JP2012143134A - Switching power supply device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a switching power supply device having high efficiency and stability which causes no delay in startup of a PFC circuit, while preventing useless power consumption.SOLUTION: The switching power supply device comprises a primary side circuit and a secondary side circuit. The primary side circuit comprises: a PFC circuit; and a power supply circuit which supplies power to the PFC circuit. The secondary side circuit comprises: a secondary coil; a DC conversion circuit which generates direct voltage from the voltage generated in the secondary coil and supplies it to a load circuit. The primary side circuit has an output circuit which outputs voltage corresponding to a load of the load circuit. The PFC circuit comprises: a switching element which controls the current to be inputted; a detection voltage generation circuit which generates detection voltage of the PFC circuit; and a PFC control circuit which controls the switching element so that the detection voltage can be a predetermined constant voltage. The power supply circuit intermittently turns on/off the power of the PFC circuit in a predetermined cycle according to the voltage of the output circuit. The detection voltage is generated only when the power of the PFC circuit turns on.

Description

  The present invention relates to a switching power supply device that converts an AC power supply voltage into a DC power supply voltage, and in particular, a primary-side PFC circuit (abbreviation of power factor collection: power factor collection) depending on the state of a load to which a secondary-side output voltage is supplied. The present invention relates to a switching power supply device having a function of controlling the operation of a rate improvement circuit.

  2. Description of the Related Art Conventionally, a switching power supply device including a DC-DC converter that converts direct current into another direct current and a PFC circuit that is provided in the front stage of the DC-DC converter and that improves the power factor of alternating current input has been used. Yes. In this switching power supply device, a PFC circuit having a choke coil, a switching element, a diode and a smoothing capacitor is provided after the full-wave rectifier circuit for full-wave rectification of the AC power supply, and the full-wave rectified output is boosted by this PFC circuit -Input a DC voltage that has been smoothed and improved in power factor into the DC-DC converter. The DC-DC converter converts the DC voltage from the PFC circuit into a high-frequency voltage by turning on / off the switching element via the primary winding of the transformer, and converts the high-frequency voltage generated in the secondary winding. Rectified and smoothed, and converted to a DC voltage required by the load device.

  In recent years, from the viewpoint of environmental protection and the like, improvement in power conversion efficiency of a switching power supply device has been demanded, and in particular, reduction of power consumption during standby has become important. For example, various methods have been proposed for on / off control of switching elements, such as reducing the switching frequency during standby or intermittent operation (burst operation) (for example, Patent Document 1).

  Also for the PFC circuit, a method of stopping power supply to the PFC circuit when there is no load has been proposed in order to suppress power consumption during standby (for example, Patent Document 2).

JP 2007-135277 A Japanese Patent No. 3751943

  However, in the configuration of Patent Document 2, although power consumption during standby is suppressed, the power supply of the PFC circuit is shut off during standby, so that the PFC circuit during startup (when returning to normal operation from standby) There is a problem that the operation of is delayed. If the operation of the PFC circuit is delayed, there is a problem that the output voltage temporarily drops until the PFC circuit operates normally. Further, in the case of the configuration of Patent Document 2, the configuration is such that the output voltage of the PFC circuit is always fed back (output) to the PFC circuit regardless of whether power is supplied to the PFC circuit. There is a problem that power consumption occurs in (loop).

  The present invention controls the power supply and feedback loop of the PFC circuit according to the state of the load on the secondary side, thereby preventing wasteful power consumption and preventing a delay in starting the PFC circuit. An object of the present invention is to provide a high-performance switching power supply device.

  In order to achieve the above object, a switching power supply device of the present invention is a switching power supply device having a primary side circuit and a secondary side circuit, and the primary side circuit includes a rectifier circuit for rectifying an AC power supply voltage, and a rectifier circuit. A first DC circuit for shaping and boosting the waveform of the current output from the first output to output a first DC voltage, a primary winding to which the first DC voltage is applied at one end, and other than the primary winding A first switching element connected to the end for turning on / off a current flowing through the primary winding, a control circuit for controlling on / off of the first switching element, and a power source for driving the first DC circuit A secondary side circuit that rectifies and smoothes a secondary winding that generates electromagnetic induction with the primary winding, and a voltage generated in the secondary winding. A second DC circuit for supplying a DC voltage to the load circuit The primary side circuit further includes an output circuit that outputs a voltage corresponding to the load of the load circuit, and the first DC circuit includes a second switching element that turns on and off the current output from the rectifier circuit, A detection voltage generation circuit that generates a detection voltage based on the first DC voltage, and a PFC control circuit that controls the second switching element so that the detection voltage becomes a predetermined constant voltage, and supplies power The circuit intermittently turns on / off a power source for driving the first DC circuit at a predetermined cycle according to a voltage output from the output circuit, and the detected voltage is a power source for the first DC circuit. It is generated only when is turned on.

  Thus, the switching power supply device of the present invention has an output circuit that outputs a voltage corresponding to the load of the load circuit, and a power source for driving the first DC circuit is converted to a voltage output from the output circuit. Since the power is intermittently turned on / off at a predetermined cycle, useless power consumption in the first DC circuit can be suppressed. Furthermore, since the detection voltage of the PFC control circuit is generated only when the power of the first DC circuit is turned on, wasteful power consumption in the detection voltage generation circuit can be suppressed. Since the first DC circuit is configured to output the first DC voltage when the power source for driving the first DC circuit is turned on, the load of the load circuit becomes heavy. Even if it is a case (when it is removed from the no-load state), the operation of the first DC circuit is not delayed, and no temporary drop occurs in the second DC voltage. That is, a highly efficient and highly stable switching power supply device is realized.

  The detection voltage generation circuit is inserted between the output of the first DC circuit and the ground of the primary circuit, and controls the resistance through which the current corresponding to the first DC voltage flows and the current through the resistance. The first switch circuit is configured to cause a current to flow through the resistor synchronously when the power source of the first DC circuit is turned on and to generate a detection voltage at one end of the resistor. be able to. In this case, the first switch circuit may be formed of a transistor. The first switch circuit is connected to the power source of the first DC circuit, and when the power source is turned on, the light emitting diode emits light with a predetermined light amount, receives light from the light emitting diode, and supplies a current to the resistor. A structure including a phototransistor that flows is also possible. In this case, it is desirable that the light emitting diode and the phototransistor constitute a photocoupler.

  The power supply circuit has a pulse generation circuit that generates a pulse having a predetermined cycle based on the voltage of the output circuit, and the power source for driving the first DC circuit is turned on / off based on the pulse It can be set as the structure to do.

  The power supply circuit has a primary auxiliary winding that generates electromagnetic induction with the primary winding, and the output circuit generates and outputs an average voltage obtained by averaging voltages generated in the primary auxiliary winding. can do. In this case, the power supply circuit turns on the power supply for driving the first DC circuit when the average voltage is larger than the first reference voltage, and the first power supply circuit turns on the power when the average voltage is smaller than the first reference voltage. A power supply for driving one DC circuit may be intermittently turned on / off at a predetermined cycle. Further, the control circuit controls on / off of the first switching element so that the second DC voltage is constant, and when the average voltage is smaller than the first reference voltage, the first switching element is determined in advance. ON / OFF in a burst state a plurality of times per period, and the average voltage is a predetermined voltage range in synchronization with ON / OFF of the first switching element when the first switching element is turned ON / OFF in a burst form. The power supply circuit can be configured to turn on / off the power supply for driving the first DC circuit in accordance with the fluctuation of the average voltage. In this case, the power supply circuit turns on the power supply for driving the first DC circuit when the average voltage is larger than the second reference voltage, and when the average voltage is smaller than the second reference voltage. A power supply for driving the first DC circuit may be turned off. As described above, since the average voltage fluctuates depending on the on / off state of the first switching element, the power source for driving the first DC circuit can be switched to the first switching circuit without providing a special circuit. It becomes possible to turn on / off in synchronization with the on / off of the element.

  The power supply circuit includes a third DC circuit that rectifies and smoothes the voltage generated in the primary auxiliary winding to generate a third DC voltage, and converts the third DC voltage to the first DC voltage. A configuration may be adopted in which power is supplied to drive the circuit. Further, the power supply circuit rectifies and smoothes the auxiliary winding that generates electromagnetic induction with the boosting inductor included in the first DC circuit and the voltage generated in the auxiliary winding to generate the third DC voltage. A third DC circuit to be generated, and the third DC voltage may be supplied as a power source for driving the first DC circuit. In this case, the power supply circuit includes a voltage difference detection circuit that detects a voltage difference between the third DC voltage and the second reference voltage, and a second that turns on / off the third DC voltage based on the voltage difference. It is good also as a structure which has these switch circuits. In this case, the voltage difference detection circuit may have a Zener diode that generates a voltage substantially equal to the voltage difference between the third DC voltage and the second reference voltage.

  As described above, according to the present invention, by controlling the power supply and the feedback loop of the PFC circuit according to the state of the load on the secondary side, the start of the PFC circuit is delayed while preventing unnecessary power consumption. It is possible to provide a highly efficient and highly stable switching power supply device.

1 is a circuit diagram showing a configuration of a switching power supply device 1 according to a first embodiment of the present invention. It is a wave form diagram which shows the voltage which arises at the both ends of the primary side auxiliary | assistant winding of the switching power supply device 1 which concerns on the 1st Embodiment of this invention. It is a wave form diagram which shows the voltage of the load detection voltage V3 (one end side of the capacitor | condenser 140) of FIG. It is a wave form diagram which shows the on / off relationship of the load detection voltage V3c and the transistor 139 when the control IC 155 according to the first embodiment of the present invention operates in the burst mode. It is a circuit diagram which shows the structure of the modification 1 of the switching power supply device 1 which concerns on the 1st Embodiment of this invention. It is a circuit diagram which shows the structure of the modification 2 of the switching power supply device 1 which concerns on the 1st Embodiment of this invention. It is a circuit diagram which shows the structure of the switching power supply device 1M which concerns on the 2nd Embodiment of this invention. It is a circuit diagram which shows the structure of the modification 1 of the switching power supply apparatus 1M which concerns on the 2nd Embodiment of this invention. It is a circuit diagram which shows the structure of the modification 2 of the switching power supply apparatus 1M which concerns on the 2nd Embodiment of this invention.

  A switching power supply device according to an embodiment of the present invention will be described below.

  FIG. 1 is a circuit diagram of a switching power supply device 1 according to the first embodiment of the present invention. The switching power supply device 1 is a power supply device that converts AC power input to the primary side circuit by the transformer 400 and outputs constant DC power from the secondary side circuit. The transformer 400 includes a primary side winding 150, a primary side auxiliary winding 170, and a secondary side winding 210. The primary side circuit of the switching power supply 1 includes a diode bridge circuit 110, a PFC circuit 120, a PFC standby control circuit 130, a primary side winding 150, an FET 152, resistors 153 and 154, a power source control IC 155, a primary side auxiliary winding 170, A diode 158, a capacitor 157, and a phototransistor 156 are included. The secondary circuit of the switching power supply device 1 includes a secondary winding 210, a diode 215, a capacitor 220, a resistor 225, a light emitting diode 230, a shunt regulator 235, and resistors 240 and 245. The light emitting diode 230 and the phototransistor 156 constitute a photocoupler 200, and light emitted from the light emitting diode 230 is received by the phototransistor 156 and subjected to photoelectric conversion. The actual circuit further includes circuit components such as a noise filter, but in FIG. 1, the circuit is simplified for convenience of explanation.

  The commercial power supply (AC 100 to 220 V) input (applied) to the diode bridge circuit 110 is full-wave rectified by the diode bridge circuit 110 and output to the PFC circuit 120.

  As will be described later, the PFC circuit 120 is a circuit in which the operating state and power supply are controlled by the PFC standby control circuit 130 to improve and boost the power factor of the rectified voltage that is full-wave rectified by the diode bridge circuit 110. The PFC circuit 120 performs control so that the voltage between the terminals of the capacitor 125 becomes a predetermined voltage. Here, the voltage on the positive terminal side of the capacitor 125 is defined as the primary DC voltage V1 (or PFC output voltage), and the voltage on the negative terminal side is defined as the ground (GND1) of the primary circuit.

  The primary DC voltage V <b> 1 is connected to one end of the primary winding 150 of the transformer 400, the VH terminal of the control IC 155, and one end of the resistor 126 of the PFC standby control circuit 130.

  The other end of the primary winding 150 is connected to the drain terminal of the FET 152. Further, the source terminal of the FET 152 is connected to the ground GND1 of the primary circuit and the IS terminal of the control IC 130 via the resistors 153 and 154, respectively, and the gate terminal is connected to the OUT terminal of the control IC 155.

  The FET 152 is a power MOSFET (Metal-Oxide Semiconductor Field-EffectTransistor), for example, and a current flowing between the drain terminal and the source terminal is controlled by a voltage input to the gate terminal. The FET 152 of this embodiment is an N-type MOSFET, and is configured such that a current flows (that is, turns on) between the drain terminal and the source terminal when the voltage input to the gate terminal rises.

  The control IC 155 is an IC for controlling on / off of the FET 152. The control IC 155 generates a switching pulse with a predetermined frequency and outputs it from the OUT terminal of the control IC 155. When a switching pulse is input to the gate terminal of the FET 152, the FET 152 is turned on, and a current (primary current) caused by the primary DC voltage V1 passes through the primary winding 150, the FET 152, and the resistor 153, and is grounded to the primary circuit. It flows to GND1. When the FET 152 is intermittently turned on / off under the control of the control IC 155, an intermittent voltage is induced in the primary side auxiliary winding 170 and the secondary side winding 210.

  The voltage induced in the primary side auxiliary winding 170 is rectified by the diode 158, smoothed by the capacitor 157, and applied to the Vcc terminal (power supply terminal) of the control IC 155 and the emitter of the transistor 139. That is, the control IC 155 is driven by applying a voltage smoothed by the capacitor 157. When the control IC 155 is activated, no voltage is induced in the primary side auxiliary winding 170, and therefore the control IC 155 is activated by a current caused by the primary DC voltage V1 supplied to the VH terminal of the control IC 155.

  The IS terminal of the control IC 155 is connected to the source terminal of the FET 152 through the resistor 154. The FET 152 and the resistor 153 constitute a so-called source follower, and the voltage at the source terminal of the FET 152 is proportional to the current flowing through the FET 152. The control IC 155 detects an overcurrent by monitoring the voltage applied to the IS terminal.

  The collector of the phototransistor 156 is connected to the FB terminal of the control IC 155, and the emitter of the phototransistor 156 is connected to the ground GND1. As will be described later, the phototransistor 156 receives light from the light emitting diode 230 whose light amount changes depending on the voltage value of the secondary DC voltage V2 (DC output), and photoelectrically converts the current according to the received light amount. Shed. The control IC 155 detects the voltage value of the secondary DC voltage V2 that varies depending on the load of the load circuit connected to the secondary circuit from the current flowing through the phototransistor 156, and the voltage value of the secondary DC voltage V2 is constant. (Ie, the current flowing through the light emitting diode 230 is constant), the duty ratio and frequency of the switching pulse supplied to the FET 152 are changed. As described above, the voltage value of the secondary DC voltage V2 is fed back to the electrically isolated primary circuit by the light emitting diode 230 and the phototransistor 156.

  The voltage intermittently induced across the secondary winding 210 is rectified by the diode 215 and smoothed by the capacitor 220 to generate the secondary DC voltage V2. The secondary DC voltage V2 is supplied to a load circuit (not shown) as a DC output (potential difference between the + V terminal and the GND terminal).

  The light emitting diode 230, the shunt regulator 235, and the resistors 225, 240, and 245 constitute a secondary DC voltage monitor circuit.

  The shunt regulator 235 is an element that controls the current flowing through the shunt regulator 235 by the voltage of the reference terminal. The resistors 240 and 245 are inserted in series between the secondary DC voltage V2 and the ground GND2 of the secondary circuit, and the voltage at the connection point of the resistors 240 and 245 is applied to the reference terminal of the shunt regulator 235. When the voltage at the reference terminal of the shunt regulator 235 is smaller than a predetermined value, the current flowing through the shunt regulator 235 decreases. Conversely, when the voltage at the reference terminal is larger than the predetermined value, the current flowing through the shunt regulator 235 is large. Become. In the case of the present embodiment, a voltage obtained by dividing the secondary DC voltage V2 by the resistors 240 and 245 is applied to the reference terminal of the shunt regulator 235. Therefore, a light emitting diode is used according to the voltage value of the secondary DC voltage V2. The amount of emitted light 230 changes.

  With the configuration as described above, the switching power supply device 1 of the present embodiment supplies a stable secondary DC voltage V2 as a DC output to a load circuit (not shown). The control IC 155 of the present embodiment includes the control IC described in Patent Document 1 in addition to the normal mode that generates and supplies a stable secondary DC voltage V2 to a load circuit that requires a predetermined power supply. Similarly, it has a frequency reduction mode in which the frequency of the switching pulse is lowered according to the load of the load circuit, and a burst mode in which the switching pulse is intermittently output. Specifically, the control IC 155 determines the change in the secondary DC voltage V2 detected by the light emitting diode 230 (that is, the change in the amount of light received by the phototransistor 156), the duty ratio of the switching pulse supplied to the FET 152, and The load of the load circuit connected to the secondary circuit is detected from the relationship with the frequency, and the normal mode, the frequency reduction mode, and the burst mode are switched in accordance with the load. For example, in the normal mode (that is, when the load of the load circuit is the rated load), the control IC 155 monitors the fluctuation of the secondary DC voltage V2 and monitors the duty of the switching pulse at a predetermined frequency (for example, 130 kHz). -Control the ratio. When the duty ratio of the switching pulse becomes smaller than a predetermined duty ratio (for example, 10%), it is determined that the load of the load circuit has become light (light load), and the frequency of the switching pulse is gradually increased. And shift to the frequency reduction mode. When the frequency of the switching pulse becomes lower than a predetermined frequency (for example, 10 kHz), it is determined that the load of the load circuit is close to no load, the frequency is further decreased (for example, 500 Hz), and an intermittent pulse ( For example, the mode shifts to a burst mode in which 5 pulses are output at a constant cycle. As described above, the control IC 155 of this embodiment changes the supply mode of the switching pulse according to the load of the load circuit, so that the primary side circuit outputs a predetermined voltage from the secondary DC voltage V2. The consumption of electricity is suppressed.

  Next, the PFC circuit 120 and the PFC standby control circuit 130 of this embodiment will be described.

  The PFC circuit 120 includes a capacitor 121, choke coil 122, FET 123, diode 124, capacitor 125, resistor 126, FET 127, PFC control IC 128 and resistor 129. The output of the diode bridge circuit 110 is connected to both ends of the capacitor 121, and one end of the capacitor 121 is connected to one end of the choke coil 122. The other end of the choke coil 122 is connected to the anode of the diode 124 and the drain terminal of the FET 123. The source terminal of the FET 123 is connected to the ground GND1. The gate terminal of the FET 123 is connected to the OUT terminal of the PFC control IC 128, and the PFC control pulse from the PFC control IC 128 is input. A capacitor 125 is connected between the cathode of the diode 124 and the ground GND1. The cathode of the diode 124 is connected to one end of the resistor 126, and the other end of the resistor 126 is connected to the drain terminal of the FET 127. The source terminal of the FET 127 is connected to one end of the resistor 129 and the FB terminal of the PFC control IC 128, and the other end of the resistor 129 is connected to the ground GND1. The GND terminal of the PFC control IC 128 is connected to the ground GND1, and the Vcc terminal (power supply terminal) is connected to the collector of the transistor 139 of the PFC standby control circuit 130 and the gate terminal of the FET 127. As will be described later, when the transistor 139 of the PFC standby control circuit 130 is turned on, power is supplied to the PFC control IC 128 and the FET 127 is turned on. When the FET 127 is turned on, the resistor 126 and the resistor 129 are connected in series, and the voltage at the connection point (that is, the voltage obtained by dividing the primary DC voltage V1 by the resistor 126 and the resistor 129 (hereinafter referred to as “sensing voltage”). ) Is input to the FB terminal of the PFC control IC 128.

  In the PFC circuit 120, a series circuit of a choke coil 122 and an FET 123 is connected between both terminals of the diode bridge circuit 110, and a series circuit of a diode 124 and a capacitor 125 is connected between both terminals of the FET 123 (between the source and drain). Thus, a boost chopper circuit is configured. The PFC control IC 128 performs on / off control of the FET 123 while monitoring the sensing voltage input to the FB terminal (that is, outputs a PFC control pulse to the gate terminal of the FET 123). The rectified current waveform is made closer to a sine wave to improve the power factor and boost the voltage. In the PFC circuit 120 of the present embodiment, the PFC control IC 128 performs on / off control of the FET 123 so that the PFC output voltage (primary DC voltage V1) is about 400V.

  The PFC standby control circuit 130 includes a Zener diode 137, a resistor 138, a transistor 139, a capacitor 140, resistors 141 and 142, and a diode 143. The PFC standby control circuit 130 turns on / off the transistor 139 based on the voltage generated at both ends of the primary side auxiliary winding 170 and controls the power supply of the PFC control IC 128. The capacitor 140 and the resistor 141 are connected in parallel, one end of which is connected to the ground GND1, and the other end is connected to one end of the resistor 142 and the anode of the Zener diode 137. The other end of the resistor 142 is connected to the anode of the diode 143, and the cathode of the diode 143 is connected to one end of the primary side auxiliary winding 170. As will be described later, the capacitor 140, the resistors 141 and 142, and the diode 143 constitute a load detection circuit that detects the load of the load circuit by detecting the switching pulse supply mode of the control IC 155. The transistor 139, the resistor 138, and the Zener diode 137 constitute a power control circuit that turns on / off the power of the PFC control IC 128 based on the output of the load detection circuit.

  FIG. 2 is a waveform diagram showing voltages generated at both ends of the primary side auxiliary winding 170 of the switching power supply device 1 according to the first embodiment of the present invention. 2A is a waveform diagram showing a voltage generated at both ends of the primary auxiliary winding 170 when the control IC 155 is operating in the normal mode. FIG. 2B is a waveform diagram showing the frequency of the control IC 155. FIG. 2C is a waveform diagram showing a voltage generated at both ends of the primary side auxiliary winding 170 when operating in the reduction mode, and FIG. 2C is a diagram illustrating a primary side auxiliary when the control IC 155 is operating in the burst mode. 4 is a waveform diagram showing a voltage generated at both ends of a winding 170. FIG.

As described above, when a certain amount of power supply is required for the load circuit (that is, when the load of the load circuit is a rated load), the control IC 155 operates in the normal mode and corresponds to the amount of light received by the phototransistor 156. A switching pulse having a predetermined frequency (for example, 130 kHz) and a predetermined duty (for example, 10% to 90%) is supplied to the gate terminal of the FET 152. When the FET 152 is intermittently turned on / off, the energy accumulated in the primary side winding 150 is transmitted to the primary side auxiliary winding 170, and the voltage shown in FIG. It occurs at both ends of 170. The voltage Va generated at both ends of the primary side auxiliary winding 170 is expressed by the following formula (1) when the number of turns of the primary side winding 150 is NP1 and the number of turns of the primary side auxiliary winding 170 is NP2.
Va = V1 × NP2 / NP1 (1)

  As described above, in the PFC circuit 120 of this embodiment, the PFC output voltage (that is, the primary DC voltage V1) is about 400V. Therefore, the amplitude of the voltage waveform shown in FIG. 2A is obtained by substituting 400 V for V1 in equation (1).

  When the load of the load circuit becomes lighter than the rated load (that is, light load), the control IC 155 operates in the frequency reduction mode, and has a predetermined frequency (for example, 10 to 130 kHz) and a predetermined duty (for example, 10%). ) Is supplied to the gate terminal of the FET 152. As a result, the voltage shown in FIG. 2B is generated at both ends of the primary side auxiliary winding 170.

  When the load of the load circuit becomes lighter than the light load and approaches a no-load state, the control IC 155 operates in a burst mode, and at a predetermined frequency (for example, 500 Hz) lower than that at the light load. Several pulses (for example, 5 pulses) are supplied as switching pulses to the gate terminal of the FET 152. As a result, the voltage shown in FIG. 2C is generated at both ends of the primary side auxiliary winding 170.

  The load detection circuit configured by the capacitor 140, the resistors 141 and 142, and the diode 143 is a circuit that averages voltages generated at both ends of the primary side auxiliary winding 170. The voltage generated at both ends of the primary side auxiliary winding 170 is filtered (integrated) by the capacitor 140 and the resistor 141, and the average value of the voltages generated at both ends of the primary side auxiliary winding 170 is output as a negative voltage at one end of the capacitor 140. To do. As described above, the voltage generated at both ends of the primary side auxiliary winding 170 varies depending on the energy stored in the primary side winding 150, that is, the on / off state (frequency, duty ratio) of the switching pulse. Since the ON / OFF state of the pulse changes depending on the load of the load circuit, the average value of the voltage generated at both ends of the primary side auxiliary winding 170 represents the load of the load circuit. Hereinafter, in this specification, the voltage at one end of the capacitor 140 is referred to as “load detection voltage V3”.

  FIG. 3 is a waveform diagram showing the load detection voltage V3 of the present embodiment. FIG. 3A is a waveform diagram showing the load detection voltage V3 when the control IC 155 is operating in the normal mode, and FIG. 3B is a waveform diagram showing the control IC 155 operating in the frequency reduction mode. FIG. 3C is a waveform diagram showing the load detection voltage V3 when the control IC 155 is operating in the burst mode. 3A to 3C are waveforms before being averaged by the load detection circuit, that is, the primary side auxiliary winding 170 shown in FIGS. 2A to 2C. The voltages generated at both ends of are respectively shown.

  As described above, the voltage waveform generated at both ends of the primary side auxiliary winding 170 when the control IC 155 is operating in the normal mode is the primary side auxiliary winding when the control IC 155 is operating in the frequency reduction mode. Compared to the voltage waveform generated at both ends of the line 170, the frequency is high. Therefore, the load detection voltage V3a when the control IC 155 is operating in the normal mode is larger than the load detection voltage V3b when the control IC 155 is operating in the frequency reduction mode, and is relatively in the negative direction. It is output as a large voltage (FIG. 3A). In this embodiment, the filter time constant of the capacitor 140 and the resistor 141 is set to be sufficiently longer than the frequency of the switching pulse when the control IC 155 is operating in the normal mode. Therefore, the load detection voltage V3a is a negative constant voltage.

  On the other hand, the load detection voltage V3b when the control IC 155 is operating in the frequency reduction mode is smaller than the load detection voltage V3a when the control IC 155 is operating in the normal mode. The voltage is output as a voltage smaller than the load detection voltage V3a (FIG. 3B). Also in this case, as in the normal mode, the time constant of the filter by the capacitor 140 and the resistor 141 is set to be longer than the frequency of the switching pulse when the control IC 155 is operating in the frequency reduction mode. Therefore, the load detection voltage V3b is a negative constant voltage.

  The voltage waveform generated at both ends of the primary side auxiliary winding 170 when the control IC 155 is operating in the burst mode is applied to both ends of the primary side auxiliary winding 170 when the control IC 155 is operating in the frequency reduction mode. Compared to the generated voltage waveform, the frequency is low and the pulse width outputted intermittently is also short. Accordingly, the load detection voltage V3c when the control IC 155 is operating in the burst mode is smaller than the load detection voltage V3b when the control IC 155 is operating in the frequency reduction mode, and the load detection voltage V3c is detected in the negative direction. A voltage smaller than the voltage V3b is output (FIG. 3C). In this embodiment, when the control IC 155 operates in the burst mode, the frequency of the switching pulse output from the control IC 155 to the FET 152 is shorter than the time constant of the filter formed by the capacitor 140 and the resistor 141. Is set to Therefore, the load detection voltage V3c fluctuates in synchronization with the switching pulse (a predetermined number of pulses) and becomes a voltage waveform having a ripple.

  As described above, the load detection circuit according to the present embodiment averages the voltage generated at both ends of the primary side auxiliary winding 170 and outputs it as a negative output voltage (load detection voltage V3). The load detection voltage V3 is a voltage indicating the switching pulse supply mode of the control IC 155 (that is, the load of the load circuit). The PFC standby control circuit 130 of the present embodiment controls the power supply of the PFC control IC 128 by using the load detection voltage V3.

  When the control IC 155 operates in the normal mode, the output of the load detection circuit (load detection voltage V3) is output as a large voltage in the negative direction (V3a). In the present embodiment, the potential difference between the emitter voltage of the transistor 139 and the load detection voltage V3a is set to be larger than the Zener voltage of the Zener diode 137. Therefore, a Zener current flows through the Zener diode 137 via the transistor 139, and the transistor 139 is turned on. When the transistor 139 is turned on, the current from the capacitor 157 is supplied to the Vcc terminal (power supply terminal) of the PFC control IC 128 via the transistor 139, and the PFC control IC 128 operates. When the transistor 139 is turned on, the voltage at the + terminal of the capacitor 157 is also applied to the gate terminal of the FET 127, and the FET 127 is turned on. When the FET 127 is turned on, the resistor 126 and the resistor 129 are connected in series between the primary DC voltage V1 and the ground GND1, and the current from the primary DC voltage V1 flows through the resistor 126 and the resistor 129. As a result, a voltage (sensing voltage) obtained by dividing the primary DC voltage V1 by the resistor 126 and the resistor 129 is input to the FB terminal of the PFC control IC 128. Based on the sensing voltage at this time, the PFC circuit 120 operates so that the primary DC voltage V1 is about 400V.

  When the control IC 155 operates in the frequency reduction mode, the output of the load detection circuit decreases in the negative direction (V3b). In this embodiment, as in the case where the control IC 155 operates in the normal mode, the potential difference between the emitter voltage of the transistor 139 and the load detection voltage V3b is larger than the Zener voltage of the Zener diode 137. Is set. That is, the transistor 139 is turned on, the current from the capacitor 157 is supplied to the Vcc terminal (power supply terminal) of the PFC control IC 128 via the transistor 139, and the PFC control IC 128 operates. When the transistor 139 is turned on, the FET 127 is turned on, and a voltage (sensing voltage) obtained by dividing the primary DC voltage V1 by the resistor 126 and the resistor 129 is input to the FB terminal of the PFC control IC 128. . Therefore, the PFC circuit 120 operates so that the primary DC voltage V1 is about 400 V, as in the case where the control IC 155 operates in the normal mode.

  When the control IC 155 operates in the burst mode, the output of the load detection circuit further decreases in the negative direction, and a ripple is generated (V3c). In the present embodiment, the potential difference between the emitter voltage of the transistor 139 and the load detection voltage V3c is larger than the Zener voltage of the Zener diode 137 at the ripple valley portion (the portion that increases in the negative direction). The voltage difference between the emitter voltage of the transistor 139 and the load detection voltage V3c is set to be smaller than the Zener voltage of the Zener diode 137 at the mountain portion (portion that decreases in the negative direction).

  FIG. 4 is a waveform diagram showing the relationship between the load detection voltage V3c and the on / off state of the transistor 139 when the control IC 155 of this embodiment operates in the burst mode. As shown in FIG. 4, when a switching pulse (predetermined number of pulses) is output from the control IC 155 to the FET 152 and the load detection voltage V3c decreases (in the negative direction), it falls within the range of the ripple voltage ΔV. When the transistor 139 is turned on at a predetermined threshold voltage, and the switching pulse is stopped and the load detection voltage V3c increases (decreases in the negative direction), the predetermined threshold voltage within the range of the ripple voltage ΔV is reached. The Zener voltage of the Zener diode 137 is set so that the transistor 139 is turned off. That is, the transistor 139 is intermittently turned on / off in synchronization with the ripple of the load detection voltage V3c. Therefore, the current from the capacitor 157 is intermittently supplied to the Vcc terminal (power supply terminal) of the PFC control IC 128 via the transistor 139, and the PFC control IC 128 operates intermittently. Further, the voltage of the capacitor 157 is intermittently applied to the gate terminal of the FET 127 via the transistor 139, and the primary DC voltage V 1 is connected to the resistor 126 in synchronization with the supply of power to the PFC control IC 128. A voltage (sensing voltage) divided by the resistor 129 is input to the FB terminal of the PFC control IC 128. While the transistor 139 is on, power is supplied to the PFC control IC 128 and the sensing voltage is input to the FB terminal of the PFC control IC 128. Therefore, the PFC control IC 128 has the primary DC voltage V1. It operates to be about 400V. Further, while the transistor 139 is off, the power supply to the PFC control IC 128 is cut off, and the current flowing from the primary DC voltage V1 to the resistor 129 is cut off, so that the power consumption in the PFC circuit 120 is minimized. It can be suppressed. As described above, the PFC standby control circuit 130 according to the present embodiment intermittently supplies power to the PFC control IC 128 and generates a sensing voltage in synchronization with the switching pulse when the control IC 155 operates in the burst mode. By doing so, power consumption is reduced and power efficiency is further improved. In other words, when the control IC 155 operates in the burst mode, the PFC control IC 128 operates only when the power supply to the primary winding 150 is necessary, and the sensing voltage is only when the PFC control IC 128 operates. Generated. Therefore, power consumption at a timing when power supply to the primary winding 150 is unnecessary is suppressed. In the present embodiment, the PFC control IC 128 stops while the transistor 139 is off. However, since there is no power consumption by the primary winding 150 during this period, the primary DC voltage V1 is Although there is a voltage drop due to spontaneous discharge of the capacitor 125, it is maintained at about 400V.

  As described above, in the PFC circuit 120 of this embodiment, when the control IC 155 operates in the burst mode (that is, when the load of the load circuit is close to no load), the PFC control is synchronized with the switching pulse. By intermittently supplying power to the IC 128 and generating a sensing voltage, the PFC circuit 120 is kept in an active state (that is, a state in which the PFC output voltage is a constant voltage), and power consumption is suppressed. Yes. That is, since the PFC circuit 120 of the present embodiment maintains the PFC output voltage (primary DC voltage V1) substantially constant even in the burst mode, the load of the load circuit becomes heavy and the normal mode is restored from the burst mode. Even so, the operation of the PFC circuit 120 is not delayed, and the output voltage (secondary DC voltage V2) is not temporarily reduced.

  The above is the description of the first embodiment of the present invention. However, the present invention is not limited to the configuration of the first embodiment described above, and various modifications can be made within the scope of the technical idea of the invention. Deformation is possible. In the present embodiment, the power supply of the PFC control IC 128 and the generation of the sensing voltage are intermittently performed using the ripple of the load detection voltage V3c when the control IC 155 operates in the burst mode. However, the present invention is not limited to this configuration. For example, the power supply of the PFC control IC 128 and the generation of the sensing voltage may be intermittently performed using the load detection voltage V3b when the control IC 155 operates in the frequency reduction mode. In this case, for example, the time constant of the filter by the capacitor 140 and the resistor 141 may be adjusted so that a ripple is generated in the load detection voltage V3b. Further, for example, a pulse generation circuit whose pulse cycle changes according to the load detection voltage V3b is provided, and when the load detection voltage V3b is lower than a predetermined threshold voltage (that is, the load of the load circuit is lighter than the predetermined load). The power supply to the PFC control IC 128 and the generation of the sensing voltage may be controlled by the pulse of the pulse generation circuit.

  In the first embodiment, the power supply to the PFC control IC 128 and the generation of the sensing voltage are intermittently performed in synchronization with the switching pulse. However, the configuration is not limited to this configuration. Absent. The PFC circuit 120 only needs to be able to supply the power consumed by the primary winding 150. When the power consumed by the primary winding 150 is reduced (that is, when the load of the load circuit is light), the PFC control IC 128 is It is not always necessary to operate in synchronization with the primary winding. In other words, if the power consumed by the primary winding 150 can be covered by the charge charged by the capacitor 125, the power supply to the PFC control IC 128 and the generation of the sensing voltage are intermittently performed asynchronously with the switching pulse. It may be done. In this case, for example, a pulse generation circuit that generates a pulse having a period corresponding to the voltage of the load detection voltage V3 is provided, and the supply of power to the PFC control IC 128 and the generation of the sensing voltage are controlled by the pulse of the pulse generation circuit. That's fine.

  In the first embodiment, the switching pulse supply mode (that is, the load of the load circuit) of the control IC 155 is set by using a load detection circuit that averages the voltages generated at both ends of the primary side auxiliary winding 170. However, the present invention is not limited to this configuration as long as the load of the load circuit can be detected. For example, the FB terminal of the control IC 155 may be monitored to detect the load, or a circuit for detecting the load of the load circuit may be provided in the secondary side circuit. Further, the load may be detected by detecting the current flowing through the FET 152.

  FIG. 5 is a circuit diagram showing Modification Example 1 (switching power supply device 1a) of the switching power supply device 1 according to the first embodiment. In the switching power supply 1 of this embodiment, the voltage induced in the primary side auxiliary winding 170 is connected to the emitter of the transistor 139 through the diode 158, and the transistor 139 is controlled to control the Vcc terminal (power supply) of the PFC control IC 128. The switching power supply device 1a of the first modification includes a PFC circuit 120a, and a voltage induced in the auxiliary winding L of the choke coil 122 included in the PFC circuit 120a is supplied to the transistor through the diode D. The transistor 139 is connected to the emitter of 139 and supplied to the Vcc terminal (power supply terminal) of the PFC control IC 128. Hereinafter, in the first modification, differences from the switching power supply device 1 of the first embodiment will be described. In FIG. 5, the same components as those in FIG. 1 are denoted by the same reference numerals, and detailed description thereof is omitted.

  As shown in FIG. 5, the PFC circuit 120 a of the first modification includes an auxiliary winding L as a secondary side of the choke coil 122. In addition, a diode D, a capacitor C, a resistor R, and a Zener diode ZD are provided. The diode D and the capacitor C are connected in series between both ends of the auxiliary winding L. One end of the resistor R is connected to the capacitor 121 and the choke coil 122, and the other end of the resistor R is connected to the cathode of the diode D and the capacitor C.

  The rectified voltage generated by the diode bridge circuit 110 is supplied to the diode 124 via the choke coil 122, and induces an intermittent voltage in the auxiliary winding L. The voltage induced in the auxiliary winding L is rectified by the diode D, smoothed by the capacitor C, and applied to the emitter of the transistor 139. That is, in the switching power supply device 1a of the first modification, a voltage is supplied to the Vcc terminal (power supply terminal) of the PFC control IC 128 without passing through the primary side auxiliary winding 170. The Zener diode ZD is connected in parallel with the capacitor C, and suppresses the supply voltage to the PFC control IC 128 to a certain level or less. In addition, since the PFC control IC 128 operates during the period in which the transistor 139 is turned on by the voltage smoothed by the capacitor C, the switching power supply device 1a of the first modification also uses the switching of the first embodiment. The same effect as that of the power supply device 1 can be obtained.

  FIG. 6 is a circuit diagram showing Modification Example 2 (switching power supply device 1b) of the switching power supply device 1 according to the first embodiment. The switching power supply device 1b according to the second modification also includes a PFC circuit 120b similar to the PFC circuit 120a according to the first modification. The voltage induced in the auxiliary winding L of the choke coil 122 included in the PFC circuit 120b is applied to the resistor R ', Capacitor C' is connected to the emitter of the transistor 139 through the diode D, and the transistor 139 is controlled and supplied to the Vcc terminal (power supply terminal) of the PFC control IC 128. Hereinafter, in Modification 2, differences from the switching power supply device 1 of the first embodiment will be described. In FIG. 6, the same components as those in FIG. 1 are denoted by the same reference numerals, and detailed description thereof is omitted.

  As shown in FIG. 6, the PFC circuit 120 b of Modification 2 also includes an auxiliary winding L as the secondary side of the choke coil 122. Further, diodes D and D ', capacitors C and C', and resistors R and R 'are provided. Between both ends of the auxiliary winding L, a resistor R ′, a capacitor C ′, diodes D ′ and D, a capacitor C, and a Zener diode ZD are connected. One end of the resistor R is connected to the capacitor 121 and the choke coil 122, and the other end of the resistor R is connected to the cathode of the diode D and the capacitor C.

  The rectified voltage generated by the diode bridge circuit 110 is supplied to the diode 124 via the choke coil 122, and induces an intermittent voltage in the auxiliary winding L. The voltage induced in the auxiliary winding L is rectified by the resistor R ′, the capacitor C ′, and the diode D, smoothed by the capacitor C, and applied to the emitter of the transistor 139. That is, also in the switching power supply device 1b of the modification 2, the voltage is supplied to the Vcc terminal (power supply terminal) of the PFC control IC 128 without passing through the primary side auxiliary winding 170. In addition, since the PFC control IC 128 operates during the period when the transistor 139 is turned on by the voltage smoothed by the capacitor C, the switching power supply device 1b according to the second modification also uses the switching according to the first embodiment. The same effect as that of the power supply device 1 can be obtained.

  FIG. 7 is a circuit diagram showing a configuration of a switching power supply apparatus 1M according to the second embodiment of the present invention. In FIG. 7, the same reference numerals are given to configurations common to FIG. 1. The second embodiment is different from the first embodiment in that a photocoupler 1270 including a phototransistor 1270a and a light emitting diode 1270b is provided instead of the FET 127 of the PFC circuit 120, and a resistor 1272 is added. Different. That is, the switching power supply device 1M according to the second embodiment is similar to the first embodiment when the control IC 155 operates in a burst mode (that is, when the load of the load circuit is close to no load). Synchronously, the power supply to the PFC control IC 128 and the generation of the sensing voltage are intermittently performed. The power supply state to the PFC control IC 128 is detected by the photocoupler 1270, and sensing is performed according to the detection result. It is configured to control the generation of voltage. Hereinafter, differences from the first embodiment will be described.

  In the PFC circuit 120 of the second embodiment, the cathode of the diode 124 is connected to one end of the resistor 126, and the other end of the resistor 126 is connected to the collector of the phototransistor 1270a. The emitter of the phototransistor 1270a is connected to one end of the resistor 129 and the FB terminal of the PFC control IC 128, and the other end of the resistor 129 is connected to the ground GND1. One end of the resistor 1272 is connected to the Vcc terminal (power supply terminal) of the PFC control IC 128, the other end is connected to the anode of the light emitting diode 1270b, and the cathode of the light emitting diode 1270b is connected to the ground GND1.

  Also in the second embodiment, as in the first embodiment, when the control IC 155 operates in the burst mode, the transistor 139 is intermittently turned on / off in synchronization with the ripple of the load detection voltage V3c. Then, according to ON / OFF of the transistor 139, the current from the capacitor 157 is supplied to the light emitting diode 1270b via the Vcc terminal (power supply terminal) of the PFC control IC 128 and the resistor 1272, and the PFC control IC 128 is intermittently supplied. While operating, the light emitting diode 1270b emits light intermittently with a predetermined amount of light.

  Light emitted from the light emitting diode 1270b when the transistor 139 is turned on is received by the phototransistor 1270a and is photoelectrically converted to turn on the phototransistor 1270a. When the phototransistor 1270a is turned on, a voltage (sensing voltage) obtained by dividing the primary DC voltage V1 by the resistor 126 and the resistor 129 is input to the FB terminal of the PFC control IC 128, as in the first embodiment. The Rukoto. As described above, the PFC circuit 120 according to the second embodiment is configured to detect the power supply state to the PFC control IC 128 by the photocoupler 1270 and to control the generation of the sensing voltage according to the detection result. Is done. As in the first embodiment, when the control IC 155 operates in the burst mode (that is, when the load of the load circuit is close to no load), the power supply to the PFC control IC 128 is synchronized with the switching pulse. Supply and generation of the sensing voltage are performed intermittently.

  FIG. 8 is a circuit diagram showing Modification Example 1 (switching power supply device 1Ma) of the switching power supply device 1M according to the second embodiment. The switching power supply device 1Ma of the first modification includes a PFC circuit 120a (a circuit in which an auxiliary winding L, a diode D, a capacitor C, a resistor R, and a Zener diode ZD are added to the PFC circuit 120 of the second embodiment). The voltage induced in the auxiliary winding L of the choke coil 122 provided in the PFC circuit 120a is connected to the emitter of the transistor 139 through the diode D, and the transistor 139 is controlled to control the Vcc terminal (power supply terminal) of the PFC control IC 128. ). That is, in the first modification, as in the first modification of the switching power supply device 1 according to the first embodiment, the voltage is applied to the Vcc terminal (power supply terminal) of the PFC control IC 128 without using the primary auxiliary winding 170. Supplied. In addition, since the PFC control IC 128 operates during the period when the transistor 139 is turned on by the voltage smoothed by the capacitor C, the switching power supply device 1Ma according to the first modification also uses the switching according to the second embodiment. The same effect as that of the power supply device 1M can be obtained.

  FIG. 9 is a circuit diagram showing Modification Example 2 (switching power supply device 1Mb) of the switching power supply device 1M according to the second embodiment. The switching power supply device 1Mb of Modification 2 includes a PFC circuit 120b (the PFC circuit 120 of the second embodiment includes an auxiliary winding L, diodes D and D ′, capacitors C and C ′, resistors R and R ′, Zener diodes). The voltage induced in the auxiliary winding L of the choke coil 122 included in the PFC circuit 120b is connected to the emitter of the transistor 139 through the resistor R ′ and the capacitor C ′ diode D, The transistor 139 is controlled and supplied to the Vcc terminal (power supply terminal) of the PFC control IC 128. That is, in the second modification, similarly to the second modification of the switching power supply device 1 according to the first embodiment, the voltage is applied to the Vcc terminal (power supply terminal) of the PFC control IC 128 without using the primary side auxiliary winding 170. Supplied. In addition, since the PFC control IC 128 operates during the period in which the transistor 139 is turned on by the voltage smoothed by the capacitor C, the switching power supply device 1Mb of the second modification also uses the switching of the second embodiment. The same effect as that of the power supply device 1M can be obtained.

1, 1a, 1b, 1M, 1Ma, 1Mb Switching power supply device 110 Diode bridge circuit 120 PFC circuit 122 Choke coil 123, 152 FET
124, 143, 158, 215 Diode 121, 125, 140, 157, 220 Capacitor 126, 129, 138, 141, 142, 153, 154, 225, 240, 245, 1272 Resistor 130 PFC standby control circuit 127, 139 Transistor 137 Zener diode 150 Primary side windings 156, 1270a Phototransistor 170 Primary side auxiliary windings 200, 1270 Photocoupler 210 Secondary side windings 230, 1270b Light emitting diode 235 Shunt regulator 400 Transformer

Claims (14)

A switching power supply device having a primary circuit and a secondary circuit,
The primary circuit is
A rectifier circuit for rectifying the AC power supply voltage;
A first DC circuit that shapes and boosts the waveform of the current output from the rectifier circuit and outputs a first DC voltage;
A primary winding to which the first DC voltage is applied at one end;
A first switching element connected to the other end of the primary winding for turning on / off a current flowing through the primary winding;
A control circuit for controlling on / off of the first switching element;
A power supply circuit for supplying power for driving the first DC circuit;
Have
The secondary circuit is
A secondary winding that generates electromagnetic induction with the primary winding;
A second DC circuit for rectifying and smoothing the voltage generated in the secondary winding and supplying a second DC voltage to the load circuit;
Have
The primary side circuit further includes an output circuit that outputs a voltage corresponding to a load of the load circuit,
The first DC circuit includes a second switching element that turns on and off a current output from the rectifier circuit, a detection voltage generation circuit that generates a detection voltage based on the first DC voltage, A PFC control circuit for controlling the second switching element so that a detection voltage becomes a predetermined constant voltage,
The power supply circuit intermittently turns on / off a power source for driving the first DC circuit at a predetermined cycle according to a voltage output from the output circuit,
The switching power supply device according to claim 1, wherein the detection voltage is generated only when the power supply of the first DC circuit is turned on. The detection voltage generating circuit is inserted between the output of the first DC circuit and the ground of the primary circuit, and a current flowing in accordance with the first DC voltage and a current flowing in the resistor A first switch circuit for controlling
2. The first switch circuit is configured to cause a current to flow through the resistor in synchronization with the power supply of the first DC circuit being turned on, and to generate the detection voltage at one end of the resistor. The switching power supply device described in 1.   The switching power supply device according to claim 2, wherein the first switch circuit is a transistor.   The first switch circuit is connected to a power source of the first DC circuit, and emits a predetermined amount of light when the power source is turned on, and receives light from the light emitting diode to the resistor. The switching power supply device according to claim 2, further comprising: a phototransistor through which a current flows.   5. The switching power supply device according to claim 4, wherein the light emitting diode and the phototransistor constitute a photocoupler.   The power supply circuit includes a pulse generation circuit that generates a pulse of the predetermined cycle based on a voltage of the output circuit, and a power source for driving the first DC circuit is turned on based on the pulse 6. The switching power supply device according to claim 1, wherein the switching power supply device is turned off / off. The power supply circuit has a primary auxiliary winding that generates electromagnetic induction with the primary winding,
The switching power supply device according to any one of claims 1 to 6, wherein the output circuit generates and outputs an average voltage obtained by averaging voltages generated in the primary auxiliary winding.   The power supply circuit turns on a power supply for driving the first DC circuit when the average voltage is larger than a first reference voltage, and when the average voltage is smaller than the first reference voltage. 8. The switching power supply device according to claim 7, wherein a power source for driving the first DC circuit is intermittently turned on / off at the predetermined cycle. The control circuit controls on / off of the first switching element so that a second DC voltage is constant, and when the average voltage is smaller than the first reference voltage, the first switching element is controlled. Turn on / off the element a plurality of times in the predetermined period,
The average voltage fluctuates in a predetermined voltage range in synchronization with on / off of the first switching element when the first switching element is turned on / off in a burst state,
9. The switching power supply device according to claim 8, wherein the power supply circuit turns on / off a power supply for driving the first DC circuit in accordance with a change in the average voltage.   The power supply circuit turns on a power supply for driving the first DC circuit when the average voltage is larger than a second reference voltage, and when the average voltage is smaller than the second reference voltage. The switching power supply device according to claim 9, wherein a power supply for driving the first DC circuit is turned off.   The power supply circuit includes a third dc circuit for rectifying and smoothing a voltage generated in the primary auxiliary winding to generate a third dc voltage, and the third dc voltage is converted into the first dc voltage. The switching power supply device according to any one of claims 7 to 10, wherein the switching power supply is supplied as a power supply for driving the circuit.   The power supply circuit includes an auxiliary winding that generates electromagnetic induction with a boosting inductor included in the first DC circuit, and a third DC voltage that rectifies and smoothes the voltage generated in the auxiliary winding. 11. A third direct current circuit for generating the first direct current circuit, and supplying the third direct current voltage as a power source for driving the first direct current circuit. The switching power supply device according to any one of the above.   The power supply circuit detects a voltage difference between the third DC voltage and the second reference voltage, and turns on / off the third DC voltage based on the voltage difference. 13. The switching power supply device according to claim 11 or 12, wherein the switching power supply device has two switch circuits.   14. The switching power supply device according to claim 13, wherein the voltage difference detection circuit includes a Zener diode that generates a voltage substantially equal to a voltage difference between the third DC voltage and the second reference voltage.

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