Overcurrent protection circuit and switching power supply

Abstract

The utility model discloses an overcurrent protection circuit and a switching power supply, and the overcurrent protection circuit comprises a current sampling unit which converts a first voltage signal representing the magnitude of the output current of the switching power supply into a second voltage signal; the signal state distinguishing unit distinguishes the state of the second voltage signal, and the first output end and the second output end respectively output voltage signals consistent with the upper tube driving signal and the lower tube driving signal; the peak current limiting unit is used for respectively comparing the voltage signal output by the signal state distinguishing unit with the first threshold voltage and the second threshold voltage; a first input end and a third input end of the driving unit are respectively connected with a first output end and a second output end of the peak current limiting unit, a second input end and a fourth input end of the driving unit respectively input a first pulse signal and a second pulse signal, and the first pulse signal and the second pulse signal are respectively consistent with upper and lower tube driving signals; and the driving unit performs AND operation and isolation amplification on voltage signals input by the first and second input ends and the third and fourth input ends and then outputs the voltage signals. The utility model has the advantages of small layout area, fast response and no false triggering.

Description

TECHNICAL FIELD

[0001] The utility model relates to power supply technical field especially relates to a kind of overcurrent protection circuit and switching power supply. BACKGROUND

[0002] When DC-DC power stage adopts LLC series resonance topology, it is often designed to be more simple in voltage mode control mode, stable in operation, but when LLC series resonance topology output load side is short-circuited or has larger impact load, the current of LLC resonance cavity of voltage mode control is often distorted into triangular wave and current peak value is extremely large, at this time, if there is no peak current limiting protection measure, LLC primary side MOS tube will be damaged due to overcurrent.

[0003] The conventional method is to connect current transformer or hall sensor in series in resonance cavity to sample peak current to protect, generally in switching power supply system, primary side to secondary side in LLC topology is strengthened insulation system, so main transformer and current transformer all need to meet strengthened insulation, so the cost of a current transformer or current hall that meets strengthened insulation is often not accepted in small and medium power products, and the primary and secondary side foot spacing of a current transformer that meets strengthened insulation is often greater than 6mm, so it also increases PCB board area. SUMMARY

[0004] Therefore, the utility model provides a kind of overcurrent protection circuit and switching power supply, at least one of the technical problems existing in the prior art can be solved to some extent.

[0005] As the first aspect of the utility model, the technical scheme of the overcurrent protection circuit embodiment provided is as follows:

[0006] An overcurrent protection circuit is applied to switching power supply, and the switching power supply includes voltage control type LLC converter, and the primary side of the LLC converter includes at least one bridge arm, and the upper tube driving signal of the bridge arm is complementary to the lower tube driving signal, wherein the overcurrent protection circuit includes:

[0007] A current sampling unit has positive input end for inputting positive voltage signal representing the magnitude of switching power supply output current, and negative input end for inputting negative voltage signal representing the magnitude of switching power supply output voltage, and the current sampling unit is used to convert the first voltage signal representing the magnitude of switching power supply output current into second voltage signal output;

[0008] A signal state distinguishing unit has input end connected to the output end of the current sampling unit, and the signal state distinguishing unit is used to distinguish the state of second voltage signal, and outputs voltage signal consistent with the upper tube driving signal from first output end, and outputs voltage signal consistent with the lower tube driving signal from second output end;

[0009] a peak current limiting unit, a first input end of which is connected to a first output end of the signal state distinguishing unit, a second input end of which inputs a first threshold voltage, a third input end of which is connected to a second output end of the signal state distinguishing unit, and a fourth input end of which inputs a second threshold voltage, the first threshold voltage being greater than the second threshold voltage, the peak current limiting unit being configured to output a voltage signal inputted through the first input end and the second input end through a first output end thereof after comparison operation, and output a voltage signal inputted through the third input end and the fourth input end through a second output end thereof after comparison operation;

[0010] a driving unit, a first input end of which is connected to the first output end of the peak current limiting unit, a second input end of which inputs a first pulse signal, a third input end of which is connected to the second output end of the peak current limiting unit, and a fourth input end of which inputs a second pulse signal, the first pulse signal being consistent with the upper tube driving signal, and the second pulse signal being consistent with the lower tube driving signal, the driving unit being configured to output a voltage signal inputted through the first input end and the second input end through a first output end thereof after AND operation and isolation amplification processing, and output a voltage signal inputted through the third input end and the fourth input end through a second output end thereof after AND operation and isolation amplification processing.

[0011] Preferably, the current sampling unit comprises a resistor R2, a resistor R3, a resistor R4, a resistor R5 and an operational amplifier U1, one end of the resistor R3 being a positive input end of the current sampling unit, one end of the resistor R2 being a negative input end of the current sampling unit, the other end of the resistor R3 and one end of the resistor R5 being connected to a non-inverting input end of the operational amplifier U1, the other end of the resistor R2 and one end of the resistor R4 being connected to an inverting input end of the operational amplifier U1, the other end of the resistor R4 and an output end of the operational amplifier U1 being connected together to form an output end of the current sampling unit, and the other end of the resistor R5 being configured to be grounded.

[0012] Preferably, the signal state distinguishing unit comprises a first switch tube and a second switch tube, one end of the first switch tube and one end of the second switch tube each being divided into two end heads, the first end head of the one end of the first switch tube and the first end head of the one end of the second switch tube being connected together to form a first input end of the signal state distinguishing unit, the second end head of the one end of the first switch tube being a first output end of the signal state distinguishing unit, the second end head of the one end of the second switch tube being a second output end of the signal state distinguishing unit, the other end of the first switch tube and the other end of the second switch tube being connected together to be grounded, the first switch tube being configured to be turned on and turned off at a time consistent with the lower tube of the bridge arm, and the second switch tube being configured to be turned on and turned off at a time consistent with the upper tube of the bridge arm.

[0013] Preferably, the first switch tube is MOS tube Q5, the second switch tube is MOS tube Q6, the source of the MOS tube Q5 is one end of the first switch tube, the drain is the other end of the first switch tube, and the gate is used to input a voltage signal consistent with the lower tube driving signal; the source of the MOS tube Q6 is one end of the second switch tube, the drain is the other end of the second switch tube, and the gate is used to input a voltage signal consistent with the upper tube driving signal.

[0014] Preferably, the peak current limiting unit comprises resistors R6, R7, comparator U2B and comparator U3B, one end of the resistor R6 is the first input end of the peak current limiting unit, the other end of the resistor R6 is connected to the inverting input end of the comparator U2B, the non-inverting input end of the comparator U2B is the second input end of the peak current limiting unit, one end of the resistor R7 is the third input end of the peak current limiting unit, the other end of the resistor R7 is connected to the inverting input end of the comparator U3B, the non-inverting input end of the comparator U3B is the fourth input end of the peak current limiting unit, the output end of the comparator U2B is the first output end of the peak current limiting unit, and the output end of the comparator U3B is the second output end of the peak current limiting unit.

[0015] Preferably, the peak current limiting unit further comprises resistors R8 and R9, the resistor R8 is connected between the non-inverting input end of the comparator U2B and the output end of the comparator U2B, and the resistor R9 is connected between the non-inverting input end of the comparator U3B and the output end of the comparator U3B.

[0016] Preferably, the driving unit comprises the logic chip U4, the logic chip U5, the transformer T2, the resistor R10 and the resistor R11, the first input end of the logic chip U4 is the first input end of the driving unit, the second input end of the logic chip U4 is the second input end of the driving unit, the first input end of the logic chip U5 is the third input end of the driving unit, the second input end of the logic chip U5 is the fourth input end of the driving unit, the output end of the logic chip U4 is connected with the same end of the primary winding of the transformer T2, the output end of the logic chip U5 is connected with the different end of the primary winding of the transformer T2, the same end of the first secondary winding of the transformer T2 is connected with one end of the resistor R10, the other end of the resistor R10 is the first output end of the driving unit and is used for providing a driving signal for the upper tube of the bridge arm, the different end of the first secondary winding of the transformer T2 is used for connecting the midpoint of the bridge arm, the same end of the second secondary winding of the transformer T2 is connected with one end of the resistor R11, the other end of the resistor R11 is the second output end of the driving unit and is used for providing a driving signal for the lower tube of the bridge arm, and the different end of the second secondary winding of the transformer T2 is used for connecting the source of the lower tube of the bridge arm.

[0017] As a second aspect of the utility model, the technical scheme of the switching power supply embodiment is as follows:

[0018] A switching power supply, the switching power supply comprises a voltage control type LLC converter, the primary side of the LLC converter at least comprises a bridge arm, the upper tube driving signal of the bridge arm and the lower tube driving signal are complementary, characterized in that: the switching power supply further comprises the overcurrent protection circuit of any one of the above first aspect.

[0019] Further, the switching power supply comprises a sampling device connected between the center tap of the secondary winding and the negative electrode of the switching power supply output, for obtaining a voltage signal representing the size of the switching power supply output current.

[0020] Preferably, the sampling device comprises a resistor RS1.

[0021] Compared with the prior art, the utility model has the following advantages and beneficial effects:

[0022] (1) the LLC converter control mode proposed in the utility model embodiment is a voltage type control mode, and the control scheme has the characteristics of mature control system, simple control, small risk and strong universality;

[0023] (2) The current sampling unit of the embodiment of the utility model is non-isolated type, has low cost, small board area, and can be applied in different secondary side rectification topology schemes, for example, the secondary side can adopt full-wave rectification (i.e. double-winding transformer), can also adopt half-wave rectification (single-winding transformer), or full-wave rectification (double-winding transformer), therefore, the versatility is strong, and the compatibility is high;

[0024] (3) The conventional peak current protection is often controlled by a digital chip, so that the current signal is processed by sampling, recognized by the digital chip, responded, and finally the pulse is turned off, and the delay of the series of actions is often too large, causing the defect that the peak current limitation is not timely, the overcurrent protection circuit embodiment of the utility model adopts analog control stop wave, and has the characteristics of fast response and no false triggering. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 It is a specific schematic diagram of the switching power supply to which the overcurrent protection circuit of the utility model is applied;

[0026] Figure 2 It is a principle block diagram of the overcurrent protection circuit of the first embodiment of the utility model;

[0027] Figure 3 It is a specific circuit diagram comprising the current sampling unit, the signal state distinguishing unit and the peak current limitation unit in the overcurrent protection circuit of the first embodiment of the utility model;

[0028] Figure 4 It is a specific circuit diagram comprising the driving unit in the overcurrent protection circuit of the first embodiment of the utility model. DETAILED DESCRIPTION

[0029] In order to make the above-mentioned purpose, features and advantages of the utility model more obvious and easy to understand, the specific embodiments of the utility model are described in detail below with reference to the drawings, obviously, the described embodiments are part of the embodiments of the utility model, rather than all the embodiments. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative labor should belong to the protection scope of the application.

[0030] It should be noted that the terms "include" and "have" and any variations thereof in the specification and claims of the application are intended to cover non-exclusive inclusion, for example, the inclusion of a series of components, unit circuits or control sequences does not have to be limited to those components, unit circuits or control sequences clearly listed, but can include components, unit circuits or control sequences not clearly listed or inherent to the circuit.

[0031] In addition, the embodiments in the application and the features in the embodiments can be combined with each other in the case of no conflict.

[0032] It should be understood that, in the specification and claims, when it is described that an element is "connected" to another element, the element can be "directly connected" to the other element, or "connected" to the other element through a third element; when it is described that a step is followed by another step, the step can be directly followed by the other step, or followed by the other step through a third step.

[0033] First embodiment

[0034] The embodiment provides a kind of overcurrent protection circuit, applied to switching power supply, switching power supply includes voltage control type LLC converter, LLC converter primary side at least includes one bridge arm, the upper tube drive signal of bridge arm and lower tube drive signal are complementary, Figure 1 It is a specific schematic diagram of the switching power supply to which the overcurrent protection circuit of the utility model is applied, which includes a bridge arm composed of upper tube Q1 and lower tube Q2, the upper tube drive signal is LLC_DVH, and the lower tube drive signal is LLC_DVL.

[0035] Figure 1 The voltage signal representing the magnitude of the output current of the switching power supply in the circuit is realized by the sampling resistor RS1, and the sampling resistor RS1 is connected between the center tap of the secondary winding and the negative electrode of the switching power supply output.

[0036] It should be noted that, Figure 1 It is only a schematic diagram, and the switching power supply to which the overcurrent protection circuit of the embodiment is applied is not limited to Figure 1 Specific circuit, and those skilled in the art can adjust the switching power supply circuit of Figure 1 For example, the main power topology of primary side can be adjusted from half-bridge LLC topology to full-bridge LLC topology or phase-shift full-bridge LLC topology, the rectifier circuit of secondary side can be adjusted from half-wave rectification to full-wave rectification or from diode rectification to MOS tube synchronous rectification, and the specific circuit is not limited by the utility model.

[0037] The overcurrent protection circuit of the embodiment utilizes non-isolated current sampling to construct pure analog circuit control wave-by-wave current limiting, Figure 2 It is the principle block diagram of the overcurrent protection circuit of the first embodiment of the utility model, please refer to Figure 2 , which includes:

[0038] The current sampling unit 101 has a positive input end for inputting a positive voltage signal VS- representing the size of the output current of the switching power supply, and a negative input end for inputing a negative voltage signal VS+ representing the size of the output current of the switching power supply, and is used for converting the first voltage signal representing the size of the output current of the switching power supply into a second voltage signal and outputting V_CS;

[0039] The signal state distinguishing unit 102 has an input end connected to the output end of the current sampling unit, and is used for distinguishing the state of the second voltage signal, outputting a voltage signal VS_H consistent with the upper tube driving signal from a first output end, and outputting a voltage signal VS_L consistent with the lower tube driving signal from a second output end.

[0040] The peak current limiting unit 103 has a first input end connected to the first output end of the signal state distinguishing unit, a second input end inputting a first threshold voltage REF_H, a third input end connected to the second output end of the signal state distinguishing unit, and a fourth input end inputting a second threshold voltage REF_L, wherein the first threshold voltage REF_H is greater than the second threshold voltage REF_L, and the peak current limiting unit is used for comparing and operating the voltage signals input from the first input end and the second input end, outputting OCP_H from the first output end, and comparing and operating the voltage signals input from the third input end and the fourth input end, outputting OCP_L from the second output end.

[0041] The driving unit 104 has a first input end connected to the first output end of the peak current limiting unit, a second input end inputting a first pulse signal PWM_H, a third input end connected to the second output end of the peak current limiting unit, and a fourth input end inputting a second pulse signal PWM_L, wherein the first pulse signal is consistent with the upper tube driving signal, the second pulse signal is consistent with the lower tube driving signal, and the driving unit is used for performing AND operation and isolation amplification processing on the voltage signals input from the first input end and the second input end, outputting LLC_DVH from the first output end, and performing AND operation and isolation amplification processing on the voltage signals input from the third input end and the fourth input end, outputting LLC_DV L from the second output end.

[0042] Figure 3 A specific circuit diagram including the current sampling unit, the signal state distinguishing unit and the peak current limiting unit in the over-current protection circuit of the first embodiment of the utility model, please refer to Figure 3 , wherein:

[0043] The current sampling unit 101 comprises resistors R2, R3, R4, R5 and an operational amplifier U1, one end of the resistor R3 is the positive input end of the current sampling unit, one end of the resistor R2 is the negative input end of the current sampling unit, the other end of the resistor R3 and one end of the resistor R5 are connected to the non-inverting input end of the operational amplifier U1, the other end of the resistor R2 and one end of the resistor R4 are connected to the inverting input end of the operational amplifier U1, the other end of the resistor R4 and the output end of the operational amplifier U1 are connected together to be the output end of the current sampling unit, and the other end of the resistor R5 is used for grounding;

[0044] The signal state distinguishing unit 102 comprises first and second switch tubes, one end of the first switch tube and one end of the second switch tube are each divided into two end heads, the first end head of the one end of the first switch tube and the first end head of the one end of the second switch tube are connected together to be the first input end of the signal state distinguishing unit, the second end head of the one end of the first switch tube is the first output end of the signal state distinguishing unit, the second end head of the one end of the second switch tube is the second output end of the signal state distinguishing unit, the other end of the first switch tube and the other end of the second switch tube are connected together to be used for grounding, the first switch tube is configured to be turned on and turned off at the same time as the lower tube of the bridge arm, and the second switch tube is configured to be turned on and turned off at the same time as the upper tube of the bridge arm.

[0045] Specifically, the first switch tube is a MOS tube Q5, the second switch tube is a MOS tube Q6, the source of the MOS tube Q5 is the one end of the first switch tube, the drain is the other end of the first switch tube, and the gate is used for inputting a voltage signal consistent with the lower tube driving signal; the source of the MOS tube Q6 is the one end of the second switch tube, the drain is the other end of the second switch tube, and the gate is used for inputting a voltage signal consistent with the upper tube driving signal.

[0046] The peak current limiting unit 103 comprises resistors R6, R7, a comparator U2B and a comparator U3B, one end of the resistor R6 is the first input end of the peak current limiting unit, the other end of the resistor R6 is connected to the inverting input end of the comparator U2B, the non-inverting input end of the comparator U2B is the second input end of the peak current limiting unit, one end of the resistor R7 is the third input end of the peak current limiting unit, the other end of the resistor R7 is connected to the inverting input end of the comparator U3B, the non-inverting input end of the comparator U3B is the fourth input end of the peak current limiting unit, the output end of the comparator U2B is the first output end of the peak current limiting unit, and the output end of the comparator U3B is the second output end of the peak current limiting unit.

[0047] Figure 4 A specific circuit diagram comprising the driving unit in the overcurrent protection circuit of the first embodiment of the utility model, please refer to Figure 4The driving unit 104 comprises the logic chip U4, the logic chip U5, the transformer T2, the resistor R10 and the resistor R11, the first input end of the driving unit is the first input end of the logic chip U4, the second input end of the driving unit is the second input end of the logic chip U4, the third input end of the driving unit is the first input end of the logic chip U5, the fourth input end of the driving unit is the second input end of the logic chip U5, the output end of the logic chip U4 is connected with the same end of the primary winding of the transformer T2, the output end of the logic chip U5 is connected with the different end of the primary winding of the transformer T2, the same end of the first secondary winding of the transformer T2 is connected with one end of the resistor R10, the other end of the resistor R10 is the first output end of the driving unit, used for providing the driving signal for the upper tube of the bridge arm, the different end of the first secondary winding of the transformer T2 is used for connecting the midpoint of the bridge arm, the same end of the second secondary winding of the transformer T2 is connected with one end of the resistor R11, the other end of the resistor R11 is the second output end of the driving unit, used for providing the driving signal for the lower tube of the bridge arm, and the different end of the second secondary winding of the transformer T2 is used for connecting the source of the lower tube of the bridge arm.

[0048] Figure 3 And Figure 4 The specific circuit of the over-current protection circuit is composed of the above-mentioned circuits, and the working principle is analyzed as follows.

[0049] The primary resonant cavity current of the switching power supply (i.e. the current on the primary MOS tube) will generate a linear corresponding voltage signal at the two ends of the secondary sampling resistor RS1 of the switching power supply after the transformation of the transformer. The voltage signal is amplified by the current sampling unit 101 composed of a differential operational amplifier to generate a triangular wave signal V_CS, and the rising and falling edges of the triangular wave signal V_CS are strictly symmetrical.

[0050] Since the gate input of the MOS tube Q5 in the signal state distinguishing unit 102 is consistent with the voltage signal of the lower tube driving signal, when the MOS tube Q5 is turned on, the triangular wave signal V_CS will be pulled down to the ground, and therefore the voltage signal VS_H consistent with the upper tube driving signal is output at the first output end of the signal state distinguishing unit 102. Specifically, the waveform of the voltage signal VS_H is the waveform after cutting off the right side of the triangular wave signal V_CS, which is a right triangle wave. Similarly, the voltage signal VS_L consistent with the lower tube driving signal is output at the second output end of the signal state distinguishing unit 102. Specifically, the waveform of the voltage signal VS_L is the waveform after cutting off the left side of the triangular wave signal V_CS, which is also a right triangle wave.

[0051] The comparator U2B compares the voltage signal VS_H with the first threshold voltage REF_H, and outputs a low level when the voltage signal VS_H reaches the first threshold voltage REF_H (i.e. when the overcurrent of the upper transistor Q1 occurs), which is input into the AND logic chip U4 in the driving unit, so that the driving signal of the upper transistor Q1 is low at this time, and the lower transistor Q2 is opened in the natural period due to the energy in the parasitic capacitor being discharged.

[0052] The reason why the left-right symmetrical triangular wave signal V_CS is converted into two right-angled triangular wave voltage signals VS_H and VS_L by the signal state distinguishing unit 102 is analyzed as follows:

[0053] If the peak current corresponding to the triangular wave signal V_CS is in a high-frequency state, when the LLC resonant cavity is in a deep continuous state, the triangular wave signal reaches the peak current protection, and due to the deep continuity, the time when the peak current is zero will be very short, which will cause the peak current protection to be unable to be accurately reached, therefore, the left-right symmetrical triangular wave signal V_CS is converted into two right-angled triangular wave voltage signals VS_H and VS_L by the signal state distinguishing unit 102, and specifically, for example, when the upper transistor Q1 of the primary side is turned off, i.e. the rising edge of the triangular wave is ended, the output of the operational amplifier U2B is forcibly pulled low by the MOS transistor Q5, so that the lower transistor Q2 can be smoothly turned on in the next half cycle after the peak current protection.

[0054] Further, please continue to Figure 3The peak current limiting unit further comprises a resistor R8 and a resistor R9, the resistor R8 is connected between the non-inverting input terminal of the comparator U2B and the output terminal of the comparator U2B, and the resistor R9 is connected between the non-inverting input terminal of the comparator U3B and the output terminal of the comparator U3B. The added resistor R8 and the resistor R9 are back difference resistors, and the purpose is to avoid the noise interference from causing the oscillation and jumping at the peak current protection threshold.

[0055] Second embodiment

[0056] The embodiment provides a switching power supply, the switching power supply comprises a voltage control type LLC converter, and the primary side of the LLC converter at least comprises one bridge arm.

[0057] The switching power supply adopts a voltage type control mode and a non-isolated current sampling scheme, and since the switching power supply comprises any one of the overcurrent protection circuits in the first embodiment, the risk of LLC resonant cavity current being too large to fail when an output load side is short-circuited or overloaded is solved, the characteristic that peak current is reliably and timely limited to a peak wave under all possible working conditions of a load is effectively achieved, and the hidden danger that a client load is short-circuited or a load impact current is too large to be damaged is solved.

[0058] Preferably, the switching power supply comprises a sampling device connected between the center tap of the secondary side winding and the negative electrode of the output of the switching power supply, and used for obtaining a voltage signal representing the size of the output voltage of the switching power supply.

[0059] Preferably, the sampling device comprises a resistor RS1.

[0060] The above is only the embodiment of the utility model, and it should be particularly pointed out that the above embodiment should not be regarded as the limitation of the utility model, and for ordinary skilled persons in the technical field, a plurality of improvements and refinements can be made without departing from the spirit and range of the utility model, and the improvements and refinements should also be regarded as the protection range of the utility model.

Claims

1. An over-current protection circuit applied to a switching power supply, the switching power supply comprising a voltage-controlled LLC converter, a primary side of the LLC converter comprising at least one bridge arm, an upper tube driving signal of the bridge arm being complementary to a lower tube driving signal, characterized in that, The overcurrent protection circuit comprises: a current sampling unit, a positive input end of which is used for inputting a positive voltage signal representing the size of the output current of the switching power supply, and a negative input end of which is used for inputting a negative voltage signal representing the size of the output current of the switching power supply, the current sampling unit being used for converting a first voltage signal representing the size of the output current of the switching power supply into a second voltage signal and outputting the second voltage signal; a signal state distinguishing unit, an input end of which is connected to an output end of the current sampling unit, the signal state distinguishing unit being used for distinguishing the state of the second voltage signal, outputting a voltage signal consistent with the upper tube driving signal from a first output end thereof, and outputting a voltage signal consistent with the lower tube driving signal from a second output end thereof; a peak current limiting unit, a first input end of which is connected to the first output end of the signal state distinguishing unit, a second input end of which inputs a first threshold voltage, a third input end of which is connected to the second output end of the signal state distinguishing unit, and a fourth input end of which inputs a second threshold voltage, the first threshold voltage being greater than the second threshold voltage, the peak current limiting unit being used for comparing and operating the voltage signals input from the first input end and the second input end thereof and outputting the result from a first output end thereof, and comparing and operating the voltage signals input from the third input end and the fourth input end thereof and outputting the result from a second output end thereof; a driving unit, a first input end of which is connected to the first output end of the peak current limiting unit, a second input end of which inputs a first pulse signal, a third input end of which is connected to the second output end of the peak current limiting unit, and a fourth input end of which inputs a second pulse signal, the first pulse signal being consistent with the upper tube driving signal, and the second pulse signal being consistent with the lower tube driving signal, the driving unit being used for performing AND operation and isolation amplification processing on the voltage signals input from the first input end and the second input end thereof and outputting the result from a first output end thereof, and performing AND operation and isolation amplification processing on the voltage signals input from the third input end and the fourth input end thereof and outputting the result from a second output end thereof.

2. The overcurrent protection circuit of claim 1, wherein: The current sampling unit comprises resistors R2, R3, R4, R5 and an operational amplifier U1, one end of the resistor R3 being a positive input end of the current sampling unit, one end of the resistor R2 being a negative input end of the current sampling unit, the other end of the resistor R3 and one end of the resistor R5 being connected to a non-inverting input end of the operational amplifier U1, the other end of the resistor R2 and one end of the resistor R4 being connected to an inverting input end of the operational amplifier U1, the other end of the resistor R4 and an output end of the operational amplifier U1 being connected together to form an output end of the current sampling unit, and the other end of the resistor R5 being used for grounding.

3. The overcurrent protection circuit of claim 1, wherein: The signal state distinguishing unit comprises a first switch tube and a second switch tube, one end of the first switch tube and one end of the second switch tube are each divided into two ends, the first end of the one end of the first switch tube and the first end of the one end of the second switch tube are connected together as a first input end of the signal state distinguishing unit, the second end of the one end of the first switch tube is a first output end of the signal state distinguishing unit, the second end of the one end of the second switch tube is a second output end of the signal state distinguishing unit, the other end of the first switch tube and the other end of the second switch tube are connected together for grounding, the first switch tube is configured to be conductive with the lower tube of the bridge arm in consistent with the turn-on and turn-off time, and the second switch tube is configured to be conductive with the upper tube of the bridge arm in consistent with the turn-on and turn-off time.

4. The overcurrent protection circuit of claim 3, wherein: The first switch tube is a MOS tube Q5, the second switch tube is a MOS tube Q6, the source of the MOS tube Q5 is the one end of the first switch tube, the drain is the other end of the first switch tube, and the gate is used for inputting a voltage signal consistent with the lower tube driving signal; the source of the MOS tube Q6 is the one end of the second switch tube, the drain is the other end of the second switch tube, and the gate is used for inputting a voltage signal consistent with the upper tube driving signal.

5. The overcurrent protection circuit of claim 1, wherein: The peak current limiting unit comprises a resistor R6, a resistor R7, a comparator U2B and a comparator U3B, one end of the resistor R6 is a first input end of the peak current limiting unit, the other end of the resistor R6 is connected to the inverting input end of the comparator U2B, the non-inverting input end of the comparator U2B is a second input end of the peak current limiting unit, one end of the resistor R7 is a third input end of the peak current limiting unit, the other end of the resistor R7 is connected to the inverting input end of the comparator U3B, the non-inverting input end of the comparator U3B is a fourth input end of the peak current limiting unit, the output end of the comparator U2B is a first output end of the peak current limiting unit, and the output end of the comparator U3B is a second output end of the peak current limiting unit.

6. The overcurrent protection circuit of claim 5, wherein: The peak current limiting unit further comprises a resistor R8 and a resistor R9, the resistor R8 is connected between the non-inverting input end of the comparator U2B and the output end of the comparator U2B, and the resistor R9 is connected between the non-inverting input end of the comparator U3B and the output end of the comparator U3B.

7. The overcurrent protection circuit of claim 1, wherein: The driving unit comprises an AND logic chip U4, an AND logic chip U5, a transformer T2, a resistor R10 and a resistor R11, a first input end of the AND logic chip U4 is a first input end of the driving unit, a second input end of the AND logic chip U4 is a second input end of the driving unit, a first input end of the AND logic chip U5 is a third input end of the driving unit, a second input end of the AND logic chip U5 is a fourth input end of the driving unit, an output end of the AND logic chip U4 is connected with a same-named end of a primary winding of the transformer T2, an output end of the AND logic chip U5 is connected with an opposite-named end of the primary winding of the transformer T2, a same-named end of a first secondary winding of the transformer T2 is connected with one end of the resistor R10, the other end of the resistor R10 is a first output end of the driving unit, used for providing a driving signal for an upper tube of the bridge arm, an opposite-named end of the first secondary winding of the transformer T2 is used for connecting a midpoint of the bridge arm, a same-named end of a second secondary winding of the transformer T2 is connected with one end of the resistor R11, the other end of the resistor R11 is a second output end of the driving unit, used for providing a driving signal for a lower tube of the bridge arm, an opposite-named end of the second secondary winding of the transformer T2 is used for connecting a source of the lower tube of the bridge arm.

8. A switching power supply comprising a voltage-controlled LLC converter, the LLC converter having a primary side comprising at least one bridge leg, the upper gate drive signal of the bridge leg being complementary to the lower gate drive signal, characterized in that: The switching power supply further comprises the over-current protection circuit according to any one of claims 1 to 7.

9. The switching power supply of claim 8, wherein: The switching power supply comprises a sampling device connected between a center tap of the secondary winding and a negative electrode of the switching power supply output, used for obtaining a voltage signal representing a magnitude of the switching power supply output current.

10. The switching power supply of claim 9, wherein: The sampling device comprises a resistor RS1.

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