LED drive circuit with current derating function

Abstract

The utility model provides an LED drive circuit with current derating, characterized in that: the anode of a diode D1 is connected with a power supply input end, and the cathode of the diode D1 is connected with a node A; one end of the resistor R2 is connected with the node A, and the other end is connected with the node C; one end of the resistor R3 is connected with the node C, and the other end is connected with the output end; the first connecting end of the triode Q2 is connected with the node C, and the second connecting end is connected with the output end; the output end is connected with the positive electrode of the LED, and the negative electrode of the LED is grounded; one end of the resistor R1 is connected with the node A, and the other end is connected with the node B; one end of the resistor R5 is connected with the node B, and the other end is grounded; the first connecting end of the triode Q1 is connected with the control end of the triode Q2 through a resistor R4, the control end of the triode Q1 is connected with the node B, and the second connecting end of the triode Q1 is grounded. Compared with the prior art, the vehicle-mounted high-power LED over-temperature protection circuit is suitable for over-temperature protection of a vehicle-mounted high-power LED, a high-temperature current derating circuit is built by adopting a separated device, and the cost is obviously lower than that of the existing scheme in the market.

Description

[Technical field]

[0001] The utility model relates to the technical field of LED driving, in particular to an LED driving circuit with current derating. [Background technology]

[0002] As the demand for the brightness of vehicle ambient lights increases, the heat on the PCB (Printed Circuit Board) also increases. How to solve the high temperature protection of the PCB has become a problem of concern to everyone. Failure to control the current at high temperature will directly affect the rise of heat, causing the junction temperature to exceed the rated value, thereby damaging the device.

[0003] The existing technologies for high-power LED high-temperature protection mainly include the following two technical solutions:

[0004] 1) High temperature protection controlled by MCU (Microcontroller Unit);

[0005] 2) High temperature protection circuit with PPTC (Polymeric Positive Temperature Coefficient);

[0006] The above two points make the cost of circuit design too high.

[0007] Therefore, it is necessary to propose a new technical solution to solve the above problems. [Utility Model Content]

[0008] One of the purposes of the utility model is to provide an LED driving circuit with current derating, which is suitable for over-temperature protection of high-power vehicle-mounted LEDs. A high-temperature current derating circuit is constructed using separation devices, and the cost is significantly lower than the solutions with MCU and PPTC on the market.

[0009] According to one aspect of the utility model, the utility model provides an LED driving circuit with current derating, which includes: an LED current main circuit, which includes a diode D1, a resistor R2, a resistor R3 and a transistor Q2, wherein the positive electrode of the diode D1 is connected to the power input terminal Vin, and the negative electrode thereof is connected to the node A; one end of the resistor R2 is connected to the node A, and the other end thereof is connected to the node C; one end of the resistor R3 is connected to the node C, and the other end thereof is connected to the output terminal VOUT; the first connection end of the transistor Q2 is connected to the node C, and the second connection end thereof is connected to the output terminal VOUT; The connection end is connected to the output end VOUT; the output end VOUT is used to be connected to the positive electrode of the LED, and the negative electrode of the LED is grounded; an over-temperature current derating control module includes a resistor R1, a resistor R4, a resistor R5 and a transistor Q1, one end of the resistor R1 is connected to the node A, and the other end thereof is connected to the node B; one end of the resistor R5 is connected to the node B, and the other end thereof is grounded; the first connection end of the transistor Q1 is connected to the control end of the transistor Q2 via the resistor R4, the control end thereof is connected to the node B, and the second connection end thereof is grounded.

[0010] Furthermore, the transistor Q1 is an NPN transistor, and the first connection end, the second connection end and the control end of the transistor Q1 are respectively the collector, the emitter and the base of the NPN transistor; the transistor Q2 is a PNP transistor, and the first connection end, the second connection end and the control end of the transistor Q2 are respectively the emitter, the collector and the base of the PNP transistor; the resistor R5 is a thermistor with a negative temperature coefficient, and the resistor R1 is a constant resistor; the preset derating temperature is set by setting the ratio of the resistance values ​​of the resistor R5 and the resistor R1.

[0011] Further, when the operating temperature is lower than the preset derating temperature, the diode D1 is turned on, and the voltage on the resistor R5 is higher than the threshold voltage Vth of the transistor Q1, then the transistor Q1 is turned on and the transistor Q2 is turned on; when the operating temperature is higher than the preset derating temperature, the diode D1 is turned on, and the voltage on the resistor R5 is lower than the threshold voltage Vth of the transistor Q1, then the transistor Q1 is turned off and the transistor Q2 is turned off.

[0012] Furthermore, the current flowing through the LED when the operating temperature is lower than the preset derating temperature is controlled by setting the resistance value of the resistor R2; the current flowing through the LED when the operating temperature is higher than the preset derating temperature is controlled by setting the resistance values ​​of the resistor R2 and the resistor R3.

[0013] Furthermore, the LED driving circuit with current derating is constructed by discrete components.

[0014] According to another aspect of the utility model, the utility model provides an LED driving circuit with current derating, which includes: an LED current main circuit, which includes a diode D1, a resistor R2, a resistor R4 and a transistor Q2, wherein the positive electrode of the diode D1 is connected to the power input terminal Vin, and the negative electrode thereof is connected to the node A; one end of the resistor R2 is connected to the node A, and the other end thereof is connected to the output terminal VOUT; the first connection end of the transistor Q2 is connected to the output terminal VOUT via the resistor R4, the control end thereof is connected to the node C, and the second connection end thereof is grounded; The output terminal VOUT is used to be connected to the positive electrode of the LED, and the negative electrode of the LED is grounded; the over-temperature current derating control module includes a resistor R1, a resistor R3, a resistor R5 and a transistor Q1, one end of the resistor R1 is connected to the node A, and the other end thereof is connected to the node B; one end of the resistor R5 is connected to the node B, and the other end thereof is grounded; one end of the resistor R3 is connected to the node A, and the other end thereof is connected to the node C; the first connection end of the transistor Q1 is connected to the node C, the control end thereof is connected to the node B, and the second connection end thereof is grounded.

[0015] Furthermore, the transistor Q1 is an NPN transistor, and the first connection end, the second connection end and the control end of the transistor Q1 are respectively the collector, the emitter and the base of the NPN transistor; the transistor Q2 is an NPN transistor, and the first connection end, the second connection end and the control end of the transistor Q2 are respectively the emitter, the collector and the base of the NPN transistor; the resistor R5 is a thermistor with a negative temperature coefficient, and the resistor R1 is a constant resistor; the preset derating temperature is set by setting the ratio of the resistance values ​​of the resistor R5 and the resistor R1.

[0016] Further, when the operating temperature is lower than the preset derating temperature, the diode D1 is turned on, and the voltage on the resistor R5 is greater than the threshold voltage Vth of the transistor Q1, then the transistor Q1 is turned on and the transistor Q2 is turned off; when the operating temperature is higher than the preset derating temperature, the diode D1 is turned on, and the voltage on the resistor R5 is less than the threshold voltage Vth of the transistor Q1, then the transistor Q1 is turned off and the transistor Q2 is turned on.

[0017] Furthermore, the resistance value of the resistor R2 is set to control the current flowing through the LED when the operating temperature is lower than the preset derating temperature; the resistance value of the resistor R4 is set to control the saturation conduction of the transistor Q2, thereby affecting the current of the LED and the power consumption of the transistor Q2.

[0018] Furthermore, the LED driving circuit with current derating is constructed by discrete components.

[0019] Compared with the prior art, the utility model is suitable for over-temperature protection of vehicle-mounted high-power LEDs, and uses separation devices to build a high-temperature current derating circuit, and the cost is significantly lower than the solutions with MCU and PPTC on the market.

Brief Description of the Drawings

[0020] In order to more clearly illustrate the technical solutions of the embodiments of the present utility model, the following briefly introduces the drawings required for the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present utility model. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative labor. Among them:

[0021] Figure 1 This is a circuit diagram of an LED driving circuit with current derating in one embodiment of the utility model;

[0022] Figure 2 FIG. 4 is a circuit diagram of an LED driving circuit with current derating in another embodiment of the utility model. [Specific implementation method]

[0023] In order to make the above-mentioned purposes, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0024] The "one embodiment" or "embodiment" referred to herein refers to a specific feature, structure or characteristic that may be included in at least one implementation of the utility model. The "in one embodiment" that appears in different places in this specification does not all refer to the same embodiment, nor is it a separate or selective embodiment that is mutually exclusive with other embodiments. Unless otherwise specified, the words "coupled", "connected", "connected" and "connected" in this document that indicate electrical connection all mean direct or indirect connection. For example, A is connected to B, which includes both direct electrical connection between A and B and connection between A and B through electrical components or circuits.

[0025] In the description of the present invention, it should be understood that the terms "upper", "lower", "front", "back", "front", "back", "left", "right", "vertical", "perpendicular", "horizontal", "top", "bottom", "inside", "outside", etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present invention.

[0026] Please refer to Figure 1 As shown, it is a circuit diagram of an LED driving circuit with current derating in one embodiment of the utility model. Figure 1 The LED driving circuit with current derating shown includes an LED current main loop 110 and an over-temperature current derating control module 120 .

[0027] The LED current main loop 110 includes a diode D1, a resistor R2, a resistor R3 and a transistor Q2, wherein the anode of the diode D1 is connected to the power input terminal Vin, and the cathode thereof is connected to the node A; one end of the resistor R2 is connected to the node A, and the other end thereof is connected to the node C; one end of the resistor R3 is connected to the node C, and the other end thereof is connected to the output terminal VOUT; the first connection end of the transistor Q2 is connected to the node C, and the second connection end thereof is connected to the output terminal VOUT. The output terminal VOUT is used to be connected to the anode of the LED1, and the cathode of the LED1 is grounded.

[0028] The over-temperature current derating control module 120 includes a resistor R1, a resistor R4, a resistor R5 and a transistor Q1. Among them, one end of the resistor R1 is connected to the node A, and the other end thereof is connected to the node B; one end of the resistor R5 is connected to the node B, and the other end thereof is grounded; the first connection end of the transistor Q1 is connected to the control end of the transistor Q2 via the resistor R4, and the control end thereof is connected to the node B, and the second connection end thereof is grounded.

[0029] exist Figure 1 In the specific embodiment shown, transistor Q1 is an NPN transistor, and the first connection end, the second connection end and the control end of transistor Q1 are respectively the collector, the emitter and the base of the NPN transistor; transistor Q2 is a PNP transistor, and the first connection end, the second connection end and the control end of transistor Q2 are respectively the emitter, the collector and the base of the PNP transistor; resistor R5 is a negative temperature coefficient thermistor (NTC, Negative Temperature Coefficient thermistor), and resistor R1 is a constant resistor. The preset derating temperature can be set by setting the ratio of the resistance values ​​of resistor R5 and resistor R1.

[0030] exist Figure 1 In the LED driving circuit with current derating shown, when the operating temperature is lower than the preset derating temperature, the diode D1 is turned on, the voltage on the resistor R5 (which is equal to the voltage at the node B) is greater than the threshold voltage Vth of the transistor Q1, then the transistor Q1 is turned on and the transistor Q2 is turned on; when the operating temperature is higher than the preset derating temperature, the diode D1 is turned on, the voltage on the resistor R5 (which is equal to the voltage at the node B) is less than the threshold voltage Vth of the transistor Q1, then the transistor Q1 is turned off and the transistor Q2 is turned off.

[0031] exist Figure 1 In the illustrated embodiment, the LED driving circuit with current derating is constructed by discrete components.

[0032] The following is a detailed introduction Figure 1 The working principle of the LED driver circuit with current derating is shown in FIG.

[0033] When working at normal temperature (i.e. when the working temperature is lower than the preset derating temperature), the voltage division of resistor R1 and resistor R5 (i.e. NTC resistor) can conduct NPN transistor Q1 (i.e. the voltage on resistor R5 is higher than the threshold voltage Vth of transistor Q1), the collector of NPN transistor Q1 will be pulled down, thereby causing the base voltage of PNP transistor Q2 to be pulled down, and PNP transistor Q2 is also turned on at this time, therefore, the effective circuit of LED current main loop 110 is composed of diode D1, resistor R2 and PNP transistor Q2, and the size of resistor R2 can be derived according to the current required by LED1. That is to say, when LED1 works at normal temperature, over-temperature current derating is not triggered, and the current mainly flows through LED1 from resistor R2 and PNP transistor Q2.

[0034] When the temperature rises, the resistance of resistor R5 (i.e., NTC resistor) will decrease, causing the base voltage of transistor Q1 to gradually decrease. When the temperature reaches a certain threshold (i.e., when the operating temperature is greater than the preset derating temperature), the voltage division of resistor R1 and resistor R5 (i.e., NTC resistor) can cut off the NPN transistor Q1 (i.e., the voltage on resistor R5 is less than the threshold voltage Vth of transistor Q1), and the NPN transistor Q1 changes from on to off, thereby causing the PNP transistor Q2 to also enter the off state. At this time, the effective circuit of the LED current main loop 110 is composed of diode D1, resistor R2 and resistor R3. The magnitude of the LED1 current after derating can be controlled by controlling the resistance of resistor R3. That is to say, when the temperature reaches the preset derating temperature set by resistor R5 and resistor R1, the current mainly flows through LED1 from resistor R2 and resistor R3, thereby reducing the current on LED1 and preventing the temperature from exceeding the preset derating temperature.

[0035] exist Figure 1 In a specific embodiment shown, the resistance value of resistor R2 is set to control the current flowing through LED1 when the operating temperature is lower than the preset derated temperature; the resistance values ​​of resistors R2 and R3 are set to control the current flowing through LED1 when the operating temperature is higher than the preset derated temperature. In other words, the design of resistors R2 and R3 determines the current on LED1 during normal temperature operation and after overheating.

[0036] In summary, the utility model is as follows Figure 1 The innovative features and corresponding beneficial effects of the LED driving circuit with current derating shown in FIG. 1 are as follows:

[0037] 1) The utility model is suitable for over-temperature protection of high-power LEDs on vehicles;

[0038] 2) The utility model uses separation devices to build a high-temperature current derating circuit, and the cost is significantly lower than the solution with MCU and PPTC on the market;

[0039] 3) The derating temperature can be set by the NTC resistor (i.e. resistor R5) and resistor R1;

[0040] 4) The design of resistors R2 and R3 determines the current on LED1 during normal operation and after overheating;

[0041] 5) The utility model solves the problem of the device exceeding the junction temperature due to the current not being reduced under high temperature conditions.

[0042] Please refer to Figure 2 As shown, it is a circuit diagram of an LED driving circuit with current derating in another embodiment of the utility model. Figure 2 The LED driving circuit with current derating shown includes an LED current main loop 210 and an over-temperature current derating control module 220 .

[0043] The LED current main loop 210 includes a diode D1, a resistor R2, a resistor R4 and a transistor Q2. The positive electrode of the diode D1 is connected to the power input terminal Vin, and the negative electrode thereof is connected to the node A; one end of the resistor R2 is connected to the node A, and the other end thereof is connected to the output terminal VOUT; the first connection end of the transistor Q2 is connected to the output terminal VOUT via the resistor R4, the control end thereof is connected to the node C, and the second connection end thereof is grounded. The output terminal VOUT is used to be connected to the positive electrode of LED1, and the negative electrode of LED1 is grounded.

[0044] The over-temperature current derating control module 220 includes a resistor R1, a resistor R3, a resistor R5 and a transistor Q1. Among them, one end of the resistor R1 is connected to the node A, and the other end thereof is connected to the node B; one end of the resistor R5 is connected to the node B, and the other end thereof is grounded; one end of the resistor R3 is connected to the node A, and the other end thereof is connected to the node C; the first connection end of the transistor Q1 is connected to the node C, the control end thereof is connected to the node B, and the second connection end thereof is grounded.

[0045] exist Figure 2In the specific embodiment shown, transistor Q1 is an NPN transistor, and the first connection end, the second connection end and the control end of transistor Q1 are respectively the collector, the emitter and the base of the NPN transistor; transistor Q2 is an NPN transistor, and the first connection end, the second connection end and the control end of transistor Q2 are respectively the collector, the emitter and the base of the NPN transistor; resistor R5 is a negative temperature coefficient thermistor (NTC, Negative Temperature Coefficient thermistor), and resistor R1 is a constant resistor. The preset derating temperature can be set by setting the ratio of the resistance values ​​of resistor R5 and resistor R1.

[0046] exist Figure 2 In the LED driving circuit with current derating shown, when the operating temperature is lower than the preset derating temperature, the diode D1 is turned on, the voltage on the resistor R5 (which is equal to the voltage at the node B) is greater than the threshold voltage Vth of the transistor Q1, then the transistor Q1 is turned on and the transistor Q2 is turned off; when the operating temperature is higher than the preset derating temperature, the diode D1 is turned on, the voltage on the resistor R5 (which is equal to the voltage at the node B) is less than the threshold voltage Vth of the transistor Q1, then the transistor Q1 is turned off and the transistor Q2 is turned on.

[0047] exist Figure 2 In the illustrated embodiment, the LED driving circuit with current derating is constructed by discrete components.

[0048] The following is a detailed introduction Figure 2 The working principle of the LED driver circuit with current derating is shown in FIG.

[0049] When working at normal temperature (i.e. when the working temperature is lower than the preset derating temperature), the voltage division of resistor R1 and resistor R5 (i.e. NTC resistor) can conduct NPN transistor Q1 (i.e. the voltage on resistor R5 is higher than the threshold voltage Vth of transistor Q1), the collector of NPN transistor Q1 will be pulled down, thereby causing the base voltage of NPN transistor Q2 to be pulled down, and NPN transistor Q2 is in the cut-off state at this time, so the effective circuit of LED current main loop 210 is composed of diode D1 and resistor R2, and the size of resistor R2 can be derived according to the current required by LED1. That is to say, when LED1 works at normal temperature, over-temperature current derating is not triggered, and the current mainly flows through LED1 from resistor R2.

[0050] When the temperature rises, the resistance of resistor R5 (i.e., NTC resistor) will decrease, causing the base voltage of transistor Q1 to gradually decrease. When the temperature reaches a certain threshold (i.e., when the operating temperature is greater than the preset derating temperature), the voltage divider of resistor R1 and resistor R5 (i.e., NTC resistor) can cut off the NPN transistor Q1 (i.e., the voltage on resistor R5 is less than the threshold voltage Vth of transistor Q1), and the NPN transistor Q1 changes from the on state to the off state, thereby causing the NPN transistor Q2 to enter the on state. At this time, the effective circuit of the LED current main loop 210 is composed of diode D1, resistor R2, resistor R4 and transistor Q2, so the current of LED1 will be shunted to resistor R4 and NPN transistor Q2, and the size of the shunting (or the size of the LED1 current after derating) can be controlled by controlling the resistance of resistor R4. That is, when the temperature reaches the preset derating temperature set by the resistors R5 and R1 , the current will be shunted through the resistor R4 and the NPN transistor Q2 , thereby reducing the current on the LED 1 and preventing the temperature from exceeding the preset derating temperature.

[0051] exist Figure 2 In a specific embodiment shown, the resistance value of resistor R2 is set to control the current flowing through LED1 when the operating temperature is less than the preset derating temperature; the saturation conduction of transistor Q2 is controlled by setting the resistance value of resistor R4, which will affect the current of LED1 and the power consumption of transistor Q2.

[0052] In summary, the utility model is as follows Figure 2 The innovative features and corresponding beneficial effects of the LED driving circuit with current derating shown in FIG. 1 are as follows:

[0053] 1) The utility model is suitable for over-temperature protection of high-power LEDs on vehicles;

[0054] 2) The utility model uses separation devices to build a high-temperature current derating circuit, and the cost is significantly lower than the solution with MCU and PPTC on the market;

[0055] 3) The derating temperature can be set by the NTC resistor (i.e. resistor R5) and resistor R1;

[0056] 4) The size of resistor R4 is related to the saturation conduction of PNP transistor Q2, which will affect the current of LED1 and the power consumption of transistor Q2;

[0057] 5) The utility model solves the problem of the device exceeding the junction temperature due to the current not being reduced under high temperature conditions.

[0058] It should be noted that any changes made by those skilled in the art to the specific implementation of the present invention do not deviate from the scope of the claims of the present invention. Accordingly, the scope of the claims of the present invention is not limited to the aforementioned specific implementation.

Claims

1. A LED driving circuit with current derating, characterized in that: It includes: The LED current main circuit includes a diode D1, a resistor R2, a resistor R3 and a transistor Q2, wherein the positive electrode of the diode D1 is connected to the power input terminal Vin, and the negative electrode thereof is connected to the node A; one end of the resistor R2 is connected to the node A, and the other end thereof is connected to the node C; one end of the resistor R3 is connected to the node C, and the other end thereof is connected to the output terminal VOUT; the first connection end of the transistor Q2 is connected to the node C, and the second connection end thereof is connected to the output terminal VOUT; the output terminal VOUT is used to be connected to the positive electrode of the LED, and the negative electrode of the LED is grounded; An over-temperature current derating control module comprises a resistor R1, a resistor R4, a resistor R5 and a transistor Q1, wherein one end of the resistor R1 is connected to the node A, and the other end thereof is connected to the node B; one end of the resistor R5 is connected to the node B, and the other end thereof is grounded; a first connection end of the transistor Q1 is connected to a control end of the transistor Q2 via the resistor R4, the control end thereof is connected to the node B, and a second connection end thereof is grounded.

2. The LED driving circuit with current derating according to claim 1, characterized in that: The transistor Q1 is an NPN transistor, and the first connection end, the second connection end and the control end of the transistor Q1 are respectively the collector, the emitter and the base of the NPN transistor; The transistor Q2 is a PNP transistor, and the first connection end, the second connection end and the control end of the transistor Q2 are respectively the emitter, the collector and the base of the PNP transistor; The resistor R5 is a thermistor with a negative temperature coefficient, and the resistor R1 is a constant resistor; The preset derating temperature is set by setting the ratio of the resistance values ​​of the resistor R5 and the resistor R1.

3. The LED driving circuit with current derating according to claim 2, characterized in that: When the operating temperature is lower than the preset derating temperature, the diode D1 is turned on, and the voltage on the resistor R5 is higher than the threshold voltage Vth of the transistor Q1, then the transistor Q1 is turned on, and the transistor Q2 is turned on; When the operating temperature is greater than the preset derating temperature, the diode D1 is turned on, and the voltage on the resistor R5 is less than the threshold voltage Vth of the transistor Q1 , then the transistor Q1 is turned off, and the transistor Q2 is turned off.

4. The LED driving circuit with current derating according to claim 3, characterized in that: By setting the resistance value of the resistor R2, the current flowing through the LED is controlled when the operating temperature is lower than the preset derating temperature; The current flowing through the LED when the operating temperature is greater than the preset derating temperature is controlled by setting the resistance values ​​of the resistor R2 and the resistor R3.

5. The LED driving circuit with current derating according to any one of claims 1 to 4, characterized in that: The LED driving circuit with current derating is constructed by discrete components.

6. An LED driving circuit with current derating, characterized in that: It includes: The LED current main circuit includes a diode D1, a resistor R2, a resistor R4 and a transistor Q2, wherein the positive electrode of the diode D1 is connected to the power input terminal Vin, and the negative electrode thereof is connected to the node A; one end of the resistor R2 is connected to the node A, and the other end thereof is connected to the output terminal VOUT; the first connection end of the transistor Q2 is connected to the output terminal VOUT via the resistor R4, the control end thereof is connected to the node C, and the second connection end thereof is grounded; the output terminal VOUT is used to be connected to the positive electrode of the LED, and the negative electrode of the LED is grounded; An over-temperature current derating control module comprises a resistor R1, a resistor R3, a resistor R5 and a transistor Q1, wherein one end of the resistor R1 is connected to the node A, and the other end thereof is connected to the node B; one end of the resistor R5 is connected to the node B, and the other end thereof is grounded; one end of the resistor R3 is connected to the node A, and the other end thereof is connected to the node C; a first connection end of the transistor Q1 is connected to the node C, a control end thereof is connected to the node B, and a second connection end thereof is grounded.

7. The LED driving circuit with current derating according to claim 6, characterized in that: The transistor Q1 is an NPN transistor, and the first connection end, the second connection end and the control end of the transistor Q1 are respectively the collector, the emitter and the base of the NPN transistor; The transistor Q2 is an NPN transistor, and the first connection end, the second connection end and the control end of the transistor Q2 are respectively the emitter, the collector and the base of the NPN transistor; The resistor R5 is a thermistor with a negative temperature coefficient, and the resistor R1 is a constant resistor; The preset derating temperature is set by setting the ratio of the resistance values ​​of the resistor R5 and the resistor R1.

8. The LED driving circuit with current derating according to claim 7, characterized in that: When the operating temperature is lower than the preset derating temperature, the diode D1 is turned on, and the voltage on the resistor R5 is higher than the threshold voltage Vth of the transistor Q1, then the transistor Q1 is turned on and the transistor Q2 is turned off; When the operating temperature is greater than the preset derating temperature, the diode D1 is turned on, and the voltage on the resistor R5 is less than the threshold voltage Vth of the transistor Q1 , then the transistor Q1 is turned off and the transistor Q2 is turned on.

9. The LED driving circuit with current derating according to claim 8, characterized in that: By setting the resistance value of the resistor R2, the current flowing through the LED is controlled when the operating temperature is lower than the preset derating temperature; The saturation conduction of the transistor Q2 is controlled by setting the resistance value of the resistor R4, thereby affecting the current of the LED and the power consumption of the transistor Q2.

10. The LED driving circuit with current derating according to any one of claims 6 to 9, characterized in that: The LED driving circuit with current derating is constructed by discrete components.

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