Power device driving method for switching circuit, driving circuit and switching circuit

Abstract

The present invention discloses a power device driving method, a driving circuit and a switching circuit for a switching circuit. The switching circuit includes a main switch tube, a synchronous rectifier tube and an inductive element. When the switch signal indicates that the synchronous rectifier tube changes from on to off and the main switch tube changes from off to on, the body effect of the MOS tube is used to pull the driving pole voltage of the synchronous rectifier tube down to a voltage lower than the threshold voltage of the synchronous rectifier tube and higher than zero voltage, and start timing. When it is detected that the driving pole voltage of the main switch tube rises to a first voltage or the timing reaches a first time, the driving pole voltage of the synchronous rectifier tube is pulled down to zero voltage. The present invention can reduce the conduction of the synchronous rectifier tube body diode when the synchronous rectifier tube is turned off to the main switch tube is turned on, reduce switching losses, and improve conversion efficiency.

Description

Technical Field

[0001] The present invention relates to the technical field of power electronics, and in particular to a power device driving method for a switching circuit, a driving circuit and a switching circuit. Background Art

[0002] In a switching power supply, in order to improve system efficiency, a synchronous rectifier is used to replace a freewheeling diode. However, when the synchronous rectifier is turned off and the main switch is turned on, a dead time needs to be added to prevent direct conduction. During the dead time, the main switch has not yet turned on, while the synchronous rectifier has been turned off, and the current passes through the body diode of the synchronous rectifier. When the main switch is turned on, there is a reverse recovery current caused by the conduction of the body diode of the synchronous rectifier. This reverse recovery current causes large switching losses. Therefore, how to improve and optimize the switching process of turning off the synchronous rectifier and turning on the main switch is an urgent problem to be solved in the switching power supply. Summary of the invention

[0003] In view of this, an object of the present invention is to provide a power device driving method, a driving circuit and a switching circuit for a switching circuit, so as to solve the problem in the prior art that the body diode of the synchronous rectifier is turned on when the synchronous rectifier is turned off to when the main switch is turned on, thereby reducing the system efficiency.

[0004] The technical solution of the present invention is to provide a power device driving method for a switching circuit, wherein the switching circuit includes a main switch tube, a synchronous rectifier tube and an inductive element. When the switching signal indicates that the synchronous rectifier tube changes from on to off and the main switch tube changes from off to on, the body effect of the MOS tube is used to pull the driving pole voltage of the synchronous rectifier tube down to a voltage lower than the threshold voltage of the synchronous rectifier tube and higher than zero voltage, and start timing. When it is detected that the driving pole voltage of the main switch tube rises to a first voltage or the timing reaches a first time, the driving pole voltage of the synchronous rectifier tube is pulled down to zero voltage.

[0005] Optionally, when the switch signal indicates that the synchronous rectifier tube changes from on to off and the main switch tube changes from off to on, the driving electrode voltage of the synchronous rectifier tube is pulled down to a level close to and lower than the threshold voltage of the synchronous rectifier tube.

[0006] Another technical solution of the present invention is to provide a power device driving circuit for a switching circuit, wherein the switching circuit includes a main switch tube, a synchronous rectifier tube and an inductive element. When the switching signal indicates that the synchronous rectifier tube changes from on to off and the main switch tube changes from off to on, the body effect of the MOS tube is used to pull the driving pole voltage of the synchronous rectifier tube down to a level lower than the threshold voltage of the synchronous rectifier tube and higher than zero voltage, and start timing. When it is detected that the driving pole voltage of the main switch tube rises to a first voltage or the timing reaches a first time, the driving pole voltage of the synchronous rectifier tube is pulled down to zero voltage.

[0007] Optionally, when the switch signal indicates that the synchronous rectifier tube changes from on to off and the main switch tube changes from off to on, the driving electrode voltage of the synchronous rectifier tube is pulled down to a level close to and lower than the threshold voltage of the synchronous rectifier tube.

[0008] Optionally, the power device driving circuit includes a synchronous rectifier driving circuit, which includes a first switch tube, a second switch tube and a driving amplifier circuit. The gate, source and body of the first switch tube are connected and connected to the driving electrode of the synchronous rectifier. The switching signal is connected to the driving electrode of the second switch tube through the driving amplifier circuit, and the drain of the first switch tube is connected to the reference ground through the second switch tube. When the switching signal indicates that the synchronous rectifier tube changes from on to off and the main switch tube changes from off to on, the driving electrode voltage of the synchronous rectifier tube is pulled down to a level lower than the threshold voltage of the synchronous rectifier tube through the body effect of the first switch tube.

[0009] Optionally, the first switching tube and the synchronous rectifier tube are devices of the same type.

[0010] Optionally, the synchronous rectification drive circuit also includes a delay circuit and a pull-down circuit, the delay circuit receives a switching signal, the pull-down circuit receives the output voltage of the delay circuit, and pulls down the drive pole of the synchronous rectifier according to the output voltage of the pull-down circuit; when the switching signal indicates that the synchronous rectifier changes from on to off, and the main switch changes from off to on, the delay circuit delays the first time, and the pull-down circuit pulls down the drive pole of the synchronous rectifier.

[0011] Optionally, the synchronous rectification drive circuit also includes a comparison circuit and a pull-down circuit, the comparison circuit receives a main switch tube drive signal, the pull-down circuit receives the output voltage of the comparison circuit, and pulls down the drive pole of the synchronous rectifier tube according to the output voltage of the comparison circuit; when the comparison circuit detects that the main switch tube drive voltage is higher than the first drive voltage, the pull-down circuit pulls down the drive pole of the synchronous rectifier tube.

[0012] Another technical solution of the present invention is to provide a switching circuit.

[0013] Compared with the prior art, the circuit structure and method of the present invention have the following advantages: reducing the conduction of the synchronous rectifier tube body diode when the synchronous rectifier tube is turned off to the main switch tube is turned on, reducing switching losses and improving conversion efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 The schematic diagram of the BUCK step-down circuit with synchronous rectifier;

[0015] Figure 2Schematic diagram of waveforms of the switch signal PWM, the main switch tube drive pole voltage TG and the synchronous rectifier tube drive pole voltage BG of the present invention;

[0016] Figure 3 The schematic diagram of the BOOST boost circuit with NMOS as the synchronous rectifier;

[0017] Figure 4 The schematic diagram of the BOOST boost circuit with the synchronous rectifier tube being PMOS;

[0018] Figure 5 A circuit diagram of a synchronous rectifier driving circuit in one embodiment of the present invention;

[0019] Figure 6 A circuit diagram of a synchronous rectifier driving circuit in another embodiment of the present invention;

[0020] Figure 7 The present invention is an embodiment of a circuit diagram of a synchronous rectifier driving circuit in which the synchronous rectifier is an NMOS in a BOOST circuit;

[0021] Figure 8 The present invention is an exemplary circuit diagram of a synchronous rectifier driving circuit in which the synchronous rectifier is a PMOS in a BOOST circuit in one embodiment of the present invention. DETAILED DESCRIPTION

[0022] The preferred embodiments of the present invention are described in detail below in conjunction with the accompanying drawings, but the present invention is not limited to these embodiments. The present invention covers any substitution, modification, equivalent method and scheme made within the spirit and scope of the present invention.

[0023] In order to make the public have a thorough understanding of the present invention, specific details are described in detail in the following preferred embodiments of the present invention, but those skilled in the art can fully understand the present invention without these detailed descriptions.

[0024] The present invention is described in more detail in the following paragraphs by way of example with reference to the accompanying drawings. It should be noted that the accompanying drawings are all simplified and not in exact proportion, and are only used for the purpose of conveniently and clearly assisting in explaining the embodiments of the present invention.

[0025] The present invention provides a power device driving circuit for a switching circuit, wherein the switching circuit includes a main switch tube, a synchronous rectifier tube and an inductive element. When the switching signal indicates that the synchronous rectifier tube changes from on to off, and the main switch tube changes from off to on, the body effect of the MOS tube is used to pull the driving pole voltage of the synchronous rectifier tube down to a level lower than the threshold voltage of the synchronous rectifier tube and higher than zero voltage, and timing is started. When it is detected that the driving pole voltage of the main switch tube rises to a first voltage or the timing reaches a first time, the driving pole voltage of the synchronous rectifier tube is pulled down to zero voltage. The main switch tube and the synchronous rectifier tube are both power devices, but the power device driving of the present invention mainly focuses on the driving of the synchronous rectifier tube. Taking the BUCK step-down circuit as an example, please refer to Figure 1 As shown in the figure, it is a BUCK circuit with synchronous rectification. The power device driving circuit receives the PWM signal generated by the control circuit and generates the main switch tube driving pole voltage TG and the synchronous rectifier tube driving pole voltage BG. Please refer to Figure 2 As shown in the figure, in the BUCK circuit, the waveforms of the switch signal PWM, the main switch tube drive pole voltage TG and the synchronous rectifier tube drive pole voltage BG, at t01, the synchronous rectifier tube drive pole voltage BG is pulled down to V01, that is, lower than the synchronous rectifier tube threshold voltage and higher than zero voltage, when it is detected that the main switch tube drive pole voltage TG rises to the first voltage, at t02, the synchronous rectifier tube drive pole voltage is pulled down to zero voltage. Another implementation is that at t01, the synchronous rectifier tube drive pole voltage is pulled down to V01, and timing is started, at t02, when the timing reaches the first time, the synchronous rectifier tube drive pole voltage is pulled down to zero voltage. The body effect of the MOS tube is the influence of the body voltage on the channel, and the threshold voltage is increased by increasing the source body bias voltage (SOURCE TO BODYREVERSE-BIAS).

[0026] In one embodiment, when the switch signal indicates that the synchronous rectifier tube changes from on to off and the main switch tube changes from off to on, the driving electrode voltage of the synchronous rectifier tube is pulled down to a level close to and lower than the synchronous rectifier tube threshold voltage.

[0027] The present invention is not limited to the BUCK step-down circuit, but can be used in any switching circuit with synchronous rectification, for example, it can also be used in the BOOST circuit. Figure 3 As shown, this is a BOOST circuit with synchronous rectifier tube M03 being NMOS; please refer to Figure 4 As shown, the BOOST circuit in which the synchronous rectifier tube M03 is PMOS.

[0028] Please refer to Figure 5As shown, taking the BUCK step-down circuit as an example, the power device driving circuit includes a synchronous rectifier driving circuit 100, and the synchronous rectifier driving circuit 100 includes a first switch tube M120, a second switch tube M130 and a driving amplifier circuit 110. The first switch tube is an NMOS, and the gate, source and body (BODY) of the first switch tube are connected, and connected to the driving electrode BG of the synchronous rectifier. The switching signal is connected to the driving electrode of the second switch tube through the driving amplifier circuit, and the drain of the first switch tube is connected to the reference ground through the second switch tube. When the switching signal indicates that the synchronous rectifier tube is turned from on to off, and the main switch tube is turned from off to on, the driving electrode voltage of the synchronous rectifier tube is pulled down to a voltage lower than the threshold voltage of the synchronous rectifier tube through the body effect of the first switch tube M120. Since the voltage on M120 is the voltage between the gate and the drain, the body voltage is higher than the drain, and the threshold voltage of the switch tube is reduced. Because in the switch tube, in many cases, the drain and the source are equivalent, so it is similar to the body effect, that is, the body voltage is lower than the source voltage, the switch tube threshold increases; the body voltage is higher than the source voltage, the switch tube threshold decreases.

[0029] In one embodiment, please continue to refer to Figure 5 As shown, the synchronous rectification driving circuit also includes a non-overlapping logic circuit 140 and a pull-up circuit. Figure 5 In the embodiment, the pull-up circuit is implemented by PMOS M110. The switch signal PWM generates non-overlapping driving signals of M110 and M130 respectively through the non-overlapping logic circuit 140, so that M110 and M130 are not turned on at the same time to prevent direct conduction. The pull-up circuit M110 turns on the synchronous rectifier by pulling up BG, and when the synchronous rectifier is turned off, M110 is turned off.

[0030] In one embodiment, the first switch tube M120 and the synchronous rectifier tube M01 are the same type of devices, so that the turn-on threshold of the first switch tube M120 is close to the turn-on threshold of the synchronous rectifier tube M01, so that the turn-on threshold of the first switch tube M120 can be adjusted by changing the body voltage of the first switch tube M120.

[0031] In one embodiment, please continue to refer to Figure 5 As shown, the synchronous rectification driving circuit 100 also includes a delay circuit 120 and a pull-down circuit 130, wherein the delay circuit 120 receives a switching signal PWM, and the pull-down circuit 130 receives the output voltage of the delay circuit 120, and pulls down the driving pole BG of the synchronous rectifier according to the output voltage of the pull-down circuit 130; when the switching signal indicates that the synchronous rectifier is switched from on to off, and the main switch is switched from off to on, the delay circuit 120 delays the first time, and the pull-down circuit 130 pulls down the driving pole BG of the synchronous rectifier.

[0032] In another embodiment, please refer to Figure 6 As shown, the synchronous rectification driving circuit also includes a comparison circuit 160 and a pull-down circuit 130, the comparison circuit 160 receives the main switch tube driving signal TG, the pull-down circuit 130 receives the output voltage of the comparison circuit 160, and pulls down the driving pole BG of the synchronous rectifier according to the output voltage of the comparison circuit 160; when the comparison circuit detects that the main switch tube driving voltage is higher than the first driving voltage, the pull-down circuit 130 pulls down the driving pole BG of the synchronous rectifier.

[0033] Please refer to Figure 7 As shown, Figure 3 An implementation of a synchronous rectifier tube driving circuit 200 of a BOOST boost circuit. And Figure 5 , Figure 6 The difference is that the power supply of the synchronous rectification drive circuit is between the BST voltage and the SW voltage, rather than between VD and the reference ground. BST and SW are maintained at a relatively stable voltage through a capacitor, and then the capacitor is replenished through VD when the lower tube is turned on, so that the voltage between BST and SW is a relatively stable supply voltage.

[0034] Please refer to Figure 8 As shown, Figure 4 An implementation of a synchronous rectifier driving circuit 200 of a BOOST boost circuit. The power device driving circuit includes a synchronous rectifier driving circuit 200, and the synchronous rectifier driving circuit 200 includes a switch tube M220, a switch tube M210 and a driving amplifier circuit 210. The switch tube M220 is a PMOS, and the gate, source and body (BODY) of M220 are connected, and connected to the driving electrode BG of the synchronous rectifier. The switching signal is connected to the driving electrode of M210 through the driving amplifier circuit 210, and the drain of M220 is connected to the power supply terminal VD through M210. When the switching signal indicates that the synchronous rectifier is turned on and off, and the main switch tube is turned off and on, the driving electrode voltage of the synchronous rectifier is pulled up to a voltage higher than the threshold voltage of the synchronous rectifier through the body effect of the switch tube M220. Since M220 is a PMOS, the synchronous rectifier is turned off by pulling the threshold voltage higher than the threshold voltage of the synchronous rectifier.

[0035] In one embodiment, please continue to refer to Figure 8 As shown, the synchronous rectification driving circuit also includes a non-overlapping logic circuit 240 and a pull-down circuit. Figure 8In the embodiment, the pull-down circuit is implemented by NMOS M230. The switch signal PWM generates non-overlapping driving signals of M210 and M230 respectively through the non-overlapping logic circuit 240, so that M210 and M230 are not turned on at the same time to prevent direct conduction. The pull-down circuit M230 turns on the synchronous rectifier by pulling down BG, and when the synchronous rectifier is turned off, M230 is turned off.

[0036] The present invention provides a switch circuit driving method, wherein the switch circuit comprises a main switch tube, a synchronous rectifier tube and an inductive element. When a switch signal indicates that the synchronous rectifier tube changes from on to off and the main switch tube changes from off to on, the body effect of the MOS tube is utilized to pull the driving pole voltage of the synchronous rectifier tube down to a voltage lower than the threshold voltage of the synchronous rectifier tube and higher than zero voltage, and timing is started. When it is detected that the driving pole voltage of the main switch tube rises to a first voltage or the timing reaches a first time, the driving pole voltage of the synchronous rectifier tube is pulled down to zero voltage.

[0037] In one embodiment, when the switch signal indicates that the synchronous rectifier tube changes from on to off and the main switch tube changes from off to on, the driving electrode voltage of the synchronous rectifier tube is pulled down to a level close to and lower than the synchronous rectifier tube threshold voltage.

[0038] Although the embodiments are described and illustrated separately above, some common technologies are involved. It is the opinion of ordinary technicians in this field that the embodiments can be replaced and integrated. If the content is not clearly recorded in one of the embodiments, reference can be made to another recorded embodiment.

[0039] The above-described implementation methods do not constitute a limitation on the protection scope of the technical solution. Any modification, equivalent replacement and improvement made within the spirit and principle of the above-described implementation methods shall be included in the protection scope of the technical solution.

Claims

1. A power device driving method for a switch circuit, the switch circuit comprising a main switch tube, a synchronous rectifier tube and an inductive element, when the switch signal indicates that the synchronous rectifier tube changes from on to off and the main switch tube changes from off to on, the body effect of the MOS tube is used to pull the driving pole voltage of the synchronous rectifier tube down to a voltage lower than the threshold voltage of the synchronous rectifier tube and higher than zero voltage, and start timing, when it is detected that the driving pole voltage of the main switch tube rises to a first voltage or the timing reaches a first time, the driving pole voltage of the synchronous rectifier tube is pulled down to zero voltage; in, The gate, source and body of the first switch tube are connected and connected to the driving electrode of the synchronous rectifier tube. The switching signal is connected to the driving electrode of the second switch tube through a driving amplifier circuit. The drain of the first switch tube is connected to the second switch tube. When the switching signal indicates that the synchronous rectifier tube is turned from on to off and the main switch tube is turned from off to on, the driving electrode voltage of the synchronous rectifier tube is pulled down to a level lower than the threshold voltage of the synchronous rectifier tube through the body effect of the first switch tube.

2. The power device driving method according to claim 1, characterized in that: When the switch signal indicates that the synchronous rectifier tube changes from on to off and the main switch tube changes from off to on, the driving pole voltage of the synchronous rectifier tube is pulled down to a level close to and lower than the threshold voltage of the synchronous rectifier tube.

3. A power device driving circuit for a switching circuit, the switching circuit comprising a main switch tube, a synchronous rectifier tube and an inductive element, when the switch signal indicates that the synchronous rectifier tube changes from on to off and the main switch tube changes from off to on, the body effect of the MOS tube is used to pull the driving pole voltage of the synchronous rectifier tube down to a voltage lower than the threshold voltage of the synchronous rectifier tube and higher than zero voltage, and start timing, and when it is detected that the driving pole voltage of the main switch tube rises to a first voltage or the timing reaches a first time, the driving pole voltage of the synchronous rectifier tube is pulled down to zero voltage; in, The power device driving circuit includes a synchronous rectifier driving circuit, which includes a first switch tube, a second switch tube and a driving amplifier circuit. The gate, source and body of the first switch tube are connected and connected to the driving electrode of the synchronous rectifier tube. The switching signal is connected to the driving electrode of the second switch tube through the driving amplifier circuit. The drain of the first switch tube is connected to the second switch tube. When the switching signal indicates that the synchronous rectifier tube changes from on to off and the main switch tube changes from off to on, the driving electrode voltage of the synchronous rectifier tube is pulled down to a level lower than the threshold voltage of the synchronous rectifier tube through the body effect of the first switch tube.

4. The power device driving circuit according to claim 3, characterized in that: When the switch signal indicates that the synchronous rectifier tube changes from on to off and the main switch tube changes from off to on, the driving pole voltage of the synchronous rectifier tube is pulled down to a level close to and lower than the threshold voltage of the synchronous rectifier tube.

5. The power device driving circuit according to claim 4, characterized in that: The drain of the first switch tube is connected to the reference ground through the second switch tube.

6. The power device driving circuit according to claim 5, characterized in that: The first switch tube and the synchronous rectifier tube are devices of the same type.

7. The power device driving circuit according to claim 5, characterized in that: The synchronous rectification driving circuit also includes a delay circuit and a pull-down circuit, the delay circuit receives a switching signal, the pull-down circuit receives the output voltage of the delay circuit, and pulls down the driving pole of the synchronous rectifier tube according to the output voltage of the pull-down circuit; when the switching signal indicates that the synchronous rectifier tube changes from on to off, and the main switch tube changes from off to on, the delay circuit delays the first time, and the pull-down circuit pulls down the driving pole of the synchronous rectifier tube.

8. The power device driving circuit according to claim 5, characterized in that: The synchronous rectification driving circuit also includes a comparison circuit and a pull-down circuit, wherein the comparison circuit receives a main switch tube driving signal, the pull-down circuit receives an output voltage of the comparison circuit, and pulls down the driving pole of the synchronous rectifier tube according to the output voltage of the comparison circuit; when the comparison circuit detects that the main switch tube driving voltage is higher than the first driving voltage, the pull-down circuit pulls down the driving pole of the synchronous rectifier tube.

9. A switch circuit, characterized in that: The invention comprises a power device driving circuit as claimed in any one of claims 3 to 8.

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