JP2015070719A - Switching power supply device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a switching power supply device capable of stabilizing a burst operation and improving efficiency at the burst operation.SOLUTION: A switching power supply device comprises: a voltage detector 2 detecting a voltage value of a secondary side DC voltage Vo; a controller IC1 selecting "a normal operation mode" or "a burst operation mode" as an operation mode of switching means Q1, making the switching means Q1 perform a switching operation at the selected operation mode, and controlling a duty ratio or a switching frequency of the switching means Q1; a mode selection command part 3, in a case where a load is in a normal operation state, making the controller IC1 select "the normal operation mode", and in a case where the load is in a standby state, making the controller IC1 select "the burst operation mode"; and a response frequency adjustment part 4, in a case where the load is in the standby state, reducing a response frequency of a secondary side DC voltage feedback loop lower than a response frequency in a case where the load is in the normal operation state.

Description

  The present invention relates to a switching power supply device, and more particularly to a switching power supply device that causes a switching means to perform an intermittent switching operation (burst operation) when a load is in a standby state.

  As a conventional switching power supply device that causes the switching means to perform a burst operation, for example, the one described in Patent Document 1 is known. As shown in FIG. 5, the switching power supply 1C includes a switching unit Q11 connected to the primary side of a transformer T11, a control unit IC14 that controls the switching unit Q11, a photocoupler PC11, a first operational amplifier IC11, and a second unit. A load state detection unit 10 including an operational amplifier IC12 and a voltage detection unit 11 are mainly provided. The load state detection unit 10 detects the voltage value of the output voltage and the current value of the output current supplied to a load (not shown) provided on the secondary side of the transformer T11.

In the switching power supply apparatus 1C, as shown in FIG. 6, when the current value detected by the load state detection unit 10 is not more than a predetermined value, that is, when the load is in a standby state, switching is performed under the control of the control unit IC14. Means Q11 performs a burst operation. Specifically, the voltage value detected by the load state detection unit 10 is decreased from a rated output voltage value (for example, 13 V) to a preset voltage value (for example, 10 V) (for example, time t _3). At time t ₄ ), since the photocoupler PC11 is turned on, the ON / OFF terminal of the control unit IC14 becomes low level, and the control unit IC14 stops the switching operation of the switching means Q11. On the other hand, between the voltage value detected by the load state detection unit 10 is set voltage value to go up to the rated output voltage value (e.g., time t _{4 ~} time t _5), since the photocoupler PC11 is turned off, the control unit The ON / OFF terminal of the IC 14 becomes high level, and the control unit IC 14 starts the switching operation of the switching means Q11.

  When the current value detected by the load state detection unit 10 is equal to or greater than a predetermined value, that is, when the load is in a normal operation state, the switching means Q11 performs a continuous switching operation (normally under the control of the control unit IC14). Operation).

Japanese Patent No. 4653350

  By the way, in the conventional switching power supply device 1C, since the output voltage feedback loop is configured by the voltage detection unit 11 and the control unit IC 14, when the output voltage fluctuates due to load fluctuation or disturbance, the voltage detection unit The control unit IC14 changes the duty ratio (ON width) of the switching means Q11 according to the voltage value detected at 11, so that the output voltage can be returned to the state before the change.

  Here, the response frequency of the output voltage feedback loop is normally set to a relatively high value of 1 kHz to 10 kHz in order to respond to the fluctuation of the output voltage at high speed. On the other hand, the burst frequency fb is a relatively low value, usually 1 Hz to 100 Hz. Note that the burst frequency fb is represented by the reciprocal of the burst period Tb (fb = 1 / Tb) shown in FIG.

  That is, in the conventional switching power supply device 1C, the response frequency of the output voltage feedback loop is set to a value much higher than the burst frequency fb, so that the ON width of the switching means Q11 is frequent in one cycle of the burst period Tb. May change. For this reason, the conventional switching power supply apparatus 1C has a problem that the burst operation becomes unstable.

  Further, in the conventional switching power supply device 1C, when the output voltage suddenly decreases during the burst operation, the control unit IC14 rapidly increases the ON width of the switching means Q11, so that the current flowing through the switching means Q11 increases rapidly and the switching loss increases. End up. For this reason, the conventional switching power supply apparatus 1 </ b> C has a problem that switching loss during the burst operation cannot be sufficiently reduced, and high efficiency cannot be expected by the burst operation.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a switching power supply apparatus that can stabilize the burst operation and improve the efficiency during the burst operation.

  In order to solve the above-described problems, a switching power supply according to the present invention includes (1) a transformer and a switching unit connected to the primary side of the transformer, and generates an AC voltage from the primary side DC voltage by a switching operation of the switching unit. A switching power supply that converts the AC voltage into a DC to generate a secondary DC voltage and supplies the secondary DC voltage to a load provided on the secondary side of the transformer. Select the normal operation mode in which the switching operation is continuously performed or the burst operation mode in which the switching operation is intermittently performed as the operation mode of the voltage detection unit for detecting the voltage value and the switching means, and the switching is performed in the selected operation mode. Means to perform the switching operation, and the duty ratio of the switching means according to the voltage value. Or a control unit that controls the switching frequency, and a mode selection command that causes the control unit to select the normal operation mode when the load is in a normal operation state and causes the control unit to select a burst operation mode when the load is in a standby state. When the load is in the standby state, the response frequency of the secondary DC voltage feedback loop composed of the voltage detection unit and the control unit is lower than the response frequency when the load is in the normal operation state. And a frequency adjustment unit.

  According to this configuration, since the response frequency of the secondary side DC voltage feedback loop can be lowered when the load is in the standby state, the number of times the duty ratio (ON width) of the switching means changes in one cycle of the burst period. Can be reduced to stabilize the burst operation. Further, according to this configuration, even when the secondary side DC voltage suddenly decreases during the burst operation, the control unit gradually increases the ON width of the switching means, so that the current flowing through the switching means increases rapidly and the switching loss increases. Can be prevented.

  In the switching power supply device of (1), (2) the mode selection command unit includes a first light emitting diode of the first photocoupler that emits light when the load is in a standby state, and a first having a collector connected to the control unit. A first phototransistor of the photocoupler, wherein the voltage detector includes a second light emitting diode of the second photocoupler that emits light according to the voltage value of the secondary side DC voltage, and a collector connected to the controller. And a second phototransistor of the second photocoupler.

  In the switching power supply device of (2), (3) the response frequency adjustment unit has a delay circuit provided on the secondary side of the transformer, and the delay circuit is connected to the secondary side when the load is in a standby state. It can be configured to delay the time from when the fluctuation occurs in the DC voltage until the fluctuation is transmitted to the primary side of the transformer.

  In the switching power supply device of (3) above, (4) the voltage detection unit is connected in parallel to the load and connected in parallel to the series circuit including the second light emitting diode and the shunt regulator. The voltage dividing point is connected to the reference terminal of the shunt regulator, the delay circuit is a switching element that is turned on when the load is in a standby state, and one end of the voltage dividing resistor circuit. A capacitor connected to the voltage dividing point and having the other end connected to the low potential side of the voltage dividing resistor circuit via a switching element.

  In the switching power supply of (2) above, (5) the response frequency adjusting unit has a delay circuit provided on the primary side of the transformer, and the delay circuit is connected to the secondary side DC when the load is in a standby state. It can be configured to delay the time from when the voltage fluctuation is transmitted to the primary side of the transformer until the duty ratio or the switching frequency changes according to the fluctuation.

  In the switching power supply of (5) above, (6) the delay circuit has a switching element that is turned on when the capacitor and the load are in a standby state, and the control terminal of the switching element is connected to the fixed potential of the control unit and the first photo The switching element is connected to a connection portion, and one end of the current path of the switching element is connected to one end of the capacitor, and the other end of the capacitor is connected to the collector of the second phototransistor.

  In the switching power supply of (1) to (6) above, (7) a load state for determining whether the load is in a normal operation state or a standby state based on the secondary side DC voltage and the secondary side DC current A determination unit is further provided, and the mode selection command unit causes the control unit to select a normal operation mode when the load state determination unit determines that the load is in a normal operation state, and the load state determination unit determines that the load is in a standby state. When it is determined that the burst operation mode is determined, the control unit can be configured to select the burst operation mode.

  ADVANTAGE OF THE INVENTION According to this invention, the switching power supply device which can stabilize the burst operation and can improve the efficiency at the time of burst operation can be provided.

1 is a circuit diagram of a switching power supply device according to a first embodiment of the present invention. It is a figure which shows operation | movement of the switching power supply device which concerns on 1st Embodiment of this invention. It is a circuit diagram of the switching power supply device concerning a 2nd embodiment of the present invention. It is an example of the circuit diagram of the load state determination part which can be used with the switching power supply device of this invention. It is a circuit diagram of the conventional switching power supply device. It is a figure which shows operation | movement of the conventional switching power supply device.

  Hereinafter, preferred embodiments of a switching power supply according to the present invention will be described with reference to the accompanying drawings.

[First Embodiment]
FIG. 1 shows a switching power supply apparatus 1A according to the first embodiment of the present invention. As shown in the figure, the switching power supply device 1A includes a transformer T1 having a primary main winding N1, a secondary main winding N2, and an auxiliary winding N3, and an FET connected to the primary side of the transformer T1. Switching means Q1, and generates a secondary side DC voltage Vo by the switching operation of the switching means Q1, and supplies the secondary side DC voltage Vo to a load (not shown) provided on the secondary side of the transformer T1. The switching power supply device 1A is generally called a flyback converter.

  The switching power supply device 1A includes a voltage detection unit 2 that detects the voltage value of the secondary side DC voltage Vo, a control unit IC1 that controls the switching means Q1 according to the selected operation mode, and an operation mode selected by the control unit IC1. And a response frequency adjustment unit 4 that lowers the response frequency f1 of the secondary side DC voltage feedback loop composed of the voltage detection unit 2 and the control unit IC1. The response frequency f1 is set to 1 kHz to 10 kHz.

  The control unit IC1 is a switching power supply control IC having a Vcc terminal, a GND terminal, an FB terminal, and a burst terminal. As the operation mode of the switching means Q1, the control unit IC1 is a “normal operation mode” in which the switching operation is continuously performed or a “burst operation mode in which the switching operation is intermittently performed at a predetermined burst frequency fb (1 Hz to 100 Hz). Is selected, and the switching means Q1 performs the switching operation in the selected operation mode. Specifically, the control unit IC1 selects the “normal operation mode” when the potential at the burst terminal is high, and selects the “burst operation mode” when the potential at the burst terminal is low.

  Further, the control unit IC1 feedback-controls the duty ratio (ON width) or switching frequency of the switching means Q1 according to the voltage value of the secondary side DC voltage Vo detected by the voltage detection unit 2. In the present embodiment, the control unit IC1 controls the duty ratio.

  The mode selection command unit 3 includes a first circuit in which the first light-emitting diode of the first photocoupler PC1 provided on the secondary side of the transformer T1 and the resistor R4, and a collector connected to the burst terminal of the control unit IC1. A first phototransistor of the photocoupler PC1.

  When the load is in a normal operation state, a low level (for example, 0 V) signal is input to the mode selection command unit 3 from the buffer unit IC3 based on an external signal. Thereby, in the mode selection command unit 3, the first photocoupler PC1 is turned off, and the collector current does not flow to the first phototransistor of the first photocoupler PC1. As a result, the potential at the burst terminal becomes high level, and the control unit IC1 selects the “normal operation mode” as the operation mode of the switching means Q1.

  On the other hand, when the load is in a standby state, a high level (for example, 5 V) signal is input to the mode selection command unit 3 from the buffer unit IC3 based on an external signal. As a result, in the mode selection command section 3, the first photocoupler PC1 is turned on, and a collector current flows through the first phototransistor (current is sucked from the burst terminal). As a result, the potential at the burst terminal becomes low level, and the control unit IC1 selects the “burst operation mode” as the operation mode of the switching means Q1.

  The voltage detection unit 2 includes a series circuit composed of the second light emitting diode of the second photocoupler PC2 and the shunt regulator IC2 connected in parallel to the load, and a divided voltage connected in parallel to the series circuit. A voltage dividing resistor circuit R2 and R3 whose points are connected to the reference terminal of the shunt regulator IC2 and a second phototransistor of the second photocoupler PC2 whose collector is connected to the FB terminal of the control unit IC1.

  The response frequency adjusting unit 4 includes a switching element Q2 composed of an FET, one end connected to a voltage dividing point of the voltage dividing resistor circuits R2 and R3 of the voltage detecting unit 2, and the other end connected to the voltage dividing resistor via the switching element Q2. A delay circuit including a capacitor C4 connected to the low potential side of the circuits R2 and R3 and lowering the response frequency f1 of the secondary side DC voltage feedback loop when the load is in a standby state. Since the response frequency f1 is lowered according to the time constants of the capacitor C4 and the voltage dividing resistor circuits R2 and R3 as described later, strictly speaking, the voltage dividing resistor circuits R2 and R3 are also included in the delay circuit.

  Since the gate terminal of the switching element Q2 is connected to the output terminal of the buffer unit IC3, when the load is in the standby state, a high level signal is input from the buffer unit IC3 and the load is in the normal operation state. In this case, a low level signal is input from the buffer unit IC3 and the signal is turned off.

  That is, in the switching power supply device 1A, when the load is in a standby state, the delay frequency due to the capacitor C4 (strictly speaking, the capacitor C4 and the voltage dividing resistor circuits R2, R3) are added to the response frequency f1 of the secondary side DC voltage feedback loop. (A delay element due to the time constant) is added, and the time from when the change occurs in the secondary side DC voltage Vo until the change is transmitted to the primary side of the transformer T1 is delayed. On the other hand, when the load is in a normal operation state, the delay element is not added to the response frequency f1. For this reason, in the switching power supply device 1A, the response frequency f2 when the load is in the standby state is lower than the response frequency f1 when the load is in the normal operation state. Specifically, the response frequency f2 is smaller than 1/10 of the response frequency f1 and larger than 1/10 of the burst frequency fb.

  Next, the operation of the switching power supply device 1A will be described with reference to FIG.

When the load is in a normal operation state (before time t ₁ ), a low level signal is output from the buffer unit IC 3, so that the first photocoupler PC 1 is turned off and the potential at the burst terminal of the control unit IC 1 is high. Become a level. In this case, since the switching element Q2 is turned off, a delay element due to the capacitor C4 is not added to the response frequency f1 of the secondary side DC voltage feedback loop.

  From these facts, when the load is in the normal operation state, the control unit IC1 selects the “normal operation mode” to cause the switching means Q1 to perform a continuous switching operation (normal operation) and has a relatively high response. The duty ratio (ON width) of the switching means Q1 is controlled at the frequency f1 (f1 = 1 kHz to 10 kHz).

On the other hand, when the load is in a standby state (time t ₁ to time t ₇ ), a high level signal is output from the buffer unit IC 3, so the first photocoupler PC 1 is turned on and the burst terminal of the control unit IC 1 Becomes a low level. In this case, since the switching element Q2 is turned on, a delay element due to the capacitor C4 is added to the response frequency f1 of the secondary side DC voltage feedback loop.

  Therefore, when the load is in the standby state, the control unit IC1 selects the “burst operation mode” to cause the switching means Q1 to perform an intermittent switching operation (burst operation), and the response frequency adjusting unit 4 (Strictly speaking, according to the time constants of the capacitor C4 and the voltage dividing resistor circuits R2 and R3), the duty ratio (ON width) of the switching means Q1 is controlled by the lowered response frequency f2.

  As a result, the switching power supply device 1A can stabilize the burst operation of the switching means Q1 by reducing the number of times the duty ratio (ON width) of the switching means Q1 changes in one burst period. Further, in the switching power supply device 1A, even when the secondary side DC voltage Vo suddenly decreases during the burst operation, the control unit IC1 gradually increases the ON width of the switching means Q1, so that the current flowing through the switching means Q1 increases rapidly. It is possible to prevent an increase in switching loss. Therefore, according to the switching power supply device 1A, it is possible to stabilize the burst operation and improve the efficiency during the burst operation.

[Second Embodiment]
FIG. 3 shows a switching power supply device 1B according to the second embodiment of the present invention. As shown in the figure, the switching power supply device 1B includes a response frequency adjusting unit 4 ′ provided on the primary side of the transformer T1 instead of the response frequency adjusting unit 4 provided on the secondary side of the transformer T1. Common to the switching power supply device 1A according to the first embodiment except that the control unit IC1 ′ is provided instead of the control unit IC1 and the buffer unit IC3 ′ is provided instead of the buffer unit IC3. Yes.

  The control unit IC1 ′ is a switching power supply control IC having a Vcc terminal, a GND terminal, an FB terminal, and a burst terminal. As the operation mode of the switching means Q1, either “normal operation mode” or “burst operation mode” is selected. Select and cause the switching means Q1 to perform a switching operation in the selected operation mode. The control unit IC1 ′ selects the “normal operation mode” when the potential of the burst terminal is low level, and selects the “burst operation mode” when the potential of the burst terminal is high level. to differ greatly. Similarly to the control unit IC1, the control unit IC1 'performs feedback control of the duty ratio (on width) of the switching means Q1 according to the voltage value of the secondary side DC voltage Vo detected by the voltage detection unit 2.

  The buffer unit IC3 'outputs a high level signal when the load is in a normal operation state, and outputs a low level signal when the load is in a standby state. For this reason, when the load is in the normal operation state, the first photocoupler PC1 of the mode selection command unit 3 is turned on, and the potential of the burst terminal of the control unit IC1 ′ becomes low level, while the load is in the standby state. In some cases, the first photocoupler PC1 is turned off, and the potential at the burst terminal becomes high level.

  The response frequency adjusting unit 4 'includes a delay circuit including a capacitor C8 and a switching element (in this embodiment, an n-channel MOS transistor) Q3. In the n-channel MOS transistor Q3, the gate terminal (control terminal) is connected to the collector of the first phototransistor constituting the light receiving unit of the first photocoupler PC1, and the source (the other end of the current path) is GND of the control unit IC1 ′. The drain (one end of the current path) is connected to one end of the capacitor C8. The other end of the capacitor C8 is connected to the collector of the second phototransistor constituting the light receiving part of the second photocoupler PC2. The MOS transistor Q3 is turned off when the first photocoupler PC1 is turned on (when the load is in a normal operation state), and is turned on when the photocoupler PC1 is turned off (when the load is in a standby state). It becomes a state.

  In the switching power supply device 1B, when the load is in a standby state, a delay element due to the capacitor C8 is added to the response frequency f1 of the secondary side DC voltage feedback loop by turning on the MOS transistor Q3, and the secondary side DC voltage Vo Is transferred to the primary side of the transformer T1, and the time from when the duty ratio (on width) of the switching means Q1 changes according to the change is delayed. Specifically, during the output voltage control in the secondary side DC voltage feedback loop, the second phototransistor is caused by the resistance component between the collector and the emitter of the second phototransistor constituting the light receiving unit of the second photocoupler PC2. A voltage is generated between the collector and the emitter, and a current flows. For this reason, a delay element corresponding to the time constant determined by the equivalent resistance component existing between the collector and the emitter of the second phototransistor and the capacitor C8 occurs. On the other hand, when the load is in the normal operation state, the MOS transistor Q3 is turned off, so that the delay element is not added to the response frequency f1.

  For this reason, in the switching power supply device 1B, similarly to the switching power supply device 1A, the response frequency f2 when the load is in the standby state is lower than the response frequency f1 when the load is in the normal operation state. Specifically, the response frequency f2 is smaller than 1/10 of the response frequency f1 and larger than 1/10 of the burst frequency fb.

  As a result, the switching power supply 1B can stabilize the burst operation of the switching means Q1 by reducing the number of times the duty ratio (ON width) of the switching means Q1 changes in one burst cycle. Further, in the switching power supply device 1B, even when the secondary side DC voltage Vo suddenly decreases during the burst operation, the control unit IC1 ′ gradually increases the ON width of the switching means Q1, so that the current flowing through the switching means Q1 increases rapidly. Therefore, it is possible to prevent the switching loss from increasing. Therefore, according to the switching power supply device 1B, it is possible to stabilize the burst operation and improve the efficiency during the burst operation.

  As mentioned above, although preferable embodiment of the switching power supply device which concerns on this invention was described, this invention is not limited to said each embodiment.

  For example, in the first embodiment (FIG. 1), an external signal is input to the mode selection command unit 3 via the buffer unit IC3 without determining whether the load is in a normal operation state or a standby state. Although it has a configuration, a load state determination unit shown in FIG. 4 can be provided instead of the buffer unit IC3 so that an external signal is not required.

  4 determines whether the load is in a normal operation state or a standby state based on the voltage value of the secondary side DC voltage Vo and the current value of the secondary side DC current (load current) Io. Is determined. The load state determination unit detects the current value of the secondary side DC current Io flowing through the resistor R12 interposed in the low potential line on the secondary side of the transformer T1 with the operational amplifier IC5, and determines the voltage value of the secondary side DC voltage Vo. Detection is performed by voltage dividing resistor circuits R7 and R8 and an operational amplifier IC4 connected in parallel to the load. The operational amplifier IC5 outputs a high level signal when the current value of the secondary side direct current Io is smaller than a preset reference current value. The operational amplifier IC4 outputs a high level signal when the voltage value of the secondary side DC voltage Vo is larger than a preset reference voltage value. The reference current value is determined by the Zener diode ZD1, the resistor R10, the resistor R11, and the resistor R12, and the reference voltage value is determined by the Zener diode ZD1.

  The output terminals of the operational amplifier IC4 and the operational amplifier IC5 are connected to the input terminal of the logic circuit (AND circuit) IC6, and the output terminal of the logic circuit IC6 becomes the output terminal of the load state determination unit. For this reason, the load state determination unit is configured such that the current value of the secondary side DC current Io is smaller than a preset reference current value, and the voltage value of the secondary side DC voltage Vo is smaller than the preset reference voltage value. When the load is large, it is determined that the load is in a standby state, and a high level signal is output. On the other hand, when the current value of the secondary side DC current Io is larger than the preset reference current value or the voltage value of the secondary side DC voltage Vo is smaller than the preset reference voltage value, the load state The determination unit determines that the load is in a normal operation state and outputs a low level signal.

  In mode selection command unit 3, when a high-level signal is output from the load state determination unit (when the load state determination unit determines that the load is in a standby state), first photocoupler PC1 is turned on. . As a result, the potential at the burst terminal becomes low level, and the control unit IC1 selects the “burst operation mode”. On the other hand, when a low level signal is output from the load state determination unit (when the load state determination unit determines that the load is in a normal operation state), the mode selection command unit 3 turns off the first photocoupler PC1. It becomes a state. As a result, the potential of the burst terminal becomes high level, and the control unit IC1 selects the “normal operation mode”.

  In the second embodiment (FIG. 3), when a load state determination unit is provided instead of the buffer unit IC3 ′, the logic circuit IC6 of the load state determination unit is a NAND circuit, and the load state determination unit has a load in a standby state. A low level signal is output when it is determined that the load is normal, and a high level signal is output when it is determined that the load is in the normal operation state. In this case, the control unit IC1 'selects the "burst operation mode" when a low level signal is output from the load state determination unit, and selects the "normal operation mode" when a high level signal is output.

  In each of the above embodiments, the switching power supply control IC having the Vcc terminal, the GND terminal, the FB terminal, and the burst terminal is used as the control units IC1 and IC1 ′. "Mode" or "Burst operation mode" is selected, and if the switching means Q1 performs the switching operation in the selected operation mode and the duty ratio or switching frequency of the switching means Q1 can be controlled, the configuration is appropriately configured. Can be changed.

  The voltage detector 2 in each of the above embodiments can appropriately change the configuration as long as the voltage value of the secondary side DC voltage Vo can be detected and a secondary side DC voltage feedback loop can be configured. .

  The mode selection command unit 3 in each of the above embodiments causes the control units IC1 and IC1 ′ to select the “normal operation mode” when the load is in the normal operation state, and the control units IC1 and IC1 when the load is in the standby state. If 'can select the “burst operation mode”, the configuration can be changed as appropriate.

  The response frequency adjustment units 4 and 4 ′ in each of the above embodiments are appropriately changed in configuration if the response frequency f1 of the secondary DC voltage feedback loop can be lowered when the load is in a standby state. Can do.

  Furthermore, as the switching power supply device according to the present invention, the flyback converter has been described as an example in each of the above embodiments, but the present invention can also be suitably applied to other converters such as a forward converter and an LLC resonant converter. It is.

1A, 1B Switching power supply device 2 Voltage detection unit 3 Mode selection command unit 4, 4 'Response frequency adjustment unit

Claims (7)

A switching means connected to a transformer and a primary side of the transformer; an alternating voltage is generated from a primary side DC voltage by a switching operation of the switching means; and the alternating voltage is converted into a direct current to generate a secondary side DC voltage; A switching power supply that supplies the secondary side DC voltage to a load provided on the secondary side of the transformer,
A voltage detector for detecting a voltage value of the secondary side DC voltage;
As an operation mode of the switching means, a normal operation mode in which the switching operation is continuously performed or a burst operation mode in which the switching operation is intermittently performed is selected, and the switching operation is performed on the switching means in the selected operation mode. A control unit that controls the duty ratio or switching frequency of the switching means according to the voltage value;
A mode selection command unit that causes the control unit to select the normal operation mode when the load is in a normal operation state, and causes the control unit to select the burst operation mode when the load is in a standby state;
When the load is in a standby state, the response frequency of a secondary side DC voltage feedback loop configured by the voltage detection unit and the control unit is set to be higher than the response frequency when the load is in a normal operation state. A response frequency adjustment unit for lowering,
A switching power supply device comprising: The mode selection command unit
A first light emitting diode of a first photocoupler that emits light when the load is in a standby state;
A first phototransistor of the first photocoupler having a collector connected to the control unit,
The voltage detector is
A second light emitting diode of a second photocoupler that emits light according to a voltage value of the secondary side DC voltage;
The switching power supply according to claim 1, further comprising: a second phototransistor of the second photocoupler connected to the control unit. The response frequency adjustment unit has a delay circuit provided on the secondary side of the transformer,
The delay circuit delays a time from when a change occurs in the secondary side DC voltage until the change is transmitted to a primary side of the transformer when the load is in a standby state. The switching power supply device according to claim 2. The voltage detector is
A series circuit comprising the second light emitting diode and a shunt regulator connected in parallel to the load;
A voltage dividing resistor connected in parallel to the series circuit and having a voltage dividing point connected to a reference terminal of the shunt regulator;
The delay circuit is
A switching element that turns on when the load is in a standby state;
A capacitor having one end connected to a voltage dividing point of the voltage dividing resistor circuit and the other end connected to a low potential side of the voltage dividing resistor circuit via the switching element. 4. The switching power supply device according to 3. The response frequency adjustment unit has a delay circuit provided on the primary side of the transformer,
When the load is in a standby state, the delay circuit is configured to change the duty ratio or the switching frequency according to the change after the change of the secondary DC voltage is transmitted to the primary side of the transformer. The switching power supply device according to claim 2, wherein time is delayed. The delay circuit has a switching element that is turned on when a capacitor and the load are in a standby state,
A control terminal of the switching element is connected to a connection portion between the fixed potential of the control unit and the first phototransistor, one end of a current path of the switching element is connected to one end of the capacitor, and the other end of the capacitor The switching power supply according to claim 5, wherein the switching power supply is connected to a collector of the second phototransistor. A load state determination unit that determines whether the load is in a normal operation state or a standby state based on the secondary side DC voltage and the secondary side DC current;
The mode selection command unit causes the control unit to select the normal operation mode when the load state determination unit determines that the load is in a normal operation state, and the load state determination unit waits for the load. The switching power supply according to any one of claims 1 to 6, wherein when the state is determined to be in a state, the control unit is caused to select the burst operation mode.

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