A circuit for compensating LED brightness at different temperatures

Abstract

This invention provides a circuit for compensating LED brightness at different temperatures, comprising: a differential voltage sampling circuit, whose first input terminal is connected to the positive terminal of the LED and its second input terminal is connected to the negative terminal of the LED; the differential voltage sampling circuit is used to collect the voltage value across the LED and output the voltage value across the LED through its output terminal; a signal control circuit, whose input terminal is connected to the output terminal of the differential voltage sampling circuit and whose output terminal outputs a control signal; the signal control circuit outputs a control signal with a corresponding duty cycle based on the voltage value across the LED; and a switch control circuit, comprising a switch device Q1, whose first connection terminal is connected to the negative terminal of the LED, its control terminal is connected to the output terminal of the signal control circuit, and its second connection terminal is grounded. Compared with the prior art, this invention can not only compensate for LED brightness in real time according to temperature changes, but also has a simple circuit design and does not require the use of a temperature sensor or an LED driver chip with specific functions.

Description

[Technical Field]

[0001] This utility model relates to the field of circuit design technology, and in particular to a circuit for compensating LED brightness at different temperatures. [Background Technology]

[0002] The brightness of LEDs changes significantly with temperature; rising temperatures typically lead to brightness decay, which affects display quality and illumination in practical applications. In scenarios such as automotive headlights, interior lights, and indoor lighting, where ambient temperature fluctuates considerably, unstable LED brightness can reduce readability, negatively impact visual experience, and even pose safety hazards. Therefore, achieving brightness compensation for LEDs at different temperatures to ensure brightness stability is crucial for improving LED application performance.

[0003] There is currently a solution 1, which involves installing a high-precision temperature sensor, such as a thermistor, near the LED module. Utilizing its negative temperature coefficient characteristic, the resistance value decreases as the temperature rises, and the temperature can be calculated by measuring the resistance value.

[0004] A second solution exists, which uses an LED driver chip with temperature compensation functionality. This type of chip integrates a temperature compensation circuit. When the LED temperature rises, the brightness is compensated by adjusting the current flowing through the LED, thus suppressing brightness decay.

[0005] However, the existing technical solutions have the following problems and drawbacks:

[0006] Solution 1 has limitations on the placement of the temperature sensor, which needs to be close to the LED device. This will restrict the PCB routing layout, and if the placement is not suitable, it will lead to inaccurate temperature prediction.

[0007] Option 2, which uses an LED driver chip, has two drawbacks. First, it affects the product topology and increases product cost. Second, some LED driver chips do not have integrated temperature sensors, making it impossible to infer the LED temperature from the LED driver chip.

[0008] Therefore, it is necessary to propose a new technical solution to address the above problems. [Utility Model Content]

[0009] One of the purposes of this invention is to provide a circuit for compensating LED brightness at different temperatures. This circuit can not only compensate for LED brightness in real time following temperature changes, but also has a simple design and does not require the use of a temperature sensor or an LED driver chip with specific functions.

[0010] According to one aspect of the present invention, a circuit for compensating LED brightness at different temperatures is provided, comprising: a differential voltage sampling circuit, wherein a first input terminal is connected to the positive terminal of the LED, and a second input terminal is connected to the negative terminal of the LED; the differential voltage sampling circuit is used to collect the voltage value across the LED and output the voltage value across the LED through its output terminal; a signal control circuit, wherein an input terminal is connected to the output terminal of the differential voltage sampling circuit and its output terminal outputs a control signal; the signal control circuit outputs the control signal with a corresponding duty cycle based on the voltage value across the LED; and a switch control circuit, comprising a switch device Q1, wherein a first connection terminal of the switch device Q1 is connected to the negative terminal of the LED, a control terminal is connected to the output terminal of the signal control circuit, and a second connection terminal is grounded; wherein the control signal is used to control the switch device Q1 to be turned on or off to adjust the effective current value of the LED.

[0011] Furthermore, when the control signal is at a first logic level, the switching device Q1 is turned on; when the control signal is at a second logic level, the switching device Q1 is turned off. When the LED temperature rises, the voltage value across the LED acquired by the differential voltage sampling circuit increases, and the duty cycle of the first logic level of the control signal output by the signal control circuit increases, thereby increasing the effective current value of the LED. When the LED temperature decreases, the voltage value across the LED acquired by the differential voltage sampling circuit decreases, and the duty cycle of the first logic level of the control signal output by the signal control circuit decreases, thereby decreasing the effective current value of the LED.

[0012] Furthermore, the voltage across the LED has a linear relationship with the LED temperature; the LED temperature has a linear relationship with the LED brightness attenuation coefficient; based on the linear relationship between the voltage across the LED and the LED temperature, and the linear relationship between the LED temperature and the LED brightness attenuation coefficient, the signal control circuit obtains the LED effective current value that needs to be compensated corresponding to the voltage across the LED, and then obtains the control signal with the corresponding duty cycle corresponding to the LED effective current value that needs to be compensated.

[0013] Furthermore, the signal control circuit pre-stores the relationship between the voltage value across the LED and the corresponding duty cycle of the control signal. Based on this relationship and the acquired voltage value across the LED, the signal control circuit obtains the effective current value of the LED that needs to be compensated. Based on the effective current value of the LED that needs to be compensated, the signal control circuit outputs the control signal with a corresponding duty cycle, so that the effective current value of the LED is the effective current value of the LED that needs to be compensated.

[0014] Furthermore, the differential voltage sampling circuit includes resistors R1, R2, R4, and R5, capacitor C1, and operational amplifier U1. The inverting input terminal of operational amplifier U1 is connected to the positive terminal of the LED via resistor R2, and its non-inverting output terminal is connected to the negative terminal of the LED via resistor R4. Its output terminal is connected to the output terminal of the differential voltage sampling circuit, its power supply terminal is connected to the power supply VDD, and its ground terminal is grounded. One end of resistor R5 is connected to the non-inverting input terminal of operational amplifier U1, and its other end is grounded. One end of capacitor C1 is connected to the power supply terminal of operational amplifier U1, and its other end is grounded. One end of resistor R1 is connected to the inverting input terminal of operational amplifier U1, and its other end is connected to the output terminal of operational amplifier U1.

[0015] Furthermore, the circuit for compensating LED brightness at different temperatures also includes a resistor R6, one end of which is connected to the first connection terminal of the switching device Q1, and the other end of which is connected to the negative terminal of the LED.

[0016] Furthermore, the switch control circuit also includes resistors R7 and R8 and capacitor C3. One end of resistor R7 is connected to the control terminal of the switch device Q1, and the other end is connected to the output terminal of the signal control circuit. One end of resistor R8 is connected to the control terminal of the switch device Q1, and the other end is grounded. One end of capacitor C3 is connected to the control terminal of the switch device Q1, and the other end is grounded.

[0017] Furthermore, the switching device Q1 is an NPN transistor, and the first connection terminal, the second connection terminal, and the control terminal of the switching device Q1 are the collector, emitter, and base of the NPN transistor, respectively.

[0018] Furthermore, the selection of resistors R7 and R8 must meet the following requirements: when the control signal is high, the switching device Q1 is turned on; when the control signal is low, the switching device Q1 is turned off.

[0019] Furthermore, the circuit for compensating LED brightness at different temperatures also includes an ADC sampling circuit, which includes a resistor R3, a capacitor C2, and a TVS1. One end of the resistor R3 is connected to the output terminal of the differential voltage sampling circuit, and the other end is connected to the input terminal of the signal control circuit. One end of the capacitor C1 is connected to the input terminal of the signal control circuit, and the other end is grounded. One end of the TVS1 is connected to the input terminal of the signal control circuit, and the other end is grounded.

[0020] Compared with the prior art, this invention can not only compensate for the brightness of LEDs in real time according to temperature changes, but also has a simple circuit design and does not require the use of temperature sensors or LED driver chips with specific functions. [Attached Image Description]

[0021] To more clearly illustrate the technical solutions of the embodiments of this utility model, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this utility model. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Among them:

[0022] Figure 1 This is a circuit diagram of a circuit for compensating LED brightness at different temperatures in one embodiment of the present invention;

[0023] Figure 2 This is a curve showing the relationship between the voltage across LED1 and the temperature of LED1 in one embodiment of the present invention.

[0024] Figure 3 This is a curve showing the relationship between the brightness attenuation coefficient of LED1 and the temperature value of LED1 in one embodiment of the present invention.

Detailed Implementation Methods

[0025] To make the above-mentioned objectives, features and advantages of this utility model more apparent and understandable, the utility model will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0026] The term "an embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that excludes other embodiments. Unless otherwise specified, the terms coupling, connection, linking, and interconnection used herein to indicate electrical connection mean direct or indirect connection. For example, A being connected to B includes both a direct electrical connection between A and B and a connection between A and B via electrical components or circuits.

[0027] In the description of this utility model, it should be understood that the terms "upper", "lower", "front", "back", "positive", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", and "outer" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this utility model and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this utility model.

[0028] Please refer to Figure 1 As shown, it is a circuit diagram of a circuit for compensating LED brightness at different temperatures in one embodiment of the present invention. Figure 1 The circuit shown for compensating LED brightness at different temperatures includes a differential voltage sampling circuit 110, a signal control circuit 120, and a switch control circuit 130.

[0029] The differential voltage sampling circuit 110 has its first input terminal 1 connected to the positive terminal of LED1 and its second input terminal 2 connected to the negative terminal of LED1. The differential voltage sampling circuit 110 collects the voltage value across LED1 and outputs the voltage value across LED1 through its output terminal 3. The input terminal of the signal control circuit 120 is connected to the output terminal 3 of the differential voltage sampling circuit 110, and its output terminal outputs a control signal Control. The signal control circuit 120 outputs a control signal Control with a corresponding duty cycle based on the voltage value across LED1. The switch control circuit 130 includes a switch device Q1. The first connection terminal of the switch device Q1 is connected to the negative terminal of LED1, its control terminal is connected to the output terminal of the signal control circuit 120, and its second connection terminal is grounded.

[0030] The positive terminal of LED1 is connected to the power supply VDD, and the control signal Control is used to control the switching device Q1 to turn on or off in order to adjust the effective current value of LED1.

[0031] When the control signal Control is at the first logic level, the switching device Q1 is turned on; when the control signal Control is at the second logic level, the switching device Q1 is turned off. When the temperature of LED1 rises, the voltage value across LED1 sampled by the differential voltage sampling circuit 110 increases, and the duty cycle of the first logic level of the control signal Control output by the signal control circuit 120 increases, thereby increasing the effective current value of LED1. When the temperature of LED1 falls, the voltage value across LED1 sampled by the differential voltage sampling circuit 110 decreases, and the duty cycle of the first logic level of the control signal Control output by the signal control circuit 120 decreases, thereby decreasing the effective current value of LED1.

[0032] exist Figure 1In the specific embodiment shown, the differential voltage sampling circuit 110 includes resistors R1, R2, R4, and R5, capacitor C1, and operational amplifier U1. The inverting input terminal of operational amplifier U1 is connected to the positive terminal of LED1 via resistor R2, and its non-inverting output terminal is connected to the negative terminal of LED1 via resistor R4. Its output terminal is connected to the output terminal 3 of the differential voltage sampling circuit 110, its power supply terminal is connected to the power supply VDD, and its ground terminal is grounded. One end of resistor R5 is connected to the non-inverting input terminal of operational amplifier U1, and the other end is grounded. One end of capacitor C1 is connected to the power supply terminal of operational amplifier U1, and the other end is grounded. One end of resistor R1 is connected to the inverting input terminal of operational amplifier U1, and the other end is connected to the output terminal of operational amplifier U1.

[0033] It should be noted that the resistance values ​​of resistors R1, R2, R4, and R5 can be calculated according to the actual application, capacitor C1 is a filter capacitor, and operational amplifier U1 can be selected according to the actual application.

[0034] exist Figure 1 In the specific embodiment shown, the signal control circuit 120 is an MCU (Micro Control Unit).

[0035] exist Figure 1 In the specific embodiment shown, the switch control circuit 130 further includes resistors R7 and R8 and capacitor C3. One end of resistor R7 is connected to the control terminal of switch device Q1, and the other end is connected to the output terminal of signal control circuit 120. One end of resistor R8 is connected to the control terminal of switch device Q1, and the other end is grounded. One end of capacitor C3 is connected to the control terminal of switch device Q1, and the other end is grounded. The control signal Control controls switch device Q1 to turn on or off, thereby controlling LED1 to turn on or off.

[0036] exist Figure 1 In the specific embodiment shown, capacitor C3 is a filter capacitor; switching device Q1 is an NPN transistor, and the first connection terminal, the second connection terminal, and the control terminal of switching device Q1 are the collector, emitter, and base of the NPN transistor, respectively; the selection of resistors R7 and R8 needs to meet the following requirements: when the control signal Control is high (which can be called the first logic level), transistor Q1 is turned on; when the control signal Control is low, transistor Q1 is turned off (or shut down).

[0037] Figure 1The circuit shown for compensating LED brightness at different temperatures also includes an ADC (Analog-to-Digital Converter) sampling circuit 130. The input terminal of the ADC sampling circuit 130 is connected to the output terminal 3 of the differential voltage sampling circuit 110, and its output terminal is connected to the input terminal of the signal control circuit 120. The ADC sampling circuit 130 is used to preprocess the voltage values ​​across the LED1 output by the differential voltage sampling circuit 110.

[0038] exist Figure 1 In the specific implementation shown, the ADC sampling circuit 130 includes a resistor R3, a capacitor C2, and a TVS1 (Transient Voltage Suppressor). One end of the resistor R3 is connected to the output terminal 3 of the differential voltage sampling circuit 110, and the other end is connected to the input terminal of the signal control circuit 120. One end of the capacitor C1 is connected to the input terminal of the signal control circuit 120, and the other end is grounded. One end of the TVS1 is connected to the input terminal of the signal control circuit 120, and the other end is grounded. The resistor R1 and capacitor C2 form a low-pass filter circuit, and the TVS1 is used for ESD electrostatic protection.

[0039] Figure 1 The circuit shown for compensating LED brightness at different temperatures also includes resistor R6. One end of resistor R6 is connected to the first connection terminal of switching device Q1, and the other end is connected to the negative terminal of LED1. Resistor R6 is a current-limiting resistor, and its resistance value is calculated based on the brightness requirement of LED1. Resistor R6 controls the maximum current flowing through LED1, and transistor Q1 controls the effective current value flowing through LED1 within a cycle. The luminous brightness of LED1 is related to the effective current value flowing through LED1 within a cycle. Therefore, controlling the on and off state of transistor Q1 (or adjusting the duty cycle of the control signal Control) can control the effective current value flowing through LED1, thereby controlling the luminous brightness of LED1.

[0040] The voltage across LED1 has a linear relationship with temperature; therefore, sampling the voltage across LED1 yields its temperature at a given moment. The brightness attenuation coefficient flowing through LED1 also has a linear relationship with temperature, allowing us to obtain the brightness attenuation coefficient of LED1 at different temperatures. After fitting these two curves into a formula, which is then written into the MCU (i.e., signal control circuit 120), the voltage across LED1 is obtained through differential voltage sampling. This allows us to determine the LED1 current value that needs compensation. By increasing the conduction time of transistor Q1, the effective value of the current flowing through LED1 is increased, thus achieving consistent brightness across different temperatures.

[0041] In other words, there is a linear relationship between the voltage across LED1 and its temperature; there is also a linear relationship between the temperature and brightness attenuation coefficient of LED1. Based on these linear relationships, the signal control circuit 120 obtains the effective current value of LED1 that needs compensation, corresponding to the voltage across LED1, and then generates a control signal Control with the corresponding duty cycle for the effective current value of LED1 that needs compensation. For example, the signal control circuit 120 may have a pre-stored formula relating the voltage across LED1 to the corresponding duty cycle of the control signal Control. Based on this formula and the acquired voltage across LED1, the signal control circuit 120 obtains the effective current value of LED1 that needs compensation. The signal control circuit 120 then outputs a control signal Control with the corresponding duty cycle based on the effective current value of LED1 that needs compensation, ensuring that the effective current value of LED1 is the effective current value of LED1 that needs compensation.

[0042] The following examples illustrate this; please refer to them. Figure 2 As shown, this is a curve depicting the relationship between the voltage across LED1 and the temperature of LED1 in one embodiment of this invention. Assuming the ADC samples a voltage of 2.7V across LED1, according to... Figure 2 The voltage-temperature curve shows that the temperature of LED1 is 60℃. Please refer to this. Figure 3 As shown, it is a curve showing the relationship between the brightness attenuation coefficient of LED1 and the temperature value of LED1 in one embodiment of this utility model. Figure 3 The relationship curve between the brightness decay coefficient and temperature shows that the brightness decay coefficient of LED1 at 60℃ is 0.95. Assuming the current of LED1 at room temperature is Ia, then dividing Ia by 0.95 yields the corresponding current value Ib at 60℃ (i.e., the effective current value of LED1 that needs compensation at 60℃). This allows us to determine the on and off times of transistor Q1 at 60℃ (or adjust the duty cycle of the control signal Control) to increase the effective current value of LED1. This ensures that the brightness of LED1 remains consistent at both room temperature and 60℃, preventing brightness decay.

[0043] In summary, the circuit for compensating LED brightness at different temperatures provided by this utility model has the following beneficial effects:

[0044] 1. This utility model can not only compensate for the brightness of LEDs in real time according to temperature changes, but also does not require the use of temperature sensor devices, and will not cause limitations in PCB layout.

[0045] 2. This utility model can not only compensate for the brightness of LEDs in real time according to temperature changes, but also does not require the use of LED driver chips with specific functions, which can save component costs.

[0046] It should be noted that any modifications made by those skilled in the art to the specific embodiments of this utility model do not depart from the scope of the claims of this utility model. Accordingly, the scope of the claims of this utility model is not limited to the foregoing specific embodiments.

Claims

1. A circuit for compensating LED brightness at different temperatures, characterized in that, It includes: A differential voltage sampling circuit has its first input terminal connected to the positive terminal of the LED and its second input terminal connected to the negative terminal of the LED. The differential voltage sampling circuit is used to collect the voltage value across the LED and output the voltage value across the LED through its output terminal. A signal control circuit, the input terminal of which is connected to the output terminal of the differential voltage sampling circuit, and the output terminal of which outputs a control signal, the signal control circuit outputs the control signal with a corresponding duty cycle based on the voltage value across the LED; A switch control circuit includes a switch device Q1, wherein the first connection terminal of the switch device Q1 is connected to the negative terminal of the LED, its control terminal is connected to the output terminal of the signal control circuit, and its second connection terminal is grounded. The control signal is used to control the switching device Q1 to turn on or off, so as to adjust the effective current value of the LED.

2. The circuit for compensating LED brightness at different temperatures according to claim 1, characterized in that, When the control signal is at the first logic level, the switching device Q1 is turned on; when the control signal is at the second logic level, the switching device Q1 is turned off. When the LED temperature rises, the voltage value across the LED acquired by the differential voltage sampling circuit increases, and the duty cycle of the first logic level of the control signal output by the signal control circuit increases, thereby increasing the effective current value of the LED. When the LED temperature decreases, the voltage value across the LED acquired by the differential voltage sampling circuit decreases, and the duty cycle of the first logic level of the control signal output by the signal control circuit decreases, thereby decreasing the effective current value of the LED.

3. The circuit for compensating LED brightness at different temperatures according to claim 2, characterized in that, The voltage across the LED has a linear relationship with the LED's temperature. The temperature value of the LED has a linear relationship with the brightness decay coefficient of the LED; The signal control circuit obtains the effective LED current value that needs to be compensated corresponding to the voltage value across the LED and the LED temperature value, as well as the linear relationship between the LED temperature value and the LED brightness attenuation coefficient, based on the linear relationship between the voltage value across the LED and the LED temperature value. Then, it obtains the control signal with the corresponding duty cycle corresponding to the effective LED current value that needs to be compensated.

4. The circuit for compensating LED brightness at different temperatures according to claim 3, characterized in that, The signal control circuit pre-stores the relationship between the voltage values ​​across the LED and the corresponding duty cycle of the control signal. Based on this relationship and the collected voltage values ​​across the LED, the signal control circuit obtains the effective current value of the LED that needs to be compensated. The signal control circuit outputs a control signal with a corresponding duty cycle based on the LED effective current value that needs to be compensated, so that the effective current value of the LED is the LED effective current value that needs to be compensated.

5. The circuit for compensating LED brightness at different temperatures according to any one of claims 1-4, characterized in that, The differential voltage sampling circuit includes resistors R1, R2, R4, and R5, capacitor C1, and operational amplifier U1. The inverting input terminal of the operational amplifier U1 is connected to the positive terminal of the LED via the resistor R2, and its non-inverting output terminal is connected to the negative terminal of the LED via the resistor R4. Its output terminal is connected to the output terminal of the differential voltage sampling circuit, its power supply terminal is connected to the power supply VDD, and its ground terminal is grounded. One end of the resistor R5 is connected to the non-inverting input of the operational amplifier U1, and the other end is grounded; one end of the capacitor C1 is connected to the power supply of the operational amplifier U1, and the other end is grounded; one end of the resistor R1 is connected to the inverting input of the operational amplifier U1, and the other end is connected to the output of the operational amplifier U1.

6. The circuit for compensating LED brightness at different temperatures according to any one of claims 1-4, characterized in that, It also includes resistor R6, One end of the resistor R6 is connected to the first connection terminal of the switching device Q1, and the other end is connected to the negative terminal of the LED.

7. The circuit for compensating LED brightness at different temperatures according to claim 6, characterized in that, The switch control circuit also includes resistors R7 and R8 and capacitor C3. One end of the resistor R7 is connected to the control terminal of the switching device Q1, and the other end is connected to the output terminal of the signal control circuit. One end of the resistor R8 is connected to the control terminal of the switching device Q1, and the other end is grounded; One end of the capacitor C3 is connected to the control terminal of the switching device Q1, and the other end is grounded.

8. The circuit for compensating LED brightness at different temperatures according to claim 7, characterized in that, The switching device Q1 is an NPN transistor. The first connection terminal, the second connection terminal, and the control terminal of the switching device Q1 are the collector, emitter, and base of an NPN transistor, respectively.

9. The circuit for compensating LED brightness at different temperatures according to claim 8, characterized in that, The selection of resistors R7 and R8 must meet the following requirements; When the control signal is high, the switching device Q1 is turned on; When the control signal is low, the switching device Q1 is turned off.

10. The circuit for compensating LED brightness at different temperatures according to any one of claims 1-4, characterized in that, It also includes an ADC sampling circuit. The ADC sampling circuit includes resistor R3, capacitor C2, and TVS1. One end of the resistor R3 is connected to the output terminal of the differential voltage sampling circuit, and the other end is connected to the input terminal of the signal control circuit. One end of the capacitor C1 is connected to the input terminal of the signal control circuit, and the other end is grounded. One end of the TVS1 is connected to the input terminal of the signal control circuit, and the other end is grounded.

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