CN107086789B - Secondary control quasi-resonance switching power supply converter - Google Patents

Abstract

The invention relates to the technical field of switching power supplies, and particularly discloses a secondary control quasi-resonant switching power supply converter which is provided with a power input positive end, a power input negative end, a power output positive end and a power output negative end which are connected with a power supply, and a switching controller. The implementation of the secondary control quasi-resonance switching power supply converter provided by the invention greatly reduces the switching loss of the switching power supply converter and has high conversion efficiency; the overlarge current flowing through the switching tube is avoided, so that the switching tube is protected from being damaged; the rectifier tube realizes soft turn-on, has high efficiency, no voltage spike and good EMI characteristics.

Description

A Secondary Controlled Quasi-Resonant Switching Power Converter

technical field

The invention relates to the technical field of switching power supplies, in particular to a switching power supply converter with secondary control quasi-resonance.

Background technique

At present, flyback switching power converters mostly use fixed frequency PWM (pulse width modulation) control mode and variable frequency PFM (pulse frequency modulation) quasi-resonant control mode. In conventional PWM control mode power converters, The power switch tube is in a hard switching state, not zero-voltage turn-off, the switching loss is large, and the conversion efficiency of the power converter is low; The conduction at the bottom of the resonant voltage wave can reduce part of the turn-on loss. When the switch tube is turned off, the voltage across the switch tube rises rapidly from zero, and the switch tube current drops rapidly from the maximum point. Therefore, the voltage across the switch tube There is inevitably an overlapping area between the voltage and current waveforms, and the overlapping of voltage and current waveforms produces switching losses, which increase rapidly as the switching frequency increases.

Regardless of the fixed-frequency PWM control mode or the variable-frequency PFM quasi-resonant control mode, after the power switch tube is turned off, the energy stored in the primary inductance winding of the transformer is switched to the secondary inductance winding, and the flyback voltage of the transformer secondary winding Rising rapidly until it is higher than the output voltage, at this time the secondary rectifier diode is turned on. During this process, the induced current of the secondary inductor winding has a large change rate from the minimum to the maximum, and the rectifier diode needs to be turned on from cut-off to conduction Recovery time, therefore, high-frequency operation will bring large loss and peak voltage when the rectifier diode is turned on, so that the voltage stress of the diode is high, and the EMI (electromagnetic interference) characteristics of the power supply are poor. In order to reduce the current change rate when the rectifier diode is turned on, it is generally realized by using a rectifier diode in series with an inductance, but the inductance stores energy during the conduction period of the rectifier tube, and it needs to be released in reverse when the rectifier tube is turned off, which will increase the rectifier tube. Spikes and losses during shutdown.

In the flyback switching power supply converter, in order to reduce the turn-off loss of the switching tube of the high-frequency switch, it is necessary to reduce the rate of change of the voltage and current. Generally, the rate of change of the voltage and current is mainly reduced by connecting capacitors in parallel at both ends of the switch tube. , or use an active clamp circuit to reduce the turn-off loss, and part of the energy stored in the capacitor connected in parallel at both ends of the switch tube during the switch off period will directly short-circuit the capacitor when the switch tube is turned on, which will bring great The loss or even damage the switch tube, while the control of the active clamp circuit is complicated, and the effect of reducing the turn-off loss is very limited.

Contents of the invention

The invention provides a switching power converter with secondary control quasi-resonance, by combining the original switch controller, switch tube, resonant capacitor, transformer, rectifier diode, polar capacitor, and the added diode, transformer, switch tube and The quasi-resonant control circuit composed only of resistors, capacitors, triodes and regulator tubes is rebuilt into the internal circuit of the switching power converter to ensure the zero-voltage turn-off of the original switch tube and the current and voltage of the original secondary rectifier tube. Technical issues with rate of change.

In order to solve the above technical problems, the present invention provides a secondary control quasi-resonant switching power converter, which is provided with a power input positive terminal connected to a power supply, a power input negative terminal, a power output positive terminal connected to a load, and a power output terminal. The negative terminal is also provided with a switch controller, the negative terminal of the power input is connected to the negative terminal of the power supply of the switch controller and one end of the current detection resistor, and the other end of the current detection resistor is connected to the switch controller. The switch current detection terminal and the voltage output terminal of the first switch tube, the control terminal of the first switch tube is connected to the switch control output terminal of the switch controller, and the voltage input terminal of the first switch tube is connected to the first transformer The opposite end of the primary winding of the first transformer, the same end of the primary winding of the first transformer is connected to the positive end of the power input;

The opposite end of the secondary winding of the first transformer, the anode of the first diode, the positive end of the power supply of the quasi-resonant control circuit, the cathode of the second diode, and the positive end of the polarity capacitor are connected to the output of the power supply The positive terminal, the cathode of the first diode is connected to the resonant capacitor and then connected to the terminal with the same name of the secondary winding of the first transformer, the rectification input terminal of the secondary rectifier tube and the control signal input terminal of the quasi-resonant control circuit ;

The negative terminal of the power supply of the quasi-resonant control circuit, the rectification output terminal of the secondary rectifier tube, the voltage output terminal of the second switch tube, the terminal with the same name of the secondary winding of the second transformer, and the negative terminal of the polar capacitor Connect the negative terminal of the output of the power supply, the control signal output terminal of the quasi-resonant control circuit is connected to the control terminal of the second switching tube;

The voltage input end of the second switching tube is connected to the opposite end of the primary winding of the second transformer, the same end of the primary winding of the second transformer is connected to the cathode of the first diode, and the second The opposite end of the secondary winding of the transformer is connected to the anode of the second diode.

Specifically, the quasi-resonant control circuit is provided with a first triode, a second triode, a third triode, a first resistor, a second resistor, a third resistor, a first regulator tube, a second Zener tube, first capacitor and second capacitor;

The collector of the first triode is connected to the positive power supply terminal of the quasi-resonant control circuit, and the positive power supply terminal of the quasi-resonant control circuit is connected to the base of the first triode after connecting the first resistor and the cathode of the first voltage regulator tube, the emitter of the first transistor is connected to one end of the first capacitor and the collector of the second transistor, the other end of the first capacitor, The anode of the first voltage regulator tube, the anode of the second voltage regulator tube, one end of the second resistor and the collector of the third triode are connected to the negative power supply terminal of the quasi-resonant control circuit;

The control signal input terminal of the quasi-resonant control circuit is connected to the second capacitor and the third resistor connected in series, and then connected to the cathode of the second voltage regulator tube, the other end of the second resistor, the second The base of the triode and the base of the third triode, the emitter of the second triode and the emitter of the third triode are connected to the control signal output of the quasi-resonant control circuit end.

Preferably, the first switch transistor and the second switch transistor are N-channel MOS transistors or NPN bipolar transistors or insulated gate bipolar transistors.

Particularly, when the first switch tube and the second switch tube are N-channel MOS tubes, the control terminal of the first switch tube or the control terminal of the second switch tube is a gate, and the first The voltage input end of the switch tube or the voltage input end of the second switch tube is a drain, and the voltage output end of the first switch tube or the voltage output end of the second switch tube is a source.

In particular, when the first switch tube and the second switch tube are NPN bipolar transistors, the control terminal of the first switch tube or the control terminal of the second switch tube is a base, and the first switch tube is a base. The voltage input end of a switch tube or the voltage input end of the second switch tube is a collector, and the voltage output end of the first switch tube or the voltage output end of the second switch tube is an emitter.

Particularly, when the first switch tube and the second switch tube are insulated gate bipolar transistors, the control terminal of the first switch tube or the control terminal of the second switch tube is a gate, and the first switch tube The voltage input end of a switch tube or the voltage input end of the second switch tube is a collector, and the voltage output end of the first switch tube or the voltage output end of the second switch tube is an emitter.

Preferably, the secondary rectifier is a rectifier diode or a field effect transistor rectifier module.

In particular, when the secondary rectifier is a rectifier diode, the rectification input end of the secondary rectifier is a cathode, and the rectification output end of the secondary rectifier is an anode.

Preferably, the first triode and the second triode are NPN bipolar transistors, and the third triode is PNP bipolar transistors.

The present invention provides a secondary control quasi-resonant switching power supply converter, the original resonant capacitor is adjusted to the secondary end of the original transformer, the energy stored in the resonant capacitor is discharged to the output end of the power supply, and the capacitor voltage starts from zero Resonant rise, so that the voltage of the original switching tube can also rise from zero resonance, thus realizing the zero-voltage turn-off of the original switching tube, which greatly reduces the switching power supply under the existing PWM control mode or PFM quasi-resonant switching control mode The switching loss of the converter, the conversion efficiency of the converter is high;

At the same time, the discharge circuit of the resonant capacitor at the secondary side of the original transformer is completely blocked from the original switching tube at the primary side of the original transformer, realizing soft switching and avoiding the capacitive opening of the switching tube caused by the resonant capacitor in the original technology. The current of the switch tube is too large, so as to protect the switch tube from being damaged;

Furthermore, the capacitor voltage of the original resonant capacitor rises resonantly from zero, and the current at the secondary end of the transformer naturally transitions from a small current flowing through the resonant capacitor to flowing through the secondary rectifier tube. The current change rate is low, and the rectifier tube realizes soft opening. High efficiency, no voltage spikes, good EMI characteristics, and the operating frequency of the switching power converter can be further increased, so that the volume of the power supply can be further reduced and the cost can be reduced on the device.

Description of drawings

Fig. 1 is the circuit principle diagram of the variable frequency PFM quasi-resonant switch mode power converter in the prior art that the embodiment of the present invention provides;

Fig. 2 is a voltage waveform diagram at both ends of the switching tube in Fig. 1 provided by an embodiment of the present invention;

Fig. 3-1 is a circuit connection diagram of a switching power converter with secondary control quasi-resonance provided by an embodiment of the present invention;

Fig. 3-2 is a circuit connection diagram in which the first switch tube and the second switch tube in Fig. 3-1 are N-channel MOS tubes and the secondary rectifier tube is a rectifier diode according to an embodiment of the present invention;

FIG. 4 is a circuit connection diagram of the quasi-resonant control circuit in FIG. 3-1 provided by an embodiment of the present invention.

Detailed ways

The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the drawings in the embodiments of the present invention. The values of the following components are only preferred embodiments, and do not constitute limitations on the scope of protection of the present invention.

Referring to FIG. 1 , it is a schematic circuit diagram of a variable-frequency PFM quasi-resonant switching mode power converter in the prior art provided by an embodiment of the present invention. In this embodiment, in the flyback switching power converter in the prior art, regardless of the fixed-frequency PWM control mode and the variable-frequency PFM quasi-resonant control mode, it is necessary to turn off the switching tube of the high-frequency switch To reduce the loss, the rate of change of voltage and current needs to be reduced. Generally, the rate of change of voltage and current is reduced by connecting the resonant capacitor Cr in parallel at both ends of the switch tube as shown in Figure 1, or using an active clamp circuit to reduce the turn-off loss. However, the control of the active clamping circuit is complicated, and the present invention does not further study it.

As shown in Figure 1, the flyback switching power supply converter in the prior art is equipped with the power input positive terminal Vin+ connected to the power supply, the power input negative terminal Vin-, the power output positive terminal Vout+ connected to the load, and the power output negative terminal. The terminal Vout- is also provided with a switch controller KC, the power input negative terminal Vin- is connected to the power supply negative terminal KC_PIN1 of the switch controller KC and one end of the current detection resistor Rs, the other end of the current detection resistor Rs One end is connected to the switch current detection terminal KC_PIN2 of the switch controller KC and the voltage output terminal KQ1_PIN1 of the switch tube KQ1, and the control terminal KQ1_PIN2 of the switch tube KQ1 is connected to the switch control output terminal KC_PIN2 of the switch controller KC. A resonant capacitor Cr is connected in parallel between the voltage output terminal KQ1_PIN1 and the voltage input terminal KQ1_PIN3 of the switch tube KQ1, and the voltage input terminal KQ1_PIN3 of the switch tube KQ1 is also connected to the anode of the diode D1 and the opposite end of the primary winding T1_1 of the transformer T1 ( The terminal with the black dot in the figure is the terminal with the same name, and the terminal without the black dot is the terminal with the same name), the cathode of the diode D1 is connected to the parallel RC circuit 1 and then connected to the terminal with the same name of the primary winding T1_1 of the transformer T1 The power input positive terminal Vin+, the opposite end of the secondary winding T1_2 of the transformer T1 is forwardly connected to the rectifier diode Di and then connected to the power output positive terminal Vout+ and the positive terminal of the polarity capacitor EC, and the negative terminal of the polarity capacitor EC terminal and the terminal with the same name of the secondary winding T1_2 of the transformer T1 is connected to the power output negative terminal Vout-.

In the circuit of Fig. 1, in conjunction with Fig. 2, Fig. 2 is a voltage waveform diagram at both ends of the switching tube KQ1 in Fig. 1 provided by the embodiment of the present invention, and the power switching tube KQ1 is at the bottom of the resonance voltage wave at both ends of the resonant capacitor Cr conduction, which can reduce part of the turn-on loss, but when the switch tube KQ1 is turned off, the voltage across the switch tube KQ1 rises rapidly from zero, and the current of the switch tube KQ1 drops rapidly from the maximum point, so the voltage and current at both ends of the switch tube KQ1 cannot Avoid overlapping areas, which will cause turn-off losses. After the switching tube KQ1 is turned off, the energy stored in the primary winding T1_1 of the transformer T1 is switched to the secondary winding T1_2, and the flyback voltage of the secondary winding T1_2 of the transformer T1 rises rapidly until it is higher than the output voltage. At this time, the rectifier diode Di conducts In this process, the induced current of the secondary winding T1_2 has a large change rate from the minimum to the maximum, and the rectifier diode Di needs recovery time from cut-off to conduction, so the high-frequency operation will bring the rectifier diode The large loss and peak voltage when Di is turned on, so that the voltage stress of the diode Di is high, and the EMI (electromagnetic interference) characteristics of the power supply are poor.

Therefore, the present invention provides a switching power converter with secondary control quasi-resonance, by combining the original switch controller KC, switch tube KQ1, resonant capacitor Cr, transformer T1, rectifier diode Di, polarity capacitor EC, and The additional diodes, transformers, switching tubes and the quasi-resonant control circuit composed of only resistors, capacitors, triodes and voltage regulator tubes are rebuilt into the internal circuit of the switching power converter.

Referring to Fig. 3-1, it is a circuit connection diagram of a secondary controlled quasi-resonant switching power converter provided by an embodiment of the present invention. In this embodiment, the described secondary control quasi-resonant switching power supply converter retains the original power input positive terminal Vin+ connected to the power supply, the power input negative terminal Vin- and the power output connected to the load Positive terminal Vout+, power output negative terminal Vout-, switch controller KC, current detection resistor Rs, resonant capacitor Cr, transformer T1 (hereinafter referred to as the first transformer T1), rectifier diode Di (hereinafter referred to as the secondary rectifier tube Di), the polar capacitor EC, and the additional diode, transformer, switching tube KQ1 and quasi-resonant control circuit 2 composed of resistors, capacitors, triodes and voltage regulator tubes are rebuilt into the internal circuit of the switching power converter. The relationship is as follows:

The power input negative terminal Vin- is connected to the negative power terminal KC_PIN1 of the switch controller KC and one end of the current detection resistor Rs, and the other end of the current detection resistor Rs is connected to the switch of the switch controller KC The current detection terminal KC_PIN2 and the voltage output terminal KQ1_PIN1 of the first switch tube KQ1, the control terminal KQ1_PIN2 of the first switch tube KQ1 is connected to the switch control output terminal KC_PIN3 of the switch controller KC, the first switch tube KQ1 The voltage input terminal KQ1_PIN3 is connected to the opposite terminal of the primary winding T1_1 of the first transformer T1, and the same terminal of the primary winding T1_1 of the first transformer T1 is connected to the positive input terminal Vin+ of the power supply;

The opposite terminal of the secondary winding T1_2 of the first transformer T1, the anode of the first diode D1, the positive power supply terminal 20 of the quasi-resonant control circuit 2, the cathode of the second diode D2, the pole The positive end of the positive capacitor EC is connected to the positive output terminal Vout+ of the power supply, the cathode of the first diode D1 is connected to the resonant capacitor Cr and then connected to the terminal with the same name of the secondary winding T1_2 of the first transformer T1, the secondary The rectification input terminal Di_1 of the rectifier Di and the control signal input terminal 21 of the quasi-resonant control circuit 2;

The negative power supply terminal 22 of the quasi-resonant control circuit 2, the rectification output terminal Di_2 of the secondary rectifier Di, the voltage output terminal KQ2_PIN1 of the second switching tube KQ2, the terminal with the same name of the secondary winding T2_1 of the second transformer T2, The negative terminal of the polarity capacitor EC is connected to the negative terminal Vout- of the power output, and the control signal output terminal 23 of the quasi-resonant control circuit 2 is connected to the control terminal KQ2_PIN2 of the second switching tube KQ2;

The voltage input terminal KQ2_PIN3 of the second switch tube KQ2 is connected to the opposite terminal of the primary winding T2_1 of the second transformer T2, and the same terminal of the primary winding T2_1 of the second transformer T2 is connected to the first diode D1 The negative terminal of the secondary winding T2_2 of the second transformer T2 is connected to the anode of the second diode D2.

It should be noted that the first switching transistor KQ1 and the second switching transistor KQ2 may be N-channel MOS transistors or NPN bipolar transistors or insulated gate bipolar transistors.

When the first switch tube KQ1 and the second switch tube KQ2 are N-channel MOS tubes, the control terminal KQ1_PIN2 of the first switch tube KQ1 or the control terminal KQ2_PIN2 of the second switch tube KQ2 is a gate G, The voltage input terminal KQ1_PIN3 of the first switching tube KQ1 or the voltage input terminal KQ2_PIN3 of the second switching tube KQ2 is the drain D, and the voltage output terminal KQ1_PIN1 of the first switching tube KQ1 or the second switching tube KQ2 The voltage output terminal KQ2_PIN1 is the source S.

When the first switch KQ1 and the second switch KQ2 are NPN bipolar transistors, the control terminal KQ1_PIN2 of the first switch KQ1 or the control terminal KQ2_PIN2 of the second switch KQ2 is the base B , the voltage input terminal KQ1_PIN3 of the first switching tube KQ1 or the voltage input terminal KQ2_PIN3 of the second switching tube KQ2 is the collector C, and the voltage output terminal KQ1_PIN1 of the first switching tube KQ1 or the second switching tube The voltage output terminal KQ2_PIN1 of KQ2 is the emitter E.

When the first switch KQ1 and the second switch KQ2 are insulated gate bipolar transistors, the control terminal KQ1_PIN2 of the first switch KQ1 or the control terminal KQ2_PIN2 of the second switch KQ2 is the gate G , the voltage input terminal KQ1_PIN3 of the first switching tube KQ1 or the voltage input terminal KQ2_PIN3 of the second switching tube KQ2 is the collector C, and the voltage output terminal KQ1_PIN1 of the first switching tube KQ1 or the second switching tube The voltage output terminal KQ2_PIN1 of KQ2 is the emitter E.

It should also be noted that the secondary rectifier Di is a rectifier diode or a field effect transistor rectification module, and the field effect transistor module is a circuit module with a rectification input terminal Di_1 and a rectification output terminal Di_2, which is a field effect transistor as the main device. . When the secondary rectifier Di is a rectifier diode, the rectifier input Di_1 of the secondary rectifier Di is a cathode, and the rectifier output Di_2 of the secondary rectifier Di is an anode.

In combination with the above description, referring to Fig. 3-2, it is a circuit in which the first switching tube and the second switching tube KQ2 in Fig. 3-1 are N-channel MOS tubes and the secondary rectifying tube Di is a rectifying diode according to an embodiment of the present invention. Connection Diagram. And when the switch tube KQ1 is an N-channel MOS tube, an NPN bipolar transistor or an insulated gate bipolar transistor, the secondary rectifier Di is a circuit under the other five arrangements and combinations of a rectifier diode and a field effect transistor rectifier module Refer to Figure 3-1 for the connection diagram, which is easy to draw and will not be illustrated here.

It should be further noted that, referring to FIG. 4 , it is a circuit connection diagram of the quasi-resonant control circuit 2 in FIG. 3-1 provided by an embodiment of the present invention. The quasi-resonant control circuit 2 is provided with a first triode Q1, a second triode Q2, a third triode Q3, a first resistor R1, a second resistor R2, a first regulator Dv1, a second Zener tube Dv2, first capacitor C1 and second capacitor C2;

The collector C of the first triode Q1 is connected to the positive power terminal 20 of the quasi-resonant control circuit 2, and the positive power terminal 20 of the quasi-resonant control circuit 2 is connected to the first resistor R1 and then connected to the first resistor R1. A base B of the triode Q1 and the cathode of the first regulator Dv1, the emitter E of the first triode Q1 is connected to one end of the first capacitor C1 and the second triode The collector C of Q2, the other end of the first capacitor C1, the anode of the first regulator Dv1, the anode of the second regulator Dv2, one end of the second resistor R2 and the first The collector C of the triode Q3 is connected to the negative power supply terminal 22 of the quasi-resonant control circuit 2;

The control signal input terminal 21 of the quasi-resonant control circuit 2 is connected to the second capacitor C2 and the third resistor R3 connected in series, and then connected to the cathode of the second regulator tube Dv2 and the other end of the second resistor R2. One end, the base B of the second transistor Q2 and the base B of the third transistor Q3, the emitter E of the second transistor Q2 and the third transistor Q3 The emitter E is connected to the control signal output terminal 23 of the quasi-resonant control circuit 2 .

Wherein, the first triode Q1 and the second triode Q2 are NPN bipolar transistors, and the third triode Q3 is a PNP bipolar transistor.

Referring to Fig. 3-1 and Fig. 4 again, in the secondary control quasi-resonant switching power converter provided by the embodiment of the present invention, when the switching controller KC turns on the first switching tube KQ1, the The primary winding T1_1 of the first transformer T1 stores energy, the induced voltage of the secondary winding T1_2 is positive at the end of the same name, the secondary rectifier Di is reverse-biased and cut off, and the first internal quasi-resonant control circuit 2 The primary switch rising edge detection circuit and delay circuit composed of the capacitor C1, the second resistor R2, the third resistor R3, and the second voltage regulator tube Dv2 are output through the first triode Q1 and the second triode Q2 Driving the second switch tube KQ2 to conduct, the resonant capacitor Cr resonates with the primary winding T2_1 of the second transformer T2, and the energy stored in the resonant capacitor Cr during the turn-off period of the first switch tube KQ1 is transferred to stored in the second transformer T2, when the delay time reaches the set value, the second switching tube KQ2 is turned off, the second diode D2 is turned on, and the energy in the second transformer T2 is transferred to The power supply output terminal (the power supply output positive terminal Vout+ and the power supply output negative terminal Vout-) is released, and the energy of the resonant capacitor Cr is released to the power supply output terminal during this process, and the terminal voltage of the resonant capacitor Cr will be reset to close to zero;

When the switch controller KC turns off the first switch tube KQ1, the induced voltage of the primary winding T1_1 of the first transformer T1 is positive, and the first switch tube KQ1 is forward-biased. through, its secondary winding T1_2 resonates with the resonant capacitor Cr, the terminal voltage of the resonant capacitor Cr resonantly rises from zero, due to the mutual inductance of the first transformer T1, the voltage input terminal of the first switching tube KQ1 The voltage between KQ1_PIN3 and the voltage output terminal KQ1_PIN1 will also rise in resonance. At this time, the current of the voltage input terminal KQ1_PIN3 of the first switching tube KQ1 has dropped to zero, so the first switching tube KQ1 is close to zero loss off. During the process of the terminal voltage of the resonant capacitor Cr resonantly rising from zero, the voltage at this time is lower than the output voltage, the reverse bias of the secondary rectifier Di is cut off, and the secondary winding T1_2 of the first transformer T1 has only A small current flows to the resonant capacitor Cr. When the terminal voltage of the resonant capacitor Cr rises above the output voltage, the secondary rectifier Di is naturally softly turned on, and the turn-on loss is small. The secondary winding of the first transformer T1 The current of T1_2 starts to switch to flow to the output, the rate of change of the current is relatively low, there is no voltage peak at both ends of the secondary rectifier Di, the stress is small, and the EMI characteristics are relatively good. The operating frequency of the entire switching power converter can be further increased, thereby The volume of the power supply can be reduced, and the cost can be reduced.

The above description is a preferred embodiment of the present invention, and it should be pointed out that for those skilled in the art, without departing from the principle of the present invention, some improvements and modifications can also be made, and these improvements and modifications are also considered Be the protection scope of the present invention.

Claims (9)

1. A switching power supply converter with secondary control quasi-resonance, which is provided with a power input positive terminal connected to a power supply, a power input negative terminal, a power output positive terminal connected to a load, and a power output negative terminal, and a switch The controller is characterized in that the negative terminal of the power input is connected to the negative terminal of the power supply of the switch controller and one end of the current detection resistor, and the other end of the current detection resistor is connected to the switch current detection of the switch controller. The measuring terminal and the voltage output terminal of the first switch tube, the control terminal of the first switch tube is connected to the switch control output terminal of the switch controller, and the voltage input terminal of the first switch tube is connected to the primary winding of the first transformer The same-named terminal of the primary winding of the first transformer is connected to the positive terminal of the power input; The opposite end of the secondary winding of the first transformer, the anode of the first diode, the positive end of the power supply of the quasi-resonant control circuit, the cathode of the second diode, and the positive end of the polarity capacitor are connected to the output of the power supply The positive terminal, the cathode of the first diode is connected to the resonant capacitor and then connected to the terminal with the same name of the secondary winding of the first transformer, the rectification input terminal of the secondary rectifier tube and the control signal input terminal of the quasi-resonant control circuit ; The negative terminal of the power supply of the quasi-resonant control circuit, the rectification output terminal of the secondary rectifier tube, the voltage output terminal of the second switch tube, the terminal with the same name of the secondary winding of the second transformer, and the negative terminal of the polar capacitor Connect the negative terminal of the output of the power supply, the control signal output terminal of the quasi-resonant control circuit is connected to the control terminal of the second switching tube; The voltage input end of the second switching tube is connected to the opposite end of the primary winding of the second transformer, the same end of the primary winding of the second transformer is connected to the cathode of the first diode, and the second The opposite end of the secondary winding of the transformer is connected to the anode of the second diode. 2. A kind of secondary control quasi-resonant switching power converter as claimed in claim 1, characterized in that: said quasi-resonant control circuit is provided with a first triode, a second triode, a third three Pole tube, first resistor, second resistor, third resistor, first voltage regulator tube, second voltage regulator tube, first capacitor and second capacitor; The collector of the first triode is connected to the positive power supply terminal of the quasi-resonant control circuit, and the positive power supply terminal of the quasi-resonant control circuit is connected to the base of the first triode after connecting the first resistor and the cathode of the first voltage regulator tube, the emitter of the first transistor is connected to one end of the first capacitor and the collector of the second transistor, the other end of the first capacitor, The anode of the first voltage regulator tube, the anode of the second voltage regulator tube, one end of the second resistor and the collector of the third triode are connected to the negative power supply terminal of the quasi-resonant control circuit; The control signal input terminal of the quasi-resonant control circuit is connected to the second capacitor and the third resistor connected in series, and then connected to the cathode of the second voltage regulator tube, the other end of the second resistor, the second The base of the triode and the base of the third triode, the emitter of the second triode and the emitter of the third triode are connected to the control signal output of the quasi-resonant control circuit end. 3. A kind of secondary control quasi-resonant switching power converter as claimed in claim 1, characterized in that: said first switch tube and second switch tube are N-channel MOS tubes or NPN bipolar transistors Or Insulated Gate Bipolar Transistor. 4. A secondary control quasi-resonant switching power converter as claimed in claim 3, characterized in that: when the first switching tube and the second switching tube are N-channel MOS tubes, the first The control terminal of the switch tube or the control terminal of the second switch tube is a gate, the voltage input terminal of the first switch tube or the voltage input terminal of the second switch tube is a drain, and the first switch tube The voltage output end of the second switch tube or the voltage output end of the second switching tube is the source. 5. A secondary control quasi-resonant switching power supply converter as claimed in claim 3, characterized in that: when the first switching tube and the second switching tube are NPN bipolar transistors, the second The control terminal of a switch tube or the control terminal of the second switch tube is a base, the voltage input terminal of the first switch tube or the voltage input terminal of the second switch tube is a collector, and the first switch The voltage output end of the tube or the voltage output end of the second switch tube is the emitter. 6. A secondary control quasi-resonant switching power supply converter as claimed in claim 3, characterized in that: when the first switching tube and the second switching tube are insulated gate bipolar transistors, the second The control terminal of a switch tube or the control terminal of the second switch tube is a grid, the voltage input terminal of the first switch tube or the voltage input terminal of the second switch tube is a collector, and the first switch The voltage output end of the tube or the voltage output end of the second switch tube is the emitter. 7. A secondary controlled quasi-resonant switching power supply converter according to claim 1, wherein the secondary rectifier is a rectifier diode or a field effect transistor rectifier module. 8. A kind of secondary control quasi-resonant switching power converter as claimed in claim 7, characterized in that: when the secondary rectifier is a rectifier diode, the rectification input of the secondary rectifier is a cathode , the rectification output terminal of the secondary rectifier tube is an anode. 9. A switching power converter with secondary control quasi-resonance as claimed in claim 2, characterized in that: said first triode and second triode are NPN bipolar transistors, said first triode The triode is a PNP bipolar transistor.

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