LED power temperature compensation circuit

Abstract

This invention belongs to the field of optoelectronic technology applications and relates to a light-emitting diode (LED) power temperature compensation circuit used in the operation of LEDs. The compensation current provided by this circuit passes through the LED, allowing the LED's light power to remain essentially constant over a wide temperature range. This invention solves the inherent temperature coefficient problem of diodes, and a single circuit can connect multiple LEDs in series. The circuit includes a temperature measurement function, enabling real-time monitoring of the LED's operating environment temperature. This invention features a simple circuit design, uses only conventional components, and has low application costs, making it highly practical in many engineering applications.

Description

Technical Field

[0001] This invention belongs to the field of optoelectronic technology applications and relates to a light-emitting diode (LED) power temperature compensation circuit used in the operation of LEDs. Background Technology

[0002] In recent years, optoelectronic technology has been widely used in more and more fields. As an important optoelectronic device, light-emitting diodes have received much attention in both military and civilian fields. The high precision, high resolution and strong anti-interference capabilities of optoelectronic technology make its application very extensive.

[0003] Luminous power is one of the most important indicators of a light-emitting diode (LED). However, due to the inherent characteristics of LEDs, the power value varies significantly and linearly with different temperatures when a fixed photocurrent is applied. Figure 2 ;

[0004] When a light-emitting diode (LED) is not subjected to a temperature compensation circuit and a fixed current is applied, its luminous intensity remains constant at a fixed temperature. As the temperature changes, we use an imported optical power meter to measure the change in its power value. Figure 3 It is clear that the light power varies significantly at different temperatures, leading to unstable light intensity in LEDs used across all temperatures. Summary of the Invention

[0005] The purpose of this invention is to provide a light-emitting diode (LED) power temperature compensation circuit that enables LEDs to maintain stable light intensity across all temperature applications.

[0006] The light power of a light-emitting diode (LED) corresponds to the photocurrent passing through it. To keep the light power consistent at different temperatures, it is necessary to ensure that the photocurrent passing through it corresponds to the temperature, thereby ensuring compensation for the light power.

[0007] The technical solution of this invention is a light-emitting diode (LED) optical power temperature compensation circuit, which includes a two-stage adder circuit and a voltage-controlled current source, such as... Figure 1 Temperature sensor W1 is placed at the front end of the circuit. Temperature sensor W1 converts the temperature current signal i into a current signal. Operational amplifier U1 in the first-stage adder circuit converts the current signal i output by temperature sensor W1 into a voltage value U. 1i ;

[0008] Zener diode D1 provides the reference voltage U d U d voltage divider value U 1+ Connected to the non-inverting input of operational amplifier U1, U 1i With reference voltage U d voltage divider value U 1+The summation yields the output value U of operational amplifier U1 in the first-stage adder circuit. 1out Output value U 1out A resistor R16 is applied to the inverting input of operational amplifier U2 in the second-stage adder circuit. Operational amplifier U2 in the second-stage adder circuit converts the output value U1 of operational amplifier U2 into the inverting input of operational amplifier U2. 1out After gain adjustment and another voltage divider U from Zener diode D1 2+ Add;

[0009] The voltage-controlled current source consists of operational amplifier U3, field-effect transistor Q1, and surrounding components. The front-end control voltage is the output voltage U of operational amplifier U2. 2out The high-side of the LED is connected to the +15V power supply, and the low-side is connected to the drain terminal of the MOSFET Q1. The current through the LED is:

[0010] I LED =kT+i0, (T represents absolute temperature; at 0℃, T = 273.2)

[0011] in:

[0012]

[0013] Operational amplifier U4 implements the temperature measurement function, and the output terminal U of operational amplifier U1... 1out After inverting amplification, the signal is connected between the inverting terminal and the output terminal of the operational amplifier in the circuit. The output signal U of operational amplifier U1 is... 1out After passing through resistor R 23 Connected to the inverting input of operational amplifier U4, the inverted amplification is used to measure the ambient temperature of LED applications. The inverting input of operational amplifier U1 is connected to resistor R. 24 Grounded, the output signal of op-amp U4 is a voltage value U that is related to the ambient temperature T. T The voltage value U is expressed by the following formula. T Convert to temperature value:

[0014]

[0015] The advantages and beneficial effects of this invention are as follows:

[0016] The compensated current provided by the circuit of this invention is passed through a light-emitting diode and compared with the previous uncompensated experiment. The results are as follows: Figure 4 It is clear that by adding this compensation circuit, the light power of the LED can remain basically consistent over a wide temperature range.

[0017] Light-emitting diodes have a wide range of applications. This invention can solve the temperature coefficient problem that diodes cannot avoid, and a single circuit can connect multiple light-emitting diodes in series.

[0018] The circuit includes a temperature measurement function, which can monitor the temperature of the LED's operating environment in real time.

[0019] The circuit of this invention is simple, and the components are all conventional, resulting in low application cost and significant practical value in many engineering applications.

[0020] Currently, many display screens use light-emitting diodes (LEDs), and the display brightness is determined by the light intensity of the LEDs. However, due to changes in ambient temperature, the characteristics of the LEDs themselves change, causing significant changes in the display light intensity. This invention can compensate for the temperature of the current passing through the LEDs, ensuring that the display brightness remains consistent at different temperatures.

[0021] This invention can also be applied to complex systems containing photoelectric sensors. When the temperature changes, the light intensity of the LED changes, causing a change in the LED light intensity calibration coefficient Kp. The change in Kp is essentially a linear temperature gain, and the system phase does not change. However, due to K... P The resulting gain change leads to a change in the total gain of the system, which in turn changes the system parameters and reduces the stability margin of the system. This compensation circuit can ensure the consistency of the system parameters across the entire temperature range. Attached Figure Description

[0022] Figure 1 Schematic diagram of LED optical power temperature compensation circuit;

[0023] Figure 2 The relationship between light intensity and temperature of LEDs;

[0024] Figure 3 The relationship between the optical power of an LED and temperature without compensation;

[0025] Figure 4 Comparison curves of luminous power of light-emitting diodes before and after compensation at different temperatures;

[0026] Figure 5 Comparison curve of measured and theoretical values ​​of temperature compensation current for LEDs. Detailed Implementation

[0027] The present invention will now be described in detail with reference to the accompanying drawings.

[0028] 1. Temperature sensor

[0029] This device uses a high-precision temperature sensor with current output to provide a reference for the circuit.

[0030] 2. Voltage-controlled current source

[0031] The operational amplifier U3, the field-effect transistor Q1, and surrounding components form a voltage-controlled current source. Its output current is determined by the field-effect transistor Q1. If a large current output is required, another transistor can be connected to increase the drive current.

[0032] 3. The intermediate two-stage adder circuit:

[0033] The two intermediate adder circuits add the current signal to the voltage divider of the reference voltage source to adjust the bias and slope of the compensation, so that this compensation device can meet the needs of different types of LEDs and different applications.

[0034] The derivation of the circuit and the actual circuit test results are explained in detail below with reference to the attached diagram:

[0035] A temperature sensor W1 is introduced at the front end of the circuit. This device converts the temperature signal into a current signal i.

[0036] U 1+ U represents the voltage at the non-inverting input terminal of U1. R12 That is, the voltage value U of photocurrent conversion i U 1OUT U1 represents the output voltage. 2OUT U represents the output voltage of U2. d represents the voltage regulation value of Zener diode D1, and i represents the current on the temperature sensor.

[0037]

[0038] U R12 =R12*i

[0039]

[0040] Derivation of the temperature measurement circuit formula:

[0041]

[0042] Example

[0043] In this example, the temperature sensor used is the AD590 from Analog Devices, Inc. The AD590 is a two-terminal integrated circuit sensor that generates an output current proportional to the absolute temperature. Laser calibration was used to adjust the chip resistance so that the current output was 298.2 μA at 298.2 K (25 °C). For every 1 degree Celsius increase in temperature, the current increases by 1 μA.

[0044] The operational amplifier used is the precision operational amplifier OP07 from Analog Devices, Inc. (ADI).

[0045] The field-effect transistor Q1 is an N-type field-effect transistor from SILICONIX, USA; the light-emitting diode is an imported SE2460 light-emitting diode from the USA.

[0046] Main parameters of resistor:

[0047] R12 = 20k

[0048] R19 = 5.9k

[0049] R16 = 10k

[0050] R31 = 210

[0051] Substituting the parameters, we derive:

[0052] I LED = 0.0841T - 5.68311 (mA)

[0053] Where T represents absolute temperature, and at 0℃, T = 273.2.

[0054] We conducted actual measurements on the assembled compensation circuit, and the data is as follows:

[0055]

[0056]

[0057] Experimental apparatus: FLUKE 45 meter (for measuring voltage), Agilent 34410A (for measuring current), ±15V power supply.

[0058] High and Low Temperature Chamber: ACS

[0059] Experimental notes: The AD590 was placed in a high and low temperature chamber while the circuit board operated at room temperature (26℃).

[0060] Plot the relationship between compensation current and temperature as follows: Figure 5 :

[0061] As can be seen, the compensation circuit can linearly increase the photocurrent flowing into the LED, and the theoretical and measured values ​​are basically consistent.

[0062] By adjusting R 12 and R 17 The size of the compensation current can be adjusted.

Claims

1. A light-emitting diode (LED) power temperature compensation circuit, characterized in that the light-emitting diode... The diode optical power temperature compensation circuit includes a two-stage adder circuit and a voltage-controlled current source. A temperature sensor W1 is placed at the front end of the circuit. The temperature sensor W1 converts the temperature current signal i into a current signal. The operational amplifier U1 in the first-stage adder circuit converts the current signal i output by the temperature sensor W1 into a voltage value U. 1i Zener diode D1 provides the reference voltage U. d U d voltage divider value U 1+ Connected to the non-inverting input of operational amplifier U1, U 1i With reference voltage U d voltage divider value U 1+ The summation yields the output value U of operational amplifier U1 in the first-stage adder circuit. 1out Output value U 1out A resistor R16 is applied to the inverting input of operational amplifier U2 in the second-stage adder circuit. Operational amplifier U2 in the second-stage adder circuit converts the output value U1 of operational amplifier U2 into the inverting input of operational amplifier U2. 1out After gain adjustment and another voltage divider U from Zener diode D1 2+ Added together; the voltage-controlled current source consists of operational amplifier U3, field-effect transistor Q1, and surrounding components, with the front-end control voltage being the output voltage U of operational amplifier U2. 2out The high-side of the LED is connected to the +15V power supply, and the low-side is connected to the drain terminal of the MOSFET Q1. The current through the LED is: I LED = kT + i0, where T represents the absolute temperature; at 0℃, T = 273.

2. in: Resistors R13, R14, and R15 form the first-stage voltage-controlled adjustment network; R12 is the first-stage gain resistor; R17, R18, and R19 form the second-stage gain adjustment network; R20 and R31 are the second-stage gain resistors; R16 is the bridging resistor between the two stages; and R21 is the sampling resistor. The first-stage voltage-controlled adjustment network is connected to the non-inverting terminal of U1, and the second-stage voltage-controlled network is connected to the non-inverting terminal of U2. Resistors R12, R16, R20, and R31 are connected in series and connected to the inverting terminals of U1 and U2, respectively. The sampling resistor R21 is connected between Q1 and ground. Operational amplifier U4 implements the temperature measurement function, and the output terminal U of operational amplifier U1... 1out After inverting amplification, the signal is connected between the inverting terminal and the output terminal of the operational amplifier in the circuit. The output signal U of operational amplifier U1 is... 1out The circuit is connected to the inverting input of operational amplifier U4 via resistor R23. After inverting and amplifying, the signal is used to measure the ambient temperature for LED applications. The inverting input of operational amplifier U1 is grounded via resistor R24. The output signal of operational amplifier U4 is a voltage value U related to the ambient temperature T. T The voltage value U is obtained through the following formula. d Converted to a voltage value U related to ambient temperature T T :

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