WO2020114248A1

WO2020114248A1 - Self drive circuit for two-transistor forward synchronous rectifier circuit

Info

Publication number: WO2020114248A1
Application number: PCT/CN2019/119577
Authority: WO
Inventors: 杨志; 潘成章; 程志勇
Original assignee: 广州金升阳科技有限公司
Priority date: 2018-12-07
Filing date: 2019-11-20
Publication date: 2020-06-11
Also published as: CN109347311A; CN109347311B

Abstract

Disclosed is a self drive circuit for a two-transistor forward synchronous rectifier circuit. The two-transistor forward synchronous rectifier circuit comprises a transformer, a two-transistor forward network at the primary side of the transformer, and a synchronous rectifier conversion network at the secondary side of the transformer. The transformer comprises a first primary winding, a first secondary winding, and a second secondary winding. The self drive circuit for the two-transistor forward synchronous rectifier circuit drives a freewheeling transistor in the synchronous rectifier conversion network. A rectifier transistor in the synchronous rectifier conversion network is driven by controlling an operation state of a first P-type MOS transistor in the self-drive circuit. When a synchronous rectifier transistor and a synchronous freewheeling transistor at the secondary side of the transformer are turned on at the same time, the freewheeling transistor is capable of obtaining a drive voltage and providing a conduction path to an output inductor at a next stage, thereby improving the efficiency of a converter, realizing adjustability of the drive voltage of the freewheeling transistor, and achieving flexible and reliable control.

Description

Self-driving driving circuit of double-tube forward synchronous rectifier circuit

Technical field

The invention relates to an AC-DC converter, in particular to a self-driving drive circuit of a converter with a double-tube forward excitation, a single-tube forward excitation, a full-bridge and other transformer winding voltages having a zero period.

Background technique

With the continuous development of society, the technology of switching converters is also developing toward low cost, miniaturization, high power density and high reliability. Under this trend, synchronous rectification technology is particularly important. The power MOSFET with extremely low on-resistance replaces the rectifier diode to reduce the rectification loss, it can greatly improve the efficiency of the converter and there is no dead zone voltage caused by the Schottky barrier voltage.

In the isolating switch converter, synchronous rectification has two methods of self-excited driving and external driving. External driving generally has an additional driver chip to detect the voltage across the synchronous rectifier and control it. This driving method not only increases Cost, and there is a risk of mistakenly opening and closing due to control reasons, reducing the reliability of the power supply. The self-excitation driving method generally uses the voltage of the secondary winding of the transformer to directly or indirectly drive the synchronous rectifier tube. This driving method has a lower cost, but in some converters, the synchronous rectifier tube and the synchronous freewheel tube of the secondary side of the transformer are simultaneously conducted. To provide a path for the output inductor current and the transformer excitation current. At this time, the secondary winding of the transformer is equivalent to a short circuit. The drive winding voltage is zero, and the drive voltage cannot be provided for the freewheeling tube. At this time, the output inductor current will pass through the freewheeling tube body diode. Circulation greatly reduces the efficiency of the converter.

Summary of the invention

In view of this, the present invention is to solve the above-mentioned problems in the self-excited synchronous rectification technology, and to provide a self-driving drive circuit. When the voltage of the transformer winding is zero, the drive signal is continuously provided to the freewheeling tube to improve the efficiency of the converter.

The purpose of the present invention is achieved as follows:

A self-driving driving circuit of a double-tube forward synchronous rectification circuit. The double-tube forward synchronous rectification circuit includes a transformer, a double-tube forward network on the primary side of the transformer, and a synchronous rectification transformation network on the secondary side of the transformer; the transformer includes the first A primary winding, a first secondary winding, and a second secondary winding; the self-driving drive circuit of the dual-tube forward synchronous rectification circuit is used to drive a freewheel in the synchronous rectification conversion network;

The self-driving drive circuit includes a second secondary winding of the transformer, which is used to provide an input signal for the self-driving drive circuit; the first and second resistors connected in series across the two secondary windings are used To sample and divide the input signal to the next stage to provide a driving signal; the first P-type MOS tube with the first midpoint of the series connection of the first resistor and the second resistor as the gate input, the first P-type MOS tube turns off or conducts in response to the driving signal It is used to drive the discharge or charge of the freewheeling tube in the synchronous rectification and conversion network; one end of which is connected to the third resistance of the connection end of the first resistor and the different end of the second secondary winding, and the third resistance is used in the synchronous rectification and conversion network The drive resistance of the freewheel tube is used to charge and discharge the freewheel tube in the synchronous rectification conversion network; the first capacitor connected between the other end of the third resistor and the grid of the freewheel tube in the synchronous rectification conversion network; first The drain of the P-type MOS tube is connected to the anode of the first diode, the source of the first P-type MOS tube is connected to the cathode of the first diode; the different-named end of the second secondary winding is connected to the first resistor end and the third resistor At one end, the same-named end of the second secondary winding is connected to the end of the second resistor and the source of the first P-type MOS tube, and the drain of the first P-type MOS tube is connected to the source of the freewheel in the synchronous rectification conversion network.

Preferably, the self-driving driving circuit further includes a second diode, a third diode, and a fifth resistor, the anode of the second diode is connected to the gate of the first P-type MOS transistor, and the second diode The cathode of the tube is connected to the cathode of the third diode and the different end of the second secondary winding, the anode of the third diode is connected to the end of the fifth resistor, and the other end of the fifth resistor is connected to the connection of the third resistor and the first capacitor end.

Preferably, the self-driving driving circuit further includes a first voltage stabilizing tube connected in parallel across the first capacitor. The anode of the first voltage stabilizing tube is connected to the first capacitor and the grid of the freewheeling tube in the synchronous rectification conversion network. At one end, the cathode of the first regulator tube is connected to the connection end of the first capacitor, the third resistor, and the fifth resistor.

Preferably, the first capacitor is a driving voltage adjustment capacitor of the freewheel in the synchronous rectification conversion network.

Preferably, the first capacitor can be used as an adjustment capacitor for the driving voltage of the freewheeling tube gate source in the synchronous rectification conversion network. Adjusted bias voltage.

Preferably, after the circuit works normally, the following working state is followed:

(1) In the excitation stage of the transformer, the output of the second secondary winding of the transformer is negative, and the first P-type MOS tube is turned on. At this time, the source voltage applied to the gate of the freewheel tube is negative, and the freewheel tube is turned off;

(2) During the demagnetization stage of the transformer, the output of the second secondary winding of the transformer is positive, the first P-type MOS tube is turned off, and the second secondary winding provides a positive drive voltage to the freewheeling tube in the synchronous rectification conversion network through a third resistor. Turn on the freewheeling tube;

(3) After the demagnetization of the transformer is completed, the rectifier tube and the freewheel tube in the synchronous rectification transformation network on the secondary side of the transformer are simultaneously turned on, the voltage on the first primary winding of the transformer is zero, and the voltage on the second secondary winding of the transformer is also zero. It is the zero-voltage driving state. At this time, the first P-type MOS tube is turned off, the source voltage of the freewheel tube gate is slowly discharged through the grounding resistance in the synchronous rectification conversion network, and the freewheel tube continues to be turned on;

(4) During the re-excitation phase of the transformer, the output of the second secondary winding of the transformer is negative, the first P-type MOS tube is turned on, and the source voltage of the freewheeling tube gate passes through the third resistor, the second secondary winding of the transformer and the first P Type MOS discharges quickly, and the freewheel is cut off.

The working idea of the present invention is to drive the freewheeling tube in the synchronous rectification conversion network by controlling the working state of the first P-type MOS tube. When the synchronous rectification tube and the synchronous freewheeling tube on the secondary side of the transformer are simultaneously conducting, the freewheeling The tube can obtain the driving voltage and provide a path for the output inductor of the subsequent stage, which can improve the efficiency of the converter. Brief description of the working principle: When the dual-tube forward converter works normally and the primary side switch in the dual-tube forward network is turned off, during the demagnetization phase of the transformer, the induced voltage on the secondary winding of the secondary side of the transformer is positive and negative. A P-type MOS is cut off, and the voltage of the second secondary winding of the transformer is added to the two ends of the grid source of the secondary freewheeling tube through the third resistor and the first diode to provide the driving voltage for the freewheeling tube; when the demagnetization of the transformer ends, The secondary rectifier and freewheel are turned on at the same time, and the original secondary winding voltage of the transformer is zero. At this time, the first P-type MOS is still cut off, and the voltage across the source of the freewheel is still there without the discharge circuit. The freewheeling tube is turned on; until the primary side switching tube of the double-tube forward network is turned on, the induced voltage of the second secondary winding is negative and positive, the first P-type MOS is turned on, and the source voltage of the freewheeling tube gate passes the third The resistance, the second secondary winding, and the first P-type MOS discharge, turning off the freewheeling tube.

It can be seen from the above working principle that the present invention has the following beneficial effects:

(1) When the voltage of the transformer winding is zero, the self-driving drive circuit still provides the drive signal for the freewheel in the synchronous rectification conversion network; when the second auxiliary winding voltage is zero, the freewheel is cut off by the first P-type MOS tube The tube driving voltage has no discharge loop and the freewheeling tube continues to conduct, greatly improving the efficiency of the converter.

(2) Because the circuit topology is simple and obvious, it is easy to implement and practical.

(3) No special synchronous rectification control chip is needed, which saves costs, and at the same time reduces the PCB size to a certain extent, achieving miniaturization and high power density.

(4) The control method of the entire synchronous rectification is very simple, and it adopts self-driving, which greatly improves the reliability of the power supply;

(5) The first capacitor is connected in series between the self-driving drive circuit and the freewheeling tube. The freewheeling tube charges and discharges the first capacitor, generates a bias voltage in the first capacitor, and realizes the driving voltage to the gate source of the freewheeling tube. Adjustable, making the control more flexible and reliable.

BRIEF DESCRIPTION

1 is a circuit diagram of the first embodiment of the present invention;

2 is a circuit diagram of a second embodiment of the invention;

3 is a circuit diagram of a third embodiment of the invention.

detailed description

First embodiment

FIG. 1 shows a circuit schematic diagram of the first embodiment, following the connection relationship of the initial technical solution described above, a self-driving drive circuit of a dual-tube forward synchronous rectifier circuit. The dual-tube forward synchronous rectifier circuit includes a transformer, a The double-tube forward network of the transformer primary side and the synchronous rectification transformation network on the secondary side of the transformer; the transformer includes a first primary winding Np1, a first secondary winding Ns1 and a second secondary winding Ns2, and the synchronous rectification transformation of the secondary side of the transformer The network includes a first secondary winding Ns1, a freewheel Q1 whose drain is connected to the same-named end of the first secondary winding Ns1, an inductor L1 connected at one end to the drain of the freewheel Q1, and the other end of the inductor L1 is a synchronous rectification conversion network The output, the drain is connected to the secondary side rectifier Q2 of the different name of the first secondary winding Ns1, the gate of the freewheel Q1 is connected to the source of the secondary rectifier Q2, and also includes the connection to the freewheel Q1 Ground resistance R4 between the gate and output ground;

The self-driving drive circuit of the dual-tube forward synchronous rectifier circuit includes a second winding Ns2 on the secondary side of the transformer, a first resistor R1 and a second resistor R2 connected across the second secondary winding Ns2, and the first resistor R1 One end is connected to the different-named end of the second secondary winding Ns2, one end is connected to the third resistor R3 connected to the first-named resistor R1 and the second-named end of the second secondary winding Ns2, and the first resistor R1 is connected to the second resistor R2 The midpoint of the series is the first P-type MOS transistor Q3 input to the gate. The source of the first P-type MOS transistor Q3 is connected to the same-named end of the second secondary winding Ns2 and the second resistor, and is connected to the first P-type MOS transistor The drain-source of Q3 is connected in parallel with the first diode D1; the anode of the first diode D1 is connected to the drain of the first P-type MOS transistor Q3, and the cathode of the first diode D1 is connected to the first P-type MOS transistor Q3 For the source, the drain of the first P-type MOS tube is also connected to the gate of the freewheeling tube Q1.

In the circuit, the second secondary winding Ns2 is a self-driving winding, which provides an input signal for the self-driving driving circuit. The input signal is divided into a series voltage by a first resistor R1 and a second resistor R2 to provide a driving signal for the first P-type MOS. A P-type MOS performs state control according to this drive signal. When the output of the second secondary winding is positive or zero, the first P-type MOS tube is turned off. When the output of the second secondary winding is negative, the first P-type MOS tube Turn on; the third resistance is the drive resistance of the freewheeling tube Q1.

The specific working principle of the circuit is: after the power supply is normally powered on, the dual-tube forward converter works normally and is in a continuous working state. Within one switching cycle, when the primary MOS tube in the dual-tube forward network is turned off, the transformer At the beginning of the demagnetization phase, the voltage direction of the first primary winding Np1 of the transformer is downward positive and negative, and the voltage direction induced by the second secondary winding Ns2 of the transformer is upward positive and negative. The induced voltage passes through the first resistor R1 and the first After the voltage divider of the second resistor R2, the gate-source voltage of the first P-type MOS transistor Q3 is positive, so that the first P-type MOS transistor Q3 is turned off. At this time, the voltage of the second secondary winding Ns2 of the transformer passes through the third resistor R3 The loop formed by the first capacitor C1, the gate and source of the freewheeling tube Q1, and the diode D1 provides a driving voltage to the freewheeling tube Q1, turns on the freewheeling tube Q1, and provides a freewheeling circuit for the output inductor L1.

When the demagnetization of the transformer ends, the secondary rectifier Q2 conducts and provides a loop for the primary excitation current. At this time, the secondary freewheel Q1 and the rectifier Q2 conduct simultaneously, the transformer secondary voltage is zero, and the first primary The voltage of the winding Np1 is also zero, and the induced voltage of the second secondary winding Ns2 is also zero. At this time, the gate-source voltage of the first P-type MOS transistor Q3 is zero, and the first P-type MOS transistor Q3 is in the off state, continued The gate-source voltage of the flow tube Q1 cannot be quickly discharged through the third resistor R3 and the second secondary winding Ns2, and can only be discharged slowly through the grounding resistor R4. Therefore, the freewheeling tube Q1 can continue to conduct and continue to provide continuous output inductor L1. Current loop.

When the primary switch in the double-tube forward network is re-opened, the voltage direction of the first primary winding Np1 of the transformer is upward positive and negative, and the induced voltage direction of the second secondary winding Ns2 of the transformer is downward positive and negative. After the resistor R1 and the second resistor R2 are divided, the gate-source voltage of the first P-type MOS transistor Q3 is negative, and the first P-type MOS transistor Q3 is turned on. At this time, the driving voltage of the freewheeling tube Q1 passes through the first capacitor C1, the first The circuit formed by the three resistors R3, the second and second winding Ns2 at the different end and the same end, the source and drain of the first P-type MOS tube Q3 is quickly discharged, so that the freewheeling tube Q1 is quickly turned off, which does not affect the double tube Normal work is working.

It should be noted that, due to the presence of the first capacitor C1 in the circuit, the driving voltage on the freewheel tube Q1 will charge and discharge C1, and a forward bias voltage will be formed on the first capacitor C1, and then the freewheel tube There is a negative bias on the gate-to-source voltage, which reduces the gate-to-source voltage of the freewheeling tube, so that the driving voltage is adjustable. At the same time, when the primary winding voltage or the secondary driving winding voltage of the transformer produces an oscillation spike, due to the presence of the first capacitor C1, this oscillation peak will be absorbed, thereby preventing the malfunction of the freewheeling tube from affecting the normal operation of the double-tube forward excitation.

The invention can provide the drive signal for the freewheeling tube under the condition that the rectifier tube and the freewheeling tube are simultaneously conducted in the secondary side synchronous rectification conversion network, so that the freewheeling tube can work to provide an output loop for the output inductor of the subsequent stage, which greatly improves The efficiency of the inverter product.

Second embodiment

FIG. 2 shows a circuit schematic diagram of the second embodiment. Unlike the first embodiment, on the basis of FIG. 1 of the first embodiment, the gate of the first P-type MOS transistor and the second secondary side of the transformer A diode D2 is connected between the different ends of the winding Ns2, which can accelerate the discharge of the gate-source voltage of the first P-type MOS transistor Q3, so that the first P-type MOS transistor Q3 is quickly turned on, so that the freewheeling tube Q1 is quickly turned off . At the same time, a series circuit composed of a resistor R5 and a diode D3 is connected in parallel at both ends of the third resistor R3. The cathode of the diode D3 is connected between the different end of the second secondary winding Ns2 and the resistor R3. The anode of the diode D3 is connected to the resistor R5. Connected between the resistor R3 and the first capacitor C1. In this way, the bleeder circuit of the driving voltage of the freewheeling tube Q1 is formed to further accelerate the turnoff of the freewheeling tube, so that when the primary side switching tube in the double-tube forward network is turned on, the secondary side freewheeling tube Q1 and the secondary side rectifier tube can be reduced The time that Q2 conducts together reduces the voltage spike across Q1.

Third embodiment

FIG. 3 shows a circuit schematic diagram of the third embodiment, which is different from the second embodiment in that, on the basis of FIG. 2 of the second embodiment, a voltage regulator ZD1 is connected in parallel across the first capacitor C1. The anode of ZD1 is connected to the connection point of the first capacitor C1 and the gate of the freewheeling tube Q1, and the cathode of the voltage regulator ZD1 is connected to the connection point of the first capacitor C1 and the resistor R3 and resistor R5. The presence of the voltage regulator ZD1 can control the first capacitor C1 The maximum bias voltage at both ends prevents the bias voltage at both ends of the first capacitor C1 from being too high so that the gate-source voltage of the freewheeling tube Q1 is too low and the freewheeling tube cannot be normally turned on.

The above are only the preferred embodiments of the present invention. It should be pointed out that the above preferred embodiments should not be regarded as limitations on the present invention. For those of ordinary skill in the art, different basic topologies of the circuits of the present invention are added The control mode can further optimize the performance of the present invention for continuously providing drive signals for the freewheeling tube at zero voltage. For those of ordinary skill in the art, without departing from the spirit and scope of the present invention, a number of improvements and retouches can be made. These improvements and retouches should also be regarded as the scope of protection of the present invention, which will not be implemented here. For details, the protection scope of the present invention shall be subject to the scope defined by the claims.

Claims

A self-driving driving circuit of a double-tube forward synchronous rectification circuit. The double-tube forward synchronous rectification circuit includes a transformer, a double-tube forward network on the primary side of the transformer, and a synchronous rectification transformation network on the secondary side of the transformer; the transformer includes the first A primary winding, a first secondary winding, and a second secondary winding; the self-driving drive circuit of the dual-tube forward synchronous rectifier circuit is used to drive the freewheeling tube in the synchronous rectification conversion network; its characteristics are:

The self-driving drive circuit includes a second secondary winding of the transformer, which is used to provide an input signal for the self-driving drive circuit; the first and second resistors connected in series across the two secondary windings are used To sample and divide the input signal to the next stage to provide a driving signal; the first P-type MOS tube with the first midpoint of the series connection of the first resistor and the second resistor as the gate input, the first P-type MOS tube turns off or conducts in response to the driving signal It is used to drive the discharge or charge of the freewheeling tube in the synchronous rectification and conversion network; one end of which is connected to the third resistance of the connection end of the first resistor and the different end of the second secondary winding, and the third resistance is used in the synchronous rectification and conversion network The drive resistance of the freewheeling tube is used to charge and discharge the freewheeling tube in the synchronous rectification conversion network; the first capacitor connected between the other end of the third resistor and the grid of the freewheeling tube in the synchronous rectification conversion network; first The drain of the P-type MOS tube is connected to the anode of the first diode, the source of the first P-type MOS tube is connected to the cathode of the first diode; the different-named end of the second secondary winding is connected to the first resistor end and the third resistor At one end, the same-named end of the second secondary winding is connected to the end of the second resistor and the source of the first P-type MOS tube, and the drain of the first P-type MOS tube is connected to the source of the freewheel in the synchronous rectification conversion network.
The self-driving drive circuit according to claim 1, wherein the self-driving drive circuit further comprises a second diode, a third diode, and a fifth resistor, and the anode of the second diode is connected to the first The gate of a P-type MOS tube, the cathode of the second diode is connected to the cathode of the third diode and the different end of the second secondary winding, the anode of the third diode is connected to the end of the fifth resistor, the fifth The other end of the resistor is connected to the connection end of the third resistor and the first capacitor.
The self-driving drive circuit according to claim 2, wherein the self-driving drive circuit further comprises a first voltage stabilizing tube connected in parallel across the first capacitor, and an anode of the first voltage stabilizing tube is connected to the first capacitor and An end of the synchronous rectification conversion network where the grid of the freewheeling tube is connected, and the cathode of the first regulator tube is connected to the connecting end of the first capacitor and the third resistor and the fifth resistor.
The self-driving drive circuit according to any one of claims 1 to 3, characterized in that the first capacitor can be used as an adjustment capacitor for the driving voltage of the freewheel tube gate source in the synchronous rectification conversion network, during the freewheel tube charging and discharging process , A bias voltage for adjusting the drive voltage of the freewheeling tube gate source is generated across the first capacitor.
The self-driving drive circuit according to any one of claims 1 to 3, characterized in that after the circuit works normally, it follows the following working state:

(1) In the excitation stage of the transformer, the output of the second secondary winding of the transformer is negative, and the first P-type MOS tube is turned on. At this time, the source voltage applied to the gate of the freewheel tube is negative, and the freewheel tube is turned off;

(2) During the demagnetization stage of the transformer, the output of the second secondary winding of the transformer is positive, the first P-type MOS tube is turned off, and the second secondary winding provides a positive drive voltage to the freewheeling tube in the synchronous rectification conversion network through a third resistor. Turn on the freewheeling tube;

(3) After the demagnetization of the transformer is completed, the rectifier tube and the freewheel tube in the synchronous rectification transformation network on the secondary side of the transformer are simultaneously turned on, the voltage on the first primary winding of the transformer is zero, and the voltage on the second secondary winding of the transformer is also zero. It is the zero-voltage driving state. At this time, the first P-type MOS tube is turned off, the source voltage of the freewheel tube gate is slowly discharged through the grounding resistance in the synchronous rectification conversion network, and the freewheel tube continues to be turned on;

(4) During the re-excitation phase of the transformer, the output of the second secondary winding of the transformer is negative, the first P-type MOS tube is turned on, and the source voltage of the freewheeling tube gate passes through the third resistor, the second secondary winding of the transformer and the first P Type MOS discharges quickly, and the freewheel is cut off.