Circuit for automatically compensating LED brightness along with temperature change

Abstract

The utility model provides a circuit for automatically compensating LED brightness along with temperature change, comprising a voltage stabilizing circuit which outputs stable voltage through the output end based on the voltage of a power supply; the temperature self-adaptive circuit comprises a triangular wave generation circuit, a temperature detection circuit and a voltage comparator; the triangular wave generation circuit is used for outputting a triangular wave signal; the temperature detection circuit outputs a temperature detection voltage reflecting the temperature of the LED; the voltage comparator is used for comparing the triangular wave signal with the temperature detection voltage to generate a PWM signal; the input end of the constant-current circuit is connected with the negative electrode of the LED, the positive electrode of the LED is connected with the power supply, the output end of the constant-current circuit is grounded, the power supply end of the constant-current circuit is connected with the output end of the voltage stabilizing circuit, the control end of the constant-current circuit is connected with the output end of the voltage comparator, and whether the constant-current circuit works or not is controlled through PWM signals. Compared with the prior art, the LED brightness compensation circuit not only can compensate the brightness of the LED in real time along with the temperature change, but also is simple in circuit design, does not need to be controlled by a single chip microcomputer, and saves the circuit cost.

Description

TECHNICAL FIELD

[0001] The utility model relates to circuit design technical field, especially relate to a circuit that follows temperature change automatic compensation LED brightness. BACKGROUND

[0002] The LED will be attenuated with the brightness of the same working current when the temperature of the LED rises, which leads to the brightness inconsistency at different temperatures. The common coping strategy in the industry is to use high-sensitivity NTC (Negative Temperature Coefficient thermistor) as a temperature sensor, which is closely attached to the LED to accurately perceive temperature changes. Subsequently, the MCU (Microcontroller Unit) ADC (analog to digital converter) module quickly collects the analog electrical signals from the NTC and converts them into digital quantities. The MCU quickly controls the output adjustment through the preset algorithm based on these data, dynamically adjusts the current, voltage and other parameters to ensure that the LED works in the appropriate temperature range, maintains stable light performance and long service life, and ensures the reliability of the lighting and display effect.

[0003] However, the prior art has the following problems and shortcomings:

[0004] ① Through the current sensor to collect, then need microcontroller to handle, through judging the value that comes back to collect to handle then in add drive control output;

[0005] ② Cannot real-time dynamic feedback temperature and current adjustment relationship.

[0006] Therefore, it is necessary to provide a new technical scheme to solve the above problems. CONTENT OF THE UTILITY MODEL

[0007] One of the purposes of the utility model is to provide a circuit that follows temperature change automatic compensation LED brightness, which can not only follow the temperature change to compensate the brightness of the LED in real time, but also ensure that there is no brightness mutation, and the circuit design is simple, does not need single-chip microcomputer control, and saves the circuit cost.

[0008] According to one aspect of the utility model, the utility model provides a circuit that automatically compensates LED brightness following temperature change, it includes: voltage stabilizing circuit, its input end is connected with power supply V1, its output end is V_LDO, voltage stabilizing circuit is based on the voltage of power supply V1 passes its output end V_LDO and exports stable voltage, temperature self -adaptation circuit includes triangle wave generation circuit, temperature detection circuit and voltage comparator, the power supply end of triangle wave generation circuit is connected with the output end V_LDO of voltage stabilizing circuit, its output end is A, triangle wave generation circuit is used for exporting triangle wave signal Ramp through its output end A, the input end of temperature detection circuit is connected with the output end V_LDO of voltage stabilizing circuit, and its output end B exports temperature detection voltage VB reflecting LED temperature, the first input end of voltage comparator is connected with the output end A of triangle wave generation circuit, and its second input end is connected with the output end B of temperature detection unit, voltage comparator is used for comparing triangle wave signal Ramp and temperature detection voltage VB to produce PWM signal, and the output end of voltage comparator exports PWM signal, constant current circuit, its input end C is connected with the negative pole of LED, the positive pole of LED is connected with power supply V1, and its output end is grounded, and its power supply end D is connected with the output end V_LDO of voltage stabilizing circuit, and its control end E is connected with the output end of voltage comparator, and whether the PWM signal exported by voltage comparator controls constant current circuit to work.

[0009] Compared with prior art, the utility model not only can follow temperature change and compensate the brightness of LED in real time, guarantee that there is no brightness mutation, and circuit design is simple, need not single-chip microcomputer control, save circuit cost.

DRAWINGS

[0010] 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, obviously, the drawing in the following description only is some embodiments of the utility model, for ordinary skilled person in the art comes, under the premise of not paying the creativity labor intensity, can also obtain other drawings according to these drawings. Wherein:

[0011] Figure 1 It is the schematic diagram of the circuit that automatically compensates LED brightness following temperature change in one embodiment of the utility model.

CONCRETE IMPLEMENTATION

[0012] In order to make the above purpose, feature and advantage 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.

[0013] As used herein, the term "one embodiment" or "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one implementation of the technology. The appearances of the phrase "in one embodiment" or "in an embodiment" in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments mutually exclusive of other embodiments. The terms coupled, connected, connected together, connected with, connecting, connecting together, connecting with, or the like, as used herein, mean the joining of two members together for electrical purposes using only an electrical cable, wire or connector, unless otherwise specifically stated.

[0014] 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 drawings 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.

[0015] Please refer to Figure 1 As shown in the figure, it is a schematic diagram of the circuit for automatically compensating the brightness of the LED according to the temperature change in an embodiment of the present application. Figure 1 The circuit for automatically compensating the brightness of the LED according to the temperature change shown in the figure includes a voltage stabilizing circuit 110, a temperature adaptive circuit 120 and a constant current circuit 130.

[0016] The input end of the voltage stabilizing circuit 110 is connected with the power supply V1, and the output end thereof is V_LDO. The voltage stabilizing circuit 110 outputs a stable voltage through the output end V_LDO based on the voltage of the power supply V1. In Figure 1 In the embodiment shown in the figure, the voltage stabilizing circuit 110 is a linear voltage stabilizing circuit, which includes a resistor R1, a voltage stabilizing tube D1A, a power device Q1 and a capacitor C1. Among them, the first connection end of the power device Q1 is connected with the power supply V1, the second connection end thereof is connected with the output end V_LDO, the control end thereof is connected with the negative electrode of the voltage stabilizing tube D1A, and the positive electrode of the voltage stabilizing tube D1A is grounded; one end of the resistor R1 is connected with the first connection end of the power device Q1, and the other end thereof is connected with the control end of the power device Q1; one end of the capacitor C1 is connected with the second connection end of the power device Q1, and the other end thereof is grounded. In Figure 1 In the specific embodiment shown in the figure, the power device Q1 is an NPN type triode, and the first connection end, the second connection end and the control end of the power device Q1 are the collector, the emitter and the base of the NPN type triode, respectively.

[0017] The temperature adaptive circuit 120 includes a triangular wave generating circuit 122, a temperature detection circuit 124, and a voltage comparator U1B. The power supply terminal of the triangular wave generating circuit 122 is connected to the output terminal V_LDO of the voltage regulator circuit 110, and its output terminal is A. The triangular wave generating circuit 122 outputs a triangular wave signal Ramp through its output terminal A. The input terminal of the temperature detection circuit 124 is connected to the output terminal V_LDO of the voltage regulator circuit 110, and its output terminal B outputs a temperature detection voltage VB reflecting the temperature of LED1. The first input terminal of the voltage comparator U1B is connected to the output terminal A of the triangular wave generating circuit 122, and its second input terminal is connected to the output terminal B of the temperature detection circuit 124. The voltage comparator U1B compares the triangular wave signal Ramp and the temperature detection voltage VB to generate a PWM signal, which is output through the output terminal of the voltage comparator U1B.

[0018] The input terminal C of the constant current circuit 130 is connected to the negative terminal of LED1, the positive terminal of LED1 is connected to the power supply V1, the output terminal of the constant current circuit 130 is grounded, its power supply terminal D is connected to the output terminal V_LDO of the voltage regulator circuit 110, and its control terminal E is connected to the output terminal of the voltage comparator U1B. The PWM signal output by the voltage comparator U1B controls whether the constant current circuit 130 works.

[0019] exist Figure 1 In the illustrated embodiment, the temperature detection circuit 124 includes a thermistor R6, which is placed near LED1 during layout. Within a predetermined temperature range, the resistance of the thermistor R6 varies such that the upper and lower limits of the temperature detection voltage VB are within the upper and lower limits of the triangular wave signal Ramp. The thermistor R6 can be a negative temperature coefficient thermistor (NTC) or a positive temperature coefficient thermistor (PTC), its purpose being to feed back temperature changes as voltage changes to alter the duty cycle output of the PWM.

[0020] When the PWM signal is at the first logic level, the constant current circuit 130 is activated, generating a constant current from its input terminal D to its output terminal, thereby providing a constant current to LED1. When the PWM signal is at the second logic level, the constant current circuit 130 is deactivated, and it does not generate current from its input terminal D to its output terminal, thus no current flows through LED1.

[0021] When the temperature of LED1 increases, the duty cycle of the first logic level of the PWM signal increases, thereby increasing the working duty cycle of the constant current circuit 130; when the temperature of LED1 decreases, the duty cycle of the first logic level of the PWM signal decreases, thereby decreasing the working duty cycle of the constant current circuit 130. In this way, the brightness of LED1 caused by temperature can be compensated in real time, so that the brightness of LED1 remains consistent within a predetermined temperature range.

[0022] In Figure 1 In the embodiment shown, the temperature detection circuit 124 includes a thermistor R6 and a constant resistance R2. The constant resistance R2 is a resistance that does not change with temperature under certain conditions. One end of the constant resistance R2 is connected to the output terminal V_LDO of the voltage stabilizing circuit 110, and the other end is connected to the output terminal B of the temperature detection circuit 124; one end of the thermistor R6 is connected to the output terminal B of the temperature detection circuit 124, and the other end is grounded.

[0023] In Figure 1 In the specific embodiment shown, the thermistor R6 is a negative temperature coefficient thermistor NTC; the first input terminal of the voltage comparator U1B is the negative phase input terminal thereof, and the second input terminal is the positive phase input terminal thereof; the first logic level of the PWM signal is a low level, and the second logic level is a high level.

[0024] In Figure 1 In the embodiment shown, the triangular wave generating circuit 122 includes an operational amplifier U1A, resistors R4, R5, R8, R9, and a capacitor C2. Among them, one end of the resistor R4 is connected to the output terminal V_LDO of the voltage stabilizing circuit 110, and the other end is connected to the node F; one end of the resistor R8 is connected to the node F, and the other end is grounded; the first input terminal of the operational amplifier U1A is connected to the node F, and the second input terminal is grounded through the capacitor C2; one end of the resistor R5 is connected to the first input terminal of the operational amplifier U1A, and the other end is connected to the output terminal of the operational amplifier U1A; one end of the resistor R9 is connected to the output terminal of the operational amplifier U1A, and the other end is connected to the second input terminal of the operational amplifier U1A; the power supply terminal of the operational amplifier U1A is connected to the output terminal V_LDO of the voltage stabilizing circuit 110. In Figure 1 In the specific embodiment shown, the first input terminal of the operational amplifier U1A is the positive phase input terminal thereof, and the second input terminal is the negative phase input terminal thereof.

[0025] It should be noted that the function of the triangular wave generating circuit 122 is to output a triangular wave signal Ramp, and in other embodiments, the triangular wave generating circuit 122 can also be replaced by other triangular wave generators in the prior art.

[0026] In Figure 1In the shown embodiment, the constant current circuit 130 comprises resistor R3, resistor R7, resistor R10, resistor R11, resistor R12, switching device Q2, power device Q3 and power device Q4. The first connection end of the power device Q4 is connected with the input end C of the constant current circuit 130, and the second connection end thereof is grounded through the resistor R12; the first connection end of the power device Q3 is connected with the power supply end D of the constant current circuit 130 through the resistor R3, the second connection end thereof is grounded through the resistor R11, the control end thereof is connected with the control end of the power device Q4, and the control end thereof is also connected with the first connection end thereof; the first connection end of the switching device Q2 is connected with the first connection end of the power device Q3, the second connection end thereof is grounded, and the control end thereof is connected with the control end E of the constant current circuit 130 through the resistor R7; one end of the resistor R10 is connected with the control end of the switching device Q2, and the other end thereof is grounded.

[0027] When the PWM signal is the first logic level, the switching device Q2 is turned off, so that the power device Q3 and the power device Q4 are turned on; when the PWM signal is the second logic level, the switching device Q2 is turned on, so that the power device Q3 and the power device Q4 are turned off.

[0028] In Figure 1 In the shown specific embodiment, the switching device Q2 is an NPN triode, the first connection end, the second connection end and the control end of the switching device Q2 are the collector, the emitter and the base of the NPN triode respectively; the power device Q3 is an NPN triode, the first connection end, the second connection end and the control end of the power device Q3 are the collector, the emitter and the base of the NPN triode respectively; the power device Q4 is an NPN triode, the first connection end, the second connection end and the control end of the power device Q4 are the collector, the emitter and the base of the NPN triode respectively.

[0029] In order to facilitate understanding of the utility model, the following specific introduction Figure 1 The design principle of the shown circuit for automatically compensating the brightness of LED according to the temperature change.

[0030] In the voltage stabilizing circuit 110, the resistor R1 is a current limiting resistor for the stabilizing tube D1A, the Vb_Q1 of the triode Q1 is equal to the stabilizing value Vz_D1A of the stabilizing tube D1A, the power supply V1 is designed to be greater than Vz_D1A by more than 2V, so that the triode Q1 is in an amplification state, Vc_Q1 is equal to Vz_D1A+0.7V, the output end V_LDO of the voltage stabilizing circuit 110 realizes the function of stabilizing voltage, and provides stable voltage for the temperature self-adapting circuit 120 and the constant current circuit 130, and the capacitor C1 filters the output end V_LDO of the voltage stabilizing circuit 110.

[0031] The triangular wave generating circuit 122 includes an operational amplifier U1A, a resistor R4, a resistor R5, a resistor R8, a resistor R9 and a capacitor C2, which can realize an output triangular wave signal Ramp. Assuming that the output 1 pin of the operational amplifier U1A is high at power-on, equal to the voltage of the output terminal V_LDO, and the voltage of the 3 pin of the operational amplifier U1A is equal to R8 / (R8+R4 / / R5)*V_LDO=2 / 3*V_LDO, the capacitor C2 is 0V at power-on, less than 2 / 3*V_LDO, that is, the voltage of the 2 pin of the operational amplifier U1A is less than that of the 3 pin, so the output 1 pin of the operational amplifier U1A is kept high, and the capacitor C2 is charged through the resistor R9 (showing a rising trend of the triangular wave); when the charging voltage of the capacitor C2 exceeds 2 / 3*V_LDO, the output 1 pin of the operational amplifier U1A is low at 0V, and the voltage of the 3 pin of the operational amplifier U1A is equal to (R8 / / R5) / (R8 / / R5+R4)*V_LDO=1 / 3*V_LDO, since the voltage of the capacitor C2 at the switching moment is still 2 / 3*V_LDO, that is, the voltage of the 2 pin of the operational amplifier U1A is greater than that of the 3 pin, so the output 1 pin is kept low, and the capacitor C2 is discharged through the resistor R9 (showing a falling trend of the triangular wave), and when the discharging voltage of the capacitor C2 is lower than 1 / 3*V_LDO, that is, the voltage of the 2 pin of the operational amplifier U1A is less than that of the 3 pin, so the output 1 pin of the operational amplifier U1A is high, and the subsequent cycle will follow the above logic; thus, this part completes the continuous output of the triangular wave signal.

[0032] If it is assumed that the output 1 pin of the operational amplifier U1A is low at power-on, the voltage of the 3 pin of the operational amplifier U1A is equal to (R8 / / R5) / (R8 / / R5+R4)*V_LDO=1 / 3*V_LDO, and the voltage of the capacitor C2 at power-on is less than 1 / 3*V_LDO, that is, the voltage of the 2 pin of the operational amplifier U1A is less than that of the 3 pin, so the output 1 pin of the operational amplifier U1A will switch to high, and the subsequent logic is consistent with the above assumption that the output 1 pin of the operational amplifier U1A is high at power-on. If the voltage of the capacitor C2 at power-on is greater than 1 / 3*V_LDO, the voltage of the capacitor C2 will continue to discharge through the resistor R9 until the voltage is less than 1 / 3*V_LDO, which causes the voltage of the 2 pin of the operational amplifier U1A to be less than that of the 3 pin, and the output 1 pin of the operational amplifier U1A will switch to high, and the subsequent logic is consistent with the above assumption that the output 1 pin of the operational amplifier U1A is high at power-on. In summary, the triangular wave generating circuit 122 can realize continuous triangular wave signal output regardless of the voltage of the 1 pin of the operational amplifier U1A at power-on and the voltage of the capacitor C2 at power-on.

[0033] The temperature detection circuit 124 comprises a negative temperature coefficient thermistor NTC and a constant resistance R2. Through the negative temperature coefficient thermistor NTC, the constant resistance R2 and the voltage comparator U1B, the positive duty cycle of the PWM signal can be made smaller by temperature rise. The NTC and the resistance R2 are connected in series to divide voltage, and the resistance ratio of the resistance R2 and the NTC is configured so that the voltage range of the temperature detection voltage VB output by the temperature detection circuit 124 within the temperature range of -40°C to 125°C (i.e. within the predetermined temperature range) can be within the voltage range of the triangular wave signal output by the triangular wave generation circuit 122. U1B acts as a voltage comparator, and the voltage at the 5pin of U1B is within the upper and lower limits of the triangular wave signal at the 6pin, so the 7pin output of U1B is a PWM waveform. When the temperature of NTC rises (i.e. when the temperature of LED1 rises), the resistance of NTC decreases, so the voltage at the 5pin of the voltage comparator U1B (i.e. the temperature detection voltage VB output by the temperature detection circuit 124) decreases, and the positive duty cycle of the PWM signal output at the 7pin of the voltage comparator U1B decreases.

[0034] In the constant current circuit 130, the transistors Q3, Q4, the resistances R3, R11 and R12 form a mirror current source circuit. The same parameters of the transistors Q4, the resistances R3, R11 and R12 are selected to achieve Ic_Q3 = Ic_Q4. Since the bases of the transistors Q3 and Q4 are connected together, and R11 = R12, Vb_Q3 = Vb_Q4, Ib_Q3 = Ib_Q4, and Ic_Q3 = Ic_Q4. The transistors Q3 and Q4 are in an amplification state, and the current values of Ic_Q3 and Ic_Q4 can be set by configuring the resistance values of R3, R11 and R12.

[0035] When the PWM signal is high, the transistor Q2 is turned on, the voltage of Vc_Q2 is equal to 0V, i.e. Vb_Q3 = Vb_Q4 = 0V, the transistors Q3 and Q4 are cut off (or turned off), so Ic_Q3 = Ic_Q4 = I_LED1 = 0A. When the PWM signal is low, the transistor Q2 is cut off (or turned off), and the transistor Q2 does not affect the base voltage of the transistors Q3 and Q4, so the transistors Q3 and Q4 are still in an amplification state, and Ic_Q3 = Ic_Q4 = I_LED1. Therefore, the positive duty cycle of the PWM signal corresponds to the positive duty cycle time of the current conduction of LED1 (or controls the working duty cycle of the constant current circuit 130).

[0036] In summary, the NTC resistance decreases with the increase of the temperature of the LED1, and the positive duty cycle of the PWM signal is increased, so the on-duty cycle of the LED1 constant current source is increased, the brightness of the LED1 is increased, and the brightness of the LED1 is compensated due to the brightness attenuation caused by the temperature rise. By controlling the change rate of the PWM in the range of-40-125 DEG C to be proportional to the change rate of the brightness attenuation of the LED1, the brightness attenuation of the LED1 caused by the temperature rise is compensated by the increase of the on-duty cycle of the LED1 constant current source, so that the brightness of the LED1 is consistent in the temperature range.

[0037] It should be noted that the above-mentioned-40-125 DEG C is an example range, and the actual application range can be less than or greater than this range, and is designed according to the parameter properties of components.

[0038] In summary, the circuit for automatically compensating the brightness of the LED according to the temperature change has the following advantages:

[0039] 1. The circuit of the present application has simple design and does not need single-chip microcomputer control, thereby saving circuit cost.

[0040] 2. The LED temperature compensation of the present application has almost no delay, can compensate in real time, is more sensitive to optical compensation, and will not have brightness mutation due to real-time compensation.

[0041] It should be noted that any modification made by those skilled in the art to the specific embodiments of the present application does not deviate from the scope of the claims of the present application. Accordingly, the scope of the claims of the present application is not limited to the foregoing specific embodiments.

Claims

1. A circuit for automatically compensating LED brightness following temperature change, characterized in that, It comprises: a voltage stabilizing circuit, the input end of which is connected with a power supply V1, and the output end thereof is V_LDO, the voltage stabilizing circuit outputs a stable voltage through the output end V_LDO based on the voltage of the power supply V1; a temperature self-adapting circuit, which comprises a triangular wave generating circuit, a temperature detecting circuit and a voltage comparator, the power supply end of the triangular wave generating circuit is connected with the output end V_LDO of the voltage stabilizing circuit, and the output end thereof is A, the triangular wave generating circuit is used to output a triangular wave signal Ramp through the output end A; the input end of the temperature detecting circuit is connected with the output end V_LDO of the voltage stabilizing circuit, and the output end B thereof outputs a temperature detecting voltage VB reflecting the temperature of the LED; the first input end of the voltage comparator is connected with the output end A of the triangular wave generating circuit, and the second input end thereof is connected with the output end B of the temperature detecting unit, the voltage comparator is used to compare the triangular wave signal Ramp and the temperature detecting voltage VB to generate a PWM signal, which is output through the output end of the voltage comparator; a constant current circuit, the input end C of which is connected with the negative electrode of the LED, the positive electrode of the LED is connected with the power supply V1, the output end thereof is grounded, the power supply end D thereof is connected with the output end V_LDO of the voltage stabilizing circuit, and the control end E thereof is connected with the output end of the voltage comparator, the PWM signal output by the voltage comparator controls whether the constant current circuit works or not.

2. The circuit for automatically compensating the brightness of the LED according to the change of temperature according to claim 1, wherein when the PWM signal is at a first logic level, the constant current circuit is caused to work, and the constant current circuit generates a constant current flowing from the input end D to the output end thereof; when the PWM signal is at a second logic level, the constant current circuit is caused not to work, and the constant current circuit does not generate a current flowing from the input end D to the output end thereof; when the temperature of the LED rises, the duty cycle of the first logic level of the PWM signal increases, thereby increasing the working duty cycle of the constant current circuit; when the temperature of the LED falls, the duty cycle of the first logic level of the PWM signal decreases, thereby decreasing the working duty cycle of the constant current circuit.

3. The circuit for automatically compensating the brightness of the LED according to the change of temperature according to claim 1 or 2, wherein the temperature detecting circuit comprises a thermistor, and the thermistor is placed near the LED in layout; in a predetermined temperature range, the resistance value of the thermistor can change in a range, which can make the voltage upper and lower limits of the temperature detecting voltage VB be within the voltage upper and lower limits of the triangular wave signal Ramp.

4. The circuit for automatically compensating the brightness of the LED according to the change of temperature according to claim 3, wherein the temperature detecting circuit comprises the thermistor and a constant resistance R2, one end of the constant resistance R2 is connected with the output end V_LDO of the voltage stabilizing circuit, and the other end thereof is connected with the output end B of the temperature detecting circuit; one end of the thermistor is connected with the output end B of the temperature detecting circuit, and the other end thereof is grounded.

5. The circuit for automatically compensating LED brightness following temperature change according to claim 4, wherein the thermistor is a negative temperature coefficient thermistor. The first input terminal of the voltage comparator is its negative phase input terminal, and the second input terminal is its positive phase input terminal.

6. The circuit for automatically compensating LED brightness following temperature change according to claim 2, wherein the constant current circuit comprises resistors R3, R7, R10, R11, R12, a switching device Q2, power devices Q3 and Q4, The first connection terminal of the power device Q4 is connected with the input terminal C of the constant current circuit, and the second connection terminal is grounded through the resistor R12; the first connection terminal of the power device Q3 is connected with the power supply terminal D of the constant current circuit through the resistor R3, and the second connection terminal is grounded through the resistor R11; the control terminal is connected with the control terminal of the power device Q4, and is also connected with the first connection terminal; the first connection terminal of the switching device Q2 is connected with the first connection terminal of the power device Q3, and the second connection terminal is grounded; the control terminal is connected with the control terminal E of the constant current circuit through the resistor R7; one end of the resistor R10 is connected with the control terminal of the switching device Q2, and the other end is grounded.

7. The circuit for automatically compensating LED brightness following temperature change according to claim 6, wherein when the PWM signal is the first logic level, the switching device Q2 is turned off, so that the power devices Q3 and Q4 are turned on; when the PWM signal is the second logic level, the switching device Q2 is turned on, so that the power devices Q3 and Q4 are turned off.

8. The circuit for automatically compensating LED brightness following temperature change according to claim 7, wherein the switching device Q2 is an NPN triode, and the first connection terminal, the second connection terminal and the control terminal of the switching device Q2 are the collector, the emitter and the base of the NPN triode, respectively; The power device Q3 is an NPN triode, and the first connection terminal, the second connection terminal and the control terminal of the power device Q3 are the collector, the emitter and the base of the NPN triode, respectively; The power device Q4 is an NPN triode, and the first connection terminal, the second connection terminal and the control terminal of the power device Q4 are the collector, the emitter and the base of the NPN triode, respectively.

9. The circuit for automatically compensating LED brightness following temperature change according to claim 1, wherein the triangular wave generating circuit comprises an operational amplifier, resistors R4, R5, R8, R9 and a capacitor C2, ​ ​ ​ ​ ​ One end of the resistor R4 is connected with the output terminal V_LDO of the voltage stabilizing circuit, and the other end is connected with the node F; one end of the resistor R8 is connected with the node F, and the other end is grounded; the first input terminal of the operational amplifier is connected with the node F, and the second input terminal is grounded through the capacitor C2; one end of the resistor R5 is connected with the first input terminal of the operational amplifier, and the other end is connected with the output terminal of the operational amplifier; one end of the resistor R9 is connected with the output terminal of the operational amplifier, and the other end is connected with the second input terminal of the operational amplifier; the power supply terminal of the operational amplifier is connected with the output terminal V_LDO of the voltage stabilizing circuit.

10. The circuit for automatically compensating LED brightness with temperature variation according to claim 1, wherein, The voltage stabilizing circuit comprises a resistor R1, a voltage stabilizing tube D1A, a power device Q1 and a capacitor C1, One end of the resistor R4 is connected with the output terminal V_LDO of the voltage stabilizing circuit, and the other end is connected with the node F; one end of the resistor R8 is connected with the node F, and the other end is grounded; the first input terminal of the operational amplifier is connected with the node F, and the second input terminal is grounded through the capacitor C2; one end of the resistor R5 is connected with the first input terminal of the operational amplifier, and the other end is connected with the output terminal of the operational amplifier; one end of the resistor R9 is connected with the output terminal of the operational amplifier, and the other end is connected with the second input terminal of the operational amplifier; the power supply terminal of the operational amplifier is connected with the output terminal V_LDO of the voltage stabilizing circuit.

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