JP7182983B2 - Power supply and image forming apparatus - Google Patents

Description

The present invention relates to a power supply device capable of switching between a continuous mode and an intermittent mode, and an image forming apparatus equipped with the power supply device.

With the increasing demand for energy saving in recent years, electronic devices such as printers and other image forming apparatuses have reduced power consumption in the first standby state, and in addition, have reduced power consumption even further than the first standby state. A second standby state is provided for the purpose of In the first standby state, for example, the liquid crystal panel section and the photosensor section for detecting that a document is placed on the scanner are operating. In the second standby state, these operating units with relatively large power consumption are stopped, and the minimum functions such as the user interface unit for detecting a trigger to return from the second standby state to the first standby state. only work. This reduces the load on the power supply device and reduces power consumption. In addition, in order to meet the demand for energy saving, the power supply control IC that controls the power supply is equipped with an intermittent mode in which switching operation is performed intermittently to reduce power consumption, in addition to a continuous mode in which switching operation is always performed. Control ICs are on the rise. Since the power supply of the image forming apparatus immediately shifts to the printing operation, the power supply control IC often operates in the continuous mode in the first standby state. On the other hand, in the second standby state, the power supply control IC operates in an intermittent mode to reduce loss due to switching in order to increase the degree of energy saving.

However, in the case of, for example, a power supply device that performs a switching operation by a current resonance method, since it operates in the continuous mode in the first standby state, a resonance current is steadily flowing in the primary side of the transformer. Therefore, even though the load connected to the power supply is small, the resonance current causes an increase in power consumption and an increase in element temperature. rice field. Therefore, for example, in Patent Document 1, not only in the first standby state and the second standby state, but also in the standby state, it operates in the intermittent mode, and in the operating state, it quickly switches to the continuous mode, thereby reducing the consumption in the standby state. Reducing power and lowering the temperature of the device have been proposed.

JP 2015-100252 A

However, in Patent Document 1 described above, since a configuration having a plurality of standby states like the image forming apparatus is not assumed, in the above-described first standby state and second standby state, an intermittent mode is set. No means are provided for switching the intermittent period. Here, the intermittent mode is automatically controlled as a function of the power control IC, and the intermittent period is generally adjusted by an external circuit connected to the power control IC. For example, a circuit for charging and discharging a capacitor is provided as an external circuit, and the power supply control IC controls the intermittent period by comparing the voltage of the external circuit with a reference voltage. In intermittent operation, the longer the intermittent cycle, the more power consumption can be reduced. is set.

Therefore, when the circuit constants of the external circuit are set to the same circuit constants as those in the second standby state and the intermittent mode is operated in the first standby state, the intermittent period becomes longer. During the idle period during the intermittent mode, no power is supplied to the secondary of the transformer. Since power is supplied to the load described above even during a period in which the switching operation is suspended, the DC voltage supplied to the load decreases if the intermittent period is long. As a result, power consumption can be reduced when the intermittent cycle is long compared to when the intermittent cycle is short, but the amount of DC voltage fluctuation (hereinafter referred to as DC voltage ripple) between the switching operation period and the switching pause period increases. An increasing problem arises. When the DC voltage ripple increases, the DC voltage supplied to an IC, etc. connected as a load exceeds the power supply voltage rating of the IC, destroying the IC. may cause malfunction.

On the other hand, in order to reduce the DC voltage ripple in the first standby state, when the circuit constant of the external circuit is set to a circuit constant different from that in the second standby state to shorten the intermittent period, the second standby state state, the switching times will increase. As a result, power consumption increases, and the degree of energy saving (hereinafter also referred to as energy saving) decreases. Thus, as in the above-described prior art, when the configuration assuming a single standby state is applied as it is to the power supply device mounted in the image forming apparatus, the DC voltage ripple is reduced in the first standby state. and the problem that low power consumption in the second standby state cannot be achieved at the same time.

The present invention has been made under such circumstances, and aims to achieve both reduction of DC voltage ripple in the first standby state and reduction of power consumption in the second standby state. for the purpose.

In order to solve the above problems, the present invention has the following configuration.

(1) rectifying and smoothing means for rectifying and smoothing an AC voltage to generate an input voltage; a transformer having a primary winding, a secondary winding and an auxiliary winding; and the primary of the transformer to which the input voltage is applied. a switching means connected to a winding; a feedback means for outputting a feedback voltage corresponding to the voltage induced in the secondary winding of the transformer; a continuous mode for continuously oscillating the switching means; or the switching means a switching control means capable of switching to an intermittent mode in which the switching means oscillates intermittently by alternately repeating an operation period for continuously oscillating the switching means and a rest period for stopping the switching means, and for controlling the switching operation of the switching means; a power supply device comprising load detection means for detecting a load connected to the secondary side of the transformer based on the voltage induced in the auxiliary winding; and a capacitor capable of accumulating electric charge, capacity switching means for switching the capacity of the capacitor based on the detection result of the load detection means; charging or discharging the capacitor of the capacity switching means based on the feedback voltage input from the feedback means; and periodic control means for controlling the switching operation by the switching means, wherein when the switching control means is in the intermittent mode, the period control means controls the voltage of the capacitor of the capacity switching means to be equal to or higher than a predetermined voltage. , the switching operation of the switching means is performed by the switching control means, and when the voltage of the capacitor of the capacity switching means is smaller than the predetermined voltage, the switching control means performs the switching operation of the switching means. When the load detected by the load detection means is in a first standby state in which the load detected by the load detection means is equal to or greater than a predetermined load, the capacity switching means stops the switching operation. The intermittent cycle of the intermittent mode is shortened by reducing the capacity of the capacitor compared to the second standby state where the load is smaller than a predetermined load, and in the case of the second standby state, the first standby state is resumed. A power supply device characterized in that the intermittent period of the intermittent mode is lengthened by increasing the capacitance of the capacitor.
(2) An image forming apparatus comprising: image forming means for forming an image on a recording material; and the power supply device according to (1).
(3) An image forming apparatus comprising image forming means for forming an image on a recording material, a controller for controlling the image forming means, and a power supply device for supplying power to the image forming means, wherein the power supply device includes rectifying and smoothing means for rectifying and smoothing an AC voltage to generate an input voltage, a transformer having a primary winding, a secondary winding and an auxiliary winding, and the primary winding of the transformer to which the input voltage is applied. a switching means connected to a line; a feedback means for outputting a feedback voltage corresponding to the voltage induced in the secondary winding of the transformer; a continuous mode for continuously oscillating the switching means; a switching control unit capable of switching to an intermittent mode in which the switching unit oscillates intermittently by alternately repeating an operation period for oscillation and a rest period for stopping the switching unit; switching control means for controlling the switching operation of the switching means; capacity switching means for switching the capacity of the capacitor based on an instruction from the controller; and charging the capacitor of the capacity switching means based on the feedback voltage input from the feedback means. or discharging, and a cycle control means for controlling the switching operation by the switching means, and when the switching control means is in the intermittent mode, the cycle control means controls the voltage of the capacitor of the capacitance switching means. is a predetermined voltage or more, the switching operation of the switching means is performed by the switching control means, and when the voltage of the capacitor of the capacitance switching means is smaller than the predetermined voltage, the switching control means performs The switching operation of the switching means is stopped, and the capacity switching means is operated when the instruction from the controller is a first standby state in which the load connected to the secondary side of the transformer is equal to or greater than a predetermined load. shortens the intermittent period of the intermittent mode by reducing the capacity of the capacitor compared to a second standby state in which the load in the instruction from the controller is smaller than the predetermined load, and the second standby state An image forming apparatus according to claim 1, wherein, in the case of the state, the intermittent cycle of the intermittent mode is lengthened by increasing the capacity of the capacitor as compared with the first standby state.

According to the present invention, it is possible to reduce the DC voltage ripple in the first standby state and reduce the power consumption in the second standby state.

FIG. 2 is a circuit diagram showing the circuit configuration of the power supply devices of Examples 1 and 3; FIG. 4 is a diagram for explaining the operation of the current resonance circuits of Examples 1 to 3; FIG. 4 is a diagram showing drain current waveforms of FETs of the current resonance circuits of Examples 1 to 3; FIG. 2 is a block diagram showing the configuration of the power supply control IC of Examples 1 to 3; Timing chart for explaining switching operation in intermittent mode of Examples 1 to 3 Diagram showing intermittent cycle vs. load area characteristics in conventional example FIG. 10 is a diagram showing intermittent cycle-load region characteristics in the configuration of Embodiment 1; A circuit diagram showing the configuration of the power supply device of Examples 2 and 3 Schematic cross-sectional view showing the configuration of an image forming apparatus of Example 3

BEST MODE FOR CARRYING OUT THE INVENTION Below, embodiments of the present invention will be described in detail with reference to the drawings.

[Configuration of power supply]
FIG. 1 is a circuit diagram showing the circuit configuration of the power supply device of Example 1. FIG. The power supply device of this embodiment is a power supply device that performs switching operation by a general current resonance method. In FIG. 1, an AC voltage input from an inlet 101 passes through a fuse 102 and a common mode coil 103, is rectified by a rectifying diode bridge 104, and smoothed by a smoothing capacitor 105. FIG. Field effect transistors (hereinafter referred to as FETs) 106 and 107 for switching the transformer 109 are connected in series. One end of smoothing capacitor 105 is connected to the drain terminal of FET 106 (first switching element), and the other end of smoothing capacitor 105 is connected to the source terminal of FET 107 (second switching element).

Transformer 109 is designed with leakage inductance controlled, and has primary winding 110 and auxiliary winding 113 on the primary side, and secondary windings 111 and 112 on the secondary side. One end of the primary winding 110 is connected to the connection point between the drain terminal of the FET 107 and the source terminal of the FET 106, the other end of the primary winding 110 is connected to one end of the current resonance capacitor, and the other end of the current resonance capacitor is , are connected to the source terminal of the FET 107 . The auxiliary winding 113 is connected to a diode 114 for rectifying and smoothing the voltage induced in the auxiliary winding 113 and a smoothing capacitor 115 . Diodes 131 and 132 are connected to the secondary windings 111 and 112 of the transformer 109, respectively. be done. The voltage stored in the smoothing capacitor 133 is output to the load 134 connected to the power supply as the DC voltage Vout, which is the output voltage on the secondary side.

A feedback section that feeds back the state of the DC voltage Vout to the primary side comprises a photocoupler 144 , a shunt regulator 143 , and resistors 141 and 142 . A voltage obtained by dividing the DC voltage Vout by resistors 141 and 142 is input to the REF terminal of the shunt regulator 143 . The operation of the feedback section will be described later. A mode switching unit for switching between continuous mode and intermittent mode of the power supply device is composed of a photocoupler 205 and a transistor 204 , and the transistor 204 is turned on and off according to a signal output from the GP01 terminal of the control unit 201 . The phototransistor of the photocoupler 205 is turned on and off by turning on and off the transistor 204, and the mode is switched according to the input voltage of the REG terminal and the SB terminal of the power supply control IC 121 to which the phototransistor of the photocoupler 205 is connected. done.

A power supply control IC 121 that controls the power supply applies a voltage to the gate terminals of the FETs 106 and 107, and the G1 and G2 terminals that control the ON/OFF operation of the FETs 106 and 107 and the power supply voltage generated by the auxiliary winding 113 is It has a VCC terminal to which it is supplied. The power control IC 121 also has a REG terminal for outputting a constant voltage and an FB (feedback) terminal for monitoring the voltage value of the DC voltage Vout output from the power supply device. Furthermore, the power supply control IC 121 has a function of switching between the continuous mode and the intermittent mode according to the signal output from the GP01 terminal of the control unit 201, and an SB terminal for determining the switching frequency and the intermittent cycle in the intermittent mode. there is When the terminal voltage VSB of the SB terminal (hereinafter referred to as the SB terminal voltage VSB) becomes equal to or higher than the mode switching threshold voltage, the power supply control IC 121 switches the FETs 106 and 107 to the continuous mode in which the FETs 106 and 107 continuously oscillate at a predetermined cycle. . On the other hand, when the SB terminal voltage VSB becomes less than the mode switching threshold, the power supply control IC 121 switches the FETs 106 and 107 to an intermittent mode in which the FETs 106 and 107 intermittently oscillate at a cycle longer than the predetermined cycle. A capacitor 122 connected in parallel with a photocoupler 144 is connected to the FB terminal of the power control IC 121 . The power supply control IC 121 internally has a constant current circuit (current source 501 in FIG. 4) connected to the FB terminal and supplies electric charge to the capacitor 122 . In addition, the power control IC 121 internally includes a constant current charging circuit and a constant current discharging circuit connected to the SB terminal in order to charge and discharge the capacitor connected to the SB terminal. Furthermore, the power supply control IC 121 controls the intermittent period in the intermittent mode and the switching frequency of the FETs 106 and 107 according to the SB terminal voltage VSB.

The load area detection unit 30 has resistors 301 and 302 and an FET 303 , and a voltage obtained by dividing the voltage input to the VCC terminal of the power supply control IC 121 by the resistors 301 and 302 is applied to the gate terminal of the FET 303 . Also, the load area signal Sload is a signal output from the load area detection unit 30, and a low level or high level signal is output depending on whether the FET 303 is on or off.

The intermittent cycle control unit 40 has capacitors 401 and 402 and an FET 403 , and the gate terminal of the FET 403 receives the load region signal Sload. FET 403 and capacitor 402 are connected in series, and capacitor 401 is connected in parallel. Depending on whether the FET 403 is on or off, the capacitors connected to the SB terminal of the power supply control IC 121 are the two capacitors 401 and 402 or only the capacitor 401, respectively.

[Description of switching operation]
In the circuit configuration described above, when the power supply voltage is supplied from the auxiliary winding 113 to the VCC terminal of the power control IC 121, the power control IC 121 is activated. When the power supply control IC 121 is activated, it outputs control signals from the G1 and G2 terminals to the gate terminals of the FETs 106 and 107 to control the operation of the FETs 106 and 107 . Next, referring to FIGS. 2 and 3, the current flow on the primary side of the transformer 109 in the normal mode (also referred to as continuous mode) in which the image forming apparatus equipped with the power supply performs image formation is shown in FETs 106 and 107. will be described along the order according to the on/off state of the . FIG. 2 shows the peripheral circuit portion of the current resonance circuit composed of the transformer 109, the FETs 106 and 107, the power supply control IC 121, and the smoothing capacitor 105 in order to explain the current flow on the primary side of the transformer 109. It is a circuit diagram extracted from. In FIG. 2, current flows are indicated by arrows in circuit diagrams (a) to (f) in the order of explanation. FIG. 3 shows current waveforms of the drain currents of the FETs 106 and 107. The upper figure shows the current waveform of the drain current of the FET 106, and the lower figure shows the current waveform of the drain current of the FET 107. FIG. In FIG. 3, the vertical axis indicates current value and the horizontal axis indicates time. The waveform diagrams of the FETs 106 and 107 shown in FIG. 3 correspond to the current flows in FIGS. 2 (a) (orders 1 and 7) to (f) (order 6).

1) Order 1 (state of FIG. 2(a))
In FIG. 2A, the FET 106 is in the ON state and the FET 107 is in the OFF state. In FIG. 2A, current flows from smoothing capacitor 105 through FET 106 to primary winding 110 of transformer 109. flow in the return current path.

2) Order 2 (state of FIG. 2(b))
In FIG. 2B, the FET 106 is in the OFF state and the FET 107 is in the OFF state. In FIG. 2(b), the current flowing through the primary winding 110 of the transformer 109 works to maintain the current flow in FIG. 2(a) even if the FET 106 is turned off from the ON state. Therefore, the current flowing through the primary winding 110 of the transformer 109 passes through the current resonance capacitor 108 , the parasitic diode of the FET 107 , and returns to the primary winding 110 .

3) Order 3 (state of FIG. 2(c))
In FIG. 2C, the FET 106 is in the OFF state and the FET 107 is in the ON state, and the current flow at this time is indicated by the dashed line of order 3 in the drawing. In FIG. 2C, even if the FET 107 is turned on in the state of order 2, the current continues to flow from the primary winding 110 of the transformer 109 through the current resonance capacitor 108 and through the parasitic diode of the FET 107. flow.

4) Order 4 (state of FIG. 2(d))
In FIG. 2D, the FET 106 is in the OFF state and the FET 107 is in the ON state following order 3, and the current flow at this time is indicated by the dashed line of order 4 in the figure. In FIG. 2D, due to the resonance action of the leakage inductance of the transformer 109 and the current resonance capacitor 108, the current gradually flows from the state of order 3 as follows. That is, the current changes so as to flow from the current resonant capacitor 108 to the primary winding 110 of the transformer 109 , through the FET 107 and back to the current resonant capacitor 108 .

5) Order 5 (state of FIG. 2(e))
In FIG. 2(e), the FET 106 is in the OFF state and the FET 107 is in the OFF state. In FIG. 2(e), even if the FET 107 is switched from ON state to OFF state in the state of order 4, the current flowing through the primary winding 110 of the transformer 109 tries to maintain the current flow in FIG. 2(d). work. Therefore, the current flows from the current resonance capacitor 108 to the primary winding 110 of the transformer 109 , and from the primary winding 110 of the transformer 109 to the smoothing capacitor 105 via the parasitic diode of the FET 106 .

6) Order 6 (state of FIG. 2(f))
In FIG. 2(f), the FET 106 is in the ON state and the FET 107 is in the OFF state. In FIG. 2(f), even if the FET 106 is turned on from the off state in the state of order 5, the current continues to flow as follows. That is, the current flows from the current resonant capacitor 108 to the primary winding 110 of the transformer 109 , from the primary winding 110 of the transformer 109 to the smoothing capacitor 105 via the parasitic diode of the FET 106 .

7) Order 7 (state of FIG. 2(a))
Continuing from FIG. 2F, the FET 106 is in the ON state and the FET 107 is in the OFF state. Due to the resonance action of the leakage inductance of the transformer 109 and the current resonance capacitor 108, the current gradually flows from the state of order 6 as follows. That is, the current flows from the smoothing capacitor 105 to the primary winding 110 of the transformer 109 via the FET 106, and from the primary winding 110 to the smoothing capacitor 105 via the current resonance capacitor 108. change as

In this manner, the primary winding 110 of the transformer 109 is alternately flowed with forward and reverse currents. As a result, a voltage is induced in the secondary windings 111 and 112 of the transformer 109, and then the induced voltage is rectified and smoothed by a rectifying and smoothing circuit composed of two diodes 131 and 132 and a smoothing capacitor 133. and a DC voltage Vout is generated. At this time, a voltage is also induced in the auxiliary winding 113 of the transformer 109. This induced voltage is rectified and smoothed by the rectifying and smoothing circuit of the diode 114 and the smoothing capacitor 115, and the power supply voltage is applied to the VCC terminal of the power control IC 121. is entered as The lower the switching frequency of the FETs 106 and 107, the longer the ON time of the FETs 106 and 107. Therefore, the drain current of the FETs 106 and 107 increases and the voltage amplitude of the primary winding 110 of the transformer 109 increases. As a result, a higher voltage is induced on the secondary side of the transformer 109, and a higher DC voltage Vout can be output.

[Description of feedback control]
Next, feedback control of the feedback section will be described. When the DC voltage Vout is output from the secondary side of the transformer 109 to the load 134 , a voltage obtained by dividing the DC voltage Vout by the resistors 141 and 142 is input to the REF terminal of the shunt regulator 143 . When the input voltage of the REF terminal is higher than the internal reference voltage of the shunt regulator 143, the shunt regulator 143 brings the cathode terminal K into conduction with the anode terminal A, thereby setting the shunt regulator 143 into the conduction state. On the other hand, when the input voltage of the REF terminal is equal to or lower than the internal reference voltage of the shunt regulator 143, the shunt regulator 143 places the cathode terminal K in a high impedance state to set the shunt regulator 143 in a non-conducting state.

The cathode terminal K of the shunt regulator 143 is connected to the light emitting diode of the photocoupler 144, and current flows through the light emitting diode of the photocoupler 144 when the shunt regulator 143 is in a conductive state. This turns on the phototransistor of the photocoupler 144 . On the other hand, when the shunt regulator 143 is in a non-conducting state, no current flows through the light emitting diode of the photocoupler 144 and the phototransistor of the photocoupler 144 is turned off. Also, the phototransistor of the photocoupler 144 is connected to the FB terminal of the power control IC 121 . Therefore, the voltage VFB of the FB terminal, which is the feedback voltage (hereinafter referred to as the FB terminal voltage VFB), is the amount of current supplied from the constant current source connected to the FB terminal, the capacitance value of the capacitor 122, the phototransistor of the photocoupler 144 changes depending on the on/off state of

When the voltage of the DC voltage Vout is high, the input voltage of the REF terminal becomes high, and the shunt regulator 143 becomes conductive. As a result, the light-emitting diode of the photocoupler 144 becomes conductive, and the phototransistor of the photocoupler 144 turns on. As a result, the charge stored in the capacitor 122 is discharged, and the FB terminal voltage VFB of the power supply control IC 121 decreases.

On the other hand, when the voltage of the DC voltage Vout decreases, the current flowing through the light emitting diode of the photocoupler 144 decreases, so the amount of light emitted decreases and the current flowing through the phototransistor also decreases. Therefore, current is supplied from the constant current charging circuit connected to the FB terminal inside the power supply control IC 121, and the capacitor 122 is charged, thereby increasing the FB terminal voltage VFB. When the voltage of the DC voltage Vout further drops and the input voltage of the REF terminal of the shunt regulator 143 becomes equal to or lower than the internal reference voltage of the shunt regulator 143, the cathode terminal K becomes a high impedance state. As a result, no current flows through the light-emitting diode of the photocoupler 144, and the phototransistor is turned off. Therefore, the capacitor 122 is charged by the current supplied from the constant-current charging circuit. Rise. Thus, the power supply control IC 121 can detect the voltage of the DC voltage Vout based on the FB terminal voltage VFB, and performs switching control of the FETs 106 and 107 based on the FB terminal voltage VFB. This enables the power supply device to output a stable DC voltage Vout.

[Description of mode switching procedure]
Since the power supply always performs switching operation in the continuous mode, power consumption increases due to the operating current of the power supply control IC 121 and loss during switching of the FETs 106 and 107 . Therefore, recent power supply control ICs have an intermittent mode in which switching operations are performed intermittently in order to reduce power consumption. Here, an operation mode switching procedure when an image forming apparatus equipped with a power supply device shifts from a printing operation to a standby state will be described.

When the image forming apparatus performs a printing operation, the load on the power supply device is large for operating actuators such as motors, and the power supply control IC 121 is set to operate in the continuous mode in order to supply the necessary power to the load. be. Therefore, the control unit 201 outputs a high-level signal from the GPO1 terminal, which turns on the transistor 204, turns on the light emitting diode of the photocoupler 205, and turns on the phototransistor of the photocoupler 205. FIG. When the phototransistor of the photocoupler 205 turns on, the SB terminal voltage VSB rises to the output voltage (constant voltage) of the REG terminal and becomes higher than the mode switching threshold, the power control IC 121 switches the operation mode to the continuous mode.

On the other hand, when the image forming apparatus completes the printing operation and shifts to a standby state, the actuators operating for the printing operation are stopped, and the load on the power supply is reduced. Therefore, when the image forming apparatus enters a standby state, the control unit 201 outputs a low level signal from the GPO1 terminal. As a result, the transistor 204 is turned off, the light emitting diode of the photocoupler 205 is rendered non-conductive, and the phototransistor of the photocoupler 205 is also turned off. When the phototransistor of the photocoupler 205 turns off, the SB terminal voltage VSB gradually decreases, and when it becomes less than the mode switching threshold, the power supply control IC 121 shifts the operation mode to the intermittent mode.

[Description of switching operation in intermittent mode]
FIG. 4 is a block diagram showing the internal configuration of the SB terminal and FB terminal of the power supply control IC 121 and their peripheral circuits. In the following, the range of loads that can occur in the first standby state is called the first load area, and the range of loads that can occur in the second standby state is called the second load area. With reference to FIG. 4, a conventional method of controlling switching operation in an intermittent mode in a load state in a first standby state, that is, a load within a first load region, which is a load state equal to or higher than a predetermined load, will be described. . To simplify the explanation, it is assumed that the SB terminal voltage VSB starts from 0V after the power supply control IC 121 shifts from the continuous mode to the intermittent mode. In addition, in order to explain the conventional example, the load range signal Sload is always kept at a high level, and is connected to the SB terminal in the first load range and the second load range, which is a load state smaller than a predetermined load. The capacitance values of the capacitors in the Therefore, in FIG. 4, when the load region signal Sload is at high level, the FET 403 of the intermittent cycle control section 40 is turned on, and the SB terminal is connected to the capacitors 402, 402. FIG.

In FIG. 4, a current source 501 is a constant current source that supplies a constant current from the FB terminal to the outside, and a comparator 502 that is period control means outputs the result of comparing the reference voltage Vref1 and the FB terminal voltage VFB. do. The switches 503 and 505 are switches that are turned on or off according to the comparison result of the comparator 502, and the switches 503 and 505 operate inversely to each other. That is, when the switch 503 is turned on, the switch 505 is turned off, and when the switch 503 is turned off, the switch 505 is turned on. The current source 504 is a constant current source that supplies a constant current to the outside from the SB terminal when the switch 503 is turned on. On the other hand, the current source 506 is a constant current source that supplies a constant current to the inside via the SB terminal when the switch 505 is turned on. It is a constant current source that draws A comparator 507 outputs a result of comparing the reference voltage Vref2 and the SB terminal voltage VSB. The output unit 508 outputs signals for controlling the switching operations of the FETs 106 and 107 from the G1 terminal and the G2 terminal according to the SB terminal voltage VSB and the comparison result output from the comparator 507 . As for the FB terminal, the current source 501 is connected inside the power control IC 121 , and the capacitor 122 and the photocoupler 144 are connected outside the power control IC 121 . As described above, the FB terminal voltage VFB increases or decreases according to the voltage value of the DC voltage Vout. Further, the intermittent cycle control unit 40 controls the capacitance of the capacitor connected to the SB terminal according to the first load region or the second load region, as will be described later.

In order to prevent malfunction, the reference voltages Vref1 and Vref2 of the comparators 502 and 507 have hysteresis characteristics. The reference voltage Vref1 when the output of the comparator 502 changes from high level to low level is referred to as reference voltage Vref1on, and the reference voltage Vref1 when the output of comparator 502 changes from low level to high level is referred to as reference voltage Vref1off. The reference voltage Vref2 when the output of the comparator 507 changes from high level to low level is referred to as reference voltage Vref2on, and the reference voltage Vref2 when the output of comparator 507 changes from low level to high level is referred to as reference voltage Vref2off. .

The comparator 502 outputs a low-level signal when the FB terminal voltage VFB input to the inverting input terminal (-) becomes equal to or higher than the reference voltage Vref1on input to the non-inverting terminal (+) (equal to or higher than the second threshold). , the switch 503 is turned on and the switch 505 is turned off. When the switch 503 is turned on, a constant current is output from the current source 504 through the SB terminal to the outside, and the constant current from the current source 504 accumulates electric charge in the capacitor in the intermittent period control unit 40, and the SB terminal voltage VSB rises. The comparator 507 outputs a low level signal when the SB terminal voltage VSB connected to the inverting input terminal (-) rises and becomes equal to or higher than the reference voltage Vref2on. When the comparator 507 outputs a low level signal, the output section 508 performs switching control of the FETs 106 and 107 via the G1 terminal and the G2 terminal. Also, the switching frequency of the FETs 106 and 107 at this time is determined according to the SB terminal voltage VSB.

On the other hand, when the FB terminal voltage VFB input to the inverting input terminal (-) falls below the reference voltage Vref1off input to the non-inverting input terminal (+), the comparator 502 outputs a high level signal, and the switch 503 is turned off and the switch 505 is turned on. When the switch 505 is turned on, a current flows from the capacitor connected to the outside of the SB terminal into the power supply control IC 121 through the SB terminal by the current source 506, and the SB terminal voltage VSB decreases. The comparator 507 outputs a high level signal when the SB terminal voltage VSB input to the inverting input terminal (-) decreases and falls below the reference voltage Vref2off input to the non-inverting input terminal (+). 508 stops switching control of FETs 106 and 107; Thus, the switching operation of the FETs 106 and 107 in the intermittent mode is controlled by the FB terminal voltage VFB and the SB terminal voltage VSB of the power control IC 121 .

In this embodiment, when the state of the load area signal Sload is switched, the intermittent period control unit 40 switches the capacitor connected to the SB terminal, thereby switching the rising speed and falling speed of the SB terminal voltage VSB. It is configured. Detailed operation will be described later.

[Explanation of operation of each part in intermittent mode]
FIG. 5 is a timing chart illustrating the conventional switching control of the FETs 106 and 107 described above using the voltages of the FB terminal and SB terminal of the power supply control IC 121 and the voltage waveforms of the DC voltage Vout which is the output voltage to the load 134. be. In FIG. 5A, the vertical axis shows, from top to bottom, the voltage waveform of the FB terminal voltage VFB, the voltage waveform of the SB terminal voltage VSB, the potentials of the gate terminals of the FETs 106 and 107 (gate potentials), and the state of the intermittent mode. , the voltage waveforms of the DC voltage Vout. The horizontal axis indicates time, and Ta, Tb, Tc, Td, and Te indicate time (timing). FIG. 5(b) is similar to FIG. 5(a), and Ta', Tb', Tc', Td', and Te' on the horizontal axis indicating time indicate time (timing). 5A and 5B, the power supply devices are connected to the same load 134, respectively. FIG. 5(a) shows the voltage waveform when the capacitance of the capacitor connected to the SB terminal is C1, and FIG. 5(b) shows the voltage waveform when the capacitance of the capacitor connected to the SB terminal is C2. Waveforms are shown. It should be noted that the magnitude relationship between the capacitances C1 and C2 of the capacitors is C1>C2.

First, FIG. 5A will be described. When the operation mode of the power supply device switches from the continuous mode to the intermittent mode, the power control IC 121 stops switching operations of the FETs 106 and 107 . Therefore, the DC voltage Vout supplied to the load 134 gradually decreases, and the feedback control described above increases the FB terminal voltage VFB. When the FB terminal voltage VFB becomes equal to or higher than the reference voltage Vref1on at time Ta, the comparator 502 outputs a low level signal, the switch 503 is turned on, and the switch 505 is turned off. As a result, current is supplied from the current source 501 to the capacitor connected to the SB terminal, and the SB terminal voltage VSB rises. When the SB terminal voltage VSB becomes equal to or higher than the reference voltage Vref2on at time Tb, the comparator 507 outputs a low level signal. As a result, the output unit 508 restarts the switching operations of the FETs 106 and 107 that have been stopped due to the rest period of the intermittent mode, and as a result, the DC voltage Vout gradually increases.

On the other hand, when the DC voltage Vout rises, the photocoupler 144 is turned on and the charge of the capacitor 122 is discharged, so that the FB terminal voltage VFB drops. When the FB terminal voltage VFB falls below the reference voltage Vref1off at time Tc, the comparator 502 outputs a high level signal, the switch 503 is turned off, and the switch 505 is turned on. As a result, the current source connected to the SB terminal is switched from the current source 504 to the current source 506, thereby lowering the SB terminal voltage VSB. Then, at time Td, when the SB terminal voltage VSB falls below the reference voltage Vref2off, the comparator 507 outputs a high level signal, and the output section 508 stops the switching operations of the FETs 106 and 107, and the rest period of the intermittent mode. to move to.

During the idle period of the intermittent mode, the FETs 106 and 107 are not switched, so no power is supplied to the secondary side of the transformer 109 . Therefore, power is supplied to the load 134 from the charge accumulated in the smoothing capacitor 133. As the power supply continues, the charge in the smoothing capacitor 133 gradually decreases, and the DC voltage Vout gradually decreases. . When the DC voltage Vout drops, the voltage input to the REF terminal of the shunt regulator 143 also drops, so the photocoupler 144 turns off, and as a result, the FB terminal voltage VFB rises. Then, when the FB terminal voltage VFB becomes equal to or higher than the reference voltage Vref1on, the control described above is performed again, and at time Te, the output section 508 shifts to an operation period in which the switching operations of the FETs 106 and 107 are resumed again, and the above-described Repeat control.

In the intermittent mode, the period from the time Tb at which the switching operation of the FETs 106 and 107 is started to the time Te at which the next switching operation is started is called an intermittent cycle (switching cycle). The waveform of the DC voltage Vout in FIG. 5A shows the DC voltage ripple (the voltage difference between the maximum voltage and the minimum voltage of the DC voltage Vout) at this time. When the load 134 increases, the rate of decrease of the DC voltage Vout during the rest period increases, shortening the time until the FB terminal voltage VFB becomes equal to or higher than the reference voltage Vref1on, resulting in shortening the intermittent period. On the other hand, when the load 134 decreases, the DC voltage Vout decreases at a lower rate during the rest period, and the time required for the FB terminal voltage VFB to rise above the reference voltage Vref1on becomes longer, resulting in a longer intermittent period.

Next, FIG. 5B will be described. The difference between FIG. 5(b) and FIG. 5(a) is the difference in the capacitance of the capacitor connected to the SB terminal, and other conditions such as the size of the load are the same. As described above, the capacitance C2 of the capacitor connected to the SB terminal in FIG. 5(b) is assumed to be smaller than the capacitance C1 of the capacitor in FIG. 5(a).

In FIG. 5B, when the FB terminal voltage VFB becomes equal to or higher than the reference voltage Vref1on at time Ta', the comparator 502 outputs a low level signal, the switch 503 is turned on, and the switch 505 is turned off. As a result, current is supplied from the current source 501 to the capacitor connected to the SB terminal. At time Ta', the switch 503 is turned on, and current is supplied from the current source 504 inside the power supply control IC 121 to the external capacitor via the SB terminal. is faster than in FIG. 5(a). At time Tb′, when the SB terminal voltage VSB becomes equal to or higher than the reference voltage Vref2on, the comparator 507 outputs a low level signal. As a result, the output unit 508 restarts the switching operations of the FETs 106 and 107 that have been stopped due to the rest period of the intermittent mode, and as a result, the DC voltage Vout gradually increases.

On the other hand, when the DC voltage Vout increases, the FB terminal voltage VFB decreases. At time Tc', when the FB terminal voltage VFB falls below the reference voltage Vref1off, the comparator 502 outputs a high level signal, the switch 503 is turned off, and the switch 505 is turned on. As a result, the current source connected to the SB terminal is switched from the current source 504 to the current source 506, and a constant current flows into the power supply control IC 121 via the SB terminal, so the SB terminal voltage VSB decreases. . Also at this time, since the capacitance of the capacitor connected to the SB terminal is small, the SB terminal voltage VSB decreases at a faster rate than in FIG. 5(a). At time Td′, when the SB terminal voltage VSB falls below the reference voltage Vref2off, the comparator 507 outputs a high level signal, and the output section 508 stops the switching operations of the FETs 106 and 107.

Thus, in FIG. 5(b), the SB terminal voltage VSB rises and falls faster than in FIG. 5(a). As a result, the operation period from time Tb' when switching of the FETs 106 and 107 is started to time Td' when switching of the FETs 106 and 107 is stopped is shortened, and the number of times of switching is reduced. Since the operation period is short and the number of times of switching is small, the amount of increase in the DC voltage Vout during the operation period is also small, and the DC voltage ripple is also smaller than in the case of FIG. 5(a).

Also, since the load 134 is the same in FIGS. 5A and 5B, the DC voltage Vout decreases at the same rate during the idle period when the switching operations of the FETs 106 and 107 in the intermittent mode are stopped. The FB terminal voltage VFB increases when the DC voltage Vout drops to a predetermined voltage value, and when it reaches or exceeds the reference voltage Vref1on, the next operation period starts. b) will cause the next operating period to start earlier.

As a result, when the capacitance of the capacitor connected to the SB terminal capacitance is small, the intermittent cycle of the intermittent mode is shortened, and the DC voltage ripple can be suppressed. However, there is a drawback that the power consumption increases due to the short rest period of the intermittent mode. On the other hand, if the capacitance of the capacitor connected to the SB terminal is large, as shown in FIG. 5A, the intermittent cycle of the intermittent mode can be lengthened, and the switching pause period can be lengthened to reduce power consumption. can. However, there is a disadvantage that the DC voltage ripple increases as compared with FIG. 5(b).

[Problem with conventional configuration]
FIGS. 6A and 6B are diagrams summarizing changes in the intermittent period and problems described above, and FIGS. 6A and 6B correspond to FIGS. 5A and 5B, respectively. 6A and 6B, the vertical axis indicates the intermittent cycle in the intermittent mode, and the horizontal axis indicates the magnitude of the load 134. In FIG. 6A and 6B, the reference load of the load 134 is indicated by Lth, the area smaller than the load Lth is the second load area, and the area larger than the load Lth is the first load area. A power supply device is required to have power consumption and output voltage ripple within a predetermined range according to the electronic equipment in which the power supply device is mounted. As described above, the specifications of power consumption and output voltage ripple are affected by the intermittent period, so the intermittent period must also be within a predetermined range. FIG. 6 shows, by hatching, the required range for the output voltage ripple in the first load region and the required range for the degree of energy saving of power consumption in the second load region in this embodiment.

In this embodiment, when the power supply device is installed in the image forming apparatus, a motor drive IC for a DC brushless motor or a stepping motor is connected as a load in the first load region. At this time, the DC voltage Vout supplied from the power supply is in the range of 22.8V to 25.2V, and the output voltage ripple is required to be 2.4V (=25.2V-22.8V) or less. shall be In order to keep the output voltage ripple below 2.4 V, it is necessary to set the intermittent period of the intermittent mode to a predetermined time or less. (hatched portion). Regarding the standard for energy saving, since the required level is lower in the first load range than in the second load range, it is assumed here that the standard is satisfied regardless of the intermittent period.

On the other hand, when the power supply device is installed in the image forming apparatus, in the second load region, power supply to the load such as the motor drive IC is cut off by a load switch such as an FET in order to reduce power consumption. be done. In the second load range, only the user interface section operates in order to detect a trigger (operation of a button or the like) for returning from the second load range to the first load range. In the second load region, in order to satisfy the standard for energy saving, it is necessary to set the intermittent cycle of the intermittent mode to a predetermined time or longer. It is shown as the required range (hatched part). Note that the user interface unit connected to the power supply as a load generally has a wider tolerance for fluctuations in the power supply voltage than the motor drive IC, so the required level for the output voltage ripple is low. Therefore, in the second load region, it is assumed that the required range for the output voltage ripple is satisfied regardless of the intermittent period.

In the case of the switching operation of the FETs 106 and 107 described with reference to FIG. 5A corresponding to FIG. 6A, the intermittent period is longer than that in FIG. satisfies the required range for power consumption in the load range. However, in FIG. 6A, since the intermittent period is long, the output voltage ripple increases, and in the first load region, the required range (hatched area) for the output voltage ripple is not met, and the required range is not satisfied. On the other hand, in the case of the switching operation of the FETs 106 and 107 described in FIG. 5B corresponding to FIG. 6B, the intermittent period is shorter than in FIG. Meets the required range of output voltage ripple. However, in FIG. 6B, since the intermittent period is short, the power consumption is large, and in the second load region, the power consumption is outside the required range (hatched portion) and does not satisfy the required range. Thus, when the power supply device is required to keep both the output voltage ripple and the power consumption within a predetermined range, the capacitance of the capacitor connected to the SB terminal is fixed. And there are cases where the demand cannot be satisfied, which is a problem.

[Description of the load area detector]
In order to solve the above-described problem, in this embodiment, the load area of the load 134 connected to the power supply is detected, and the capacity of the capacitor connected to the SB terminal is switched according to the detection result. Switches the intermittent cycle. First, the load area detection section, which is load detection means for detecting the load area, will be described.

In general, a current resonance type transformer is designed to have a large leakage inductance in order to allow resonance current to flow. can be represented by a value. Therefore, when the auxiliary winding 113 is wound around the primary winding 110 as in the present embodiment, the voltage generated in the auxiliary winding 113 is magnetically coupled with the exciting inductance and the leakage inductance. affected by the voltage generated in Since the load current to the secondary side flows through the leakage inductance, the voltage generated in the leakage inductance depends on the magnitude of the load 134 . Therefore, the voltage induced in auxiliary winding 113 is dependent on the magnitude of load 134 . As a result, if there is a large difference in the voltage induced in the auxiliary winding 113 between the first load region and the second load region, the load region of the load 134 can be detected based on the induced voltage. can. The load area detection unit 30 shown in FIG. 1 is an example of a circuit that detects the load area of the load 134 based on the voltage induced in the auxiliary winding 113 . A voltage obtained by rectifying and smoothing the voltage induced in the auxiliary winding 113 by the diode 114 and the smoothing capacitor 115 is input to the load region detection unit 30 . The input voltage is divided by resistors 301 and 302 and applied to the gate terminal of FET 303, which is the first switch element.

Since the load in the first load area is larger than that in the second load area, the voltage induced in the auxiliary winding 113 increases. As a result, the voltage is divided by the resistors 301 and 302 and the potential applied to the gate terminal of the FET 303 rises, and when the potential rises above the threshold voltage (above the first threshold), the FET 303 is turned on. When the FET 303 is turned on, the potential of the drain terminal of the FET 303 decreases, and the load area signal Sload output from the load area detection section 30 becomes low level (first signal). On the other hand, since the load in the second load range is smaller than that in the first load range, the voltage induced in the auxiliary winding 113 decreases. As a result, the potential applied to the gate terminal of the FET 303 after being voltage-divided by the resistors 301 and 302 is lowered, and the FET 303 is turned off when it becomes less than the threshold voltage (less than the first threshold). When the FET 303 is turned off, the potential of the drain terminal of the FET 303 rises, and the load area signal Sload output from the load area detector 30 becomes high level (second signal). In order to perform the above operation, it is necessary to appropriately select the resistance values of the resistors 301 and 302 and the threshold level at which the FET 303 is turned on, considering the voltage value induced in the auxiliary winding 113 .

[Explanation of intermittent cycle control part]
Next, the configuration and operation of the intermittent cycle control section 40 that switches the intermittent cycle of the intermittent mode according to the load region will be described. When the load region signal Sload is input from the load region detection unit 30 to the intermittent cycle control unit 40, the intermittent cycle control unit 40, which is capacity switching means, connects to the SB terminal of the power supply control IC 121 according to the load region signal Sload. switch the capacitance of the capacitor that The load region signal Sload is input to the gate terminal of the FET 403, and the FET 403 is turned off when the load region signal Sload is at low level, that is, when the load 134 is in the first load region. As a result, only the capacitor 401 (first capacitor) is connected to the SB terminal. On the other hand, when the load region signal Sload is at high level, that is, when the load 134 is in the second load region, the FET 403 (second switch element) is turned on. As a result, in addition to the capacitor 401, the capacitor 402 (second capacitor) connected in parallel with the capacitor 401 is also connected to the SB terminal. Therefore, compared to the case of the first load region, the capacity of the capacitor connected to the SB terminal that can store electric charge is increased. As described with reference to FIG. 5, the current sources 504 and 506 are constant current sources, so the amount of current is constant. Therefore, when the capacitance of the capacitor connected to the SB terminal increases or decreases, the rising speed and falling speed of the SB terminal voltage VSB also fluctuate.

When the rising speed and falling speed of the SB terminal voltage VSB decrease, the intermittent cycle of the intermittent mode becomes longer as shown in FIG. The longer the time, the less power is consumed. In the second load region where low power consumption is required, the desired specifications can be achieved by lengthening the intermittent period of the simple mode. On the other hand, when the SB terminal voltage VSB increases in rising speed and falling speed, the intermittent cycle in the intermittent mode becomes shorter as shown in FIG. Power consumption increases as the rest period becomes shorter. In the first load region where a low DC voltage ripple is required, the desired specifications can be achieved by shortening the intermittent cycle.

FIG. 7 is a diagram summarizing the operation of the power supply in the intermittent mode described above. In FIG. 6, which describes the prior art, the intermittent period for the load is represented by a straight line and has continuity for the first load area and the second load area, so that the power consumption in the load area is , or output voltage ripple. On the other hand, in FIG. 7 showing the relationship of the intermittent cycle with respect to the load in this embodiment, the intermittent cycle with respect to the load is continuous within the first load region or within the same load region within the second load region. However, there is a discontinuity between the first load range and the second load range. In this way, by switching the intermittent cycle of the intermittent mode largely according to the load area of the load 134 connected to the power supply, the power supply can be operated so as to satisfy the desired specifications according to the load area. .

Although the intermittent cycle-load characteristics described with reference to FIGS. 6 and 7 are linear, this characteristic is determined by the specifications of the power supply control IC and does not necessarily have to be linear. It can also be a characteristic.

As described above, in this embodiment, the winding voltage induced in the auxiliary winding 113 is used to detect the load region of the load 134, and the capacitor connected to the SB terminal is controlled according to the detected load region. By switching the capacity of , the intermittent cycle is switched according to the load region. By switching the intermittent cycle of the intermittent mode according to the load region, low power consumption in the second load region that is the second standby state and low output voltage ripple in the first load region that is the first standby state can be compatible with Furthermore, in this embodiment, by detecting the load region based on the induced voltage of the auxiliary winding 113 that the transformer 109 normally has, it is possible to suppress an increase in cost due to the addition of a new detection circuit. can. In this embodiment, the intermittent mode is switched by switching the capacitance of the capacitor in the intermittent cycle control section 40 connected to the SB terminal. Similar control may be performed by switching the capacity.

As described above, according to this embodiment, it is possible to reduce the DC voltage ripple in the first standby state and reduce the power consumption in the second standby state.

In the first embodiment, a configuration has been described in which the load area is detected based on the voltage induced in the auxiliary winding, and the intermittent cycle of the intermittent mode is switched according to the detected load area. In the case of the configuration of the first embodiment, there is a large difference in the voltage generated in the auxiliary winding 113 between the first load region, which is the first standby state, and the second load region, which is the second standby state. However, it may be difficult to apply when the voltage difference is small. Therefore, the second embodiment can be applied even when there is no large difference in the voltage generated in the auxiliary winding 113 between the first load region and the second load region. A configuration for switching between the standby state and the second standby state will be described.

[Configuration of power supply]
FIG. 8 is a circuit diagram showing the circuit configuration of the power supply device of the second embodiment. In FIG. 8, when compared with FIG. 1 of the first embodiment, the load region detection section 30 is removed, the control unit 201 is provided with a GPO2 terminal, and the output signal from the GP02 terminal is sent to the gate terminal of the FET 403 of the intermittent cycle control section 40. The difference is that an input circuit is added. A photocoupler 206 is provided to transmit the standby state from the secondary side to the primary side. A light-emitting diode of the photocoupler 206 is connected to the GPO2 terminal of the control unit 201 , and a phototransistor of the photocoupler 206 is connected to the gate terminal of the FET 403 of the intermittent cycle control section 40 .

In Example 1, the load area signal Sload output from the load area detection unit 30 is output to the gate terminal of the FET 403 of the intermittent cycle control unit 40 . In the second embodiment, instead of the load area signal Sload, a control signal indicating a standby state is output from the GPO2 terminal of the control unit 201 to the gate terminal of the FET 403 of the intermittent cycle control section 40 . Since the control unit 201 performs switching between the first standby state and the second standby state, the control unit 201 can detect which standby state the power supply is in, even if the load region detection unit 30 is not provided. can determine whether there is

When setting the power supply to the first standby state, the control unit 201 outputs a high-level signal from the GPO2 terminal to turn on the light emitting diode of the photocoupler 206 and turn on the phototransistor. By turning on the phototransistor of the photocoupler 206, the load region signal Sload input to the gate terminal of the FET 403 is set to low level, and the FET 403 is turned off. As described in the first embodiment, when the FET 403 is turned off, the capacity of the capacitor connected to the SB terminal of the power control IC 121 is only the capacity of the capacitor 401, and the capacity of the connected capacitor becomes smaller. The rising speed of the SB terminal voltage VSB increases. As a result, in the first standby state, the intermittent period of the intermittent mode can be shortened and the output voltage ripple can be reduced.

On the other hand, when setting the power supply to the second standby state, the control unit 201 outputs a low-level signal from the GPO2 terminal to turn off the light-emitting diode of the photocoupler 206 and turn on the phototransistor. turn it off. By turning off the phototransistor of the photocoupler 206, the load region signal Sload input to the gate terminal of the FET 403 becomes high level, turning the FET 403 on. As described in the first embodiment, when the FET 403 is turned on, the capacitance of the capacitor connected to the SB terminal of the power control IC 121 becomes the total capacitance of the capacitors 401 and 402 . As a result, the capacitance of the connected capacitor is increased, and the rising speed of the SB terminal voltage VSB is reduced. As a result, in the second standby state, the intermittent cycle of the intermittent mode can be lengthened, and power consumption can be suppressed.

As described above, in this embodiment, the control signal from the control unit 201 instructing switching to the first standby state or the second standby state controls the intermittent cycle control section 40 to send the signal to the SB terminal. The connected capacitor is switched. As described above, in this embodiment, even if there is not a large difference in the load between the first standby state and the second standby state as in the first embodiment, the control unit 201 changes the standby state of the power supply according to the load. can be switched.

As described above, according to this embodiment, it is possible to reduce the DC voltage ripple in the first standby state and reduce the power consumption in the second standby state.

The power supply device described in the first and second embodiments can be applied, for example, as a low-voltage power supply for an image forming apparatus, that is, a power supply for supplying power to a drive unit such as a controller (control unit) and a motor. The configuration of an image forming apparatus to which the power supply devices of Embodiments 1 and 2 are applied will be described below.

[Configuration of Image Forming Apparatus]
A laser beam printer will be described as an example of an image forming apparatus. FIG. 9 shows a schematic configuration of a laser beam printer, which is an example of an electrophotographic printer. The laser beam printer 300 includes a photosensitive drum 311 as an image carrier on which an electrostatic latent image is formed, a charging section 317 (charging means) that uniformly charges the photosensitive drum 311 , and an electrostatic latent image formed on the photosensitive drum 311 . A developing section 312 (developing means) for developing an image with toner is provided. Then, the toner image developed on the photosensitive drum 311 is transferred to a sheet (not shown) as a recording material supplied from a cassette 316 by a transfer unit 318 (transfer means), and the toner image transferred to the sheet is transferred to a fixing device 314 . , and is discharged to the tray 315 . The photosensitive drum 311, charging section 317, developing section 312, and transfer section 318 constitute an image forming section (image forming means). The laser beam printer 300 also includes the power supply device 500 described in the first and second embodiments. The image forming apparatus to which the power supply device 500 of Embodiments 1 and 2 can be applied is not limited to the one illustrated in FIG. 9, and may be an image forming apparatus including a plurality of image forming units. Furthermore, the image forming apparatus may include a primary transfer section that transfers the toner image on the photosensitive drum 311 to the intermediate transfer belt, and a secondary transfer section that transfers the toner image on the intermediate transfer belt to a sheet.

The laser beam printer 300 includes a controller 320 that controls the image forming operation of the image forming unit and the sheet conveying operation. . Further, the power supply device 500 described in the first and second embodiments supplies power to a drive unit such as a motor for rotating the photosensitive drum 311 or driving various rollers for conveying sheets. Note that the controller 320 corresponds to the control unit 201 shown in FIG. 1 of the first embodiment and FIG. 8 of the second embodiment. When the power supply device 500 of the present embodiment is the power supply device of the first embodiment, the power control IC 121 switches between the continuous mode and the intermittent mode according to instructions from the controller 320 . Further, the load region detection unit 30 detects the load region of the load 134 based on the voltage induced in the auxiliary winding 113, and the intermittent cycle control unit 40 is connected to the SB terminal according to the detected load region. The capacitance of the capacitor is switched, and the intermittent cycle is switched according to the load area. Accordingly, it is possible to achieve both low power consumption in the second load range, which is the second standby state, and low output voltage ripple in the first load range, which is the first standby state.

In the intermittent mode, the image forming apparatus of this embodiment can operate in a standby mode corresponding to the first standby state or a sleep mode corresponding to the second standby state. The standby mode is a mode in which the image forming operation can be performed as soon as a print instruction is received while reducing the power consumption compared to the normal operation mode (also referred to as the continuous mode) in which the image forming operation is performed. The sleep mode is a mode in which power consumption is further reduced than in the standby mode. When the power supply device 500 is the power supply device of the second embodiment, switching between the continuous mode and the intermittent mode is performed according to the instruction output from the GP01 terminal of the controller 320 . Furthermore, in the case of the power supply device of the second embodiment, switching between the first standby state and the second standby state is performed according to an instruction output from the GP02 terminal of the controller 320 . As a result, in the power supply device of the second embodiment, the standby state of the power supply device can be switched according to an instruction from the controller 320 even when there is no large difference in load between the first standby state and the second standby state. .

As described above, according to this embodiment, it is possible to reduce the DC voltage ripple in the first standby state and reduce the power consumption in the second standby state.

30 load area detector 40 intermittent cycle controller 106, 107 FET
113 auxiliary winding 121 power control IC
134 load 134

Claims (11)

rectifying and smoothing means for rectifying and smoothing an AC voltage to generate an input voltage;
a transformer having a primary winding, a secondary winding and an auxiliary winding;
switching means connected to the primary winding of the transformer to which the input voltage is applied;
feedback means for outputting a feedback voltage corresponding to the voltage induced in the secondary winding of the transformer;
It is possible to switch to a continuous mode in which the switching means continuously oscillates , or an intermittent mode in which the switching means oscillates intermittently by alternately repeating an operation period in which the switching means continuously oscillates and a rest period in which the switching means stops, switching control means for controlling the switching operation of the switching means;
A power supply device comprising:
load detection means for detecting a load connected to the secondary side of the transformer based on the voltage induced in the auxiliary winding;
capacity switching means having a capacitor capable of accumulating electric charge and switching the capacity of the capacitor based on the detection result of the load detection means;
cycle control means for charging or discharging the capacitor of the capacity switching means based on the feedback voltage input from the feedback means, and for controlling the switching operation by the switching means;
with
When the switching control means is in the intermittent mode,
The period control means performs the switching operation of the switching means by the switching control means when the voltage of the capacitor of the capacity switching means is equal to or higher than a predetermined voltage, and the voltage of the capacitor of the capacity switching means is if the voltage is smaller than the predetermined voltage, stopping the switching operation of the switching means by the switching control means;
When the load detected by the load detection means is in a first standby state in which the load detected by the load detection means is equal to or greater than a predetermined load, the capacity switching means switches the load detected by the load detection means to a second load smaller than the predetermined load. The intermittent cycle of the intermittent mode is shortened by reducing the capacity of the capacitor compared to the second standby state, and in the case of the second standby state, the capacity of the capacitor is reduced compared to the first standby state. A power supply device characterized in that the intermittent period of the intermittent mode is lengthened by increasing the capacity. 2. The power supply device according to claim 1, wherein the voltage induced in said auxiliary winding increases according to said load connected to the secondary side of said transformer. The load detection means has a resistor that divides the voltage induced in the auxiliary winding, and a first switch element to which the voltage divided by the resistor is input,
The first switch element outputs a first signal in the first standby state in which the input voltage is equal to or higher than the first threshold, and the input voltage is equal to or higher than the first threshold. 3. The power supply device according to claim 2, wherein a second signal different from the first signal is output in the case of the second standby state in which the power supply is less than. The capacity switching means has a circuit in which a first capacitor and a second capacitor connected in series with a second switch element are connected in parallel,
the first signal or the second signal is input from the load detection means to the second switch element;
The capacity of the capacitor of the capacity switching means is
When the second signal is input to the second switch element, the second switch element is turned on, and the total capacitance of the first capacitor and the second capacitor is can be,
4. The apparatus according to claim 3, wherein when said first signal is input to said second switch element, said second switch element is turned off, and the capacitance is that of said first capacitor. Power supply. The period control means charges the capacitor of the capacity switching means when the feedback voltage is equal to or higher than the second threshold, and the capacity switching means when the feedback voltage is smaller than the second threshold. 5. The power supply device according to claim 4, wherein the capacitor is discharged. 6. The power supply device according to claim 1, wherein said switching control means switches said switching means to said continuous mode or said intermittent mode based on a signal from the outside. The switching means has a first switching element and a second switching element connected in series,
The first switching element has one end connected to one end of the rectifying/smoothing means and the other end connected to the second switching element,
the second switching element has one end connected to the other end of the first switching element and the other end connected to the other end of the rectifying/smoothing means;
the primary winding has one end connected to the other end of the first switching element and the one end of the second switching element, and the other end connected to one end of the resonance capacitor;
7. The power supply device according to claim 1, wherein the other end of said resonance capacitor is connected to said other end of said second switching element. an image forming means for forming an image on a recording material;
A power supply device according to any one of claims 1 to 7;
An image forming apparatus comprising: an image forming means for forming an image on a recording material;
A power supply device according to claim 6;
An image forming apparatus comprising
A controller for controlling the image forming means,
The image forming apparatus, wherein the signal from the outside is a signal output from the controller. an image forming means for forming an image on a recording material;
a controller that controls the image forming means;
a power supply device that supplies power to the image forming means;
An image forming apparatus comprising
The power supply device
rectifying and smoothing means for rectifying and smoothing an AC voltage to generate an input voltage;
a transformer having a primary winding, a secondary winding and an auxiliary winding;
switching means connected to the primary winding of the transformer to which the input voltage is applied;
feedback means for outputting a feedback voltage corresponding to the voltage induced in the secondary winding of the transformer;
It is possible to switch to a continuous mode in which the switching means continuously oscillates , or an intermittent mode in which the switching means oscillates intermittently by alternately repeating an operation period in which the switching means continuously oscillates and a rest period in which the switching means stops, switching control means for controlling the switching operation of the switching means;
capacity switching means having a capacitor capable of accumulating electric charge and switching the capacity of the capacitor based on an instruction from the controller;
cycle control means for charging or discharging the capacitor of the capacity switching means based on the feedback voltage input from the feedback means, and for controlling the switching operation by the switching means;
with
When the switching control means is in the intermittent mode,
The period control means performs the switching operation of the switching means by the switching control means when the voltage of the capacitor of the capacity switching means is equal to or higher than a predetermined voltage, and the voltage of the capacitor of the capacity switching means is if the voltage is smaller than the predetermined voltage, stopping the switching operation of the switching means by the switching control means;
When the instruction from the controller indicates a first standby state in which the load connected to the secondary side of the transformer is equal to or higher than a predetermined load, the capacity switching means switches the load from the instruction from the controller. is smaller than the predetermined load, the intermittent period of the intermittent mode is shortened by reducing the capacity of the capacitor, and in the case of the second standby state, the first standby An image forming apparatus, wherein the intermittent cycle of the intermittent mode is lengthened by increasing the capacity of the capacitor compared to the state. 11. The image forming apparatus according to claim 10, wherein said controller instructs said switching control means to switch said switching means to said continuous mode or said intermittent mode.

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