A driving circuit and a switching circuit of a gallium nitride power tube

Abstract

The present invention proposes a driving circuit and a switching circuit for a gallium nitride power tube, wherein the driving circuit comprises: a pull-up power tube, connected to the gate of the gallium nitride power tube and the power supply voltage, and pulling up the gate voltage of the gallium nitride power tube when turned on; a sampling circuit, the input end of which is connected to the gate of the gallium nitride power tube, the ground end of which is connected to the source of the gallium nitride power tube, and the output end of which generates a feedback signal representing the gate-source voltage of the gallium nitride power tube; a reference circuit, the ground end of which is connected to the source of the gallium nitride power tube, and is used to generate a reference signal; and an operational amplifier circuit, which operationally amplifies the feedback signal and the reference signal to obtain an operational amplification signal to adjust the on-resistance of the pull-up power tube so that the gate-source voltage is a constant value. The relative reference of the driving circuit proposed by the present invention to the sampling circuit and the reference circuit is the source voltage of the gallium nitride power tube, so that the gate-source voltage of the gallium nitride power tube can be stabilized at a constant value, and the gallium nitride power tube can continue to work in the optimal conduction state.

Description

Technical Field

[0001] The present invention belongs to the technical field of switching power supplies, and in particular relates to a driving circuit and a switching circuit of a gallium nitride power tube. Background Art

[0002] Compared with traditional MOSFETs, gallium nitride power tubes have lower on-resistance, parasitic capacitance, and better frequency characteristics. Therefore, gallium nitride power tubes are widely used in switching power supplies, which greatly improves the operating frequency and working efficiency of switching power supplies.

[0003] like Figure 1 As shown, the driving circuit of the GaN power tube in the prior art controls the gate voltage to be stable at the reference voltage according to the reference voltage and the feedback voltage representing the gate voltage, thereby controlling the gate-source voltage of the GaN power tube to be constant, thereby controlling the GaN power tube to be in the best conduction state. Figure 1 As shown in the figure, when the switch circuit is running, the sampling voltage Vcs may change, that is, the source voltage of the GaN power tube will change. Therefore, the gate-source voltage of the GaN power tube will change, and the GaN power tube cannot be maintained in the optimal conduction state (in the optimal conduction state, the system has the highest efficiency and the lowest loss).

[0004] In addition, since the gate-source parasitic capacitance Cgs of the GaN power tube is small, and there is a control delay when the driving circuit pulls up the gate voltage of the GaN power tube, it is easy for the gate-source parasitic capacitance Cgs to be charged, resulting in an overvoltage risk on the gate of the GaN power tube, thereby damaging the GaN power tube.

[0005] Therefore, the driving circuit in the prior art needs to be optimized to solve the above problems. Summary of the invention

[0006] In order to solve various problems in the prior art, the present invention proposes a driving circuit and a switching circuit of a gallium nitride power tube, wherein the source and the drain of the gallium nitride power tube are connected in the main circuit, and the driving circuit of the gallium nitride comprises:

[0007] A pull-up power tube, connected to the gate of the gallium nitride power tube and the supply voltage, and pulling up the gate voltage of the gallium nitride power tube when turned on;

[0008] A sampling circuit, wherein the input end is connected to the gate of the GaN power tube, the ground end is connected to the source of the GaN power tube, and the output end generates a feedback signal representing the gate-source voltage of the GaN power tube;

[0009] A reference circuit, the ground end of which is connected to the source of the gallium nitride power tube, for generating a reference signal;

[0010] The operational amplifier circuit performs operational amplification on the feedback signal and the reference signal to obtain an operational amplified signal, so as to adjust the on-resistance of the pull-up power tube so that the gate-source voltage is a constant value.

[0011] Preferably, the sampling circuit comprises: a second resistor and a third resistor connected in series between the gate and the source, and a voltage at a connection point between the second resistor and the third resistor is the feedback signal.

[0012] Preferably, the reference circuit includes: a first current source and a first resistor, one end of the first resistor is connected to the output end of the first current source, and the other end is connected to the source, and the voltage of the first resistor is the reference signal.

[0013] Furthermore, the driving circuit further comprises a plurality of pull-up power tubes connected in parallel, the plurality of pull-up power tubes connected in parallel are connected to the gate of the gallium nitride power tube and the supply voltage, and the driving circuit comprises a pull-up control circuit,

[0014] The pull-up control circuit controls the pull-up speed of the pull-up power tube by adjusting the number of the pull-up power tubes that are turned on according to the sampling signal and the threshold signal.

[0015] The sampling signal represents the gate voltage of the GaN power tube, and the threshold signal represents the overvoltage threshold of the gate of the GaN power tube.

[0016] Furthermore, the operational amplifier circuit includes an error amplifier, which performs error amplification on the feedback signal and the reference signal to control the gate voltage of the pull-up power tube.

[0017] The driving circuit includes a pull-up control circuit, and the pull-up control circuit controls the pull-up speed of the pull-up power tube by adjusting the tail current of the error amplifier according to the sampling signal and the threshold signal.

[0018] The sampling signal represents the gate voltage of the GaN power tube, and the threshold signal represents the overvoltage threshold of the gate of the GaN power tube.

[0019] Furthermore, when the sampling signal is greater than the threshold signal, the pull-up speed is slowed down; when the sampling signal is less than the threshold signal, the pull-up speed is increased.

[0020] Furthermore, it also includes a pull-down power tube, which is connected to the gate of the gallium nitride power tube and the reference ground, and pulls down the gate voltage of the gallium nitride power tube when it is turned on.

[0021] Furthermore, it also includes a third power tube, which is connected to the gate of the pull-up power tube and the reference ground, and the PWM signal controls the pull-down power tube and the third power tube to be turned on or off at the same time.

[0022] Further, when the third power tube and the pull-down power tube are turned on, the pull-up power tube is turned off, and the gallium nitride power tube is turned off; when the third power tube and the pull-down power tube are turned off, the pull-up power tube is turned on, and the gallium nitride power tube is turned on.

[0023] A switch circuit includes a gallium nitride power tube connected in a main loop and also includes the drive circuit mentioned above.

[0024] The driving circuit proposed in the present invention optimizes the sampling circuit and the reference circuit. The sampling circuit uses the source voltage of the GaN power tube as a relative reference to sample and obtain the gate voltage of the GaN power tube. Similarly, the reference circuit also generates a reference signal relative to the source voltage of the GaN power tube, that is, the sampling signal and the reference signal change with the source voltage of the GaN power tube. Therefore, the gate-source voltage of the GaN power tube changes synchronously with the source voltage. Even if the source voltage of the GaN power tube changes, the gate-source voltage of the GaN power tube can be stabilized at a constant value, and the GaN power tube can continue to work in the best conduction state. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 A driving circuit for a gallium nitride power tube in the prior art;

[0026] Figure 2 This is a structural block diagram of the driving circuit of the gallium nitride power tube proposed by the present invention;

[0027] Figure 3 This is a circuit structure diagram of the driving circuit of the gallium nitride power tube proposed by the present invention;

[0028] Figure 4 and Figure 5 This is the structural diagram of the pull-up control circuit in the driving circuit. DETAILED DESCRIPTION

[0029] In order to facilitate the understanding of the present invention, the present invention will be described more fully below with reference to the relevant drawings. The preferred embodiments of the present invention are shown in the drawings. However, the present invention can be implemented in different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the understanding of the disclosure of the present invention more thorough and comprehensive.

[0030] like Figure 1As shown, the driving circuit of the GaN power tube in the prior art cannot control the gate-source voltage of the GaN power tube to be stable at a constant value, so that the GaN power tube cannot continuously work in the optimal conduction state.

[0031] Based on the above problems, the present invention proposes a driving circuit for a gallium nitride power tube, such as Figure 2 As shown, including:

[0032] The pull-up power tube connects the gate of the GaN power tube and the power supply voltage, and pulls up the gate voltage of the GaN power tube when it is turned on, so that the GaN power tube is turned on;

[0033] A sampling circuit, wherein the input end is connected to the gate of the GaN power tube, the ground end is connected to the source of the GaN power tube, and the output end generates a feedback signal representing the gate-source voltage of the GaN power tube;

[0034] A reference circuit, wherein the ground terminal is connected to the source of the GaN power tube and is used to generate a reference signal;

[0035] The operational amplifier circuit operationally amplifies the feedback signal and the reference signal to obtain an operational amplified signal to adjust the on-resistance of the pull-up power tube so that the gate-source voltage of the gallium nitride power tube is stabilized to a constant value.

[0036] In summary, the driving circuit proposed in the present invention optimizes the sampling circuit and the reference circuit. The sampling circuit uses the source voltage of the GaN power tube as a relative reference to sample and obtain the gate voltage of the GaN power tube. Similarly, the reference circuit also generates a reference signal relative to the source voltage of the GaN power tube, that is, the sampling signal and the reference signal change with the source voltage of the GaN power tube. Therefore, the gate-source voltage of the GaN power tube changes synchronously with the source voltage. Even if the source voltage of the GaN power tube changes, the gate-source voltage of the GaN power tube can be stabilized at a constant value, and the GaN power tube can continue to work in the best conduction state.

[0037] Specifically, Figure 3As shown, the drain of the pull-up power tube M1 is connected to the power supply voltage VCC, and the source is connected to the gate of the gallium nitride power tube M0. The sampling circuit includes a second resistor R2 and a third resistor R3 connected in series. The other end of the second resistor R2 is connected to the gate of the gallium nitride power tube M0, and the other end of the third resistor R3 is connected to the source of the gallium nitride power tube M0. The connection point between the second resistor R2 and the third resistor R3 is the output end of the sampling circuit to generate a voltage Vfb as a feedback signal. The voltage Vfb represents the gate-source voltage of the gallium nitride power tube M0. The reference circuit includes a current source I1 and a first resistor R1. One end of the first resistor R1 is connected to the source of the gallium nitride power tube M0. The first current source I1 generates a current flowing through the first resistor R1. The voltage Vref on the first resistor R1 is a reference signal. The reference signal represents that the gate-source voltage of the gallium nitride power tube is expected to be stable at a preset threshold. The operational amplifier circuit includes an error amplifier EA. The positive input end of the error amplifier EA receives the voltage Vref, the reverse input end receives the voltage Vfb, and the output end is connected to the gate of the pull-up power tube M1. The error amplifier EA controls the pull-up power tube M1 to turn on, and adjusts the gate voltage of the GaN power tube M0 according to the difference between Vref and Vfb to adjust the conduction degree of the pull-up power tube M1, so as to stabilize the gate-source voltage of the GaN power tube M0 at a preset threshold.

[0038] In addition, the driving circuit also includes a pull-down power tube M2, the drain of the pull-down power tube M2 is connected to the gate of the gallium nitride power tube M0, and the source is connected to the reference ground. When the pull-down power tube M2 is turned on, the gate voltage of the gallium nitride power tube M0 is pulled down and the gallium nitride power tube M0 is turned off. At the same time, in order to simplify the circuit and reduce the cost, the driving circuit also includes a third power tube M3, the drain of the third power tube M3 is connected to the gate of the pull-up power tube M1, and the source is connected to the reference ground. The PWM control signal controls the on and off of the third power tube M3 and the pull-down power tube M2. When the PWM control signal controls the third power tube M3 and the pull-down power tube M2 to be turned on, the gate voltage of the pull-up power tube M1 is pulled down to the ground by the third power tube M3, and the pull-up power tube M1 is turned off; when the PWM control signal controls the third power tube M3 and the pull-down power tube M2 to be turned off, the operational amplifier circuit controls the pull-up power tube M1 to be turned on. It should be noted that the driving circuit is different from the prior art in how to control the on and off of the pull-up power tube and the pull-down power tube to drive the gallium nitride power tube M0 to turn on or off. The prior art controls the pull-up power tube by a PWM driving signal and controls the pull-down power tube by a PWM driving signal inverted by an inverter, thereby driving the pull-up power tube and the pull-down power tube to turn on alternately. In this solution, there is no need to set an inverter, and the operational amplifier circuit is reused to control the on-resistance of the pull-up power tube, so that the circuit setting and related control strategies are simpler, the chip area is smaller, and the production cost is lower.

[0039] Furthermore, considering that the gate-source parasitic capacitance Cgs of the GaN power tube M0 is relatively small, and the above-mentioned driving circuit has a control delay when adjusting the gate voltage of the GaN power tube M0, the gate-source parasitic capacitance Cgs may be charged to cause the gate of the GaN power tube M0 to be over-voltaged, thereby damaging the GaN power tube M0. Figure 4 As shown, the present invention proposes that the pull-up power tube is composed of a plurality of power tubes connected in parallel, and the pull-up control circuit controls the number of the pull-up power tube M1 to be turned on according to the sampling signal (characterizing the gate voltage of the gallium nitride power tube M0) and the threshold signal (characterizing whether the gate voltage of the gallium nitride power tube M0 is over-voltage) to control the pull-up speed of the gate voltage of the gallium nitride power tube M0. Specifically, when the sampling signal is greater than the threshold signal (i.e., the gate voltage of the gallium nitride power tube M0 is over-voltage), the number of the pull-up power tube M1 to be turned on is reduced to slow down the pull-up speed, thereby suppressing the overshoot of the gate voltage of the gallium nitride power tube M0; when the sampling signal is less than the threshold signal, the number of the pull-up power tube M1 to be turned on is increased to speed up the pull-up speed, so as to facilitate the gallium nitride power tube to work in a high-frequency state.

[0040] It should be noted that in actual circuit design, the feedback signal mentioned above can be reused to represent the gate voltage of the GaN power tube M0, that is, the sampling signal includes the feedback signal mentioned above. Similarly, the threshold signal also includes the reference signal mentioned above. Therefore, when actually designing the circuit, it is possible to determine whether the gate voltage of the GaN power tube M0 is overvoltage by comparing the feedback signal and the reference signal.

[0041] Furthermore, in addition to controlling the pull-up speed by controlling the number of pull-up power tubes M1 that are turned on, Figure 5 As shown, the present invention also proposes that the pull-up control circuit adjusts the tail current of the error amplifier according to the sampling signal and the threshold signal to adjust the pull-up speed of the pull-up power tube M1 (consisting of only one power tube). Specifically, when the sampling signal is greater than the threshold signal, the tail current of the error amplifier is reduced to slow down the pull-up speed of the pull-up power tube M1; when the sampling signal is less than the threshold signal, the tail current of the error amplifier is increased to increase the pull-up speed of the pull-up power tube M1.

[0042] In addition, the present invention also proposes a switching power supply, in which a gallium nitride power tube is connected to the main circuit of the switching power supply, and the gallium nitride power tube is driven by the driving circuit proposed above. For example, the switching power supply is a flyback conversion circuit, and the drain of the gallium nitride power tube is connected to the primary winding, and the source is connected to the reference ground through a sampling resistor.

[0043] It should be noted that the specific implementation and corresponding illustrations given are merely a way of describing the implementation method of the present invention, and do not limit the specific structure of the implementation scheme of the present invention. Various changes or modifications can be made to these implementation schemes without departing from the principle and essence of the present invention, but these changes and modifications fall within the scope of protection of the present invention.

[0044] 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.

[0045] 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 driving circuit for a gallium nitride power tube, wherein the source and drain of the gallium nitride power tube are connected in a main circuit, characterized in that: The driving circuit comprises: A pull-up power tube, connected to the gate of the gallium nitride power tube and the supply voltage, and pulling up the gate voltage of the gallium nitride power tube when turned on; A sampling circuit, wherein the input end is connected to the gate of the GaN power tube, the ground end is connected to the source of the GaN power tube, and the output end generates a feedback signal representing the gate-source voltage of the GaN power tube; A reference circuit, the ground end of which is connected to the source of the gallium nitride power tube, for generating a reference signal; The operational amplifier circuit performs operational amplification on the feedback signal and the reference signal to obtain an operational amplified signal, so as to adjust the on-resistance of the pull-up power tube so that the gate-source voltage is a constant value.

2. The driving circuit according to claim 1, characterized in that: The sampling circuit includes: a second resistor and a third resistor connected in series between the gate and the source, and a voltage at a connection point between the second resistor and the third resistor is the feedback signal.

3. The driving circuit according to claim 1, wherein: The reference circuit includes: a first current source and a first resistor, one end of the first resistor is connected to the output end of the first current source, and the other end is connected to the source, and the voltage of the first resistor is the reference signal.

4. The driving circuit according to claim 1, wherein: The driving circuit further comprises a plurality of parallel pull-up power tubes, the plurality of parallel pull-up power tubes are connected to the gate of the gallium nitride power tube and the power supply voltage, and the driving circuit comprises a pull-up control circuit, The pull-up control circuit controls the pull-up speed of the pull-up power tube by adjusting the number of the pull-up power tubes that are turned on according to the sampling signal and the threshold signal. The sampling signal represents the gate voltage of the GaN power tube, and the threshold signal represents the overvoltage threshold of the gate of the GaN power tube.

5. The driving circuit according to claim 1, characterized in that: The operational amplifier circuit includes an error amplifier, and the error amplifier performs error amplification on the feedback signal and the reference signal to control the gate voltage of the pull-up power tube. The driving circuit includes a pull-up control circuit, and the pull-up control circuit controls the pull-up speed of the pull-up power tube by adjusting the tail current of the error amplifier according to the sampling signal and the threshold signal. The sampling signal represents the gate voltage of the GaN power tube, and the threshold signal represents the overvoltage threshold of the gate of the GaN power tube.

6. The driving circuit according to claim 4 or 5, characterized in that: When the sampling signal is greater than the threshold signal, the pull-up speed is slowed down; when the sampling signal is less than the threshold signal, the pull-up speed is increased.

7. The driving circuit according to claim 1, characterized in that: It also includes a pull-down power tube, which is connected to the gate of the gallium nitride power tube and a reference ground, and pulls down the gate voltage of the gallium nitride power tube when it is turned on.

8. The driving circuit according to claim 7, characterized in that: It also includes a third power tube, which is connected to the gate of the pull-up power tube and a reference ground, and a PWM signal controls the pull-down power tube and the third power tube to be turned on or off at the same time.

9. The driving circuit according to claim 8, characterized in that: When the third power tube and the pull-down power tube are turned on, the pull-up power tube is turned off and the gallium nitride power tube is turned off; when the third power tube and the pull-down power tube are turned off, the pull-up power tube is turned on and the gallium nitride power tube is turned on.

10. A switching circuit, comprising a gallium nitride power tube connected in a main circuit, characterized in that: It also includes the driving circuit according to any one of claims 1 to 9.

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