LED constant-current driving circuit capable of automatically derating over-temperature

Abstract

The utility model provides an over-temperature automatic derating LED constant current drive circuit, comprising a reference voltage generation unit whose input end is connected with a power supply end VS and whose output end outputs a reference voltage Vref; the input end of the temperature detection unit is connected with the reference voltage Vref, and the output end of the temperature detection unit outputs temperature detection voltage Vntc reflecting the environment temperature; the comparison unit comprises a resistor R4, a resistor R8, a resistor R10, an operational amplifier U2 and a switching tube Q2; and the constant current driving unit comprises a resistor R1, a resistor R2, a resistor R3, a resistor R5, a resistor R9, an operational amplifier U1 and an output tube Q1. Compared with the prior art, software is not needed for control, automatic over-temperature detection can be achieved through a simple pure hardware circuit, derating processing is carried out on the constant-current driving current, cost is greatly saved, and the over-temperature detection circuit has the advantages of being high in response speed, high in stability and the like.

Description

[Technical field]

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

[0002] At present, the ambient light on the car has become an increasingly popular decorative element. These ambient lights usually use LED as the light source, which has the advantages of low power consumption, long life and colorful effects. However, the temperature resistance of LED lights is generally low, around 125℃. When working normally, LED lights will also generate a lot of heat to further increase the ambient temperature. When the operating temperature is exceeded, the life of the LED light will be greatly affected, the normal working performance cannot be guaranteed, and it may even be damaged.

[0003] The existing technology generally uses a single-chip microcomputer to collect the temperature around the LED through the ADC (Analog-to-Digital Converter) port. When the temperature exceeds the set threshold, the LED lamp is derated to reduce the power of the LED lamp and reduce the heat generation to protect the LED lamp. However, this solution uses a relatively complex single-chip microcomputer and software logic, which is costly.

[0004] Therefore, it is necessary to propose a new technical solution to solve the above problems. [Contents of the utility model]

[0005] One of the purposes of the utility model is to provide an LED constant current drive circuit with automatic over-temperature derating, which does not require software control and can realize automatic over-temperature detection and derating of the constant current drive current through a simple pure hardware circuit, thereby greatly saving costs and having the characteristics of fast response speed and strong stability.

[0006] According to one aspect of the utility model, the utility model provides an LED constant current driving circuit with automatic over-temperature derating, which includes: a reference voltage generating unit, whose input end is connected to the power supply end VS, and whose output end outputs a reference voltage Vref; a temperature detection unit, whose input end is connected to the reference voltage Vref, and whose output end outputs a temperature detection voltage Vntc reflecting the ambient temperature; a comparison unit, which includes a resistor R4, a resistor R8, a resistor R10, an operational amplifier U2 and a switch tube Q2, wherein the resistor R8 is connected between the reference voltage Vref and a connection node A; the resistor R10 is connected between the connection node A and a ground terminal; the first input end of the operational amplifier U2 is connected to the connection node A, and the second input end thereof is connected to the temperature detection voltage Vntc; the first connection end of the switch tube Q2 is connected to the connection node B via the resistor R4, the second connection end thereof is grounded, and the control end thereof is connected to the operational amplifier U2 The output end is connected; the constant current driving unit includes a resistor R1, a resistor R2, a resistor R3, a resistor R5, a resistor R9, an operational amplifier U1 and an output tube Q1, one end of the resistor R3 is connected to the reference voltage Vref, and the other end thereof is connected to the connection node B; one end of the resistor R5 is connected to the connection node B, and the other end thereof is grounded; the first input end of the operational amplifier U1 is connected to the reference voltage Vref via the resistor R2, and the second input end thereof is connected to the connection node B; the first connection end of the output tube Q1 is connected to the output end Vout, the second connection end thereof is grounded via the resistor R9, and the control end thereof is connected to the output end of the operational amplifier U1; one end of the resistor R1 is connected to the first input end of the operational amplifier U1, and the other end thereof is connected to the second connection end of the output tube Q1; the power supply end VS is connected to the positive electrode of the LED, and the output end Vout is connected to the negative electrode of the LED.

[0007] Furthermore, the reference voltage generating unit includes a resistor R6 and a Zener diode D1, one end of the resistor R6 is connected to the power supply terminal VS, and the other end thereof is connected to the connection node C; the cathode of the Zener diode D1 is connected to the connection node C, and the anode thereof is grounded; the connection node C is the output end of the reference voltage generating unit, and the voltage on the connection node C is the reference voltage Vref.

[0008] Furthermore, the temperature detection unit includes a resistor R7 and a resistor R11, one end of the resistor R7 is connected to the reference voltage Vref, and the other end thereof is connected to the connection node D; one end of the resistor R11 is connected to the connection node D, and the other end thereof is grounded; the connection node D is the output end of the temperature detection unit, and the voltage on the connection node D is the temperature detection voltage Vntc; the resistor R7 is a thermistor with a negative temperature coefficient, and the resistor R11 is a constant resistor.

[0009] Furthermore, the LED constant current driving circuit with automatic derating upon over-temperature further includes a capacitor C1 and a capacitor C2, wherein one end of the capacitor C1 is connected to the connection node C, and the other end thereof is grounded; one end of the capacitor C2 is connected to the second input end of the operational amplifier U1, and the other end thereof is grounded.

[0010] Furthermore, when the ambient temperature is lower than a preset over-temperature threshold, the voltage of the connection node A is higher than the temperature detection voltage Vntc, the operational amplifier U2 outputs a first logic level, and the switch tube Q2 is turned off. At this time, the output tube Q1 is turned on, and the output terminal Vout maintains the set constant current state; when the ambient temperature is higher than the preset over-temperature threshold, the voltage of the connection node A is lower than the temperature detection voltage Vntc, the operational amplifier U2 outputs a second logic level, and the switch tube Q2 is turned on. At this time, the output tube Q1 is turned on, the voltage of the connection node B is reduced, and the constant current of the output terminal Vout is reduced.

[0011] Furthermore, the output tube Q1 is an NMOS transistor, and the first connection end, the second connection end and the control end of the output tube Q1 are respectively the drain, the source and the gate of the NMOS transistor; the switch tube Q2 is an NMOS transistor, and the first connection end, the second connection end and the control end of the switch tube Q2 are respectively the drain, the source and the gate of the NMOS transistor.

[0012] Furthermore, the first input terminal and the second input terminal of the operational amplifier U1 are respectively its negative input terminal and positive input terminal; the first input terminal and the second input terminal of the operational amplifier U2 are respectively its negative input terminal and positive input terminal.

[0013] Furthermore, the constant current derating range during over-temperature is determined by configuring different resistance values ​​of the resistors R4 and R5; and different over-temperature thresholds are determined by configuring the resistance values ​​of the resistors R8, R10, and R11.

[0014] Furthermore, the resistance values ​​of the resistors R7, R8, R10 and R11 satisfy the following conditions: when the ambient temperature is lower than a preset over-temperature threshold, the voltage of the connection node A is higher than the temperature detection voltage Vntc; when the ambient temperature is higher than the preset over-temperature threshold, the voltage of the connection node A is lower than the temperature detection voltage Vntc.

[0015] Compared with the prior art, the utility model does not require software control, and can realize automatic over-temperature detection through a simple pure hardware circuit, and derating the constant current drive current, which greatly saves costs and has the characteristics of fast response speed and strong stability.

Brief Description of the Drawings

[0016] 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:

[0017] Figure 1 The present invention is a circuit diagram of an LED constant current driving circuit with automatic over-temperature derating in one embodiment of the present invention. [Specific implementation method]

[0018] 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.

[0019] The "one embodiment" or "embodiment" referred to herein refers to specific features, structures or characteristics that may be included in at least one implementation of the present invention. 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 A is connected to B through electrical components or circuits. In the present utility model, "greater than" means greater than, and "less than or equal to" means less than or equal to.

[0020] 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.

[0021] Please refer to Figure 1 As shown, it is a circuit diagram of an LED constant current driving circuit with automatic over-temperature derating in one embodiment of the utility model. Figure 1 The LED constant current driving circuit with automatic over-temperature derating includes a reference voltage generating unit 110 , a temperature detecting unit 120 , a comparing unit 130 and a constant current driving unit 140 .

[0022] The input terminal of the reference voltage generating unit 110 is connected to the power supply terminal VS, and the output terminal thereof outputs the reference voltage Vref, wherein the reference voltage generating unit 110 generates the reference voltage Vref based on the voltage of the power supply terminal VS. The input terminal of the temperature detecting unit 120 is connected to the reference voltage Vref, and the output terminal thereof outputs the temperature detecting voltage Vntc reflecting the ambient temperature, wherein the temperature detecting unit 120 generates the temperature detecting voltage Vntc reflecting the ambient temperature based on the reference voltage Vref.

[0023] The comparison unit 130 includes a resistor R4, a resistor R8, a resistor R10, an operational amplifier U2, and a switch tube Q2. The resistor R8 is connected between the reference voltage Vref and the connection node A; the resistor R10 is connected between the connection node A and the ground terminal; the first input terminal of the operational amplifier U2 is connected to the connection node A, and the second input terminal thereof is connected to the temperature detection voltage Vntc; the first connection terminal of the switch tube Q2 is connected to the connection node B via the resistor R4, the second connection terminal thereof is grounded, and the control terminal thereof is connected to the output terminal of the operational amplifier U2.

[0024] The constant current driving unit 140 includes a resistor R1, a resistor R2, a resistor R3, a resistor R5, a resistor R9, an operational amplifier U1 and an output tube Q1. Among them, one end of the resistor R3 is connected to the reference voltage Vref, and the other end thereof is connected to the connection node B; one end of the resistor R5 is connected to the connection node B, and the other end thereof is grounded; the first input end of the operational amplifier U1 is connected to the reference voltage Vref via the resistor R2, and the second input end thereof is connected to the connection node B; the first connection end of the output tube Q1 is connected to the output end Vout, the second connection end thereof is grounded via the resistor R9, and the control end thereof is connected to the output end of the operational amplifier U1; one end of the resistor R1 is connected to the first input end of the operational amplifier U1, and the other end thereof is connected to the second connection end of the output tube Q1. The power supply end VS is connected to the positive electrode of LED1, and the output end Vout is connected to the negative electrode of LED1.

[0025] exist Figure 1 In the specific embodiment shown, the reference voltage generating unit 110 includes a resistor R6 and a Zener diode D1, one end of the resistor R6 is connected to the power supply terminal VS, and the other end thereof is connected to the connection node C; the cathode of the Zener diode D1 is connected to the connection node C, and the anode thereof is grounded; the connection node C is the output end of the reference voltage generating unit 110, and the voltage on the connection node C is the reference voltage Vref.

[0026] exist Figure 1 In the specific embodiment shown, the temperature detection unit 120 includes a resistor R7 and a resistor R11, one end of the resistor R7 is connected to the reference voltage Vref (or the connection node C), and the other end thereof is connected to the connection node D; one end of the resistor R11 is connected to the connection node D, and the other end thereof is grounded; the connection node D is the output end of the temperature detection unit 120, and the voltage on the connection node D is the temperature detection voltage Vntc; the resistor R7 is an NTC (Negative Temperature Coefficient, i.e., a negative temperature coefficient thermistor), and the resistor R11 is a constant resistor.

[0027] exist Figure 1 In the specific embodiment shown, the LED constant current driving circuit with automatic over-temperature derating also includes a capacitor C1 and a capacitor C2, one end of the capacitor C1 is connected to the reference voltage Vref (or the connection node C), and the other end thereof is grounded; one end of the capacitor C2 is connected to the second input terminal of the operational amplifier U1, and the other end thereof is grounded.

[0028] exist Figure 1In the specific embodiment shown, the output tube Q1 is an NMOS (N-Metal-Oxide-Semiconductor) transistor, and the first connection terminal, the second connection terminal and the control terminal of the output tube Q1 are the drain, the source and the gate of the NMOS transistor respectively; the switch tube Q2 is an NMOS transistor, and the first connection terminal, the second connection terminal and the control terminal of the switch tube Q2 are the drain, the source and the gate of the NMOS transistor respectively.

[0029] exist Figure 1 In the specific embodiment shown, the first input terminal and the second input terminal of the operational amplifier U1 are respectively its negative input terminal and positive input terminal; the first input terminal and the second input terminal of the operational amplifier U2 are respectively its negative input terminal and positive input terminal.

[0030] Among them, the resistance values ​​of resistors R7, R8, R10 and R11 satisfy: when the ambient temperature is lower than a preset over-temperature threshold (i.e., when the ambient temperature is within a normal range), the voltage of connection node A (which is a voltage corresponding to the set over-temperature threshold) is greater than the temperature detection voltage Vntc (which is a voltage corresponding to the ambient temperature); when the ambient temperature is higher than a preset over-temperature threshold (i.e., when the ambient temperature is overheated), the voltage of connection node A is lower than the temperature detection voltage Vntc.

[0031] The following is a detailed introduction Figure 1 The working principle of the LED constant current drive circuit with automatic over-temperature derating is shown in the figure.

[0032] When the ambient temperature is within the normal range (i.e., when the ambient temperature is less than the preset over-temperature threshold), the temperature detection voltage Vntc (i.e., the voltage connected to node D) generated by the voltage division of the NTC resistor R7 and the resistor R11 is less than the voltage divided by the reference voltage Vref on the resistors R8 and R10 (i.e., the voltage connected to node A), that is, the voltage at the positive input terminal of the operational amplifier U2 is lower than the voltage at its negative input terminal, and the operational amplifier U2 outputs a low level (which can become the first logic level) to the NMOS transistor Q2. At this time, the NMOS transistor Q2 is not turned on (i.e., turned off), the resistor R4 does not work, and the voltage at the positive input terminal of the operational amplifier U1 is determined by the voltage division of the resistors R3 and R5. At this time, the input voltage at the positive input terminal of the operational amplifier U1 is: V_U1=Vref*R5 / (R3+R5). At this time, the current of the power supply terminal VS flows to the NMOS transistor Q1 through the LED1 at the same time, and then flows to the ground terminal through the resistor R9. The current of LED1 will produce a corresponding voltage drop on the resistor R9. The voltage signal Current (i.e., the feedback voltage Current) is connected to the negative input terminal of the operational amplifier U1 through the resistor R1. After the voltage is divided by the resistor R2, the voltage value is input to the negative input terminal of the operational amplifier U1 and compared with the voltage divided by the resistors R3 and R5 (i.e., the voltage connected to the node B). According to the principle of virtual short of the operational amplifier, the voltage of the positive input terminal and the negative input terminal are equal, so the current value flowing through the resistor R9 is finally constant as follows: I_Nom = (V_U1*(R1+R2)-Vref*R1) / (R2*R9). If the voltage of the power supply terminal VS changes, if the voltage increases, it will instantly cause the current of the LED lamp driving circuit to increase. At this time, the Current voltage signal above the resistor R9 becomes larger, thereby being greater than the positive input terminal voltage of the operational amplifier U1. At this time, the operational amplifier U1 will control the output voltage, which will cause the internal resistance of the NMOS transistor Q1 to increase, and will consume the increased voltage value of the power supply terminal VS, so that the system maintains the original constant current state. That is to say, when the ambient temperature is lower than the preset over-temperature threshold, the voltage of the connection node A is higher than the temperature detection voltage Vntc, the operational amplifier U2 outputs the first logic level, the switch tube Q2 is turned off, at this time, the output tube Q1 is turned on, and the output terminal Vout maintains the set constant current state.

[0033] When the ambient temperature gradually increases, the resistance of NTC resistor R7 gradually decreases, and the temperature detection voltage Vntc (i.e., the positive input voltage of operational amplifier U2) generated by the voltage division of NTC resistor R7 and resistor R11 will also gradually increase. When the set over-temperature threshold is exceeded, the positive input voltage of operational amplifier U2 is greater than its negative input voltage (i.e., the voltage connected to node A), and operational amplifier U2 outputs a high level (which can be called the second logic level) to NMOS transistor Q2. At this time, NMOS transistor Q2 becomes conductive and resistor R4 is grounded. At this time, the parallel connection of resistors R4 and R5 causes the resistance to decrease, which will also cause the positive input voltage V_U1 of operational amplifier U1 (i.e., the voltage connected to node B) to decrease. Assuming R4=R5, at this time, the voltage of V_U1 will become (R3+R5) / (2*R3+R5) times of the original voltage. As V_U1 decreases, the feedback voltage Current above resistor R9 will also decrease, thereby reducing the current flowing through resistor R9 and the current of LED1 lamp will also be derated. That is to say, when the ambient temperature is greater than the preset over-temperature threshold, the voltage of the connection node A is less than the temperature detection voltage Vntc, the operational amplifier U2 outputs the second logic level, and the switch tube Q2 is turned on. At this time, the output tube Q1 is turned on, the voltage of the connection node B is reduced, and the constant current of the output terminal Vout is reduced.

[0034] It should be noted that the constant current derating range during over-temperature can be determined by configuring different resistance values ​​of the resistors R4 and R5; and different over-temperature thresholds can be determined by configuring the resistance values ​​of the resistors R8, R10, and R11.

[0035] In summary, the utility model provides an LED constant current drive circuit that automatically derates when over-temperature occurs. It does not require software control, and can realize automatic over-temperature detection and derate the constant current drive current through a simple pure hardware circuit, which greatly saves costs and has the characteristics of fast response speed and strong stability. Through the technical solution provided by the utility model, the atmosphere light on the car can be more safely and reliably applied to various driving scenarios, while achieving the advantages of simple circuit and low cost. The solution can automatically detect the temperature of the LED lamp, and derate the driving current of the LED lamp according to the set temperature value, thereby extending the service life of the LED lamp and improving the use effect. In addition, the solution has a simple structure and does not require an additional single-chip microcomputer for temperature acquisition. The function of over-temperature detection is realized by pure hardware, and the derated output in the constant current mode is realized.

[0036] 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. An LED constant current drive circuit with automatic derating when over temperature, characterized in that: It includes: A reference voltage generating unit, whose input terminal is connected to the power supply terminal VS, and whose output terminal outputs the reference voltage Vref; A temperature detection unit, whose input terminal is connected to the reference voltage Vref, and whose output terminal outputs a temperature detection voltage Vntc reflecting the ambient temperature; A comparison unit, comprising a resistor R4, a resistor R8, a resistor R10, an operational amplifier U2 and a switch tube Q2, wherein the resistor R8 is connected between the reference voltage Vref and a connection node A; the resistor R10 is connected between the connection node A and a ground terminal; a first input terminal of the operational amplifier U2 is connected to the connection node A, and a second input terminal thereof is connected to the temperature detection voltage Vntc; a first connection terminal of the switch tube Q2 is connected to a connection node B via the resistor R4, a second connection terminal thereof is grounded, and a control terminal thereof is connected to an output terminal of the operational amplifier U2; A constant current driving unit, comprising a resistor R1, a resistor R2, a resistor R3, a resistor R5, a resistor R9, an operational amplifier U1 and an output tube Q1, wherein one end of the resistor R3 is connected to the reference voltage Vref, and the other end thereof is connected to the connection node B; one end of the resistor R5 is connected to the connection node B, and the other end thereof is grounded; a first input end of the operational amplifier U1 is connected to the reference voltage Vref via the resistor R2, and a second input end thereof is connected to the connection node B; a first connection end of the output tube Q1 is connected to an output end Vout, a second connection end thereof is grounded via the resistor R9, and a control end thereof is connected to an output end of the operational amplifier U1; one end of the resistor R1 is connected to a first input end of the operational amplifier U1, and the other end thereof is connected to a second connection end of the output tube Q1; The power supply terminal VS is connected to the positive electrode of the LED, and the output terminal Vout is connected to the negative electrode of the LED.

2. The LED constant current driving circuit with automatic over-temperature derating according to claim 1, characterized in that: The reference voltage generating unit includes a resistor R6 and a Zener diode D1, one end of the resistor R6 is connected to the power supply terminal VS, and the other end thereof is connected to a connection node C; a cathode of the Zener diode D1 is connected to the connection node C, and a positive electrode thereof is grounded; the connection node C is the output end of the reference voltage generating unit, and a voltage on the connection node C is the reference voltage Vref.

3. The LED constant current driving circuit with automatic over-temperature derating according to claim 2, characterized in that: The temperature detection unit includes a resistor R7 and a resistor R11. One end of the resistor R7 is connected to the reference voltage Vref, and the other end thereof is connected to the connection node D; one end of the resistor R11 is connected to the connection node D, and the other end thereof is grounded; The connection node D is the output end of the temperature detection unit, and the voltage on the connection node D is the temperature detection voltage Vntc; The resistor R7 is a thermistor with a negative temperature coefficient, and the resistor R11 is a constant resistor.

4. The LED constant current driving circuit with automatic over-temperature derating according to claim 3, characterized in that: It also includes capacitor C1 and capacitor C2, One end of the capacitor C1 is connected to the connection node C, and the other end thereof is grounded; One end of the capacitor C2 is connected to the second input end of the operational amplifier U1 , and the other end thereof is grounded.

5. The LED constant current driving circuit with automatic over-temperature derating according to any one of claims 1 to 4, characterized in that: When the ambient temperature is lower than the preset over-temperature threshold, the voltage of the connection node A is higher than the temperature detection voltage Vntc, the operational amplifier U2 outputs a first logic level, the switch tube Q2 is turned off, and at this time, the output tube Q1 is turned on, and the output terminal Vout maintains a set constant current state; When the ambient temperature is greater than the preset over-temperature threshold, the voltage of the connection node A is less than the temperature detection voltage Vntc, the operational amplifier U2 outputs a second logic level, the switch tube Q2 is turned on, at this time, the output tube Q1 is turned on, the voltage of the connection node B is reduced, and the constant current of the output end Vout is reduced.

6. The LED constant current driving circuit with automatic over-temperature derating according to claim 5, characterized in that: The output tube Q1 is an NMOS transistor, and the first connection end, the second connection end and the control end of the output tube Q1 are respectively the drain, the source and the gate of the NMOS transistor; The switch tube Q2 is an NMOS transistor, and the first connection terminal, the second connection terminal and the control terminal of the switch tube Q2 are respectively the drain, the source and the gate of the NMOS transistor.

7. The LED constant current driving circuit with automatic over-temperature derating according to claim 6, characterized in that: The first input terminal and the second input terminal of the operational amplifier U1 are respectively its negative input terminal and positive input terminal; The first input terminal and the second input terminal of the operational amplifier U2 are respectively the negative input terminal and the positive input terminal thereof.

8. The LED constant current driving circuit with automatic over-temperature derating according to claim 3, characterized in that: The constant current derating range when over-temperature occurs is determined by configuring different resistance values ​​of the resistors R4 and R5; Different over-temperature thresholds are determined by configuring the resistance values ​​of the resistors R8 , R10 , and R11 .

9. The LED constant current driving circuit with automatic over-temperature derating according to claim 1, characterized in that: The resistance values ​​of the resistors R7, R8, R10 and R11 satisfy: When the ambient temperature is lower than a preset over-temperature threshold, the voltage of the connection node A is higher than the temperature detection voltage Vntc; When the ambient temperature is greater than a preset over-temperature threshold, the voltage of the connection node A is less than the temperature detection voltage Vntc.

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