CN103411702A - Device for non-contact measurement of junction temperature of white LED by use of peak wavelength displacement method - Google Patents

Abstract

获得待测LED白光光源工作状态下的结温，所得结温精确度可达0.1℃。The invention discloses a device for rapidly and non-contact measuring white light LED junction temperature using a peak wavelength shift method, which includes a measurement system and a calibration system. The measurement system includes a white light LED light source (1) to be measured and a spectrometer for measuring blue light wavelength shift. (2) and computer (3); The spectrometer is made of spherical reflector (10), incident slit (11), plane grating (12), exit slit (13), CCD (14) and driving circuit (15) , characterized in that the wavelength measurement range is 440nm ~ 480nm, and the accuracy is better than 0.02nm. The calibration system includes a temperature controller (4), a constant temperature box (5), a calibration LED (6), an LED lamp bracket (7), a pulse constant current source (8), a spectrometer (2) and a computer (3). By calibrating the peak wavelength-junction temperature coefficient K of high-power white LEDs, and measuring the shift of the peak wavelength when the LED is actually working, it is determined by

Obtain the junction temperature under the working state of the LED white light source to be tested, and the accuracy of the obtained junction temperature can reach 0.1°C.

Description

Device for non-contact measurement of junction temperature of white light LEDs using peak wavelength shift method

technical field

The invention relates to a detection technology of a semiconductor light-emitting diode (LED), in particular to an instrument for measuring the inner junction temperature of an LED chip.

Background technique

The emergence of high-brightness LED has epoch-making significance. It will be one of the greatest inventions of human beings after Edison invented the incandescent light bulb. It is called the fourth-generation lighting source or green light source. Compared with traditional light sources, it has many advantages: Light High efficiency, mercury-free environmental protection, long life, small size, etc., have been widely used in various special lighting fields such as indications, displays, decorations, backlights, and urban night scenes. At present, the luminous rate of LED can only reach 10%-30%, and at the same time, 70%-90% of the energy is converted into heat energy. The improvement of optical performance and reliability of high-performance white LED depends on the junction temperature of the chip. Therefore, how to monitor the junction temperature, especially the online non-destructive junction temperature monitoring, has become an urgent problem that may restrict the application of white light LEDs.

The basic structure of LED is a semiconductor P-N junction. When the current flows through the LED element, the temperature of the P-N junction will rise. Strictly speaking, the temperature of the P-N junction area is defined as the junction temperature of the LED. Usually, because the component chips have a small size, it is not strict Sometimes the temperature of the LED chip can also be regarded as the junction temperature. The chip size of the white LED is small and the current density is high, so the temperature rise caused by it is relatively obvious. Moreover, its luminescence spectrum does not include the infrared part, so the heat generated by the device cannot be released by thermal radiation, and about 70-90% of the input electric energy is converted into heat, most of which are converted into energy that raises the temperature of the chip itself. For semiconductor devices, their characteristics will change significantly as the temperature changes. Especially for high-power LEDs, this effect will be more obvious. The chip temperature directly affects the luminous efficiency, dominant wavelength and service life of the LED. According to data, about 70% of LED product failures come from excessive junction temperature. And when the load is half of the rated power, the failure will double every time the temperature rises by 20°C. Therefore, how to quickly and accurately measure the junction temperature of the LED can help us to design the LED structure more reasonably and optimize the heat dissipation design of the LED lighting project.

At present, there are mainly methods for measuring the junction temperature of white light LEDs: 1. Forward voltage method, using the temperature effect of LED electric transmission, under the condition of constant current, the linear relationship between forward voltage and junction temperature is obtained; 2. Pin method, It is measured by the power ratio of blue light and white light in the emission spectrum of LED. These methods are all contact measurements, limited to the junction temperature measurement of single-tube LED devices. Now some researchers have proposed some non-contact junction temperature measurement methods: blue-white ratio method, infrared camera method and peak wavelength method. Due to the limited range of use of these methods, and the accuracy is relatively low. In the peak wavelength method, the peak value of the light emitting spectrum of the LED will increase with the increase of the junction temperature. However, due to the increase in junction temperature, the peak wavelength drift is not large. When the temperature rises by 10°C, the peak wavelength will change by about 1.4nm, which will definitely bring a lot of error to the test results. If a conventional high-precision spectrometer is used , will greatly increase the testing cost.

Therefore, it is necessary to design a non-contact, high-precision, low-cost, and easy-to-operate white light LED junction temperature measuring instrument.

Contents of the invention

In view of the shortcomings of the above methods and technologies, the purpose of the present invention is to design a high-power white LED junction temperature measurement device with high precision, low cost and easy operation by using the peak wavelength shift method.

In order to realize the purpose of the present invention, it is proposed to adopt the following technologies:

快速计算出该工作状态下待测LED的结温。A fast non-contact measuring device for white light LED junction temperature, characterized in that the system consists of two parts: calibration and measurement. During calibration, the calibration LED (6) is installed in the thermostat (5), and a The light-guiding optical fiber (9) conducts the light emitted by the calibration LED (6) to the spectrum analyzer (2) for measuring the wavelength shift of blue light. The peak wavelength at this temperature is obtained by the computer (3) connected to the spectrometer (2), and the peak wavelength of the calibration LED is obtained through multiple sets of data-junction temperature coefficient K, initial junction temperature T _a and initial peak wavelength λ _a . During the measurement, the peak wavelength of the LED to be tested (1) under normal working conditions is directly measured by the spectrometer (2), combined with the formula

Quickly calculate the junction temperature of the LED to be tested in this working state.

The calibration system includes a temperature controller (4) located outside the thermostat (2) to control the temperature of the thermostat (5), thereby changing the ambient temperature of the calibration LED (6). The calibration LED (6) is fixed on the bracket (7) and connected with the pulse constant current source (8). The light emitted by the calibration LED (6) is collected by the light-guiding fiber (9) extending into the thermostat (5) and enters the high-precision spectrometer (2) connected to the computer (3). The measuring system includes a white LED light source (1) to be tested and a computer (3). The spectrometer (2) for measuring the wavelength shift of blue light is composed of a spherical mirror (10), an entrance slit (11), a plane grating (12), an exit slit (13), a CCD (14) and a drive circuit (15) .

Adopt above-mentioned technical scheme, its characteristic is:

1. During calibration, the calibration LED in the power-off state is placed in the incubator for 30 minutes to ensure that the junction temperature of the LED at the moment of power-on is equal to the ambient temperature, avoiding the use of other methods to measure the actual junction temperature and reducing the error .

2. A constant temperature box with a temperature controller is used to provide the ambient temperature of the calibration LED, and the error does not exceed 1°C. In addition, the ambient temperature and junction temperature of the calibration LED can be changed, and multiple sets of experiments can be carried out to improve the accuracy of the LED peak wavelength-junction temperature coefficient K.

3. The pulse constant current source can provide instantaneous working current for the calibration LED, so that it can work normally in a short time, so that the peak wavelength of the LED at a specific temperature can be calibrated without causing a change in the junction temperature.

4. The LED bracket can conveniently fix the calibration LED, stabilize its measurement circuit, and reduce the error caused by the vibration of the device to the experiment.

5. One end of the light-guiding fiber extends into the incubator, and the other end is connected to the spectrometer. The light emitted by the LED to be tested is transmitted to the spectrometer faster and with as little loss as possible.

6. The wavelength measurement range of the spectrometer for measuring the blue light wavelength shift is 440nm-470nm, which is larger than the shift range of the peak wavelength caused by the change of the junction temperature of the white light LED. And it greatly improves the precise value of spectrum measurement, and the precision is better than 0.02nm.

7. The device can calibrate the peak wavelength-junction temperature coefficient K, initial junction temperature T _a and initial wavelength λ _a of high-power white LEDs, and store them in a computer. Provides data for junction temperature measurements of white LEDs.

8. When measuring, as long as the luminescence spectrum of the LED is measured under normal operating current, the junction temperature can be quickly calculated. When measuring the spectrum, it can be measured directly in the LED working environment without disassembling the lamp. Whether it is a single LED or an integrated light source, it can be measured conveniently and quickly, and has a wide range of applications.

9. The spectrometer for measuring the wavelength shift of blue light, through the design of the beam splitter, makes the light emitted by the LED to be tested enter the beam splitter horizontally, and enter the plane grating through the reflector. The light diffracted by the grating is reflected by the mirror, and only the light energy with a wavelength range of 440nm to 470nm passes through the exit slit with a length of d, and irradiates the CCD with a photosensitive surface with a width of d, and is sampled by the driving circuit. And photoelectric conversion, and finally get a high-precision spectral curve on the computer.

Description of drawings

Fig. 1 has shown the composition diagram of device calibration system of the present invention

Fig. 2 shows the composition schematic diagram of device measuring system of the present invention

Fig. 3 shows the structural representation of the special blue light wavelength shift spectrometer of the present invention

Fig. 4 shows the peak wavelength-junction temperature coefficient statistical table of different types of LEDs in the present invention

Detailed ways

The invention uses a peak wavelength shifting method to design a fast non-contact measuring white light LED junction temperature device. The device includes the design of a spectrometer for measuring the wavelength shift of blue light, the calibration of the peak wavelength-junction temperature coefficient K of commonly used white light LEDs, and the measurement of the junction temperature of LEDs under normal working conditions.

The spectrometer for measuring the blue light wavelength shift of the present invention controls the diffracted light by determining the parameters and angles of the plane grating, so that the reflected diffracted light can pass through the exit slit only when the wavelength is within the range of 440nm-470nm. In this embodiment, a linear array CCD with 2048 pixel elements is selected, and the height of the photosensitive surface of the CCD is equal to the width of the exit slit. The optical signal obtained by the detector is converted into an electrical signal, and through the signal processing of the driving circuit, the spectrum of the detected LED is finally displayed on the computer. The spectrum measured by the device has a wavelength range of 440nm to 470nm and an accuracy of 0.015nm.

During calibration, the calibration LED is installed on the LED bracket, and the temperature of the incubator is controlled by the temperature controller, and 5 experimental groups are set up at 10°C, 30°C, 50°C, 70°C, and 90°C.

When T ₁ =10°C, the calibration LED is placed in a 10°C incubator with power off for half an hour, then it can be considered that the junction temperature of the calibration LED at this time is 10°C. Then, the calibration LED is given an instantaneous current I equal to the working current and the time is 5s through the pulse constant current source, and through the detection of the spectrometer, the spectral curve of the calibration LED in normal operation can be obtained on the computer, so as to obtain the Label the peak wavelength λ ₁ when the LED junction temperature T _j1 =10°C.

两两组合求出10个K值，再取平均值。即可获得该定标LED的峰值波长-结温系数K、初始结温T_a以及初始峰值波长λ_a，记录数据。Repeat the above process to get 5 sets of junction temperatures and corresponding peak wavelengths. T _j1 ~λ ₁ , T _j2 ~λ ₂ , T _j3 ~λ ₃ , T _j4 ~λ ₄ , T _j5 ~λ ₅ . The formula for measuring junction temperature combined with the peak wavelength method

Find 10 K values by combining them in pairs, and then take the average value. The peak wavelength-junction temperature coefficient K, the initial junction temperature T _a and the initial peak wavelength λ _a of the calibration LED can be obtained, and the data is recorded.

Calibrate the commonly used white light LEDs on the market according to the above method, organize the obtained data K, T _a , λ _a into a table, and then complete the calibration.

即可快速求出待测LED在该工作状态下的结温。When measuring, no matter it is a single LED or an integrated light source, under the normal working state of the LED to be tested, measure its luminescence spectrum when it emits light stably, and obtain the peak wavelength λ of the LED under test under this working state through the computer. Query the peak wavelength-junction temperature coefficient statistical table to get the peak wavelength-junction temperature coefficient K, initial junction temperature T _a and initial wavelength λ _a of this type of LED, and substitute the data into the formula

The junction temperature of the LED to be tested in this working state can be quickly calculated.

Since the spectrometer of the device is dedicated to measuring the wavelength shift of blue light, its spectral accuracy can reach 0.015nm, that is, the calculated junction temperature accuracy is 0.1°C. Meet the design requirements.

Claims (8)

1. one kind is utilized peak wavelength displacement method, quick non-cpntact measurement white light LEDs junction temperature device, structure comprises measuring system and scaling system, and measuring system comprises white LED light source to be measured (1), specially surveys spectrometer (2) and the computing machine (3) of blue light wavelength displacement; Scaling system comprises temperature controller (4), constant temperature oven (5), calibration LED (6), LED lamp support (7), pulsed constant current supply (8), spectrometer (2) and computing machine (3).It is characterized in that: non-contact type is measured junction temperature, and convenient and swift, precision is high.The designed spectrometer wavelength measurement range of this device is 440nm～470nm, and precision is better than 0.02nm.

2. a kind of quick non-cpntact measurement white light LEDs junction temperature device according to claim 1 is characterized in that: to the peak wavelength of large power white light LED-junction temperature COEFFICIENT K, initial junction temperature T _aAnd initial spike wavelength X _aCalibrate, for the junction temperature measurement of white light LEDs provides data, make junction temperature measurement easier, quick.

3. a kind of quick non-cpntact measurement white light LEDs junction temperature device according to claim 1, it is characterized in that: during calibration, by the calibration LED that makes off-position, in constant temperature oven, place 30min and guarantee that this LED equates with environment temperature in the junction temperature of the moment of switching on, has reduced error.

4. a kind of quick non-cpntact measurement white light LEDs junction temperature device according to claim 1, it is characterized in that: during calibration, the instantaneity of the working current that provides of calibration LED is provided pulsed constant current supply, makes the temperature rise of calibration LED within conduction time very little, can ignore.

5. a kind of quick non-cpntact measurement white light LEDs junction temperature device according to claim 1 is characterized in that: during calibration, the light-conductive optic fibre by stretching into constant temperature oven can be more fast, loss more is transmitted to spectroanalysis instrument by the light that tested LED sends in lowland.The response time of spectrometer and the conduction time of calibration LED have been shortened.

6. a kind of quick non-cpntact measurement white light LEDs junction temperature device according to claim 1 is characterized in that: during measurement directly under the LED duty, record the peak wavelength under this state by spectrometer, in conjunction with formula

Can calculate fast the junction temperature of this LED under this duty, easy and simple to handle, can be widely used in single led or integrated optical source.Gained junction temperature degree of accuracy can reach 0.1 ℃.

7. a kind of quick non-cpntact measurement white light LEDs junction temperature device according to claim 1, it is characterized in that: the wavelength measurement scope that this system special secondary school is surveyed the spectrometer of blue light wavelength displacement is 440nm～470nm, be greater than the moving range of white light LEDs causes when junction temperature changes peak wavelength, the peak wavelength measuring accuracy is better than 0.02nm.

8. a kind of quick non-cpntact measurement white light LEDs junction temperature device according to claim 1, it is characterized in that: the spectrometer of specially surveying blue light wavelength displacement is the optical design that utilizes catoptron and plane grating, makes the light of wavelength in 440nm～470nm just shine on the CCD of photosurface that width is d.

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