor R4 in parallel with the resistor R2. According to such a configuration, when the switch Q2 is turned on, the switch Q1 is turned on, and the resistor R4 and the resistor R2 are connected in parallel to the reference voltage terminal of the shunt regulator 67. FIG. Therefore, the resistance value between the output terminal of the rectifying/smoothing circuit 65 and the reference voltage terminal of the shunt regulator 67 is the combined resistance of the parallel connection of the resistors R4 and R2. The combined resistance of the parallel connection of the resistors R4 and R2 has a lower resistance value than the resistor R2. On the other hand, the voltage of the reference voltage terminal grounded via the resistor R3 is a fixed value determined by the resistance value of the resistor R3. In this way, the voltage at the reference voltage terminal grounded through the resistor R3 is a fixed value, and the resistance between the output terminal of the rectifying/smoothing circuit 65 and the reference voltage terminal of the shunt regulator 67 is reduced. A voltage Vout2 output from the output terminal of the conversion circuit 1 decreases.

When the switch Q2 is turned on, current flows between the anode and cathode of the photocoupler PC2, causing the light emitting diode LED2 to emit light. This turns on the phototransistor PT2 of the photocoupler PC2. The auxiliary winding L4 is connected to the control circuit 64 when the phototransistor PT2 of the photocoupler PC2 is turned on. As a result, power is supplied to the control circuit 64 from the auxiliary winding L3 and the auxiliary winding L4. Thus, photocoupler PC2 functions as a switch that connects auxiliary winding L4 to control circuit 64 in response to the current in the conduction path of switch Q2. That is, the photocoupler PC2 is a switch that makes the conductive path (collector-emitter) conductive according to the current flow in the conductive path (anode-cathode).

Thus, the power conversion circuit 1 increases the number of auxiliary windings connected to the control circuit 64 when the output voltage is switched to a low value, thereby supplying the control circuit 64 with the voltage necessary for operation. can. Accordingly, it is possible to provide a power converter and an image forming apparatus that operate stably.

In the above embodiment, the anode-cathode of photocoupler PC2 is connected to the conductive path of switch Q2, but the configuration is not limited to this. The anode-cathode of the photocoupler PC2 may be connected to any point where current does not flow when the switch Q2 is off and current flows when the switch Q2 is on.

Further, in the above embodiment, the switch Q2 is switched on and off based on a signal from the system controller 17 of the image forming apparatus 2, but the configuration is not limited to this. The switch Q2 may be arranged so as to be switchable from the outside of the image forming apparatus 2, and configured as a switch that can be physically switched between on and off.

Further, in the above embodiment, it has been explained that the auxiliary winding L4 is connected to the control circuit 64 by connecting the collector terminal and the emitter terminal of the photocoupler PC2 in conjunction with turning on the switch Q2. is not limited to this configuration. A relay switch 71 may be used instead of the photocoupler PC2.

FIG. 3 shows an example in which a relay switch 71 is used as the switch for connecting the auxiliary winding L4 to the control circuit 64 instead of the photocoupler PC2.

The relay switch 71 has a first conductive path and a second conductive path. A coil is provided on the first conductive path. The second conductive path is provided with a switch that is switched on and off by the magnetic field generated by the coil. In the example of FIG. 3, the first conductive path is connected to the conductive path of switch Q2, and the second conductive path is connected to the cathode of diode D2 and the high potential side of smoothing capacitor C2. . With such a configuration, the auxiliary winding L4 is not connected to the control circuit 64 when the switch Q2 is off, and the auxiliary winding L4 is connected to the control circuit 64 when the switch Q2 is on. Such a configuration can also achieve the same effects as in the example of FIG.

In the above-described embodiment, the switch Q2 is switched by the sleep signal from the system controller 17 of the image forming apparatus 2, but the configuration is not limited to this. The switch Q<b>2 may be switched by any signal from the system controller 17 of the image forming apparatus 2 .

Further, in the above embodiment, an example in which the image forming apparatus 2 is provided with the power conversion circuit 1 has been described, but the configuration is not limited to this. The power conversion circuit 1 may be used in any device as long as it switches the output voltage output from the secondary side.

FIG. 4 shows an example in which the power conversion circuit 1 is provided in the product information processing device 3. As shown in FIG.
The product information processing device 3 is a system that generates a product list indicating a list of products that a user purchases in a store such as a retail store, and performs settlement based on the product list.

The product information processing device 3 includes a power supply unit 18 and a product information processing section 81 . The product information processing section 81 includes a scanner 82 , a first printer 83 , a second printer 84 , a control section 85 and a touch panel 86 .

The scanner 82 acquires a code (bar code, two-dimensional code, etc.) from the product and supplies it to the control section 85 .

The first printer 83 and the second printer 84 print receipts under the control of the controller 85 . The second printer 84 has a lower rated voltage than the first printer 83 .

The control unit 85 is a processing unit that executes various processes. The control unit 85 has a processor 87 and a memory 88 . The processor 87 is an arithmetic element that executes arithmetic processing. The processor 87 is configured as, for example, a CPU. Processor 87 performs various processes based on programs stored in memory 88 . The memory 88 is a storage device that stores programs and data. The memory 88 includes, for example, one or more of a ROM that is a read-only nonvolatile memory, a RAM that temporarily stores data, and a storage that stores data.

The touch panel 86 is a device that displays a screen and generates an operation signal based on an operation. The touch panel 86 has a display 89 and a touch sensor 90 . The display 89 displays a screen based on display data (screen data) supplied from the control unit 85 or a graphic controller (not shown). The touch sensor 90 generates an operation signal indicating the position touched by the user operating the product information processing device 3 on the screen displayed on the display 89 .

The control unit 85 acquires information from the products by the scanner 82 and generates a product list. The control unit 85 performs settlement based on the product list and the information input by the user through the touch panel. Furthermore, the control unit 85 outputs the settlement result. For example, the control unit 85 outputs the settlement result as a receipt from the first printer 83 . Also, for example, the control unit 85 outputs the settlement result as a receipt from the second printer 84 . Specifically, the control unit 85 outputs a receipt from the first printer 83 when payment is made with a prepaid card, electronic money, or the like. Also, the control unit 85 outputs a receipt from the second printer 84 when the payment is made by credit card.

The control unit 85 inputs a signal to the power supply unit 18 based on which of the first printer 83 and the second printer 84 should output the receipt. A signal from the control unit 85 is used to turn on/off the switch Q2 of the power conversion circuit 1 of the power supply unit 18 . For example, when outputting a receipt from the first printer 83, the controller 85 inputs a signal to turn off the switch Q2. Thereby, the output voltage of the power conversion circuit 1 is adjusted to a high voltage. Further, for example, when a receipt is output by the second printer 84, the control section 85 inputs a signal to turn on the switch Q2. As a result, the output voltage of the power conversion circuit 1 is adjusted to a low voltage.

While several embodiments of the invention have been described, these embodiments have been presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and modifications can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the scope of the invention described in the claims and equivalents thereof.
In addition, the description of the scope of claims as originally filed for this application will be added below.
[C1]
an isolation transformer comprising a primary winding, a secondary winding electromagnetically coupled to the primary winding, a first auxiliary winding, and a second auxiliary winding;
a DC power supply that outputs a DC voltage to the primary winding;
a first switch that switches connection between the DC power supply and the primary winding;
a control circuit connected to the first auxiliary winding and controlling the first switch;
a rectifying and smoothing circuit connected to the secondary winding, rectifying and smoothing the current generated in the secondary winding, and outputting a DC voltage;
a voltage adjustment circuit that adjusts the output voltage of the rectifying/smoothing circuit and connects the second auxiliary winding to the control circuit in accordance with the adjustment of the output voltage;
A power conversion device comprising:
[C2]
The voltage adjustment circuit is
a shunt regulator that adjusts the output voltage based on the voltage of a reference voltage terminal that is connected to the output terminal of the rectifying/smoothing circuit via a first resistor and grounded via a second resistor;
a third resistor connected to the reference voltage terminal;
a second switch connected between the third resistor and an output terminal of the rectifying/smoothing circuit;
a third switch that controls the second switch;
a fourth switch that connects the second auxiliary winding to the control circuit in response to the current in the conduction path of the third switch;
The power conversion device according to [C1], comprising:
[C3]
The power converter according to [C2], wherein the control circuit controls the on/off duty ratio of the first switch based on the current flowing from the output terminal of the rectifying/smoothing circuit to the shunt regulator.
[C4]
The fourth switch is a photocoupler having an anode and a cathode connected to the conduction path of the third switch, a collector terminal connected to the second auxiliary winding, and an emitter terminal connected to the control circuit. The power converter according to a certain [C2].
[C5]
an image forming unit that forms an image on a print medium;
an isolation transformer comprising a primary winding, a secondary winding electromagnetically coupled to the primary winding, a first auxiliary winding, and a second auxiliary winding;
a DC power supply that outputs a DC voltage to the primary winding;
a first switch that switches connection between the DC power supply and the primary winding;
a control circuit connected to the first auxiliary winding and controlling the first switch;
a rectifying/smoothing circuit connected to the secondary winding, rectifying and smoothing the current generated in the secondary winding, and outputting a DC voltage to the image forming unit;
a voltage adjustment circuit that adjusts the output voltage of the rectifying/smoothing circuit and connects the second auxiliary winding to the control circuit in accordance with the adjustment of the output voltage;
An image forming apparatus comprising:

DESCRIPTION OF SYMBOLS 1... Power conversion circuit 2... Image forming apparatus 3... Product information processing apparatus 11... Housing 12... Paper feed cassette 13... Paper discharge tray 14... Conveyance part 15... Image forming part 16... Fixing Device 17 System controller 18 Power supply unit 21 Paper feed path 22 Paper discharge path 31 Photoreceptor 32 Charger 33 Exposure device 34 Developing device 35 Transfer mechanism , 41... Processor, 42... Memory, 51... Filter circuit, 52... Rectifier circuit, 61... DC voltage source, 62... Insulation transformer, 63... Switch circuit, 64... Control circuit, 65... Rectification/smoothing circuit, 66... Voltage adjustment Circuit 67 Shunt regulator 71 Relay switch 81 Product information processing unit 82 Scanner 83 Printer 84 Printer 85 Control unit 86 Touch panel 87 Processor 88 Memory 89 Display 90 Touch sensor C1 Smoothing capacitor C2 Smoothing capacitor C3 Smoothing capacitor D1 Diode D2 Diode D3 Diode D4 Diode L1 Primary winding L2 Secondary winding L3 Auxiliary winding L4 Auxiliary winding PC1 Photocoupler PC2 Photocoupler LED1 Light emitting diode LED2 Light emitting diode PT1 Phototransistor PT2 Phototransistor Q1 Switch , Q2...switch, R1...resistor, R2...resistor, R3...resistor, R4...resistor, R5...resistor, R6...resistor, S1...semiconductor switch.

Claims (4)

an isolation transformer comprising a primary winding, a secondary winding electromagnetically coupled to the primary winding, a first auxiliary winding, and a second auxiliary winding;
a DC power supply that outputs a DC voltage to the primary winding;
a first switch that switches connection between the DC power supply and the primary winding;
a control circuit connected to the first auxiliary winding and controlling the first switch;
a rectifying and smoothing circuit connected to the secondary winding, rectifying and smoothing the current generated in the secondary winding, and outputting a DC voltage;
a voltage adjustment circuit that adjusts the output voltage of the rectifying/smoothing circuit and connects the second auxiliary winding to the control circuit in accordance with the adjustment of the output voltage;
and
The voltage adjustment circuit is
a shunt regulator that adjusts the output voltage based on the voltage of a reference voltage terminal that is connected to the output terminal of the rectifying/smoothing circuit via a first resistor and grounded via a second resistor;
a third resistor connected to the reference voltage terminal;
a second switch connected between the third resistor and an output terminal of the rectifying/smoothing circuit;
a third switch that controls the second switch;
a fourth switch that connects the second auxiliary winding to the control circuit in response to the current in the conduction path of the third switch;
A power conversion device comprising: The power converter according to claim 1 , wherein the control circuit controls the on/off duty ratio of the first switch based on the current flowing from the output terminal of the rectifying/smoothing circuit to the shunt regulator. The third switch is a photocoupler having an anode and a cathode connected to the conduction path of the third switch, a collector terminal connected to the second auxiliary winding, and an emitter terminal connected to the control circuit. A power converter as claimed in claim 1 . an image forming unit that forms an image on a print medium;
an isolation transformer comprising a primary winding, a secondary winding electromagnetically coupled to the primary winding, a first auxiliary winding, and a second auxiliary winding;
a DC power supply that outputs a DC voltage to the primary winding;
a first switch that switches connection between the DC power supply and the primary winding;
a control circuit connected to the first auxiliary winding and controlling the first switch;
a rectifying and smoothing circuit connected to the secondary winding, rectifying and smoothing the current generated in the secondary winding, and outputting a DC voltage;
a voltage adjustment circuit that adjusts the output voltage of the rectifying/smoothing circuit and connects the second auxiliary winding to the control circuit in accordance with the adjustment of the output voltage;
and
The voltage adjustment circuit is
a shunt regulator that adjusts the output voltage based on the voltage of a reference voltage terminal that is connected to the output terminal of the rectifying/smoothing circuit via a first resistor and grounded via a second resistor;
a third resistor connected to the reference voltage terminal;
a second switch connected between the third resistor and an output terminal of the rectifying/smoothing circuit;
a third switch that controls the second switch;
a fourth switch that connects the second auxiliary winding to the control circuit in response to the current in the conduction path of the third switch;
An image forming apparatus comprising:

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