CN218733846U

CN218733846U - Double-tube flyback conversion circuit

Info

Publication number: CN218733846U
Application number: CN202222851485.8U
Authority: CN
Inventors: 罗云申; 朱钦柳
Original assignee: Guangdong Gausbao Electric Technology Co ltd
Current assignee: Guangdong Gausbao Electric Technology Co ltd
Priority date: 2022-10-28
Filing date: 2022-10-28
Publication date: 2023-03-24
Anticipated expiration: 2032-10-28

Abstract

The utility model discloses a double-barrelled flyback conversion circuit, including main circuit and switch tube drive circuit, switch tube drive circuit includes PWM control chip and forward drive circuit, and forward drive circuit includes driving transformer, drive switch tube, reset diode and two drive signal output pins, and driving transformer includes primary winding, two secondary windings and reset winding; the same name of the primary winding of the driving transformer is connected with the anode of the auxiliary power supply. The synonym end of the primary winding of the driving transformer is grounded through a driving switch tube, and the control end of the driving switch tube is connected with the control signal output end of the PWM control chip; the dotted terminal of the reset winding is grounded, the unlike terminal is connected with the anode of the reset diode, and the cathode of the reset diode is connected with the anode of the auxiliary power supply; the same-name ends of the two secondary windings of the driving transformer are respectively connected with corresponding driving signal output pins. The utility model discloses can solve the power tube and turn-off incomplete problem, the temperature rise of power tube is lower.

Description

Double-tube flyback conversion circuit

[ technical field ]

The utility model relates to a DC/DC converting circuit especially relates to a double-barrelled flyback converter circuit.

[ background Art ]

Various power electronic converter systems are not separated from integrated chips and power switches, so that a switching power supply is required to provide various grades of auxiliary working voltages of +5V, +/-15V and the like for a control circuit, a driving circuit, a conditioning and sampling circuit, a sensor and the like in the power electronic converter system, and the auxiliary switching power supply becomes an important component of the power electronic converter. The input of the auxiliary switch power supply is provided by the bus voltage of the power electronic converter, and in order to ensure the stable operation of the power electronic converter, the auxiliary switch power supply needs to work stably no matter how the bus voltage changes, namely, the auxiliary switch power supply can output stable voltage in a high voltage and wide input range, so that the normal operation of the power electronic converter is ensured.

Most high-voltage wide-input auxiliary switching power supplies adopt single-ended flyback converters, but the voltage borne by a switching tube of the single-ended flyback converter when the switching tube is switched off is equal to the sum of the maximum direct-current input voltage, secondary side refraction voltage and leakage inductance peak voltage, and the voltage stress of the switching tube is very large when the input voltage is high, so that the cost of the switching tube is greatly increased.

The utility model discloses a patent number is CN202021667629.9 'S utility model discloses a double-barrelled flyback converter circuit of wide input of high voltage, including primary circuit and secondary circuit, primary circuit comprises first switch tube S1, second switch tube S2, first reset diode D1, second reset diode D2, high frequency transformer T1' S primary winding Lm, and secondary circuit comprises high frequency transformer T1 secondary winding Ls, third reset diode D3 and filter capacitor C1. The utility model discloses a well double-barrelled flyback converter switch tube maximum voltage stress is far less than the voltage stress of single tube flyback converter switch tube, is applicable to the wide input occasion of high voltage.

In the conventional double-tube flyback circuit, after the MOS tube is turned off, the transformer can transfer the energy of the primary side to the secondary side. However, the energy in the leakage inductance cannot be transferred, so that an oscillation wave, namely a voltage peak waveform of a pin DS of the MOS tube, is formed in the transformer, and the peak voltage is formed by the distributed capacitance and the leakage inductance, so that the frequency is high.

The specific process is as follows: when the MOS tube is turned off, leakage inductance energy flows out to charge the junction capacitor to a high point, namely the peak of the voltage peak of the DS pin of the MOS tube. When the leakage inductance phase is reversed after reaching the highest point, the junction capacitor reversely discharges, and at the moment, the current flows out, namely the generation of a negative current part on the MOS tube. Therefore, when the current of the secondary side of the transformer is reduced to zero, leakage inductance and junction capacitance generate oscillation, the MOS tube is not completely turned off, and the power tube has large loss and high temperature.

[ summary of the invention ]

The to-be-solved technical problem of the utility model is to provide a double-barrelled flyback converter circuit that power tube turn-offs thoroughly, the temperature rise is lower.

In order to solve the technical problem, the utility model adopts the technical scheme that a double-tube flyback conversion circuit comprises a main circuit and a switch tube driving circuit, wherein the switch tube driving circuit comprises a PWM control chip and a forward driving circuit, the forward driving circuit comprises a driving transformer, a driving switch tube, a reset diode and two driving signal output pins, and the driving transformer comprises a primary winding, two secondary windings and a reset winding; the homonymous end of the primary winding of the driving transformer is connected with the anode of the auxiliary power supply, the synonym end of the primary winding of the driving transformer is grounded through the driving switch tube, and the control end of the driving switch tube is connected with the control signal output end of the PWM control chip; the homonymous end of the reset winding is grounded, the synonym end of the reset winding is connected with the anode of the reset diode, and the cathode of the reset diode is connected with the anode of the auxiliary power supply; the same-name ends of the two secondary windings of the driving transformer are respectively connected with corresponding driving signal output pins.

The double-tube flyback conversion circuit comprises a main circuit, a secondary circuit and a primary circuit, wherein the main circuit comprises a direct current input end, a direct current output end, a main transformer, the primary circuit and the secondary circuit; the secondary side circuit comprises a third diode and an output filter capacitor; the drain electrode of the first MOS tube is connected with the anode of the direct-current input end, the source electrode of the first MOS tube is connected with the synonym end of the primary winding of the main transformer, the synonym end of the primary winding of the main transformer is connected with the drain electrode of the second MOS tube, and the source electrode of the second MOS tube is connected with the cathode of the direct-current input end; the anode of the first diode is connected with the drain electrode of the second MOS tube, and the cathode of the first diode is connected with the anode of the direct current input end; the cathode of the second diode is connected with the source electrode of the second MOS tube, and the anode of the second diode is connected with the cathode of the direct current input end; the anode of the third diode is connected with the dotted terminal of the secondary winding of the main transformer, and the cathode of the third diode is connected with the anode of the direct current output end; the synonym end of the secondary winding of the main transformer is connected with the negative electrode of the direct current output end, and the output filter capacitor is connected between the positive electrode and the negative electrode of the direct current output end.

The double-tube flyback conversion circuit comprises an output voltage sampling circuit, wherein the output voltage sampling circuit comprises a resistance voltage division circuit, a voltage stabilization reference source and an optical coupler; the resistance voltage-dividing circuit is connected between the positive pole and the negative pole of the direct current output end, and the voltage signal output end of the resistance voltage-dividing circuit is connected with the reference pole of the voltage-stabilizing reference source; the anode of the voltage-stabilizing reference source is connected with the cathode of the direct current output end, the cathode of the voltage-stabilizing reference source is connected with the cathode of the optocoupler light-emitting diode, and the anode of the optocoupler light-emitting diode is connected with the anode of the direct current output end through a first current-limiting resistor; the collector of the optocoupler phototriode is connected with the input pin of the output voltage sampling signal of the PWM control chip, and the emitter of the optocoupler phototriode is connected with the negative electrode of the direct current output end.

In the double-tube flyback conversion circuit, the main circuit comprises a peak voltage absorption circuit, and the peak voltage absorption circuit comprises an absorption capacitor, an absorption resistor and an absorption diode; the anode of the absorption diode is connected with the drain electrode of the second MOS tube, the cathode of the absorption diode is connected with the source electrode of the first MOS tube through the absorption resistor, and the absorption capacitor is connected with the absorption resistor in parallel.

The double-tube flyback conversion circuit comprises an overcurrent protection circuit, wherein the overcurrent protection circuit comprises a sampling resistor, a second current-limiting resistor and a second filter capacitor; the source electrode of the second MOS tube is connected with the first end of the sampling resistor, and the second end of the sampling resistor is connected with the negative electrode of the direct current input end; the first end of the sampling resistor is connected with a current sampling signal input pin of the PWM control chip through a second current limiting resistor; the second filter capacitor is connected between the current sampling signal input pin of the PWM control chip and the negative electrode of the direct current input end.

In the double-tube flyback conversion circuit, the driving signal output pin of the switching tube driving circuit is connected with the grid electrode of the MOS tube corresponding to the main circuit through the corresponding grid electrode resistor.

The switch tube driving circuit of the double-tube flyback conversion circuit of the utility model adopts the forward driving circuit, which can solve the problem that the power tube in the prior art is not completely turned off, and the temperature rise of the power tube is lower; the excess energy can also be transferred back to the auxiliary power supply through the magnetic reset winding of the forward drive circuit.

[ description of the drawings ]

The present invention will be described in further detail with reference to the accompanying drawings and specific embodiments.

Fig. 1 is a circuit diagram of a main circuit of a double-transistor flyback converter circuit according to an embodiment of the present invention.

Fig. 2 is a circuit diagram of a forward driving circuit according to an embodiment of the present invention.

Fig. 3 is a circuit diagram of an output voltage sampling circuit according to an embodiment of the present invention.

Fig. 4 is a circuit diagram of a primary side circuit according to an embodiment of the present invention.

[ detailed description of the invention ]

The embodiment of the utility model provides a double-barrelled flyback conversion circuit's structure is as shown in fig. 1 to fig. 4, including main circuit and switch tube drive circuit.

The main circuit comprises a direct current input end Vin, a direct current output end VOUT, a main transformer T, a primary circuit and a secondary circuit. The primary side circuit comprises a first MOS tube Q1, a second MOS tube Q2, a first diode D1 and a second diode D2. The secondary side circuit comprises a third diode D3 and an output filter capacitor C1. The drain electrode of the first MOS tube Q1 is connected with the anode Vin + of the direct current input end Vin, the source electrode of the first MOS tube Q1 is connected with the synonym end of the primary winding Lp of the main transformer T, the synonym end of the primary winding Lp of the main transformer T is connected with the drain electrode of the second MOS tube Q2, and the source electrode of the second MOS tube Q2 is connected with the cathode Vin-of the direct current input end Vin. The anode of the first diode D1 is connected to the drain of the second MOS transistor Q2, and the cathode is connected to the positive electrode Vin + of the dc input terminal Vin. The cathode of the second diode D2 is connected to the source of the second MOS transistor Q2, and the anode is connected to the cathode Vin-of the dc input terminal Vin. The anode of the third diode D3 is connected to the dotted terminal of the secondary winding Ls of the main transformer T, and the cathode is connected to the positive terminal VOUT + of the dc output terminal VOUT. The synonym end of a secondary winding Ls of the main transformer T is connected with the negative pole VOUT < - > of the direct current output end VOUT, and the output filter capacitor C1 is connected between the positive pole VOUT + and the negative pole VOUT < - > of the direct current output end. The negative electrode Vin-of the DC input end Vin is connected with the original side ground GND, and the negative electrode VOUT-of the DC output end is connected with the secondary side ground AGND.

The switching tube driving circuit comprises a PWM control chip FAN6755UWMY and a forward driving circuit, wherein the forward driving circuit comprises a driving transformer T15, a driving MOS tube Q5, a reset diode D4 and two driving signal output pins. As shown in fig. 4, the first driving signal output pin is connected to the gate of the first MOS transistor Q1 of the main circuit through a gate resistor R3, and the second driving signal output pin is connected to the gate of the second MOS transistor Q2 of the main circuit through a gate resistor R4. The driving transformer T15 comprises a primary winding T15-A, two secondary windings T15-B, T15-C and a reset winding T15-D. The same name of a primary winding T15-A of the driving transformer T15 is connected with an anode VCC of the auxiliary power supply. The synonym end of the primary winding T15-A of the driving transformer T15 is grounded through the driving MOS tube Q5, and the grid electrode of the driving MOS tube Q5 is connected with a control signal output pin GATE pin of the PWM control chip. The homonymy end of the reset winding T15-D is connected with the primary ground GND, the synonym end is connected with the anode of the reset diode D4, and the cathode of the reset diode D4 is connected with the anode VCC of the auxiliary power supply. The same-name ends of two secondary windings T15-B and T15-C of the driving transformer T15 are respectively connected with corresponding driving signal output pins.

The output voltage sampling circuit comprises a resistance voltage division circuit, a voltage stabilization reference source U23 (IC 431) and an optical coupler OT12. The resistance voltage division circuit is formed by connecting a resistor R431 and a resistor R433 in series, the resistance voltage division circuit is connected between the positive pole and the negative pole of the direct current output end VOUT, and the voltage signal output end (the connection point of the resistor R431 and the resistor R433) of the resistance voltage division circuit is connected with the reference pole of the voltage-stabilizing reference source U23. The anode of the voltage-stabilizing reference source U23 is connected with the cathode VOUT- (secondary side AGND) of the direct-current output end VOUT, the cathode of the voltage-stabilizing reference source U23 is connected with the cathode of the OT12 light-emitting diode OT12-B, and the anode of the OT12 light-emitting diode OT12-B is connected with the anode VOUT + of the direct-current output end VOUT through the first current-limiting resistor R432. The collector of an optocoupler OT12 phototriode OT12-A is connected with an output voltage sampling signal input pin FB pin of the PWM control chip, and the emitter of the optocoupler phototriode OT12-A is connected with the negative electrode Vin- (primary side ground GND) of Vin at the direct current output end.

The peak voltage absorption circuit comprises an absorption capacitor C5, an absorption resistor R6 and an absorption diode D5. The anode of the absorption diode D5 is connected to the drain of the second MOS transistor Q2, the cathode is connected to the source of the first MOS transistor Q1 through the absorption resistor R6, and the absorption capacitor C5 is connected in parallel to the absorption resistor R6.

The overcurrent protection circuit comprises a sampling resistor R2, a second current limiting resistor R5 and a second filter capacitor C2. The source electrode of the second MOS tube Q2 is connected with the first end of the sampling resistor R2, and the second end of the sampling resistor R2 is connected with the cathode Vin- (primary ground GND) of the direct-current input end Vin. And a first end of the sampling resistor R2 is connected with a current sampling signal input pin SENSE of the PWM control chip through a second current limiting resistor R5. The second filter capacitor C2 is connected between a current sampling signal input pin SENSE of the PWM control chip and a negative electrode Vin- (primary side ground GND) of the dc input terminal Vin.

The utility model discloses the working process of just swashing drive circuit of above embodiment is shown in fig. 2, and V0 is the driving voltage that PWM control chip FAN6755UWMY sent, and T15 is that the turn ratio is 1:1, VCC is the operating voltage of the PWM control chip, and is supplied by the auxiliary power supply, and V1 and V2 are two driving voltages output by the forward driving circuit, respectively, and respectively drive the first MOS transistor Q1 and the second MOS transistor Q2. When the driving MOS tube Q5 is conducted, the transformer windings T15-B, T15-C and T15-A are all voltages which are positive up and negative down, the primary side transmits energy to the secondary side, the reset winding T15-D is voltage which is positive up and negative down, and the diode D1 is not conducted. When the driving MOS tube Q5 is switched off, the reset winding T15-D induces the voltage of the upper positive and the lower negative, the diode D1 is switched on, the magnetization energy is fed back to the VCC power supply, and the magnetic core completes the reset.

As shown in fig. 1, when the first MOS transistor Q1 and the second MOS transistor Q2 are turned on, the current flowing through the primary winding Lp of the main transformer T gradually increases, and the first diode D1 and the second diode D2 are turned off. The primary winding Lp induces a voltage with positive upper and negative lower, the secondary winding Ls induces a voltage with positive lower and negative upper, and the diode D3 is cut off. The negative side has no current, and the load R1 is powered by the output filter capacitor C1. When the first MOS transistor Q1 and the second MOS transistor Q2 are turned off, the current flowing through the primary winding Lp of the main transformer T is reduced, the voltage at two ends of the primary winding Lp is reversed, the first diode D1 and the second diode D2 are turned on, the induced potential of the primary winding caused by leakage inductance is clamped, the induced potential is clamped at the input voltage Vin, the redundant energy is fed back to the input power supply, and the reverse voltages borne by the first MOS transistor Q1 and the second MOS transistor Q2 are both Vin. The voltage of the secondary winding Ls is positive, negative and positive, the diode D3 is conducted, the secondary current is gradually increased, and the secondary winding Ls charges the output filter capacitor C1 of the output capacitor and provides energy for the load R1.

The voltage of a direct-current output end VOUT of the double-tube flyback conversion circuit is divided by the resistor voltage dividing circuit and then is transmitted to a reference electrode of the voltage stabilizing reference source U23, when the voltage V =2.5V at two ends of the resistor R431, the voltage stabilizing reference source U23 is conducted, and the optical coupler OT12 is conducted. The collected voltage signal is fed back to the PWM control chip through the optical coupler OT12. After the pulse width of the PWM control chip is modulated, the PWM control chip drives two flyback MOS tubes through a forward driving circuit to control a power conversion circuit of a main circuit.

When the first MOS transistor Q1 and the second MOS transistor Q2 are turned off, a voltage spike and a current spike are easily generated in the primary winding of the transformer T. The absorption circuit consisting of the absorption capacitor C5, the absorption resistor R6 and the absorption diode D5 absorbs the peak voltage. The buffer composed of R2, R5 and C2 limits the current, the current peak value signal passing through the resistance sampling resistor R2 can participate in the duty ratio control of the current working cycle, and the current is limited by the current working cycle. When the voltage output by the resistor R5 reaches 0.83V, the PWM control chip FAN6755UWMY stops working, and the first MOS tube Q1 and the second MOS tube Q2 are switched off, so that the current limiting protection effect is achieved. The first diode D1 and the second diode D2 are used as clamping diodes, and voltage spikes borne by the switching tube are clamped at the input power supply voltage in the flyback process. The grid resistor R3 and the grid resistor R4 and junction capacitors CGS and CGD in the first MOS tube Q1 and the second MOS tube Q2 form an RC network together, and the charging and discharging of the capacitors directly influence the switching speed of the switching tube. The resistances of the resistor R3 and the resistor R4 are too small, so that oscillation is easily caused, and electromagnetic interference is also large; the resistance values of the resistor R3 and the resistor R4 are too large, which reduces the switching response speed of the switching tubes Q1 and Q2.

The utility model discloses the switching tube drive circuit of the double-tube flyback conversion circuit of the above embodiment adopts forward drive circuit, can solve the problem that the power tube in the prior art is not turned off completely, and the power tube temperature is too high because the power tube is not turned off completely; the excess energy can also be transferred back to the auxiliary power supply by positively exciting the magnetic reset winding of the drive circuit.

When the double-tube flyback conversion circuit adopts the PWM control chip to control the MOS tube, the switching frequency is higher at the moment, and the MOS tube needs to be switched rapidly. The turn-off speed of a MOSFET is theoretically dependent on the gate drive circuit. When the gate drive current is high, the turn-off circuit can discharge the input capacitor quickly, so that the switching time is shortened, and the switching loss is reduced. The discharge current can be increased by typically using a MOSFET driver with a lower output impedance and/or a negative off-voltage.

In the forward driving circuit, the driving capability of a GATE pin of a PWM control chip is increased by using transformer windings T15-A, T15-B and T15-B, so that two switch MOS (metal oxide semiconductor) tubes are driven to be switched on and off simultaneously, when a driving voltage V0 sent by the PWM control chip is a low level and Q5 is switched off, a reset winding T15-D induces a voltage with positive and negative polarities, a diode D4 is switched on, magnetizing energy is fed back to a VCC (voltage converter) power supply, and the magnetic core finishes resetting; the reverse voltage of T15-A, T15-B and T15-B can accelerate the energy consumption of the MOS transistor GS pin junction capacitance, thereby accelerating the turn-off of the MOS transistor.

Claims

1. A double-tube flyback conversion circuit comprises a main circuit and a switching tube driving circuit, wherein the switching tube driving circuit comprises a PWM control chip and is characterized in that the switching tube driving circuit comprises a forward driving circuit, the forward driving circuit comprises a driving transformer, a driving switching tube, a reset diode and two driving signal output pins, and the driving transformer comprises a primary winding, two secondary windings and a reset winding; the homonymous end of the primary winding of the driving transformer is connected with the anode of the auxiliary power supply, the synonym end of the primary winding of the driving transformer is grounded through the driving switch tube, and the control end of the driving switch tube is connected with the control signal output end of the PWM control chip; the homonymous end of the reset winding is grounded, the synonym end of the reset winding is connected with the anode of the reset diode, and the cathode of the reset diode is connected with the anode of the auxiliary power supply; the same-name ends of the two secondary windings of the driving transformer are respectively connected with corresponding driving signal output pins.

2. The double-tube flyback conversion circuit of claim 1, wherein the main circuit comprises a dc input terminal, a dc output terminal, a main transformer, a primary circuit and a secondary circuit, the primary circuit comprises two MOS transistors, a first diode and a second diode; the secondary side circuit comprises a third diode and an output filter capacitor; the drain electrode of the first MOS tube is connected with the anode of the direct-current input end, the source electrode of the first MOS tube is connected with the synonym end of the primary winding of the main transformer, the synonym end of the primary winding of the main transformer is connected with the drain electrode of the second MOS tube, and the source electrode of the second MOS tube is connected with the cathode of the direct-current input end; the anode of the first diode is connected with the drain electrode of the second MOS tube, and the cathode of the first diode is connected with the anode of the direct current input end; the cathode of the second diode is connected with the source electrode of the second MOS tube, and the anode of the second diode is connected with the cathode of the direct current input end; the anode of the third diode is connected with the dotted terminal of the secondary winding of the main transformer, and the cathode of the third diode is connected with the anode of the direct current output terminal; the synonym end of the secondary winding of the main transformer is connected with the negative electrode of the direct current output end, and the output filter capacitor is connected between the positive electrode and the negative electrode of the direct current output end.

3. The double-tube flyback conversion circuit of claim 2, comprising an output voltage sampling circuit, wherein the output voltage sampling circuit comprises a resistor voltage dividing circuit, a voltage-stabilizing reference source and an optical coupler; the resistance voltage-dividing circuit is connected between the positive pole and the negative pole of the direct current output end, and the voltage signal output end of the resistance voltage-dividing circuit is connected with the reference pole of the voltage-stabilizing reference source; the anode of the voltage-stabilizing reference source is connected with the cathode of the direct-current output end, the cathode of the voltage-stabilizing reference source is connected with the cathode of the optocoupler light-emitting diode, and the anode of the optocoupler light-emitting diode is connected with the anode of the direct-current output end through a first current-limiting resistor; and the collector of the optocoupler phototriode is connected with an output voltage sampling signal input pin of the PWM control chip.

4. The double-tube flyback conversion circuit of claim 2, wherein the main circuit comprises a peak voltage absorption circuit, the peak voltage absorption circuit comprising an absorption capacitor, an absorption resistor and an absorption diode; the anode of the absorption diode is connected with the drain electrode of the second MOS tube, the cathode of the absorption diode is connected with the source electrode of the first MOS tube through the absorption resistor, and the absorption capacitor is connected with the absorption resistor in parallel.

5. The double-tube flyback conversion circuit of claim 1, comprising an overcurrent protection circuit, wherein the overcurrent protection circuit comprises a sampling resistor, a second current limiting resistor and a second filter capacitor; the source electrode of the second MOS tube is connected with the first end of the sampling resistor, and the second end of the sampling resistor is connected with the negative electrode of the direct current input end; the first end of the sampling resistor is connected with a current sampling signal input pin of the PWM control chip through a second current limiting resistor; the second filter capacitor is connected between a current sampling signal input pin of the PWM control chip and the negative electrode of the direct current input end.

6. The double-transistor flyback converter circuit of claim 2, wherein a driving signal output pin of the switching transistor driving circuit is connected to a gate of a corresponding MOS transistor of the main circuit through a corresponding gate resistor.