Grid driving circuit of power tube and switching power supply

Abstract

The invention provides a gate drive circuit of a power tube and a switching power supply, and the circuit comprises a first pull-up switching tube, the first end of which receives a power supply voltage, and the second end of which is connected with the gate of the power tube; the feedback unit is used for acquiring a feedback signal containing current information of the first pull-up switching tube and voltage information of the power tube; and the error amplifier performs error amplification on a reference signal and the feedback signal to obtain an error amplification signal, and when the switch control signal of the main power tube is effective, the error amplification signal drives the first pull-up switch tube to be switched on. The grid driving voltage of the power tube is more stable, has no overvoltage risk and does not change along with the change of the voltage of the power tube, and the system efficiency can be kept at the optimal point.

Description

Technical Field

[0001] The present invention relates to the field of power electronics, and particularly to a gate drive circuit for a power transistor and a switching power supply. Background Art

[0002] In a switching power supply, it is necessary to control the on / off of a power transistor to convert the input voltage of the switching power supply into an output voltage, thereby realizing the power conversion of the power supply.

[0003] The on / off of the power transistor needs to be driven by a drive circuit. An existing drive circuit for the power transistor M0 is as Figure 1 shown. This drive circuit is a push-pull drive structure, including a P-type MOS transistor as the pull-up switch transistor Q1 and an N-type MOS transistor as the pull-down switch transistor Q2. The source of the pull-up switch transistor Q1 receives the power supply voltage VCC, and the drain is connected to the gate of the power transistor. The drain of the pull-down switch transistor Q2 is connected to the gate of the power transistor, and the source is connected to the reference ground. The switching control signal PWM is used to control the on / off of the pull-up switch transistor Q1 and the pull-down switch transistor Q2 after passing through an inverter. When the switching control signal PWM is at a high level, the gates of the pull-up switch transistor Q1 and the pull-down switch transistor Q2 receive a low-level signal. The pull-up switch transistor Q1 is turned on, and the pull-down switch transistor Q2 is turned off. The pull-up switch transistor Q1 is used to provide a pull-up current for the power transistor M0 to drive the power transistor to turn on. When the switching control signal PWM is at a low level, the gates of the pull-up switch transistor Q1 and the pull-down switch transistor Q2 receive a high-level signal. The pull-up switch transistor Q1 is turned off, and the pull-down switch transistor Q2 is turned on. The pull-down switch transistor Q2 is used to provide a pull-down current for the power transistor M0 to drive the power transistor to turn off.

[0004] The power supply voltage VCC of the existing drive circuit is usually provided by the drain voltage of the power transistor. In many switching power supply applications, the drain voltage follows the input voltage or the output voltage. For example, when the power transistor M0 is a rectifier diode on the secondary side of a flyback converter, the power supply voltage VCC is provided by the output voltage. If the output voltage is too high, the drive loss is too large. Therefore, the existing drive circuit cannot ensure that the power operates at the optimal efficiency point. Summary of the Invention

[0005] The purpose of the present invention is to provide a gate drive circuit for a power transistor and a switching power supply, which can make the gate voltage of the power transistor more stable, without the risk of overshoot, and ensure that the drive efficiency remains at the optimal point.

[0006] The present invention also provides a gate drive circuit for a power transistor, including: A first pull-up switch transistor, whose first end receives a supply voltage, and whose second end is connected to the gate of the power transistor; A feedback unit, configured to obtain a feedback signal including the current information of the first pull-up switch transistor and the voltage information of the power transistor; An error amplifier amplifies the error between the reference signal and the feedback signal to obtain an error amplified signal. When the switching control signal of the main power transistor is valid, the error amplified signal drives the first pull-up switch transistor to turn on.

[0007] Optionally, it further includes a second pull-up switch transistor. The first end of the second pull-up switch transistor receives a supply voltage, its second end is connected to the gate of the power transistor, and the gate of the second pull-up switch transistor is connected to the gate of the first pull-up switch transistor.

[0008] Optionally, when the switching control signal is valid, the error amplified signal drives the first pull-down switch transistor and the second pull-down switch transistor to turn on. The current flowing through the first pull-down switch transistor and the current flowing through the second switch transistor provide a pull-up current for the power transistor to drive the power transistor to turn on; wherein, the current flowing through the second pull-up switch transistor is greater than the current flowing through the first pull-up switch transistor.

[0009] Optionally, the power transistor, the first pull-up switch transistor, and the second pull-up switch transistor are all N-type transistors.

[0010] Optionally, after the first pull-up switch transistor turns on, the driving voltage of the gate of the power transistor is clamped at a preset voltage to drive the power transistor to turn on; The reference signal represents the magnitude of the preset voltage.

[0011] Optionally, the feedback signal is obtained according to the sum of the current sampling signal representing the current of the first pull-up switch transistor and the voltage sampling signal representing the gate voltage of the power transistor.

[0012] Optionally, the feedback unit includes a first sampling unit, a second sampling unit, and an adder. The first sampling unit samples the current flowing through the first pull-up switch transistor to obtain the current sampling signal. The second sampling unit samples the gate voltage of the power transistor to obtain the voltage sampling signal, and the adder adds the current sampling signal and the second sampling signal to obtain the feedback signal.

[0013] Optionally, the feedback unit includes a first resistor, a second resistor, and a third resistor. The first resistor and the second resistor are connected in series between the second end of the first pull-up switch transistor and the ground terminal; The third resistor is connected between the first pull-up switch transistor and the gate of the power transistor; The voltage at the connection end of the first resistor and the second resistor is the feedback signal.

[0014] Optionally, the feedback unit further includes a first capacitor, and the first capacitor is connected in parallel with the first resistor.

[0015] Optionally, a first pull - down switch tube is further included. A first end of the first pull - down switch tube is connected to a gate of the first pull - up switch tube, and a second end of the first pull - down switch tube is connected to a reference ground. When the switch control signal is valid, the first pull - down switch tube is controlled to turn off; when the switch control signal is invalid, the first pull - down switch tube is controlled to turn on.

[0016] Optionally, a second pull - down switch tube is further included. A first end of the second pull - down switch tube is connected to a gate of the power tube, and a second end of the second pull - down switch tube is connected to a reference ground. When the switch control signal is valid, the second pull - down switch tube turns off; When the switch control signal is invalid, the second pull - down switch tube turns on, and is used to provide a pull - down current to the power tube to control the power tube to turn off.

[0017] The present invention further provides a switching power supply, including a power tube and any one of the above - mentioned gate driving circuits. The gate driving circuit is used to drive the power tube to turn on and off to control the working state of the switching power supply.

[0018] Compared with the prior art, the present invention has the following advantages: By feeding back the gate voltage information of the power tube and the pull - up current information of the power tube, the voltage of the power tube gate is clamped at a preset voltage, ensuring the stability of the power tube gate voltage and avoiding the risk of overshoot. At the same time, the gate voltage does not change with the change of the power supply voltage, and the obtained preset voltage can ensure that the driving efficiency of the power tube remains at the optimal point. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 is a schematic diagram of a gate driving circuit for a conventional power tube; Figure 2 is a schematic diagram of Embodiment 1 of the gate driving circuit for the power tube of the present invention; Figure 3 is a schematic diagram of Embodiment 2 of the gate driving circuit for the power tube of the present invention; Figure 4 is a schematic diagram of Embodiment 3 of the gate driving circuit for the power tube of the present invention; Figure 5 is a schematic diagram of Embodiment 4 of the gate driving circuit for the power tube of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0020] The preferred embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings, but the present invention is not limited to these embodiments. The present invention encompasses any alternatives, modifications, equivalent methods, and solutions made within the spirit and scope of the present invention.

[0021] In order to enable the public to have a thorough understanding of the present invention, specific details are described in detail in the following preferred embodiments of the present invention, and those skilled in the art can fully understand the present invention without the description of these details. In the following paragraphs, the present invention will be described more specifically by way of example with reference to the accompanying drawings. It should be noted that the accompanying drawings are all in a relatively simplified form and use non-precise scales to conveniently and clearly assist in explaining the purpose of the embodiments of the present invention.

[0022] Refer to the accompanying drawings of the present invention Figure 2 、 3 As shown in FIGS. 3, 4, and 5, the drive circuit of the power transistor includes a first pull-up switch transistor Q1, a feedback unit O1, and an error amplifier O2. The first pull-up switch transistor Q1 is preferably an N-type transistor, such as the NMOS transistor in the figure. The feedback circuit is connected to the common connection end of the first pull-up switch transistor Q1 and the gate of the power transistor M0. The feedback signal obtained by the feedback circuit includes the current information of the first pull-up switch transistor Q1 and the drive voltage information of the power transistor M0. The error amplifier O2 amplifies the error between the reference signal Vref and the feedback signal VFB to obtain an error signal Vx. When the high level of the switch control signal PWM is valid, this error signal drives the first pull-up switch transistor Q1 to turn on, thereby providing a pull-up current for the power transistor to drive the power transistor to turn on.

[0023] When the switch control signal PWM is valid, since the power transistor M0 needs to turn on quickly, a relatively large pull-up current is required to pull up the power transistor. If the drive voltage information is directly fed back, that is, the reference signal and the signal representing the drive voltage of the power transistor are amplified for error, the output voltage of the error amplifier will have a relatively large feedback delay. When driving a power transistor with a smaller size, there is a risk of overshoot in the gate voltage of the power transistor, increasing losses, reducing efficiency, and decreasing drive reliability. The present invention obtains the power transistor voltage information and the pull-up current information and feeds them back to the input end of the error amplifier, so that the output voltage Vx of the error amplifier drops faster (because the feedback of the pull-up current information to the input end of the error amplifier is faster), allowing the error amplifier to see the feedback information in advance to compensate for the delay of the voltage Vx, so that the drive voltage of the power transistor rises faster. At the same time, due to the feedback of the drive voltage information, the drive voltage can finally quickly rise to the preset voltage, and the drive voltage stabilizes after reaching the preset voltage and no longer continues to increase to avoid increasing drive losses.

[0024] The drive circuit further includes a first pull-down switch tube Q3, a second pull-down switch tube Q4, and an inverter 03. The switch control signal PWM drives the first pull-down switch tube Q3 and the second pull-down switch tube Q4 respectively after passing through the inverter 03. The first pull-down switch tube Q3 is connected between the output terminal of the error amplifier 02 and the ground terminal, and the second pull-down switch tube Q4 is connected between the gate of the power tube M0 and the ground terminal. When the PWM signal is at a high level, the first pull-down switch tube Q3 is turned off, and the second pull-down switch tube Q4 is turned off. The error signal output by the error amplifier 02 drives the first pull-up switch tube Q1 to pull up the power tube. When the PWM signal is at a high level, the first pull-down switch tube Q3 is turned on, and the second pull-down switch tube Q4 is turned on. The output terminal of the error amplifier is connected to the ground. The first pull-up switch tube Q1 is turned off, and the pull-down current generated by the second pull-down switch tube Q4 drives the power tube to turn off.

[0025] See Figure 2 , which shows the schematic diagram of Embodiment 1 of the gate drive circuit of the present invention. The feedback unit includes a sampling unit 11, a sampling unit 12, and an adder 13. The sampling unit 11 samples the current flowing through the first pull-up switch tube Q1 to obtain a current sampling signal VCS. The sampling unit 12 samples the voltage of the gate of the power tube to obtain a voltage sampling signal VG1. The adder 13 adds the current sampling signal VCS and the voltage sampling signal VG1 to obtain a feedback signal VFB. This feedback signal contains the pull-up current information and the gate drive voltage information of the power tube.

[0026] See Figure 3 , which shows the schematic diagram of Embodiment 2 of the gate drive circuit of the present invention. The feedback unit includes a resistor R1, a resistor R2, and a resistor R3. The resistor R1 and the resistor R2 are connected in series between the source of the first pull-up switch tube Q1 and the ground terminal, and the resistor R3 is connected between the source of the first pull-up switch tube Q1 and the gate of the power tube M0. The gate voltage of the power tube M0 is VG, and the pull-up current flowing through the first pull-up switch tube Q1 is I1. Then there is a feedback signal VFB = (I1×R2 + VG)×(R0 / (R0 + R1)), which is equivalent to the feedback signal VFB being equal to the sampling signal I1×R3×(R0 / (R0 + R1)) and the sampling signal VG×(R0 / (R0 + R1)) representing the gate voltage VG (the resistor R2 is much smaller than the resistors R0 and R1, and the current flowing into the resistors R1 and R0 is ignored). In this embodiment, since the power tube requires a relatively large pull-up current, the drive loss generated when the pull-up current I1 flows through the resistor R2 is relatively large, reducing the drive efficiency of the power tube. On this basis, the present invention further proposes Figure 3 The embodiment shown.

[0027] See Figure 4 , which shows the schematic diagram of Embodiment 3 of the gate drive circuit. InFigure 3 On this basis, it further includes a second pull-up switch transistor Q2, which is the same type of device as the first pull-up switch transistor Q1. The second pull-up switch transistor Q2 and the first switch transistor Q1 form a current mirror. The gates of the second pull-up switch transistor Q2 and the first pull-up switch transistor Q1 are connected to the output terminal of the error amplifier 02 together. The drains of the second pull-up switch transistor Q2 and the first pull-up switch transistor Q1 receive the power supply voltage VCC, and the source of the second pull-up switch transistor Q2 is connected to the gate of the power transistor M0. The resistors R1 and R0 are connected in series between the source of the first pull-up switch transistor Q1 and the ground terminal, and the resistor R2 is connected between the source of the first pull-up switch transistor Q1 and the source of the second pull-up switch transistor Q2. Here, the size of the second pull-up switch transistor Q2 is much larger than that of the first pull-up switch transistor Q1, and the size ratio of the two switch transistors Q1 and Q2 is 1:N, and the current ratio flowing through the two switch transistors Q1 and Q2 is 1:N, where N is a constant greater than 1. After the first pull-up switch transistor Q1 and the second pull-up switch transistor Q2 are turned on, the pull-up current mainly generated by the second pull-up switch transistor Q2 is used to drive the power transistor M0 to turn on. The current of the first pull-up switch transistor Q1 is I1, and the current of the second pull-up switch transistor Q2 is N×I1. It still satisfies the feedback signal VFB = (I1×R2 + VG)×(R0 / (R0 + R1)), and the feedback signal VFB is equal to the sum of the sampling signal of the pull-up current I1 and the sampling signal of the gate voltage VG. In this embodiment, only a very small current flows through the resistor R2, and the pull-up current for driving the power transistor M0 to turn on is mainly provided by the conduction current of the switch transistor Q2. Therefore, a large turn-on loss will not be caused on the resistor R2, and the driving efficiency can be greatly improved.

[0028] In addition, when the gate of the power transistor is short-circuited, the short-circuit state can be detected by the feedback circuit. When the gate of the power transistor is in the short-circuit state, the feedback signal will be very large, which will cause the error amplifier to output a low-level signal, controlling the pull-up switch transistors Q1 and Q2 to turn off to avoid damage to the pull-up switch transistors Q1 and Q2. At the same time, the power transistor can be turned off in time to avoid damage to the power transistor, realizing the short-circuit protection of the power transistor.

[0029] See Figure 5 , which shows the schematic diagram of Embodiment 4 of the gate driving circuit. On the basis of Embodiment 3, the feedback circuit further includes a first capacitor C1, and the first capacitor C1 is connected in parallel with the resistor R1. The first capacitor is used to further increase the stability of the feedback signal. At the same time, since the capacitor requires current to charge it, the effect of the first pull-up current feedback can be further increased.

[0030] Furthermore, the driving circuit of the present invention is applied in a switching power supply to drive the power transistor of the switching power supply, realizing the conversion of the input signal of the switching power supply into an output signal and realizing the power conversion of the switching power supply.

[0031] Further, when the driving circuit of the present invention is used to drive the synchronous rectifier tube in the flyback converter, the power supply voltage is the output voltage of the flyback converter. When the output voltage changes, the driving voltage can still remain stable and operate at the optimal efficiency point.

[0032] Although the above embodiments are separately described and elaborated, for the common technologies involved, in the view of those of ordinary skill in the art, substitutions and integrations can be made between the embodiments. For the content not explicitly recorded in one of the embodiments, reference can be made to the other embodiment with records.

[0033] The above-described embodiments do not constitute a limitation on the protection scope of the technical solution. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the above embodiments shall be included within the protection scope of the technical solution.

Claims

1. A gate drive circuit for a power transistor, characterized in that, Including: A first pull-up switch transistor, whose first end receives a supply voltage, and whose second end is connected to the gate of the power transistor; A feedback unit, configured to obtain a feedback signal including current information of the first pull-up switch transistor and voltage information of the power transistor; An error amplifier, which amplifies the error between a reference signal and the feedback signal to obtain an error amplified signal. When the switching control signal of the main power transistor is valid, the error amplified signal drives the first pull-up switch transistor to turn on.

2. The gate driving circuit according to claim 1, wherein: It further includes a second pull-up switch transistor. The first end of the second pull-up switch transistor receives a supply voltage, its second end is connected to the gate of the power transistor, and the gate of the second pull-up switch transistor is connected to the gate of the first pull-up switch transistor.

3. The gate driving circuit according to claim 2, wherein: When the switching control signal is valid, the error amplified signal drives the first pull-down switch transistor and the second pull-down switch transistor to turn on. The current flowing through the first pull-down switch transistor and the current flowing through the second switch transistor provide a pull-up current for the power transistor to drive the power transistor to turn on; Wherein, the current flowing through the second pull-up switch transistor is greater than the current flowing through the first pull-up switch transistor.

4. The gate driving circuit according to claim 2, wherein: The power transistor, the first pull-up switch transistor, and the second pull-up switch transistor are all N-type transistors.

5. The gate driving circuit according to claim 1, wherein: After the first pull-up switch transistor turns on, the driving voltage of the gate of the power transistor is clamped at a preset voltage to drive the power transistor to turn on; The reference signal represents the magnitude of the preset voltage.

6. The gate driving circuit according to claim 1, wherein: The feedback signal is obtained according to the sum of a current sampling signal representing the current of the first pull-up switch transistor and a voltage sampling signal representing the gate voltage of the power transistor.

7. The gate driving circuit according to claim 6, wherein: The feedback unit includes a first sampling unit, a second sampling unit, and an adder. The first sampling unit samples the current flowing through the first pull-up switch transistor to obtain the current sampling signal. The second sampling unit samples the gate voltage of the power transistor to obtain the voltage sampling signal, and the adder adds the current sampling signal and the second sampling signal to obtain the feedback signal.

8. The gate driving circuit according to claim 6, wherein: The feedback unit includes a first resistor, a second resistor, and a third resistor. The first resistor and the second resistor are connected in series between the second end of the first pull-up switch transistor and the ground terminal; The third resistor is connected between the first pull-up switch transistor and the gate of the power transistor; The voltage at the connection end of the first resistor and the second resistor is the feedback signal.

9. The gate driving circuit according to claim 8, wherein: The feedback unit further includes a first capacitor, and the first capacitor is connected in parallel with the first resistor.

10. The gate driving circuit according to claim 1, wherein: It further includes a first pull-down switch transistor. The first end of the first pull-down switch transistor is connected to the gate of the first pull-up switch transistor, and the second end of the first pull-down switch transistor is connected to the reference ground; When the switching control signal is valid, control the first pull-down switch transistor to turn off. When the switching control signal is invalid, control the first pull-down switch transistor to turn on.

11. The gate driving circuit according to claim 1, wherein: It further includes a second pull-down switch transistor. The first end of the second pull-down switch transistor is connected to the gate of the power transistor, and the second end of the second pull-down switch transistor is connected to the reference ground; When the switching control signal is valid, the second pull-down switch transistor turns off; When the switch control signal is invalid, the second pull-down switch transistor is turned on to provide a pull-down current to the power transistor to control the power transistor to turn off.

12. A switching power supply, characterized in that: It includes a power transistor and the gate drive circuit according to any one of claims 1-11. The gate drive circuit is used to drive the power transistor to turn on and off to control the working state of the switching power supply.

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