LED temperature control constant current drive circuit

Abstract

An LED temperature control constant-current driving circuit comprises a constant-current triode Q1, the constant-current triode Q1 is of an NPN type, a collector electrode of the constant-current triode Q1 is connected with a positive power supply VCC through an LED lamp group, an emitter electrode of the constant-current triode Q1 is grounded, a base electrode of the constant-current triode Q1 is connected with a clamp current triode Q3, and the base electrode of the constant-current triode Q1 is further connected with a high-temperature derating circuit. The high-temperature derating circuit comprises an NPN type shunt triode Q2, a collector electrode of the shunt triode Q2 is connected with a base electrode of the constant-current triode Q1, an emitter electrode of the shunt triode Q2 is connected with a resistor R4 in series and grounded, a base electrode of the shunt triode Q2 is connected with a resistor R1 in series and connected with a positive power supply VCC, a base electrode of the shunt triode Q2 is connected with a thermistor R3 in series and grounded, and the thermistor R3 is close to a heat source of the LED driving circuit. According to the LED driving circuit, automatic derating work can be realized, the working temperature of the LED driving circuit is reduced, the LED driving circuit is prevented from being damaged by high temperature, and the stability of the LED driving circuit is improved.

Description

Technical Field

[0001] The utility model relates to the technical field of automobile lamps, in particular to an LED temperature-controlled constant-current driving circuit. Background Art

[0002] With the development of the automotive industry, the brightness requirements of LEDs are getting higher and higher. In order to ensure the constant brightness of LEDs, it is necessary to prevent the LED operating current from changing with the fluctuation of the input voltage during operation, thereby causing brightness fluctuations. For this reason, a constant current circuit is generally used to drive the LED to keep the LED brightness stable and uniform LED brightness and color.

[0003] At the same time, in the automotive industry, the operating environment of the LED constant current drive circuit is generally -40℃~+85℃. However, with the development of the automotive industry, the brightness requirements of LEDs are getting higher and higher, and what comes with it is that the current required is getting larger and larger. As the current increases, the power consumed by the LED and transistors in the LED constant current drive circuit will also increase, which will cause the working environment temperature of the LED and transistor to increase. As the working environment temperature increases, the brightness of the LED will decrease, the color coordinates will shift, and the internal temperature of the LED and transistor will also increase, thereby exceeding the junction temperature of the LED and transistor, damaging the LED and transistor, and causing the LED constant current drive circuit to not work. Utility Model Content

[0004] The purpose of the utility model is to provide an LED temperature-controlled constant current drive circuit, which can automatically reduce the rated operation, reduce the operating temperature of the LED drive circuit, ensure that the LED drive circuit is not damaged by high temperature, and improve the stability of the LED drive circuit.

[0005] An LED temperature-controlled constant-current drive circuit includes a constant-current transistor Q1. The constant-current transistor Q1 is an NPN type. The collector of the constant-current transistor Q1 is connected to a positive power supply VCC via an LED lamp assembly, the emitter of the constant-current transistor Q1 is grounded, and the base of the constant-current transistor Q1 is connected to a current-clamping transistor Q3. The key point is that the base of the constant-current transistor Q1 is also connected to a high-temperature derating circuit. The high-temperature derating circuit includes an NPN type shunt transistor Q2. The collector of the shunt transistor Q2 is connected to the base of the constant-current transistor Q1. The emitter string resistor R4 of the shunt transistor Q2 is grounded. The base string resistor R1 of the shunt transistor Q2 is connected to the positive power supply VCC. The base string thermistor R3 of the shunt transistor Q2 is grounded. The thermistor R3 is close to the heat source of the LED drive circuit.

[0006] The resistance value of the thermistor R3 increases as the operating temperature of the LED constant current drive circuit increases, and the base voltage of the shunt transistor Q2 increases accordingly. When the difference between the base voltage of the shunt transistor Q2 and the emitter voltage of the shunt transistor Q2 is greater than 0.7V, the shunt transistor Q2 is turned on and reduces the operating current of the constant current transistor Q1, causing the LED lamp group to operate at a reduced rating, thereby reducing the temperature of the heat source of the LED drive circuit. When the temperature of the heat source of the LED drive circuit decreases, the resistance value of the thermistor R3 decreases, and the base voltage of the shunt transistor Q2 decreases. When the difference between the base voltage of the shunt transistor Q2 and the emitter voltage of the shunt transistor Q2 is less than 0.7V, the shunt transistor Q2 is turned off, and the operating current of the constant current transistor Q1 returns to normal.

[0007] Therefore, the high-temperature automatic derating circuit can control the derating operation of the LED driver circuit according to the temperature of the heat source, so that the LED driver circuit can operate under high temperature conditions. At the same time, the derating operation of the LED driver circuit will reduce the temperature of the heat source, preventing the temperature of the heat source from further increasing, ensuring that the LED driver circuit is not damaged by high temperature, thereby improving the stability of the LED driver circuit. When the temperature of the heat source drops to a normal value, the LED driver circuit can automatically resume normal working state.

[0008] In addition, the derating degree of the LED driving circuit is related to the resistance value of resistor R4.

[0009] Furthermore, the base of the constant current transistor Q1 is connected to a PWM control source via a resistor R2.

[0010] Furthermore, the emitter string resistor R5 of the constant current transistor Q1 is grounded, the emitter of the constant current transistor Q1 is also connected to the base of the current clamp transistor Q3, the base of the current clamp transistor Q3 is grounded via the capacitor C1, the emitter of the current clamp transistor Q3 is grounded, and the collector of the current clamp transistor Q3 is connected to the base of the constant current transistor Q1.

[0011] The current clamping transistor Q1 and the constant current transistor Q3 clamp each other. After the current clamping transistor Q1 and the constant current transistor Q3 are turned on, the current flowing through the LED lamp group gradually stabilizes, thereby driving the LED lamp group with constant current. When the input voltage fluctuates, the brightness of the LED lamp group can be kept stable, the brightness and color of the LED lamp group are uniform, the temperature rise of the LED lamp group is reduced, the LED lamp group is prevented from overheating, the light decay of the LED is delayed, and its service life is extended.

[0012] Furthermore, the heat source is the constant current transistor Q1.

[0013] Furthermore, the heat source is the current clamp transistor Q3.

[0014] Furthermore, the heat source is the LED light group.

[0015] Furthermore, at least one light emitting diode is provided in the LED lamp group.

[0016] Beneficial effects: 1. The high-temperature derating circuit can control the derating operation of the LED driver circuit according to the temperature of the heat source of the LED driver circuit, so that the LED driver circuit can work under high temperature conditions. At the same time, the derating operation of the LED driver circuit will reduce the temperature of the heat source and prevent the temperature of the heat source from further increasing, ensuring that the LED driver circuit is not damaged by high temperature, thereby improving the stability of the LED driver circuit. When the temperature of the heat source drops to a normal value, the LED driver circuit can automatically resume normal working state.

[0017] 2. The constant current transistor Q1 and the current clamping transistor Q3 can drive the LED light group to work at a constant current, so that the brightness of the LED light group remains stable, the brightness and color of the LED light group are uniform, the temperature rise of the LED light group is reduced, the LED light group is prevented from overheating, the light decay of the LED is delayed, and its service life is extended.

[0018] 3. Thermistors, transistors and light-emitting diodes are not only low in cost but also easy to purchase, so the manufacturing cost of the present invention is low. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is the circuit diagram of the utility model. DETAILED DESCRIPTION

[0020] The specific implementation manner and working principle of the present invention are further described in detail below with reference to the accompanying drawings.

[0021] like Figure 1 As shown, an LED temperature-controlled constant current drive circuit is provided with an LED constant current drive circuit and a high-temperature automatic derating circuit. The LED constant current drive circuit is provided with a constant current transistor Q1. The base of the constant current transistor Q1 is connected to the PWM control source via a resistor R2. The collector of the constant current transistor Q1 is connected to the cathode of a light-emitting diode D1, which is connected to the positive power supply VCC. The emitter of the constant current transistor Q1 is grounded via a resistor R5. The emitter of the constant current transistor Q1 is also connected to the base of a current clamp transistor Q3. The collector of the current clamp transistor Q3 is connected to the base of the constant current transistor Q1. The emitter of the current clamp transistor Q3 is grounded. The base of the current clamp transistor Q3 is also grounded via a capacitor C1.

[0022] The base of the constant current transistor Q1 is also connected to the collector of the shunt transistor Q2 in the high temperature derating circuit. The base of the shunt transistor Q2 is grounded via the thermistor R3, and the emitter of the shunt transistor Q2 is grounded via the resistor R4.

[0023] The base of the shunt transistor Q2 is also connected to the positive power supply VCC via the resistor R1.

[0024] When the LED temperature-controlled constant current drive circuit is arranged on a PCB, the thermistor R3 is arranged near the constant current transistor Q1 or the current clamping transistor Q3 or the light-emitting diode D1. The resistance value of the thermistor R3 increases as the operating temperature of the constant current transistor Q1 or the current clamping transistor Q3 or the light-emitting diode D1 increases, thereby controlling the LED constant current drive circuit to operate at a derating rate.

Claims

1. An LED temperature-controlled constant current drive circuit, comprising a constant current transistor Q1, which is an NPN type, with the collector of the constant current transistor Q1 connected to a positive power supply VCC via an LED lamp assembly, the emitter of the constant current transistor Q1 connected to ground, and the base of the constant current transistor Q1 connected to a current clamp transistor Q3, characterized in that: The base of the constant current transistor Q1 is also connected to a high temperature derating circuit, which includes an NPN type shunt transistor Q2. The collector of the shunt transistor Q2 is connected to the base of the constant current transistor Q1, the emitter string resistor R4 of the shunt transistor Q2 is grounded, the base string resistor R1 of the shunt transistor Q2 is connected to the positive power supply VCC, and the base string thermistor R3 of the shunt transistor Q2 is grounded. The thermistor R3 is close to the heat source of the LED drive circuit.

2. The LED temperature-controlled constant current driving circuit according to claim 1, characterized in that: The base of the constant current transistor Q1 is connected to a PWM control source via a resistor R2.

3. The LED temperature-controlled constant current driving circuit according to claim 1, characterized in that: The emitter string resistor R5 of the constant current transistor Q1 is grounded, the emitter of the constant current transistor Q1 is also connected to the base of the current clamp transistor Q3, the base of the current clamp transistor Q3 is grounded via the capacitor C1, the emitter of the current clamp transistor Q3 is grounded, and the collector of the current clamp transistor Q3 is connected to the base of the constant current transistor Q1.

4. The LED temperature-controlled constant current driving circuit according to claim 1, characterized in that: The heat source is the constant current transistor Q1.

5. The LED temperature-controlled constant current driving circuit according to claim 1, characterized in that: The heat source is the current clamp transistor Q3.

6. The LED temperature-controlled constant current driving circuit according to claim 1, characterized in that: The heat source is the LED lamp group.

7. The LED temperature-controlled constant current driving circuit according to claim 6, characterized in that: At least one light emitting diode is provided in the LED lamp group.

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