Constant current protection circuit and push-pull converter

Abstract

This invention provides a constant current protection circuit and a push-pull converter, relating to the technical field of push-pull converters. The constant current protection circuit and push-pull converter provided by this invention can be divided into an overcurrent protection circuit and a buffer circuit connected in sequence. The overcurrent protection circuit is used to acquire the drain signal. When the drain signal is lower than a preset signal threshold, it operates in an open-loop state and outputs a first drive signal to the buffer circuit. When the drain signal is higher than the signal threshold, it triggers an overcurrent protection mode and outputs a second drive signal to the buffer circuit. The buffer circuit can then output a drive signal to the gate of the power transistor according to the first or second drive signal to drive the power transistor. Since the buffer circuit can isolate the overcurrent protection circuit and the transformer leakage inductance of the push-pull converter, it can effectively improve the stability of the entire push-pull converter's control circuit.

Description

Technical Field

[0001] This invention relates to the technical field of push-pull converters, and in particular to a constant current protection circuit and a push-pull converter. Background Technology

[0002] In push-pull converter drivers, the chip output is typically directly connected to both ends of the transformer. When current protection of the transformer's primary current is required, the chip internally achieves constant current by pulling the gate signal low, thereby increasing the on-resistance of the power transistor. Because the entire control circuit is a loop, a large leakage inductance in the transformer can make the loop design difficult and easily cause chip output oscillation. Summary of the Invention

[0003] In view of this, the purpose of the present invention is to provide a constant current protection circuit and a push-pull converter to alleviate the above-mentioned technical problems.

[0004] In a first aspect, embodiments of the present invention provide a constant current protection circuit applied to a push-pull converter. The constant current protection circuit includes an overcurrent protection circuit and a BUFFER circuit connected in sequence. The input terminal of the overcurrent protection circuit is connected to the drain of the power transistor of the push-pull converter to acquire the drain signal of the power transistor. The output terminal of the overcurrent protection circuit is connected to the input terminal of the BUFFER circuit, and the output terminal of the BUFFER circuit is connected to the gate of the power transistor. The overcurrent protection circuit is used to acquire the drain signal, operate in an open-loop state when the drain signal is lower than a preset signal threshold, and output a first drive signal to the BUFFER circuit. When the drain signal is higher than the signal threshold, an overcurrent protection mode is triggered, and a second drive signal is output to the BUFFER circuit. The BUFFER circuit is used to output a drive signal to the gate of the power transistor according to the first drive signal or the second drive signal to drive the power transistor.

[0005] In conjunction with the first aspect, the present invention provides a first possible implementation of the first aspect, wherein the overcurrent protection circuit includes a comparator, a sampling transistor, and a bias current source; wherein one input terminal of the comparator is connected to the drain of the power transistor, and the other input terminal is connected to the output terminal of the bias current source; the output terminal of the comparator serves as the output terminal of the overcurrent protection circuit and is connected to the BUFFER circuit; the output terminal of the bias current source is also connected to the drain of the sampling transistor; the gate of the sampling transistor is connected to the output terminal of the comparator, and the source of the sampling transistor is grounded.

[0006] In conjunction with the first possible implementation of the first aspect, this embodiment of the invention provides a second possible implementation of the first aspect, wherein the sampling tube is a P-type sampling tube, and the sampling tube is a sampling tube scaled down from the power tube according to a preset ratio.

[0007] In conjunction with the first possible implementation of the first aspect, the present invention provides a third possible implementation of the first aspect, wherein the overcurrent protection circuit further includes a hysteresis resistor disposed on the sampling tube and the bias current source path; the hysteresis resistor is used to generate overcurrent protection with hysteresis.

[0008] In conjunction with the first aspect, this invention provides a fourth possible implementation of the first aspect, wherein the aforementioned BUFFER circuit includes an operational amplifier chip and a state switching circuit connected to the operational amplifier chip; wherein the input terminal of the operational amplifier chip is connected to the output terminal of the overcurrent protection circuit; the output terminal of the operational amplifier chip is connected to the state switching circuit; the output terminal of the state switching circuit is connected to the gate of the power transistor; the state switching circuit is used to respond to a state switching operation, control the state of the power transistor based on the state switching operation, and control the drive signal of the gate of the power transistor according to whether the overcurrent protection mode of the overcurrent protection circuit is triggered.

[0009] In conjunction with the fourth possible implementation of the first aspect, this embodiment of the invention provides a fifth possible implementation of the first aspect, wherein the state switching circuit includes a first MOS transistor, a second MOS transistor, a third MOS transistor, and an isolation unit; wherein the source of the first MOS transistor is connected to a preset power supply; the gate of the first MOS transistor is the response terminal of the state switching circuit, used to respond to a state switching operation; the drain of the first MOS transistor is connected to the drain of the second MOS transistor; the gate of the second MOS transistor is connected to the output terminal of the operational amplifier chip; the source of the second MOS transistor is grounded; wherein the drains of the first MOS transistor and the second MOS transistor are also connected to the input terminal of the operational amplifier chip; one end of the isolation unit is connected to the drains of the first MOS transistor and the second MOS transistor, and the other end is connected to the drain of the third MOS transistor; the gate of the third MOS transistor is the response terminal of the state switching circuit, used to respond to a state switching operation; the source of the third MOS transistor is grounded.

[0010] In conjunction with the fifth possible implementation of the first aspect, this embodiment of the invention provides a sixth possible implementation of the first aspect, wherein the first MOS transistor is an N-type MOS transistor, and the second MOS transistor and the third MOS transistor are P-type MOS transistors.

[0011] In conjunction with the fifth possible implementation of the first aspect, this embodiment of the invention provides a seventh possible implementation of the first aspect, wherein the isolation unit includes an isolation resistor, or the isolation unit includes an isolation circuit composed of a MOS transistor.

[0012] In conjunction with the fifth possible implementation of the first aspect, this embodiment of the invention provides an eighth possible implementation of the first aspect, wherein the BUFFER circuit further includes a comparison unit; the comparison unit includes a comparison circuit and a MOS circuit; wherein the output terminal of the comparison circuit is used to acquire the input signals of the non-inverting input terminal and the inverting input terminal of the operational amplifier chip, and to determine the difference between the input signals of the operational amplifier chip; wherein the non-inverting input terminal is used to acquire the drain signal of the first MOS transistor, and the inverting input terminal is used to acquire the output signal of the overcurrent protection circuit; the MOS circuit includes a fourth MOS transistor; the gate of the fourth MOS transistor is connected to the output terminal of the comparison circuit, and the source of the fourth MOS transistor is connected to a preset power supply; the drain of the fourth MOS transistor is connected to the non-inverting input terminal of the operational amplifier chip; the MOS circuit is used to provide a pull-up signal to the state switching circuit according to the difference between the input signals of the operational amplifier chip.

[0013] Secondly, embodiments of the present invention also provide a push-pull converter, wherein the push-pull converter is configured with the constant current protection circuit described in the first aspect; the constant current protection circuit is used to provide overcurrent protection for the power transistors of the push-pull converter.

[0014] The embodiments of the present invention bring the following beneficial effects:

[0015] The constant current protection circuit and push-pull converter provided in this embodiment of the invention can be divided into an overcurrent protection circuit and a BUFFER circuit connected in sequence. The input terminal of the overcurrent protection circuit is connected to the drain of the power transistor of the push-pull converter to obtain the drain signal of the power transistor. The output terminal of the overcurrent protection circuit is connected to the input terminal of the BUFFER circuit, and the output terminal of the BUFFER circuit is connected to the gate of the power transistor. The overcurrent protection circuit is used to obtain the drain signal. When the drain signal is lower than a preset signal threshold, it operates in an open-loop state and outputs a first drive signal to the BUFFER circuit. When the drain signal is higher than the signal threshold, it triggers the overcurrent protection mode and outputs a second drive signal to the BUFFER circuit. The BUFFER circuit is used to provide driving capability and can output a drive signal to the gate of the power transistor according to the first drive signal or the second drive signal to drive the power transistor. Since the BUFFER circuit can isolate the overcurrent protection circuit and the transformer leakage inductance of the push-pull converter, the stability of the entire push-pull converter control circuit can be effectively improved.

[0016] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention are realized and obtained in accordance with the structures particularly pointed out in the description, claims and drawings.

[0017] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, preferred embodiments are described below in detail with reference to the accompanying drawings. Attached Figure Description

[0018] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0019] Figure 1 A structural block diagram of a constant current protection circuit provided in an embodiment of the present invention;

[0020] Figure 2 A schematic diagram of the circuit principle of a constant current protection circuit provided in an embodiment of the present invention;

[0021] Figure 3 A schematic diagram of a signal waveform provided in an embodiment of the present invention;

[0022] Figure 4 A schematic diagram of the circuit principle of a BUFFER circuit provided in an embodiment of the present invention;

[0023] Figure 5 A schematic diagram of an overcurrent protection circuit provided in an embodiment of the present invention;

[0024] Figure 6 A schematic diagram of another BUFFER circuit provided in an embodiment of the present invention. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] Currently, in push-pull converter drivers, the entire control circuit is a loop. When the transformer leakage inductance of the push-pull converter is large, it increases the difficulty of loop design and can easily cause chip output oscillation, reducing the stability of the entire control circuit.

[0027] Based on this, the constant current protection circuit and push-pull converter provided in this embodiment of the invention can effectively alleviate the above-mentioned technical problems.

[0028] To facilitate understanding of this embodiment, a constant current protection circuit disclosed in this embodiment of the invention will first be described in detail.

[0029] In one possible implementation, embodiments of the present invention provide a constant current protection circuit, such as... Figure 1 The diagram shows a structural block diagram of a constant current protection circuit. In this embodiment of the invention, the constant current protection circuit is applied to a push-pull converter. Specifically, as shown... Figure 1 As shown, the constant current protection circuit in this embodiment of the invention includes an overcurrent protection circuit 10 and a BUFFER circuit 20 connected in sequence. The overcurrent protection circuit 10 and the BUFFER circuit 20 can split the loop of the control circuit of the push-pull converter.

[0030] Specifically, the input terminal of the overcurrent protection circuit 10 is connected to the power transistor of the push-pull converter. Figure 1 The drain connection (not shown) is used to obtain the drain signal of the power transistor;

[0031] The output terminal of the overcurrent protection circuit 10 is connected to the input terminal of the BUFFER circuit 20, and the output terminal of the BUFFER circuit 20 is connected to the gate of the power transistor.

[0032] The overcurrent protection circuit 10 is used to acquire the drain signal mentioned above. When the drain signal is lower than the preset signal threshold, it operates in an open-loop state and outputs a first drive signal to the BUFFER circuit 20. When the drain signal is higher than the signal threshold, it triggers the overcurrent protection mode and outputs a second drive signal to the BUFFER circuit 20.

[0033] The BUFFER circuit 20 is used to output a drive signal to the gate of the power transistor according to the first drive signal or the second drive signal, so as to drive the power transistor.

[0034] In this embodiment of the invention, the constant current protection circuit can provide constant current protection for the entire control circuit. Typically, in the entire control circuit, only the drain of the power transistor in the push-pull converter can be used as a current detection signal. Therefore, the drain signal of this power transistor is usually used as the input of the overcurrent protection circuit. However, if a conventional current detection circuit is used and modified to form a closed-loop feedback, for the power transistor, there is actually a capacitance from the gate to the drain, and a leakage inductance from the drain to a voltage similar to a fixed voltage. Therefore, this loop will have an LC double pole. Furthermore, the capacitance from the gate to the drain will be amplified because the power transistor operates in the saturation region, so this double pole will be very low, limiting the maximum bandwidth and resulting in a very slow response speed.

[0035] In this embodiment of the invention, the overcurrent protection circuit and the BUFFER circuit described above can decompose the control circuit loop of the push-pull converter. Therefore, the function of calculating the gate voltage and the function of driving the gate in the overcurrent protection circuit can be separated. In this way, the modified overcurrent protection circuit does not need to be directly connected to the gate signal, so there will be no double poles, and the bandwidth can be set at a very high point. An isolation unit can be further added between the BUFFER circuit providing the drive and the gate to reduce the influence of double poles. This allows the overcurrent protection circuit to stabilize quickly after triggering an overcurrent and output a drive signal, such as the second drive signal mentioned above. The BUFFER circuit then converts this signal into the gate voltage, thereby driving the power transistor.

[0036] Therefore, the constant current protection circuit provided in this embodiment of the invention can be divided into an overcurrent protection circuit and a BUFFER circuit connected in sequence. The input terminal of the overcurrent protection circuit is connected to the drain of the power transistor of the push-pull converter to obtain the drain signal of the power transistor. The output terminal of the overcurrent protection circuit is connected to the input terminal of the BUFFER circuit, and the output terminal of the BUFFER circuit is connected to the gate of the power transistor. The overcurrent protection circuit is used to obtain the drain signal. When the drain signal is lower than a preset signal threshold, it operates in an open-loop state and outputs a first drive signal to the BUFFER circuit. When the drain signal is higher than the signal threshold, it triggers the overcurrent protection mode and outputs a second drive signal to the BUFFER circuit. The BUFFER circuit is used to provide driving capability and can output a drive signal to the gate of the power transistor according to the first drive signal or the second drive signal to drive the power transistor. Since the BUFFER circuit can isolate the overcurrent protection circuit and the transformer leakage inductance of the push-pull converter, the stability of the entire push-pull converter control circuit can be effectively improved.

[0037] In practical applications, the above-mentioned overcurrent protection circuit is also called an OCP (Over Current Protection) circuit. Specifically, the overcurrent protection circuit provided in this embodiment typically includes a comparator, a sampling transistor, and a bias current source. For ease of understanding, in... Figure 1 On this basis, Figure 2 A schematic diagram of a constant current protection circuit is shown, wherein, Figure 2 The diagram shows the overcurrent protection circuit and the buffer circuit.

[0038] Specifically, such as Figure 2 As shown, the overcurrent protection circuit includes a comparator OTA1, a sampling transistor Sensefet, and a bias current source Ibias.

[0039] One input of comparator OTA1 is connected to the drain of the power transistor to obtain the drain signal of the power transistor. Figure 2 The Drain signal is connected to the output of the bias current source Ibias; the output of the comparator OTA1 is used as the output of the overcurrent protection circuit and is connected to the BUFFER circuit; the output of the bias current source Ibias is also connected to the drain of the sampling transistor Sense fet; the gate of the sampling transistor Sense fet is connected to the output of the comparator OTA1, and the source of the sampling transistor is grounded.

[0040] Furthermore, such as Figure 2 As shown, the sampling tube Sense fet is a P-type sampling tube, and VCC is the preset power supply, which is usually the power supply voltage. Figure 2 The diagram further illustrates the power transistor (Power FET) of the push-pull converter. Capacitor C is the capacitance between the gate and drain of the Power FET, and L is the leakage inductance of the external transformer.

[0041] Furthermore, such as Figure 2 As shown, the BUFFER circuit in this embodiment of the invention includes an operational amplifier chip OTA2 and a state switching circuit connected to the operational amplifier chip OTA2.

[0042] Specifically, Figure 2 In the circuit, the input terminal of the operational amplifier chip OTA2 is connected to the output terminal of the overcurrent protection circuit; the output terminal of the operational amplifier chip OTA2 is connected to the state switching circuit; and the output terminal of the state switching circuit is connected to the gate of the power transistor PowerFET.

[0043] In practical use, the aforementioned state switching circuit is used to respond to state switching operations, control the state of the power transistor based on the state switching operations, and control the gate drive signal of the power transistor according to whether the overcurrent protection mode of the overcurrent protection circuit is triggered. The state switching operation responded to by the aforementioned state switching circuit is usually an operation generated by the controller of the push-pull converter. The controller can control the control circuit of the push-pull converter and trigger the state of the state switching circuit to control the power transistor and control the operating state of the push-pull converter. In the embodiment of the present invention, the state switching circuit can respond to the state switching operation and then control the state of the power transistor. The specific state switching operation can be performed according to the actual use situation, and the embodiment of the present invention does not limit it.

[0044] Furthermore, such as Figure 2 As shown, the state switching circuit in this embodiment of the invention includes a first MOS transistor M1, a second MOS transistor NM0, a third MOS transistor NM1, and an isolation unit;

[0045] In this circuit, the source of the first MOSFET M1 is connected to the preset power supply VCC; the gate of the first MOSFET is the response terminal of the state switching circuit, i.e. Figure 2 The IN pin in the circuit is used to respond to state switching operations; the drain of the first MOSFET M1 is connected to the drain of the second MOSFET NM0; the gate of the second MOSFET NM0 is connected to the output of the operational amplifier chip OTA2; the source of the second MOSFET NM0 is grounded; the drains of the first MOSFET M1 and the second MOSFET NM0 are also connected to the input of the operational amplifier chip; one end of the isolation unit is connected to the drains of the first MOSFET M1 and the second MOSFET NM0, and the other end is connected to the drain of the third MOSFET NM1; the gate of the third MOSFET NM1 is the response terminal of the state switching circuit, i.e. Figure 2 The IN pin in the diagram is used to respond to the aforementioned state switching operation; the source of the third MOSFET is grounded.

[0046] Furthermore, such as Figure 2 As shown, in this embodiment of the invention, the first MOS transistor M1 is an N-type MOS transistor, and the second MOS transistor NM0 and the third MOS transistor NM1 are P-type MOS transistors.

[0047] Furthermore, the aforementioned isolation unit includes an isolation resistor, or the isolation unit includes an isolation circuit composed of MOSFETs. For ease of explanation, Figure 2 In this example, we will use an isolation unit including an isolation resistor as an example for explanation. Figure 2 The isolation resistor R in the middle.

[0048] In specific implementation, based on Figure 2The constant current protection circuit shown has an actual overcurrent protection circuit current determined by K*Ibias, where K is the scaling factor of the sampling transistor according to the preset power transistor. During operation, the constant current protection circuit switches between two states, one of which is IN=1. The push-pull converter controller can adjust the response of the state switching circuit based on the actual operating state. Figure 2 The pin corresponding to IN in the output shows IN=1. Figure 2 In the first state, the third MOSFET NM1 is turned on, the first MOSFET M1 is turned off, the gate signal of the power transistor is pulled to ground, and the power transistor is turned off. In the second state, IN=0, the first MOSFET M1 is turned on, the third MOSFET NM1 is turned off, the gate signal of the power transistor is pulled up by the first MOSFET M1, and whether the second MOSFET NM0 is turned on depends on whether the overcurrent protection mode of the overcurrent protection circuit is triggered.

[0049] Specifically, in the mode where overcurrent protection is not triggered, i.e., in normal operating mode, Figure 2 In the overcurrent protection circuit, the voltage at the Drain input of comparator OTA1 is less than the voltage at the Drain_FB input. Drain_FB is the reference voltage of comparator OTA1, obtained by ron*Ibias. Here, ron is the on-resistance of the sampling transistor Sensefet when the gate-to-source voltage VGS equals VCC. When operating within half a cycle of the power transistor Powerfet being on, the overcurrent protection circuit actually operates in an open-loop state, and the output gate0 signal is pulled to VCC in a very short time. After a period of time, the BUFFER circuit also pulls gate1 to VCC, and then pulls the Gate signal to VCC through the isolation resistor R. Therefore, this structure can ensure operation in normal mode.

[0050] Furthermore, in the overcurrent protection mode, i.e., when the drain voltage is greater than ron*Ibias, the overcurrent protection circuit starts working. This circuit can form a single-pole system, achieving stability without additional compensation. After stabilization, it clamps the drain voltage and the drain_FB signal voltage to the same value, outputting a gate0 voltage between 0 and VCC. This gate0 voltage makes the drain voltage equal to ron1*Ibias, where ron1 is the on-resistance of the sampling transistor Sensefet when VGS equals gate0. The buffer circuit then converts this gate0 voltage into a gate1 voltage with sufficient driving capability, such as... Figure 2 As shown, the gate1 voltage is further pulled to the same voltage by the isolation resistor R.

[0051] For ease of understanding, Figure 3 A schematic diagram of a signal waveform is shown, such as Figure 3 As shown, respectively Figure 2 The changes in the voltages of gate0, gate1, and the gate itself, and... Figure 3 The ID in the diagram refers to the current signal at the drain terminal of the power transistor. This should be understood. Figure 3 The 2V and 1A values ​​are not actual values, but are only used for illustration. Furthermore, in this embodiment of the invention, isolation units are used for isolation, such as... Figure 2 The isolation resistor R is used instead of directly connecting the gate1 signal and the Gate signal because it is necessary to reduce the influence of the double pole. Under the same switching speed conditions, that is, under the condition that the Gate voltage pull-up speed is constant, the delay in the isolation resistor R can significantly improve the system bandwidth. In addition, it can still provide stable constant current protection even when the leakage inductance of the transformer connected outside the chip is large.

[0052] Furthermore, the overcurrent protection circuit described above can be established not only during the power transistor's turn-on cycle, but can be kept in a continuous working state, allowing the gate0 voltage to have an initial state voltage. At this time, simply pulling up the drain voltage can generate the initial state of the gate0 voltage, which is exactly the gate voltage required for constant current protection. Moreover, this can effectively improve the response speed of the overcurrent protection circuit. The specific pull-up method can be set according to the actual application, and this embodiment of the invention does not limit it.

[0053] In addition, for the aforementioned isolation units, except Figure 2 The isolation resistor shown is in the form of... Figure 4 An implementation of an isolation circuit composed of MOSFETs is also shown. Specifically, Figure 4 The diagram shown is a schematic of the BUFFER circuit. The isolation unit uses a P-type MOSFET, and its specific connection method is as follows: Figure 4 As shown, the gate of the P-type MOSFET P is grounded, its source is connected to the drain of the first MOSFET M1 and the drain of the second MOSFET NM0, and its drain is connected to the drain of the third MOSFET NM1.

[0054] Furthermore, the aforementioned overcurrent protection circuit also includes a hysteresis resistor disposed on the sampling tube and the bias current source path; this hysteresis resistor is used to generate hysteretic overcurrent protection. Based on this hysteresis resistor, the overcurrent protection circuit can generate hysteretic overcurrent protection by adding hysteresis. For ease of understanding, Figure 5 A schematic diagram of an overcurrent protection circuit is also shown, in which, except... Figure 2The overcurrent protection circuit shown also includes a hysteresis resistor r. By adding a resistor r between the sampling transistor Sensefet and Ibias, the hysteresis ratio is equal to the relative size of r and ron. For example, if the constant current value is 2A in steady state, the trigger point is 2.2A, and the hysteresis is 0.2A, then r = 0.1 * ron, thereby achieving overcurrent protection with hysteresis.

[0055] Furthermore, the BUFFER circuit in this embodiment of the invention may also include a comparison unit; this comparison unit includes a comparison circuit and a MOS circuit; for ease of understanding, Figure 6 A schematic diagram of another type of buffer circuit is shown, such as... Figure 6 As shown, the comparator circuit is implemented using an operational amplifier chip COMP, which is typically a comparator operational amplifier chip. Figure 6 In this circuit, the output of the comparator circuit is used to obtain the input signals from the non-inverting and inverting input terminals of the aforementioned operational amplifier chip OTA2, i.e. Figure 2 The difference between the input signals of the op-amp chip OTA2 and the gate0 and gate1 in the op-amp chip is then determined. The non-inverting input terminal of the op-amp chip OTA2 is used to obtain the drain signal of the first MOS transistor, and the inverting input terminal is used to obtain the output signal of the overcurrent protection circuit.

[0056] further, Figure 6 In this example, the isolation unit includes an isolation circuit composed of MOSFETs, specifically a P-type MOSFET P. The MOSFET circuit of the comparator unit includes a fourth MOSFET M2. The gate of the fourth MOSFET M2 is connected to the output of the comparator circuit, and the source of the fourth MOSFET M2 is connected to a preset power supply, namely VCC in the figure. The drain of the fourth MOSFET is connected to the non-inverting input of the operational amplifier chip OTA2. This MOSFET circuit is used to provide a pull-up signal to the state switching circuit based on the difference between the input signals of the operational amplifier chip OTA2. That is, by adding an additional comparator to determine gate0 and gate1, when gate1 is lower than gate0, an additional pull-up is added to gate1. The pull-up is implemented through the fourth MOSFET M2 to improve the large signal response speed of gate1.

[0057] Furthermore, based on the above embodiments, this embodiment of the invention also provides a push-pull converter, which is configured with the above-mentioned constant current protection circuit; and the constant current protection circuit is used to provide overcurrent protection for the power transistors of the push-pull converter. Through the constant current protection circuit of this embodiment of the invention, not only can the constant current protection function of the power transistors of the push-pull converter be realized, but it can also be adapted to transformers with larger leakage inductance.

[0058] The push-pull converter provided in this embodiment of the invention has the same technical features as the constant current protection circuit provided in the above embodiment, so it can also solve the same technical problems and achieve the same technical effects.

[0059] The computer program product of the constant current protection circuit and push-pull converter provided in the embodiments of the present invention includes a computer-readable storage medium storing program code. The instructions included in the program code can be used to execute the methods described in the preceding method embodiments. For specific implementation, please refer to the method embodiments, which will not be repeated here.

[0060] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the specific working process of the push-pull converter described above can be referred to the corresponding process in the foregoing embodiments, and will not be repeated here.

[0061] Furthermore, in the description of the embodiments of the present invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in the present invention based on the specific circumstances.

[0062] If the aforementioned functions are implemented as software functional units and sold or used as independent products, they can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of this invention, essentially, or the part that contributes to the prior art, or a portion of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of this invention. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.

[0063] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0064] Finally, it should be noted that the above embodiments are merely specific implementations of the present invention, used to illustrate the technical solutions of the present invention, and not to limit it. The scope of protection of the present invention is not limited thereto. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that any person skilled in the art can still modify or easily conceive of changes to the technical solutions described in the foregoing embodiments within the technical scope disclosed in the present invention, or make equivalent substitutions for some of the technical features; and these modifications, changes, or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be covered within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A constant current protection circuit, characterized in that, Applied to push-pull converters, the constant current protection circuit includes an overcurrent protection circuit and a BUFFER circuit connected in sequence. The input terminal of the overcurrent protection circuit is connected to the drain of the power transistor of the push-pull converter to obtain the drain signal of the power transistor. The output terminal of the overcurrent protection circuit is connected to the input terminal of the BUFFER circuit, and the output terminal of the BUFFER circuit is connected to the gate of the power transistor. The overcurrent protection circuit is used to acquire the drain signal, operate in an open-loop state when the drain signal is lower than a preset signal threshold, and output a first drive signal to the BUFFER circuit; and trigger an overcurrent protection mode when the drain signal is higher than the signal threshold, and output a second drive signal to the BUFFER circuit. The BUFFER circuit is used to output a drive signal to the gate of the power transistor according to the first drive signal or the second drive signal, so as to drive the power transistor.

2. The constant current protection circuit according to claim 1, characterized in that, The overcurrent protection circuit includes a comparator, a sampling transistor, and a bias current source; One input terminal of the comparator is connected to the drain of the power transistor, and the other input terminal is connected to the output terminal of the bias current source; the output terminal of the comparator serves as the output terminal of the overcurrent protection circuit and is connected to the BUFFER circuit. The output terminal of the bias current source is also connected to the drain of the sampling tube; The gate of the sampling tube is connected to the output of the comparator, and the source of the sampling tube is grounded.

3. The constant current protection circuit according to claim 2, characterized in that, The sampling tube is a P-type sampling tube, and the sampling tube is a scaled-down version of the power tube according to a preset ratio.

4. The constant current protection circuit according to claim 2, characterized in that, The overcurrent protection circuit also includes a hysteresis resistor disposed on the sampling tube and the bias current source path; The hysteresis resistor is used to generate overcurrent protection with hysteresis.

5. The constant current protection circuit according to claim 1, characterized in that, The BUFFER circuit includes an operational amplifier chip and a state switching circuit connected to the operational amplifier chip; Wherein, the input terminal of the operational amplifier chip is connected to the output terminal of the overcurrent protection circuit; the output terminal of the operational amplifier chip is connected to the state switching circuit; and the output terminal of the state switching circuit is connected to the gate of the power transistor. The state switching circuit is used to respond to a state switching operation, control the state of the power transistor based on the state switching operation, and control the drive signal of the gate of the power transistor according to whether the overcurrent protection mode of the overcurrent protection circuit is triggered.

6. The constant current protection circuit according to claim 5, characterized in that, The state switching circuit includes a first MOSFET, a second MOSFET, a third MOSFET, and an isolation unit; The source of the first MOS transistor is connected to a preset power supply; the gate of the first MOS transistor is the response terminal of the state switching circuit, used to respond to the state switching operation; the drain of the first MOS transistor is connected to the drain of the second MOS transistor. The gate of the second MOS transistor is connected to the output terminal of the operational amplifier chip; the source of the second MOS transistor is grounded; wherein, the drains of the first MOS transistor and the drains of the second MOS transistor are also connected to the input terminal of the operational amplifier chip; One end of the isolation unit is connected to the drain of the first MOS transistor and the drain of the second MOS transistor, and the other end is connected to the drain of the third MOS transistor; The gate of the third MOS transistor is the response terminal of the state switching circuit, used to respond to the state switching operation; the source of the third MOS transistor is grounded.

7. The constant current protection circuit according to claim 6, characterized in that, The first MOSFET is an N-type MOSFET, and the second and third MOSFETs are P-type MOSFETs.

8. The constant current protection circuit according to claim 6, characterized in that, The isolation unit includes an isolation resistor, or the isolation unit includes an isolation circuit composed of MOS transistors.

9. The constant current protection circuit according to claim 6, characterized in that, The BUFFER circuit also includes a comparison unit; The comparison unit includes a comparison circuit and a MOS circuit; The input terminal of the comparator circuit is used to acquire the input signals of the non-inverting input terminal and the inverting input terminal of the operational amplifier chip, and to determine the difference between the input signals of the operational amplifier chip; wherein, the non-inverting input terminal is used to acquire the drain signal of the first MOS transistor, and the inverting input terminal is used to acquire the output signal of the overcurrent protection circuit; The MOS circuit includes a fourth MOS transistor; The gate of the fourth MOS transistor is connected to the output terminal of the comparator circuit, the source of the fourth MOS transistor is connected to a preset power supply, and the drain of the fourth MOS transistor is connected to the non-inverting input terminal of the operational amplifier chip. The MOS circuit is used to provide a pull-up signal to the state switching circuit based on the difference between the input signals of the operational amplifier chip and the input signals of the operational amplifier chip.

10. A push-pull converter, characterized in that, The push-pull converter is equipped with the constant current protection circuit as described in any one of claims 1 to 9; The constant current protection circuit is used to provide overcurrent protection for the power transistors of the push-pull converter.

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