JP2015050890A - Switching power-supply device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce standby power of an output-voltage detection circuit and an output-overvoltage detection circuit that perform feedback to a control circuit for a switching element in a power-factor correction circuit.SOLUTION: A switching power-supply device includes: a power-factor correction circuit 20 turning on and off a full-wave rectification waveform inputted from a choke coil L1 by a first switching element Q1 and obtaining an intermediate DC voltage V1; a DC-DC converter 30 turning on and off the voltage V1 by a second switching element Q2, inducing the voltage to a secondary winding 32b, and outputting a DC output voltage V2; and an auxiliary rectifier smoothing circuit 40 generating an auxiliary DC voltage V3 from an output of an auxiliary winding 32c. An output-voltage detection circuit 41 outputs the voltage V1 as the auxiliary DC voltage V3, and an output-overvoltage detection circuit 42 detects an overvoltage state of the voltage V1 as an overvoltage state of the auxiliary DC voltage V3. A control circuit 21 turns on and off the switching element Q1 by feeding back the auxiliary DC voltage V3, and stops turning on and off the switching element Q1 by detection of an overvoltage state.

Description

  The present invention relates to a technique for reducing standby power when a power supply is stopped for a switching power supply device having a power factor correction circuit and a DC-DC converter.

  FIG. 3 shows a first conventional switching power supply apparatus. This is listed in FIG. 4 in Patent Document 1. The switching element 68 in the power factor correction circuit 5 is turned on / off by the output from the AND gate 64 of the control circuit 6 to boost and rectify the full-wave rectified waveform input from the filter 4 via the choke coil main winding 67a. The output capacitor 71 is charged from the diode 70. In the DC-DC converter 89, the switching elements 91 and 92 are turned on / off by the second control circuit 90, whereby the intermediate DC voltage Vo of the output capacitor 71 is guided to the primary winding 93a of the transformer 93. The smoothing capacitor 97 is charged from the secondary windings 93b and 93c through the rectifier diodes 95 and 96, respectively, and the DC output voltage Vout is output. The change of the DC output voltage Vo detected at the connection point of the detection resistance elements 74 and 75 of the output voltage detection circuit 72 is compared with the reference voltage 58 by the comparator 57, and the difference is sent to the multiplier 55. A current target value Vm is generated by multiplying the reference voltage AC of the full-wave rectified waveform obtained by dividing the output voltage of the filter 4 by the resistance elements 51 and 52 by the difference. A comparison result between the conversion detection voltage VS of the switching current and the current target value Vm is generated by the comparator 56, and the switching element 68 is on / off controlled via the OR gate 61, the flip-flop 62, and the AND gate 64. Magnetic energy is stored in the choke coil main winding 67 a when the switching element 68 is turned on, and the stored energy is released from the rectifier diode 70 to the smoothing capacitor 71 when the switching element 68 is turned off. The comparator 54 compares the voltage detected by the criticality detection winding 67b with the reference voltage 53, and the switching element 68 is turned on at the zero cross point. When the output overvoltage detection circuit 81 having the overvoltage detection resistance elements 83 and 84 detects an overvoltage state on the output line from the smoothing capacitor 71, the output of the comparator 85 activates the flip-flop 87 and switches by the signal from the inverter 63. The on / off control of the element 68 is stopped.

  In the switching power supply device of the first conventional example, overvoltage detection resistance elements 83 and 84 in the output overvoltage detection circuit 81 are connected between both terminals of the output capacitor 71 in the power factor correction circuit 5. Therefore, power is consumed by the overvoltage detection resistance elements 83 and 84 even when the power supply is stopped, and there is a problem that standby power characteristics deteriorate.

  The second conventional example shown in FIG. 4 is a switching power supply apparatus proposed by Patent Document 1 as a solution. Resistive elements 83 and 84 for detecting overvoltage in the output overvoltage detection circuit 81 are moved to the position of the main winding 93 a of the transformer 93. As a result, no voltage is applied to the overvoltage detection resistance elements 83 and 84 when the power is stopped, and the standby power characteristic is improved as compared with the first conventional example.

JP 2011-55596 A

  In the second conventional example, the output voltage detection circuit 72 having the output voltage detection resistance elements 73, 74, and 75 is connected between both ends of the output capacitor 71 of the power factor correction circuit 5. In addition, even when the power supply is stopped, current continues to flow from the output capacitor 71 to the resistance elements 73, 74, and 75 for detecting the output voltage, so that power consumption is performed and the standby power characteristic is deteriorated.

  The present invention was created in view of such circumstances, and in a two-converter type switching power supply device composed of a power factor correction circuit and a DC-DC converter, it is fed back to the control circuit of the switching element in the power factor correction circuit. It is an object to reduce standby power in the output voltage detection circuit and the output overvoltage detection circuit.

  The present invention solves the above problems by taking the following measures.

The switching power supply device according to the present invention includes:
A power factor correction circuit that receives a full-wave rectified waveform of an AC voltage via a choke coil, is turned on / off by a first switching element controlled by a first control circuit, and is rectified and smoothed to obtain an intermediate DC voltage; ,
The intermediate DC voltage generated by the power factor correction circuit is turned on / off by the second switching element controlled by the second control circuit, guided from the primary winding of the transformer to the secondary winding, and rectified and smoothed. A DC-DC converter that outputs a DC output voltage;
An auxiliary rectifying and smoothing circuit for generating an auxiliary DC voltage by rectifying and smoothing the output of the auxiliary winding in the transformer;
An output voltage detection circuit that outputs a change in the auxiliary DC voltage of the auxiliary rectifying and smoothing circuit by replacing the change in the intermediate DC voltage generated by the power factor correction circuit;
An output overvoltage detection circuit that detects an overvoltage state of the intermediate DC voltage by replacing it with an overvoltage state of the auxiliary rectifying and smoothing circuit;
The first control circuit performs feedback input of a change in the auxiliary DC voltage from the output voltage detection circuit and performs on / off control of the first switching element so that the intermediate DC voltage is stabilized. The on / off control of the first switching element is stopped when the output overvoltage detection circuit detects an overvoltage state.

In the switching power supply device of the present invention having the above configuration,
<1> An output voltage detection circuit that captures a change in the intermediate DC voltage of the power factor correction circuit is replaced with a change in the auxiliary DC voltage output from the auxiliary rectification smoothing circuit associated with the transformer of the DC-DC converter, and is output. And
<2> The output overvoltage detection circuit that captures the overvoltage state of the intermediate DC voltage is detected by replacing the overvoltage state of the auxiliary rectifying and smoothing circuit.

  The intermediate DC voltage generated by the power factor correction circuit during power supply operation is stored when the power supply is stopped. However, when the power supply is stopped, the operation of the second switching element of the DC-DC converter is stopped. No current flows through the auxiliary rectifying / smoothing circuit associated with the transformer. As a result, no current flows in either the output voltage detection circuit or the output overvoltage detection circuit, and standby power when the power is stopped can be reduced.

  According to the present invention, the output voltage detection circuit for capturing the change in the intermediate DC voltage generated by the power factor correction circuit and the output overvoltage detection circuit for capturing the overvoltage state of the intermediate DC voltage are connected to the auxiliary winding of the transformer. Therefore, when the power is stopped, no current flows in either the output voltage detection circuit or the output overvoltage detection circuit, and standby power can be reduced.

The block diagram which shows an example of the fundamental structure of the switching power supply device of this invention The circuit diagram which shows the structure of the switching power supply device in the Example of this invention 1 is a circuit diagram showing the configuration of a first conventional switching power supply device The circuit diagram which shows the structure of the switching power supply device of the 2nd prior art example

  The switching power supply device of the present invention having the above configuration has several preferred modes as follows.

The intermediate DC voltage output from the power factor correction circuit is V1, the auxiliary DC voltage generated by the auxiliary rectifying / smoothing circuit connected to the auxiliary winding of the transformer is V3, the number of turns of the primary winding of the transformer is N1, and the number of turns of the auxiliary winding is Assuming N3, V1: V3 = N1: N3,
V3 = (N3 / N1) · V1
Thus, the auxiliary DC voltage V3 can be lowered by setting the number of turns N3 of the auxiliary winding to be smaller than the number of turns N1 of the primary winding. If the auxiliary DC voltage V3 is lowered, the power consumed by the output voltage detection circuit and the output overvoltage detection circuit can be reduced not only when the power supply is stopped but also when the power supply is operating.

  In the switching power supply device having the above-described configuration, it is important that the operation of the second control circuit is stabilized first in order to quickly stabilize the operation at the time of power-on. If the first switching element in the preceding power factor correction circuit is turned on / off before the operation of the second control circuit is stabilized, it becomes difficult to stabilize the operation of the switching power supply device at the initial stage of power-on. Therefore, at the initial stage of power-on, the first switching element of the power factor correction circuit is not operated, but first, the second switching element of the DC-DC converter in the subsequent stage is operated to be induced from the primary winding to the auxiliary winding. The auxiliary rectifying / smoothing circuit is started up with the power to generate the output voltage detection circuit and the output overvoltage detection circuit. Thereby, priority is given to the detection of the change of the intermediate DC voltage generated by the power factor correction circuit and the determination of the presence or absence of the overvoltage state of the intermediate DC voltage. Next, the first control circuit in the power factor correction circuit performs on / off control for the first switching element based on the detection result of the intermediate DC voltage obtained in preference to the initial stage of power-on and the determination result of the presence or absence of the overvoltage state. To start. As a result, it is possible to quickly stabilize the operation of the switching power supply device at the initial power-on time.

  FIG. 1 is a block diagram showing an example of a basic configuration of a switching power supply device of the present invention. In FIG. 1, A is a switching power supply device, 20 is a power factor correction circuit, 30 is a DC-DC converter, 40 is an auxiliary rectification smoothing circuit, 41 is an output voltage detection circuit, and 42 is an output overvoltage detection circuit. The power factor correction circuit 20 receives the full-wave rectified waveform of the AC voltage via the choke coil L1, is turned on / off by the first switching element Q1, and rectified and smoothed to obtain the intermediate DC voltage V1. The first switching element Q1 is controlled by the first control circuit 21. The DC-DC converter 30 turns on / off the intermediate DC voltage V1 generated by the power factor correction circuit 20 by means of the second switching element Q2, guides it from the primary winding 32a of the transformer 32 to the secondary winding 32b, and rectifies and smoothes it. The DC output voltage V2 is output. The second switching element Q2 is controlled by the second control circuit 31. The auxiliary rectifying / smoothing circuit 40 rectifies and smoothes the output of the auxiliary winding 32c in the transformer 32 to generate an auxiliary DC voltage V3. The output voltage detection circuit 41 replaces the change of the intermediate DC voltage V1 generated by the power factor correction circuit 20 with the change of the auxiliary DC voltage V3 of the auxiliary rectification smoothing circuit 40 and outputs the change. The output overvoltage detection circuit 42 detects by replacing the overvoltage state of the intermediate DC voltage V1 with the overvoltage state of the auxiliary DC voltage V3. The first control circuit 21 feeds back the change of the auxiliary DC voltage V3 from the output voltage detection circuit 41, and turns on the first switching element Q1 so that the intermediate DC voltage V1 and thus the DC output voltage V2 are stabilized. In addition to performing on / off control, the on / off control of the first switching element Q1 is stopped when the output overvoltage detection circuit 42 detects an overvoltage state.

  The operation of the switching power supply device A configured as described above is as follows.

  In the power factor correction circuit 20, the first control circuit 21 appropriately controls the state in which the first switching element Q1 is turned on / off to store magnetic energy in the choke coil L1 and the state in which the stored energy is released. The intermediate DC voltage V1 with improved power factor can be obtained by alternately repeating and rectifying and smoothing at appropriate timing.

  In the DC-DC converter 30, the intermediate DC voltage V1 generated by the power factor correction circuit 20 is input, and the second control circuit 31 performs on / off control of the second switching element Q2 so that the primary winding of the transformer 32 is obtained. A state in which magnetic energy is stored in 32a and a state in which the stored energy is discharged from the secondary winding 32b are alternately repeated at an appropriate timing, and rectified and smoothed to output a DC output voltage V2.

  With the above cooperation, the DC-DC converter 30 outputs the DC output voltage V2 with improved power factor.

  The first control circuit 21 detects the change of the intermediate DC voltage V1 generated by the power factor correction circuit 20 with the change of the auxiliary DC voltage V3 from the output voltage detection circuit 41, and the first switching element according to the detection result. Adjust the on / off feedback control for Q1. As a result, the level of the intermediate DC voltage V1 is stabilized, and the phase of the current flowing out from the power factor correction circuit 20 to the DC-DC converter 30 substantially coincides with the phase of the input full-wave rectified waveform. The rate will be improved. The first control circuit 21 further determines the presence or absence of an overvoltage state of the intermediate DC voltage V1 generated by the power factor correction circuit 20 based on whether or not an overvoltage state is detected from the output overvoltage detection circuit 42. When the determination result indicates an overvoltage state, the switching control for the first switching element Q1 is stopped. Thereby, the overvoltage state of the intermediate DC voltage V1 is eliminated.

  In the switching power supply A having the above configuration, the output voltage detection circuit 41 captures a change in the intermediate DC voltage V1 of the power factor correction circuit 20 as a result, but directly the transformer 32 of the DC-DC converter 30. The auxiliary rectifying / smoothing circuit 40 associated with the rectifying / smoothing circuit 40 is configured to capture a change in the auxiliary DC voltage V3 output. The output overvoltage detection circuit 42 eventually captures the overvoltage state of the intermediate DC voltage V1 of the power factor correction circuit 20, but directly the overvoltage state of the auxiliary DC voltage V3 of the auxiliary rectification smoothing circuit 40. It is configured to capture.

  The intermediate DC voltage V1 generated by the power factor correction circuit 20 during power supply operation is stored in the rectifying and smoothing unit of the power factor correction circuit 20 (charging the smoothing capacitor). This intermediate DC voltage V1 is preserved even when the power supply is stopped. However, when the power is stopped, the switching operation of the second switching element Q2 by the second control circuit 31 is stopped in the DC-DC converter 30. Therefore, no current based on the intermediate DC voltage V1 flows through the primary winding 32a of the transformer 32, and no current flows through the auxiliary rectifying / smoothing circuit 40 associated with the auxiliary winding 32c of the transformer 32. As a result, no current flows in either the output voltage detection circuit 41 or the output overvoltage detection circuit 42.

  As described above, the switching power supply device A of the present embodiment can reduce standby power when the power is stopped.

  Embodiments of a switching power supply apparatus according to the present invention will be described below in detail with reference to the drawings.

  FIG. 2 is a circuit diagram showing a configuration of the switching power supply device according to the embodiment of the present invention. First, the components are listed. 2, A is a switching power supply device, T1p and T1n are first and second input terminals of the AC power supply 10 in the switching power supply device A, and T2p and T2n are first and second DC voltages in the switching power supply device A. Output terminal, 11 is a first filter, 12 is a full-wave rectifier circuit using a diode bridge, 13 is a second filter, 20 is a power factor correction circuit, 30 is a DC-DC converter, 40 is an auxiliary rectification smoothing circuit, and 41 is An output voltage detection circuit 42 is an output overvoltage detection circuit. As components of the power factor correction circuit 20, L1 is a choke coil (inductor), D1 is a first rectifier diode, Q1 is a first switching element, C1 is an output capacitor that is a first smoothing capacitor, R1, R2, and so on. R3 and R4 are resistance elements, and 21 is a first control circuit for power factor improvement composed of an integrated circuit (IC). As constituent elements of the DC-DC converter 30, Q2 is a second switching element, D2 is a second rectifier diode, C2 is a second smoothing capacitor, and 31 is a second converter for controlling a converter constituted by an integrated circuit (IC). 2 is a control circuit, 32 is a transformer, 32a is a primary winding of the transformer 32, and 32b is a secondary winding. As components of the auxiliary rectifying / smoothing circuit 40, 32c is an auxiliary winding of the transformer 32, D3 is a third rectifier diode, and C3 is a third smoothing capacitor. As constituent elements of the output voltage detection circuit 41, R5 and R6 are resistance elements, and as constituent elements of the output overvoltage detection circuit 42, R7 and R8 are resistance elements.

  The first filter 11 is inserted between the pair of input terminals T1p and T1n, the pair of input terminals of the full-wave rectifier circuit 12 is connected between the pair of output terminals of the first filter 11, and the full-wave rectifier circuit 12 A second filter 13 is inserted between the pair of output terminals. The first filter 11 and the second filter 13 have a function of removing a noise component that tends to leak from the switching power supply A to the AC power supply 10 side (normal mode filter, common mode filter).

  A power factor correction circuit 20 is connected between a pair of output terminals of the second filter 13. That is, one terminal of the choke coil (main winding) L1 is connected to the high side output terminal of the second filter 13, the anode of the first rectifier diode D1 is connected to the other terminal of the choke coil L1, and the cathode is connected to the cathode. One terminal (positive electrode terminal) of the first output capacitor C <b> 1 is connected, and the other terminal is connected to the low-side output terminal of the second filter 13. A series circuit of a first switching element Q1 and a current detection resistor element R1 is connected to a connection point between the choke coil L1 and the first rectifier diode D1, and the other terminal of the current detection resistor element R1 is a low-side output terminal. It is connected to the. Specifically, an N-channel MOSFET (a field effect transistor made of a metal oxide semiconductor) is used here as the first switching element Q1. The drain of the first switching element Q1, which is an NMOS, is connected to the connection point between the choke coil L1 and the anode of the first rectifier diode D1, and the source of the first switching element Q1 is one of the resistance elements R1 for current detection. The other terminal of the resistance element R1 is connected to the low side line LL.

  A series circuit of a resistance element R 2 and a resistance element R 3 is connected between the high side line LH and the low side line LL from the second filter 13, and the resistance division point is led to the first control circuit 21. This is a configuration in which the reference voltage AC of the full-wave rectified waveform is taken into the first control circuit 21. A criticality detection winding L1 'is coupled to the magnetic core of the choke coil L1. A series circuit of the criticality detection winding L 1 ′ and the resistance element R 4 is connected between the low side line LL and the first control circuit 21. The first control circuit 21 includes a voltage obtained by converting a switching current detection signal from the resistance element R1 into a voltage from a connection point between the first switching element Q1 and the current detection resistance element R1, that is, a conversion detection voltage of the switching current. VS is input. The first control circuit 21 is supplied with the detection output voltage CV from the output voltage detection circuit 41 and the output overvoltage detection voltage So from the output overvoltage detection circuit 42. ing.

  The specific internal configuration of the first control circuit 21 is the same as that of the conventional example described above, but any circuit configuration may be used as long as it has the following functions. Its functions are as follows.

  The first control circuit 21 performs on / off switching control of the first switching element Q1 at a predetermined duty cycle. A difference voltage between the detection output voltage CV detected by the output voltage detection circuit 41 and the first reference voltage is obtained, and the product of the reference voltage AC of the full-wave rectified waveform detected by the resistance elements R2 and R3 and the difference voltage ( Multiplication result) is generated as a current target value (Vm). On / off switching control of the first switching element Q1 is performed based on the timing and duty cycle when the conversion detection voltage VS of the switching current becomes the current target value (Vm).

  When the first switching element Q1 is turned on, a switching current flows through the choke coil (main winding) L1 and magnetic energy is stored in the choke coil L1, but when the first switching element Q1 is turned off, the choke coil L1 stores the magnetic energy. The stored energy and the voltage supplied from the second filter 13 are combined, and the output capacitor C1 is charged through the first rectifier diode D1. As a result, a voltage boosted higher than the peak value of the full-wave rectified waveform supplied from the second filter 13 is output to the output capacitor C1. When the energy release ends, the winding voltage of the choke coil L1 is reversed. This winding voltage is detected by the criticality detection winding L1 ′ and input to the first control circuit 21 via the resistance element R4. When the winding voltage of the choke coil L1 reaches the third reference voltage, the first switching element Q1 is turned on. Thereafter, the level of the intermediate DC voltage V1 output from the output capacitor C1 of the power factor correction circuit 20 is kept constant by repeating such an operation. At the same time, the current flowing through the AC power supply 10 becomes a sine wave current waveform that follows the voltage of the AC power supply 10, and the power factor is improved.

  Next, the DC-DC converter 30 will be described. A DC-DC converter 30 is connected to the output side of the power factor correction circuit 20. A series circuit of a primary winding 32a of the transformer 32 and the second switching element Q2 is connected between the positive terminal and the negative terminal of the output capacitor C1 of the power factor correction circuit 20. Here, an N-channel type MOSFET is used as the second switching element Q2. One terminal of the primary winding 32a is connected to the positive terminal of the output capacitor C1, and the other terminal is connected to the drain of the second switching element Q2, which is an NMOS. The source of the second switching element Q2 is connected to the negative terminal of the output capacitor C1. The second switching element Q2 is on / off controlled by the second control circuit 31 at a predetermined duty cycle. A series circuit of a second rectifier diode D2 and a second smoothing capacitor C2 is connected between both ends of the secondary winding 32b of the transformer 32, and a pair of output terminals are connected to the positive terminal and the negative terminal of the second smoothing capacitor C2. T2p and T2n are connected. The secondary winding 32b has a reverse polarity with respect to the primary winding 32a. In FIG. 2, the black circle symbol “●” written on the side of the winding indicates “winding start” of the winding. The symbol “●” is written at the upper end of the primary winding 32a and the lower end of the secondary winding 32b, and it can be seen that the polarities are opposite to each other. Therefore, this DC-DC converter 30 is a flyback system. That is, this is a system in which magnetic energy is stored in the transformer 32 during the ON period of the second switching element Q2, and energy is released to the secondary side by the turn-off of the second switching element Q2.

  The auxiliary rectifying / smoothing circuit 40 is configured as follows. The auxiliary rectifying / smoothing circuit 40 has a configuration in which a series circuit of a third rectifier diode D3 and a third smoothing capacitor C3 is connected between both ends of the auxiliary winding 32c coupled to the core of the transformer 32. The auxiliary winding 32c has the same polarity as the primary winding 32a, and the change in the auxiliary DC voltage V3 output from the auxiliary rectifying and smoothing circuit 40 is an output capacitor input from the power factor correction circuit 20 to the DC-DC converter 30. It is directly proportional to the change of the intermediate DC voltage V1 of C1.

  The number of turns N3 of the auxiliary winding 32c is set to be sufficiently smaller than the number of turns N1 of the primary winding 32a. Therefore, the auxiliary DC voltage V3 induced in the auxiliary winding 32c is sufficiently lower than the intermediate DC voltage V1 output from the power factor correction circuit 20.

  The output voltage detection circuit 41 used for feedback control of the first control circuit 21 is configured as follows. A series circuit of a resistance element R5 and a resistance element R6 constituting a resistance dividing circuit is connected between both ends of the third smoothing capacitor C3, and a connection point between the resistance elements R5 and R6 is a feedback control terminal of the first control circuit 21. It is connected to the. The detected output voltage CV appearing at the connection point between the two resistance elements R5 and R6 reflects the change in the intermediate DC voltage V1 of the output capacitor C1. The intermediate DC voltage V1 exceeding the predetermined specified voltage Vref1 corresponds equivalently to the detected output voltage CV exceeding the predetermined specified voltage Vref1 ′.

  The output overvoltage detection circuit 42 used for feedback control (protection operation) of the first control circuit 21 is configured as follows. A series circuit of a resistance element R7 and a resistance element R8 constituting a resistance dividing circuit is connected between both ends of the third smoothing capacitor C3, and a connection point between the resistance elements R7 and R8 is an off control terminal of the first control circuit 21. It is connected to the. The change in the output overvoltage detection voltage So that appears at the connection point between the two resistance elements R7 and R8 reflects the overvoltage situation of the intermediate DC voltage V1 of the output capacitor C1. The fact that the intermediate DC voltage V1 exceeds the predetermined overvoltage determination voltage Vref2 corresponds equivalently to the fact that the output overvoltage detection voltage So exceeds the predetermined overvoltage determination voltage Vref2 ′.

  In the above description, the output overvoltage detection voltage So that appears across the resistance element R8 is higher than the detection output voltage CV that appears across the resistance element R6. As a guarantee, the resistance ratio R7 / R8 is made smaller than the resistance ratio R5 / R6. In other words, the ratio of R8 to the total resistance (R7 + R8) is made larger than the ratio of R6 to the total resistance (R5 + R6).

  Next, the operation of the switching power supply device A of the present embodiment configured as described above will be described.

<Operation at power-on>
The sine wave voltage from the AC power supply 10 passes through the first filter 11 and is full-wave rectified by the full-wave rectifier circuit 12, and the full-wave rectified waveform passes through the second filter 13 to the power factor correction circuit 20. Supplied. In the initial stage of power-on, the first control circuit 21 in the power factor correction circuit 20 does not immediately operate, and the first switching element Q1 is kept off. The current due to the voltage of the full-wave rectified waveform that appears at the output terminal of the second filter 13 flows through the path of the choke coil (main winding) L1 → first rectifier diode D1 → output capacitor C1, and charges the output capacitor C1. To generate an intermediate DC voltage V1 across the output capacitor C1. This intermediate DC voltage V <b> 1 is applied to the input terminal of the DC-DC converter 30. The second control circuit 31 in the DC-DC converter 30 operates in preference to the first control circuit 21 in the power factor correction circuit 20, and controls the second switching element Q2 on / off. In the ON period of the second switching element Q2, the current of the primary winding 32a of the transformer 32 increases with time, and energy is stored in the transformer 32. Next, when the second control circuit 31 turns off the second switching element Q2, the energy stored in the transformer 32 is rectified and smoothed from the secondary winding 32b by the second rectifier diode D2 and the second smoothing capacitor C2. Thus, the DC output voltage V2 is output from the pair of output terminals T2p and T2n. When the release of the energy stored in the transformer 32 is completed, the second switching element Q2 is turned on again. Thereafter, the oscillation operation continues by repeating the above operation. Although not shown, an error signal between the detection voltage on the secondary side and the reference voltage is fed back to the second control circuit 31 on the primary side by the photocoupler, and the timing at which the second switching element Q2 is turned off is As a result, the DC output voltage V2 becomes constant.

  On the other hand, when a voltage is applied to the primary winding 32a as the second switching element Q2 is turned on at the beginning of power-on, a feedback voltage is generated in the auxiliary winding 32c in the auxiliary rectifying and smoothing circuit 40. The feedback voltage is rectified by the third rectifier diode D3 and smoothed by the third smoothing capacitor C3. The voltage across the third smoothing capacitor C3 in the auxiliary rectifying and smoothing circuit 40 is the auxiliary DC voltage V3.

  The output voltage detection circuit 41 generates a detection output voltage CV obtained by dividing the auxiliary DC voltage V3 between both ends of the third smoothing capacitor C3 by the resistance elements R5 and R6, and feeds it back to the first control circuit 21. At the same time, the output overvoltage detection circuit 42 feedback-inputs the output overvoltage detection voltage So obtained by dividing the auxiliary DC voltage V3 by the resistance elements R7 and R8 to the first control circuit 21.

  Changes in the detected output voltage CV by the output voltage detection circuit 41 and changes in the output overvoltage detection voltage So by the output overvoltage detection circuit 42 correspond to changes in the intermediate DC voltage V1 from the power factor correction circuit 20, respectively. An output voltage detection circuit 41 for generating a detection output voltage CV corresponding to the intermediate DC voltage V1 captures a voltage change in the auxiliary rectification smoothing circuit 40.

  If the output overvoltage detection voltage So detected by the output overvoltage detection circuit 42 does not exceed a specified value at the initial stage of power-on, the first control circuit 21 starts a control operation. When the detection output voltage CV input from the output voltage detection circuit 41 is equal to or less than a specified value, the first control circuit 21 turns on the first switching element Q1 and supplies magnetic energy to the choke coil (main winding) L1. Accumulate, then turn off at a predetermined duty cycle timing, generate a back electromotive force at the connection point of the choke coil L1 and the first switching element Q1, and charge the output capacitor C1 via the first rectifier diode D1 I do. As a result, the intermediate DC voltage V1 of the output capacitor C1 increases.

  Here, the reason why priority is given to the switching operation in the DC-DC converter 30 at the beginning of power-on and the switching operation in the power factor correction circuit 20 is postponed.

  The detection output voltage CV by the output voltage detection circuit 41 is used when the first control circuit 21 performs on / off switching control of the first switching element Q1 so that the switching current becomes the current target value (Vm). is there. Therefore, if the first switching element Q1 is controlled to be turned on / off before the detected output voltage CV reaches a predetermined level at the beginning of power-on, the operation of the power factor improvement circuit 20 becomes unstable, and the power factor is improved. The effect will be low.

  Therefore, at the beginning of power-on, the first control circuit 21 performs control so that a voltage is generated in the auxiliary winding 32c of the auxiliary rectifying and smoothing circuit 40 prior to operating the power factor correction circuit 20. . Assume that the switching operation for the first switching element Q1 is started after a voltage is generated in the auxiliary winding 32c and the detection output voltage CV by the output voltage detection circuit 41 reaches a predetermined level. If comprised in this way, the effect of the power factor improvement by the power factor improvement circuit 20 does not need to be reduced.

  When the first control circuit 21 in the power factor correction circuit 20 detects that the output voltage CV detected by the output voltage detection circuit 41 has reached a predetermined level, it starts on / off control for the first switching element Q1. When the first switching element Q1 is turned on, a switching current flows from the second filter 13 to the path of the choke coil (main winding) L1 → the first switching element Q1 → the resistance element R1 for current detection. Magnetic energy is accumulated in the main winding L1. At this time, the detection voltage VS by the resistance element R1 for current detection is compared with the current target value (Vm) of the switching current. The current target value (Vm) at this time is obtained by multiplying the full-wave rectified waveform appearing at the connection point of the resistance elements R2 and R3 with the reference voltage AC and multiplying this by the detection output voltage CV from the output voltage detection circuit 41. It has become. When the detection voltage VS by the resistance element R1 for current detection reaches the current target value (Vm), the first switching element Q1 is turned off. Then, the energy stored in the choke coil L1 and the voltage supplied from the second filter 13 are combined, and the output capacitor C1 is charged through the first rectifier diode D1 and supplied from the second filter 13. A voltage boosted higher than the peak value of the full-wave rectified waveform is output.

  When the release of energy stored in the choke coil L1 is completed, the winding voltage of the choke coil L1 is inverted. This winding voltage is detected by the criticality detection winding L1 ′ of the choke coil L1 and input to the first control circuit 21 via the resistance element R4. When the winding voltage becomes equal to or lower than the reference voltage, the first control circuit 21 turns on the first switching element Q1 again. That is, when the energy release from the choke coil L1 is completed, the first switching element Q1 is turned on again.

  Thereafter, the intermediate DC voltage V1 of the output capacitor C1 of the power factor correction circuit 20 is kept constant by repeating such an operation. At the same time, the current flowing through the AC power supply 10 becomes a sine wave current waveform following the voltage of the AC power supply 10.

  The first control circuit 21 takes in the output overvoltage detection voltage So that appears at the connection point of the resistance elements R7 and R8 in the output overvoltage detection circuit 42, compares it with the reference voltage, and detects an overvoltage in the power factor improvement circuit 20 The switching operation of the first switching element Q1 is stopped.

  During normal operation of the switching power supply device A, both resistance elements R7 and R8 of the output overvoltage detection circuit 42 and both resistance elements of the output voltage detection circuit 41 are powered by the third smoothing capacitor C3 in the auxiliary rectification smoothing circuit 40. Current continues to flow through R5 and R6.

  However, since the number of turns N3 of the auxiliary winding 32c is set to be smaller than the number N1 of the primary winding 32a, the voltage generated in the auxiliary winding 32c of the auxiliary rectifying and smoothing circuit 40 is a low level voltage. Sometimes the power consumed by these resistance elements R7, R8 and resistance elements R5, R6 can be reduced.

<Operation when the power is turned off>
When the device connected to the pair of output terminals T2p and T2n of the switching power supply device A is disconnected and opened, the first control circuit 21 and the second control circuit 31 stop operating, and the first switching circuit The switching operation of both the element Q1 and the second switching element Q2 is stopped. The output capacitor C1 of the power factor correction circuit 20 is already charged and constitutes a DC power source. However, if the second switching element Q2 stops the switching operation, the induction of power from the primary winding 32a of the transformer 32 to the auxiliary winding 32c does not occur, and the charging voltage of the third smoothing capacitor C3 disappears. As a result, no current flows through the series-connected resistance elements R7 and R8 in the output overvoltage detection circuit 42. That is, when the power is stopped, no power is consumed by the resistance elements R7 and R8 of the output overvoltage detection circuit 42. In addition, no current flows through the series-connected resistance elements R5 and R6 in the output voltage detection circuit 41. That is, when the power is stopped, no power is consumed by the resistance elements R5 and R6 of the output voltage detection circuit 41.

  As described above, according to the present embodiment, in the DC-DC converter 30, the auxiliary winding 32c is added to the transformer 32 that transmits power from the primary side to the secondary side by electromagnetic coupling, and is connected to the auxiliary winding 32c. Since the output overvoltage detection circuit 42 and the output voltage detection circuit 41 are configured by using the auxiliary rectifying and smoothing circuit 40 as a DC power supply, not only the output overvoltage detection circuit 42 but also the output voltage detection circuit 41 consumes power when the power supply is stopped. In order to prevent this, it is possible to promote a reduction in standby power of the switching power supply device A with the power factor correction circuit.

  INDUSTRIAL APPLICABILITY The present invention is useful as a technique for reducing power loss (standby power) of an output voltage detection circuit and an output overvoltage detection circuit when a power supply is stopped in a two-converter switching power supply device including a power factor correction circuit and a DC-DC converter. It is. The present invention can be applied to both resonant and non-resonant DC-DC converters.

20 power factor improvement circuit 21 first control circuit 30 DC-DC converter 31 second control circuit 32 transformer 32a primary winding 32b secondary winding 32c auxiliary winding 40 auxiliary rectification smoothing circuit 41 output voltage detection circuit 42 output overvoltage Detection circuit A Switching power supply L1 Choke coil (main winding)
Q1 First switching element Q2 Second switching element V1 Intermediate DC voltage V2 DC output voltage V3 Auxiliary DC voltage

Claims (3)

A power factor correction circuit that receives a full-wave rectified waveform of an AC voltage via a choke coil, is turned on / off by a first switching element controlled by a first control circuit, and is rectified and smoothed to obtain an intermediate DC voltage; ,
The intermediate DC voltage generated by the power factor correction circuit is turned on / off by the second switching element controlled by the second control circuit, guided from the primary winding of the transformer to the secondary winding, and rectified and smoothed. A DC-DC converter that outputs a DC output voltage;
An auxiliary rectifying and smoothing circuit for generating an auxiliary DC voltage by rectifying and smoothing the output of the auxiliary winding in the transformer;
An output voltage detection circuit that outputs a change in the auxiliary DC voltage of the auxiliary rectifying and smoothing circuit by replacing the change in the intermediate DC voltage generated by the power factor correction circuit;
An output overvoltage detection circuit that detects an overvoltage state of the intermediate DC voltage by replacing it with an overvoltage state of the auxiliary rectifying and smoothing circuit;
The first control circuit performs feedback input of a change in the auxiliary DC voltage from the output voltage detection circuit and performs on / off control of the first switching element so that the intermediate DC voltage is stabilized. A switching power supply device configured to stop on / off control of the first switching element when the output overvoltage detection circuit detects an overvoltage state.   The switching power supply according to claim 1, wherein the number of turns of the auxiliary winding is set to be smaller than the number of turns of the primary winding.   The first control circuit and the second control circuit do not operate the first switching element of the power factor correction circuit in the initial stage of power-on, and give priority to the second switching element of the DC-DC converter. The switching power supply device according to claim 1 or 2, wherein the switching power supply device is configured to operate.

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