LED overcurrent protection circuit with self-locking function

Abstract

The utility model provides an LED over-current protection circuit with a self-locking function. The LED over-current protection circuit comprises an LED lamp string, a power tube Q3, a current detection circuit, an over-current protection self-locking circuit and a driving circuit. The input end of the LED lamp string is connected with the first power supply Vbat, and the output end of the LED lamp string is connected with the first connecting end of the power tube Q3; the input end A of the current detection circuit is connected with the second connecting end of the power tube Q3, and the output end B of the current detection circuit outputs sampling voltage Vb; the input end C of the overcurrent protection self-locking circuit is connected with the output end B of the current detection circuit; the input end E of the drive circuit is connected with the output end D of the PWM signal and overcurrent protection self-locking circuit, and the output end F of the drive circuit is connected with the control end of the power tube Q3. Compared with the prior art, the hardware over-current protection circuit is built through discrete devices, the cost is low, the circuit is simple, and the over-current protection has a self-locking function. In addition, according to products with different powers, overcurrent protection points can be adjusted at will.

Description

TECHNICAL FIELD

[0001] The utility model relates to circuit design technical field, especially relate to a LED overcurrent protection circuit with self locking function.

BACKGROUND TECHNIQUE

[0002] LED has the advantages of small size, high brightness, long life, is widely used in the field of automobile and industrial market, with the development of LED technology, LED drive protection circuit is more and more important.But the existing market LED drive dimming overcurrent protection circuit overcurrent protection, can not be locked, the product will be in a overcurrent oscillation process, if the circuit can not lock the circuit overcurrent state in time, may damage the circuit.In addition, some overcurrent protection circuit is based on integrated chip, its overcurrent protection point can not be adjusted, and the cost is high, the optional chip is not much, chip supply is not stable.

[0003] Therefore, it is necessary to provide a new technical scheme to solve the above problems.

UTILITY MODEL CONTENTS

[0004] One of the purposes of the utility model is to provide a LED overcurrent protection circuit with self locking function, which can build a hardware overcurrent protection circuit through discrete devices, has low cost, simple circuit, and overcurrent protection has self locking function.In addition, according to different power products, the overcurrent protection point can be adjusted arbitrarily.

[0005] According to one aspect of the utility model, the utility model provides a LED overcurrent protection circuit with self locking function, it includes LED lamp string, power tube Q3, current detection circuit, overcurrent protection self locking circuit and drive circuit, the input of LED lamp string and first power Vbat are connected, its output and power tube Q3's first connection end are connected, the input of current detection circuit A and power tube Q3's second connection end are connected, its output B exports sampling voltage Vb, sampling voltage Vb reflects the current value of flowing through LED lamp string, the input of overcurrent protection self locking circuit C and current detection circuit's output B are connected, when sampling voltage Vb is less than the reference voltage of prearranging, overcurrent protection self locking circuit's output D does not export overcurrent protection signal, when sampling voltage Vb is greater than the reference voltage of prearranging, overcurrent protection self locking circuit's output D continues to export overcurrent protection signal, the input of drive circuit E and PWM signal and overcurrent protection self locking circuit's output D are connected, its output F and power tube Q3's control end are connected, when overcurrent protection self locking circuit's output D does not export overcurrent protection signal, drive circuit exports periodic drive signal based on PWM signal, and the periodic drive signal is exported through drive circuit's output F to drive power tube Q3 periodic conduction and cut-off, when overcurrent protection self locking circuit's output D continues to export overcurrent protection signal, drive circuit exports constant drive signal through its output F based on overcurrent protection signal to cut off power tube Q3 continuously.

[0006] Compared with the prior art, the utility model discloses a discrete device builds hardware overcurrent protection circuit, and its cost is low, and circuit is simple, and overcurrent protection has self locking function.

DRAWINGS

[0007] In order to more clearly illustrate the technical scheme of the utility model embodiment, the following will be briefly introduced to the drawing needed to be used in the embodiment description, and obviously, the drawing in the following description is only some embodiments of the utility model, and for those skilled in the art, under the premise of not paying the creative labor, other drawings can also be obtained according to these drawings. Wherein:

[0008] Figure 1 It is the circuit schematic diagram of the LED overcurrent protection circuit with self locking function in one embodiment of the utility model.

CONCRETE IMPLEMENTATION

[0009] In order to make the above purpose, features and advantages of the utility model more apparent and easy to understand, the following will be further detailed to the utility model with the drawings and specific implementation.

[0010] Reference herein to "one implementation" or "an implementation" means that a particular feature, structure, or characteristic following can be included in at least one implementation of the present application. The appearances of "in one implementation" or "in an implementation" at various places in the specification are not necessarily all referring to the same implementation, nor are they necessarily alternatives with priority to one over another. Unless specifically stated otherwise, coupled, connected, linked, or the like, as used herein, means an electrical connection, which can be direct or indirect.

[0011] In the description of the present application, it is to be understood that the terms "upper", "lower", "front", "rear", "right", "left", "vertical", "horizontal", "top", "bottom", "inner", "outer", and the like, indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application.

[0012] Reference is made to Figure 1 As shown in FIG. 1, which is a circuit schematic diagram of the LED overcurrent protection circuit with self-locking function in one embodiment of the present application. Figure 1 The LED overcurrent protection circuit with self-locking function shown in FIG. 1 includes an LED lamp string LED1, a power tube (Metal Oxide Semiconductor Field Effect Transistor, Mosfet) Q3, a current detection circuit 110, an overcurrent protection self-locking circuit 120, and a driving circuit 130.

[0013] The input end (or anode) of the LED lamp string LED1 is connected with the first power supply Vbat, and the output end (or cathode) thereof is connected with the first connecting end of the power tube Q3. The input end A of the current detection circuit 110 is connected with the second connecting end of the power tube Q3, and the output end B outputs a sampling voltage Vb, which reflects the current value flowing through the LED lamp string LED1 (or the power tube Q3), that is, the sampling voltage Vb is generated by the current detection circuit 110 through detecting the current value flowing through the LED lamp string LED1. The input end C of the overcurrent protection self-locking circuit 120 is connected with the output end B of the current detection circuit 110. When the sampling voltage Vb is less than a preset reference voltage Vref (which indicates that the current value flowing through the LED lamp string LED1 is less than a preset overcurrent protection threshold), the output end D of the overcurrent protection self-locking circuit 120 does not output an overcurrent protection signal. When the sampling voltage Vb is greater than the preset reference voltage Vref (which indicates that the current value flowing through the LED lamp string LED1 is greater than the preset overcurrent protection threshold), the output end D of the overcurrent protection self-locking circuit 120 continuously outputs the overcurrent protection signal.

[0014] The input end E of the driving circuit 130 is connected with a PWM (Pulse Width Modulation) signal, and the input end E of the driving circuit 130 is connected with the output end D of the overcurrent protection self-locking circuit 120, and the output end F thereof is connected with the control end of the power tube Q3. When the output end D of the overcurrent protection self-locking circuit 120 does not output the overcurrent protection signal, the driving circuit 130 generates a periodic driving signal based on the PWM signal, and the periodic driving signal is output through the output end F of the driving circuit 130 to drive the power tube Q3 to be periodically turned on and turned off. When the output end D of the overcurrent protection self-locking circuit 120 continuously outputs the overcurrent protection signal, the driving circuit 130 outputs a constant driving signal through the output end F thereof based on the overcurrent protection signal to continuously turn off the power tube Q3, so as to lock the overcurrent protection state and ensure that the product will not be damaged due to repeated overcurrent failure. The PWM signal is a periodic high-low square wave signal. In the normal working state (or non-overcurrent state), the power tube Q3 can be controlled by changing the duty ratio of the PWM signal, so as to adjust the luminous brightness of the LED lamp string LED1. In other words, the PWM signal, the power tube Q3, the LED lamp string LED1, the first power supply Vbat, the current detection circuit 110 and the driving circuit 130 constitute a main loop of the dimmable LED, and the loop completes the dimming function of the LED in the normal state.

[0015] The current detection circuit 110 comprises a sampling resistor R11, one end of the sampling resistor R11 is connected with the input end A (or the second connecting end of the power tube Q3) of the current detection circuit 110, the other end is grounded, the output end B of the current detection circuit 110 is connected with the input end A, and the voltage drop on the sampling resistor R11 is the sampling voltage Vb output by the output end B.

[0016] In Figure 1 In the specific embodiment shown, the current detection circuit 110 further comprises a resistor R12 and a capacitor C2, one end of the resistor R12 is connected with the output end B, the other end is connected with the input end A, one end of the capacitor C2 is connected with the output end B, and the other end is grounded. The resistor R12 and the capacitor C2 form an RC filter, which filters out the interference signals of the sampling resistor R11.

[0017] The overcurrent protection self-locking circuit 120 comprises a comparator U1 and an overcurrent protection self-locking unit 122. The first input end of the comparator U1 is connected with the output end B of the current detection circuit 110, the second input end receives a preset reference voltage Vref, the comparator U1 is used for comparing the sizes of the sampling voltage Vb and the preset reference voltage Vref, and outputs the comparison results through the output end. For example, when the sampling voltage Vb is less than the preset reference voltage Vref, the output end of the comparator U1 outputs a first comparison result, indicating that the current value flowing through the LED lamp string LED1 is less than the preset overcurrent protection threshold value; when the sampling voltage Vb is greater than the preset reference voltage Vref, the output end of the comparator U1 outputs a second comparison result, indicating that the current value flowing through the LED lamp string LED1 is greater than the preset overcurrent protection threshold value.

[0018] The input end of the overcurrent protection self-locking unit 122 is connected with the output end of the comparator U1, the output end serves as the output end D of the overcurrent protection self-locking circuit 120, when the sampling voltage Vb is less than the preset reference voltage Vref, the output end of the comparator U1 outputs the first comparison result, the overcurrent protection self-locking unit 122 controls the output end D not to output the overcurrent protection signal based on the first comparison result; when the sampling voltage Vb is greater than the preset reference voltage Vref, the output end of the comparator U1 outputs the second comparison result, the overcurrent protection self-locking unit 122 enters the overcurrent protection self-locking state based on the second comparison result, so that the output end D continuously outputs the overcurrent protection signal.

[0019] The over-current protection self-locking unit 122 comprises a switching device Q5, a switching device Q6, a switching device Q7, a resistor R6, a resistor R7, a resistor R8 and a resistor R9. One end of the resistor R6 is connected with the second power supply VCC, and the other end thereof is connected with a node G. One end of the resistor R7 is connected with the node G, and the other end thereof is connected with a first connection end of the switching device Q7. A second connection end of the switching device Q7 is grounded, and a control end thereof is connected with an output end of the comparator U1. A first connection end of the switching device Q6 is connected with the second power supply VCC, a control end thereof is connected with the node G, and a second connection end thereof is connected with the control end of the switching device Q7 through the resistor R8. A first connection end of the switching device Q5 is connected with an output end D of the over-current protection self-locking circuit 120, a second connection end thereof is grounded, and a control end thereof is connected with the second connection end of the switching device Q6 through the resistor R9. Figure 1 In the specific embodiment shown, the over-current protection self-locking unit 122 further comprises a diode D1. A negative electrode of the diode D1 is connected with the control end of the switching device Q7, and a positive electrode thereof is connected with the output end of the comparator U1.

[0020] When the output end of the comparator U1 outputs the first comparison result, the switching device Q5, the switching device Q6 and the switching device Q7 are all turned off, so that the output end D of the over-current protection self-locking circuit 120 does not output the over-current protection signal. When the output end of the comparator U1 outputs the second comparison result, the switching device Q5, the switching device Q6 and the switching device Q7 are all turned on, so that the over-current protection self-locking unit 122 enters the over-current protection self-locking state, and the output end D continuously outputs the over-current protection signal.

[0021] The driving circuit 130 comprises a switching device Q1, a switching device Q2, a switching device Q4, a resistor R3, a resistor R4 and a resistor R5. A first connection end of the switching device Q1 is connected with the second power supply VCC through the resistor R3, a second connection end thereof is grounded, and a control end thereof is connected with an input end E of the driving circuit 130. A first connection end of the switching device Q2 is connected with the second power supply VCC, a control end thereof is connected with the first connection end of the switching device Q1, and a second connection end thereof is connected with an output end F of the driving circuit 130 through the resistor R4. A first connection end of the switching device Q4 is connected with the output end F of the driving circuit 130, a second connection end thereof is grounded, and a control end thereof is connected with the second connection end of the switching device Q2. One end of the resistor R5 is connected with the control end of the switching device Q4, and the other end thereof is grounded.

[0022] When the output terminal D of the overcurrent protection self-locking circuit 120 continuously outputs an overcurrent protection signal, switching devices Q1, Q2, and Q4 are turned on, thereby driving the output terminal F of the drive circuit 130 to output a constant drive signal, causing the power transistor Q3 to remain off. When the output terminal D of the overcurrent protection self-locking circuit 120 does not output an overcurrent protection signal, if the PWM signal is at the first logic level, then switching devices Q1, Q2, and Q4 are turned on, thereby driving the output terminal F of the drive circuit 120 to output a periodic drive signal at the first logic level, causing the power transistor Q3 to turn off. If the PWM signal is at the second logic level, then switching devices Q1, Q2, and Q4 are turned on, thereby driving the output terminal F of the drive circuit 130 to output a periodic drive signal at the second logic level, causing the power transistor Q3 to turn on.

[0023] exist Figure 1 In the specific embodiment shown, the switching device Q1 is an NPN transistor, and the first connection terminal, the second connection terminal, and the control terminal of the switching device Q1 are the collector, emitter, and base of the NPN transistor, respectively.

[0024] Switching device Q2 is a PNP transistor, and the first connection terminal, the second connection terminal, and the control terminal of switching device Q2 are the emitter, collector, and base of the PNP transistor, respectively; power transistor Q3 is an NMOS transistor, and the first connection terminal, the second connection terminal, and the control terminal of power transistor Q3 are the drain, source, and gate of the NMOS transistor, respectively.

[0025] Switching device Q4 is a PNP transistor, with its first connection terminal, second connection terminal, and control terminal being the emitter, collector, and base of the PNP transistor, respectively; switching device Q5 is an NPN transistor, with its first connection terminal, second connection terminal, and control terminal being the collector, emitter, and base of the NPN transistor, respectively; switching device Q6 is a PNP transistor, with its first connection terminal, second connection terminal, and control terminal being the emitter, collector, and base of the PNP transistor, respectively; switching device Q7 is an NPN transistor, with its first connection terminal, second connection terminal, and control terminal being the collector, emitter, and base of the NPN transistor, respectively; the first input terminal and second input terminal of comparator U1 are its non-inverting input terminal and inverting input terminal, respectively.

[0026] Figure 1The LED overcurrent protection circuit with self-locking function shown further comprises an overcurrent protection threshold setting circuit 140, which comprises a resistor R13 and a resistor R14. One end of the resistor R13 is connected with the third power supply VREF, and the other end thereof is connected with a node H. One end of the resistor R14 is connected with the node H, and the other end thereof is grounded. The voltage of the node H is a preset reference voltage Vref (which corresponds to a preset overcurrent protection threshold). By setting the resistance division ratio of the resistor R13 and the resistor R14, the preset reference voltage Vref can be changed, so that the overcurrent protection threshold (or overcurrent protection point) can be set arbitrarily.

[0027] In Figure 1 In the specific embodiment shown, the overcurrent protection threshold setting circuit 140 further comprises a capacitor C1, one end of which is connected with the node H, and the other end thereof is grounded. The comparator U1 further comprises a resistor R10, a power supply end of the comparator U1 is connected with the third power supply VREF, and a ground end thereof is grounded. One end of the resistor R10 is connected with the power supply end of the comparator U1, and the other end thereof is connected with an output end of the comparator U1, that is, the output of the comparator U1 is an open-drain output, which is pulled up to the third power supply VREF through the resistor R10.

[0028] In Figure 1 In the specific embodiment shown, the driving circuit 130 further comprises a resistor R1 and a resistor R2. One end of the resistor R1 is connected with a PWM signal, and the other end thereof is connected with a control end of the switching device Q1. One end of the resistor R2 is connected with the PWM signal, and the other end thereof is grounded. The resistor R2 is pulled down to the ground for reliable turn-off of the switching device Q1.

[0029] The resistance values of the resistor R6 and the resistor R7 are selected to satisfy that when the switching device Q7 is turned on, the voltage value of the voltage division on the resistor R6 is greater than the turn-on voltage threshold of the switching device Q6, so that the switching device Q6 is in a turn-on state.

[0030] The working principle of the LED overcurrent protection circuit with self-locking function shown will be specifically introduced below. Figure 1 The working principle of the LED overcurrent protection circuit with self-locking function shown will be specifically introduced below.

[0031] 1. When the system is working normally, the PWM driver sends out a PWM square wave. When the PWM signal is at a high level (which can be referred to as the second logic level of the PWM signal), the NPN transistor Q1 is saturated and turned on, the collector of Q1 is pulled down to 0V, the base of the PNP transistor Q2 is also at 0V, and Q2 meets the saturated conduction condition. The collector voltage of Q2 is basically the same as the voltage of the first power supply VCC. Since Q4 is a PNP transistor, the base and emitter voltages of Q4 are the same, and Q4 cannot meet the conduction condition. Q4 is in an off state (or an off state). In this way, the first power supply VCC can drive the conduction of Q3 through the PNP transistor Q2 and the resistor R4, that is, the output end F of the driving circuit 130 outputs a high level (which can be referred to as the second logic level of the periodic driving signal), so that the power transistor Q3 is turned on. When the PWM signal is at a low level (which can be referred to as the first logic level of the PWM signal), the NPN transistor Q1 cannot meet the conduction condition, and Q1 is in an off state (or an off state). The emitter and base voltages of Q2 are the same, and since Q2 is a PNP transistor, Q2 is in an off state (or an off state). The base of Q4 is pulled down to the ground end GND through the resistor R5, and Q2 is in an off state. The PNP transistor Q4 is in a saturated conduction state, and can quickly discharge the gate voltage of Q3 to 0V, that is, the output end F of the driving circuit 130 outputs a low level (which can be referred to as the first logic level of the periodic driving signal), so that the power transistor Q3 is turned off. In this way, the brightness of LED1 can be adjusted according to the different duty cycles of the PWM signal.

[0032] 2. When the system is working normally, the current flowing through the current sampling resistor R11 is small, and the voltage drop of R11 is also small. The reference voltage Vref of the inverting input end of the comparator U1 cannot be reached, and the comparator U1 outputs a low level. Therefore, the NPN transistor Q7 is in an off state. Q6 is a PNP transistor. Since Q7 is in an off state, the base of Q6 is pulled up to the second power supply VCC through the resistor R6. The base voltage value of Q6 is basically the same as the emitter voltage value of Q6, and Q6 is also in an off state (or an off state). Therefore, the voltage of the second power supply VCC will not affect the collector voltage of Q6, and will not cause the conduction of the NPN transistor Q5, and will not affect the driving circuit 130 of the power transistor Q3. Therefore, when the system is working normally, the overcurrent protection self-locking circuit 120 does not affect the normal work of the system.

[0033] 3. When overcurrent occurs in the drive circuit (i.e. overcurrent occurs in the LED lamp string LED1), the current value flowing through the current sampling resistor R11 becomes larger, and the voltage drop value of R11 also becomes larger, when the voltage value exceeds the reference voltage Vref of the inverting input terminal of the comparator U1, the comparator U1 outputs a high level, since the output of the comparator U1 is pulled up to the third power supply VREF, the NPN transistor Q7 is turned on. The collector of Q7 is pulled down to 0V, and the base voltage of the PNP transistor Q6 is divided by R6 and R7, and the condition of saturation conduction of Q6 is met, after Q6 is turned on, the collector voltage of Q6 is approximately the voltage of the second power supply VCC. After Q6 is turned on, the second power supply VCC, the resistor R8 and the transistor Q7 form a positive feedback loop, even if the overcurrent condition is removed, the transistor Q7 can always remain conductive, and the overcurrent state will be in a locked state. Since Q6 is in the conductive state, the collector voltage of Q6 is close to the voltage of the second power supply VCC, and the collector of Q6 is connected to the base of Q5 through the resistor R9, since Q5 is an NPN transistor, Q5 will also be turned on, and the collector of Q5 will be pulled down to 0V, since the collector of Q5 is connected to the base of Q1, Q1 will always be in the off state, and Q3 will be turned off, i.e. the output end F of the drive circuit 130 outputs a low level (which can be called a constant drive signal), so that the power tube Q3 is continuously turned off. Thus, this loop forms an overcurrent protection circuit with self-locking for dimming LED driving, and in addition, due to the biasing effect of the unidirectional conduction of the diode D1, the voltage of the overcurrent self-locking loop does not affect the overcurrent protection threshold setting circuit 140, ensuring the reliability of the overcurrent protection self-locking loop.

[0034] 4. If the required overcurrent point (i.e. overcurrent protection threshold) is different for different power products, the resistance voltage division ratio of R13 and R14 can be adjusted to meet the requirements of different overcurrent points of different power products, and the circuit is simple and easy to design and implement.

[0035] In summary, the LED overcurrent protection circuit with self-locking function has the following advantages

[0036] Advantages:

[0037] 1. The circuit of the utility model is simple and reliable, a pure hardware scheme, the overcurrent protection state can be locked, the reliability of the product is guaranteed, and no software resource is occupied for processing the overcurrent protection circuit.

[0038] 2. The utility model is built by discrete components, uses less material, has low price cost, occupies small PCB space, and is beneficial to product integration.

[0039] 3. The overcurrent protection point (or overcurrent protection threshold) of the utility model can be set arbitrarily, and the requirements of different power products can be met.

[0040] It should be noted that any modifications made by those skilled in the art to the specific embodiments of this utility model do not depart from the scope of the claims of this utility model. Accordingly, the scope of the claims of this utility model is not limited to the foregoing specific embodiments.

Claims

1. An LED overcurrent protection circuit with self-locking function, characterized in that, It includes LED light strings, power transistor Q3, current detection circuit, overcurrent protection self-locking circuit, and driver circuit. The input terminal of the LED string is connected to the first power supply Vbat, and its output terminal is connected to the first connection terminal of the power transistor Q3. The input terminal A of the current detection circuit is connected to the second connection terminal of the power transistor Q3, and its output terminal B outputs a sampling voltage Vb, which reflects the current value flowing through the LED string. The input terminal C of the overcurrent protection self-locking circuit is connected to the output terminal B of the current detection circuit. When the sampling voltage Vb is less than the preset reference voltage, the output terminal D of the overcurrent protection self-locking circuit does not output an overcurrent protection signal; when the sampling voltage Vb is greater than the preset reference voltage, the output terminal D of the overcurrent protection self-locking circuit continuously outputs an overcurrent protection signal. The input terminal E of the driving circuit is connected to the PWM signal and the output terminal D of the overcurrent protection self-locking circuit. Its output terminal F is connected to the control terminal of the power transistor Q3. When the output terminal D of the overcurrent protection self-locking circuit does not output an overcurrent protection signal, the driving circuit generates a periodic driving signal based on the PWM signal. The periodic driving signal is output through the output terminal F of the driving circuit to drive the power transistor Q3 to periodically turn on and off. When the output terminal D of the overcurrent protection self-locking circuit continuously outputs an overcurrent protection signal, the drive circuit outputs a constant drive signal through its output terminal F based on the overcurrent protection signal to continuously turn off the power transistor Q3.

2. The LED overcurrent protection circuit with self-locking function according to claim 1, characterized in that, The current detection circuit includes a sampling resistor R11, one end of which is connected to the input terminal A of the current detection circuit, and the other end is grounded. The output terminal B of the current detection circuit is connected to the input terminal A.

3. The LED overcurrent protection circuit with self-locking function according to claim 2, characterized in that, The current detection circuit also includes a resistor R12 and a capacitor C2. One end of the resistor R12 is connected to the output terminal B, and the other end is connected to the input terminal A; One end of the capacitor C2 is connected to the output terminal B, and the other end is grounded.

4. The LED overcurrent protection circuit with self-locking function according to claim 2, characterized in that, The overcurrent protection self-locking circuit includes a comparator U1 and an overcurrent protection self-locking unit. The first input terminal of the comparator U1 is connected to the output terminal B of the current detection circuit, and its second input terminal receives a preset reference voltage. The comparator U1 is used to compare the sampled voltage Vb with the preset reference voltage and output the comparison result through its output terminal. The input terminal of the overcurrent protection self-locking unit is connected to the output terminal of the comparator U1, and its output terminal serves as the output terminal D of the overcurrent protection self-locking circuit. When the sampled voltage Vb is less than the preset reference voltage, the output of the comparator U1 outputs a first comparison result, and the overcurrent protection self-locking unit controls the output D not to output an overcurrent protection signal based on the first comparison result; when the sampled voltage Vb is greater than the preset reference voltage, the output of the comparator U1 outputs a second comparison result, and the overcurrent protection self-locking unit enters an overcurrent protection self-locking state based on the second comparison result, so that the output D continuously outputs an overcurrent protection signal.

5. The LED overcurrent protection circuit with self-locking function according to claim 4, characterized in that, The overcurrent protection self-locking unit includes switching devices Q5, Q6, and Q7, resistors R6, R7, R8, and R9. One end of resistor R6 is connected to the second power supply VCC, and the other end is connected to node G; one end of resistor R7 is connected to node G, and the other end is connected to the first connection terminal of switching device Q7, the second connection terminal of switching device Q7 is grounded, and its control terminal is connected to the output terminal of comparator U1; the first connection terminal of switching device Q6 is connected to the second power supply VCC, its control terminal is connected to node G, and its second connection terminal is connected to the control terminal of switching device Q7 via resistor R8; the first connection terminal of switching device Q5 is connected to the output terminal D of the overcurrent protection self-locking circuit, its second connection terminal is grounded, and its control terminal is connected to the second connection terminal of switching device Q6 via resistor R9.

6. The LED overcurrent protection circuit with self-locking function according to claim 5, characterized in that, The overcurrent protection self-locking unit also includes a diode D1, the negative terminal of which is connected to the control terminal of the switching device Q7, and the positive terminal of which is connected to the output terminal of the comparator U1.

7. The LED overcurrent protection circuit with self-locking function according to claim 5 or 6, characterized in that, When the output of the comparator U1 outputs the first comparison result, the switching devices Q5, Q6 and Q7 are all turned off. When the output of the comparator U1 outputs the second comparison result, the switching devices Q5, Q6 and Q7 are all turned on.

8. The LED overcurrent protection circuit with self-locking function according to claim 7, characterized in that, The driving circuit includes switching devices Q1, Q2, and Q4, resistors R3, R4, and R5. The first connection terminal of the switching device Q1 is connected to the second power supply VCC via the resistor R3, and its second connection terminal is grounded. Its control terminal is connected to the input terminal E of the driving circuit. The first connection terminal of the switching device Q2 is connected to the second power supply VCC, and its control terminal is connected to the first connection terminal of the switching device Q1. Its second connection terminal is connected to the output terminal F of the driving circuit via the resistor R4. The first connection terminal of the switching device Q4 is connected to the output terminal F of the driving circuit, and its second connection terminal is grounded. Its control terminal is connected to the second connection terminal of the switching device Q2. One end of the resistor R5 is connected to the control terminal of the switching device Q4, and the other end is grounded.

9. The LED overcurrent protection circuit with self-locking function according to claim 8, characterized in that, When the output terminal D of the overcurrent protection self-locking circuit continuously outputs an overcurrent protection signal, the switching device Q1 is turned off, the switching device Q2 is turned off, and the switching device Q4 is turned on, thereby the output terminal F of the drive circuit outputs a constant drive signal, causing the power transistor Q3 to be continuously turned off. When the output terminal D of the overcurrent protection self-locking circuit does not output an overcurrent protection signal, if the PWM signal is at the first logic level, then the switching device Q1 is off, the switching device Q2 is off, and the switching device Q4 is on, thereby the output terminal F of the drive circuit outputs the first logic level of the periodic drive signal, causing the power transistor Q3 to be off; if the PWM signal is at the second logic level, then the switching device Q1 is on, the switching device Q2 is on, and the switching device Q4 is off, thereby the output terminal F of the drive circuit outputs the second logic level of the periodic drive signal, causing the power transistor Q3 to be on.

10. The LED overcurrent protection circuit with self-locking function according to claim 9, characterized in that, The switching device Q1 is an NPN transistor, and the first connection terminal, the second connection terminal, and the control terminal of the switching device Q1 are the collector, emitter, and base of the NPN transistor, respectively. The switching device Q2 is a PNP transistor, and the first connection terminal, the second connection terminal, and the control terminal of the switching device Q2 are the emitter, collector, and base of the PNP transistor, respectively. The power transistor Q3 is an NMOS transistor, and the first connection terminal, the second connection terminal, and the control terminal of the power transistor Q3 are the drain, source, and gate of the NMOS transistor, respectively. The switching device Q4 is a PNP transistor, and the first connection terminal, the second connection terminal, and the control terminal of the switching device Q4 are the emitter, collector, and base of the PNP transistor, respectively. The switching device Q5 is an NPN transistor, and the first connection terminal, the second connection terminal, and the control terminal of the switching device Q5 are the collector, emitter, and base of the NPN transistor, respectively. The switching device Q6 is a PNP transistor, and the first connection terminal, the second connection terminal, and the control terminal of the switching device Q6 are the emitter, collector, and base of the PNP transistor, respectively. The switching device Q7 is an NPN transistor, and the first connection terminal, the second connection terminal, and the control terminal of the switching device Q7 are the collector, emitter, and base of the NPN transistor, respectively. The first and second input terminals of the comparator U1 are its non-inverting input and inverting input, respectively.

11. The LED overcurrent protection circuit with self-locking function according to claim 1, characterized in that, It also includes an overcurrent protection threshold setting circuit. The overcurrent protection threshold setting circuit includes resistors R13 and R14. One end of resistor R13 is connected to the third power supply VREF, and the other end is connected to node H; one end of resistor R14 is connected to node H, and the other end is grounded; the voltage of node H is the preset reference voltage.

12. The LED overcurrent protection circuit with self-locking function according to claim 4, characterized in that, The comparator U1 also includes a resistor R10. The power supply terminal of the comparator U1 is connected to the third power supply VREF, and its ground terminal is grounded. One end of the resistor R10 is connected to the power supply terminal of the comparator U1, and the other end is connected to the output terminal of the comparator U1.

13. The LED overcurrent protection circuit with self-locking function according to claim 8, characterized in that, The driving circuit also includes resistors R1 and R2. One end of resistor R1 is connected to the PWM signal, and the other end is connected to the control terminal of the switching device Q1; one end of resistor R2 is connected to the PWM signal, and the other end is grounded.

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