Research Of Online Measurement On Junction Temperature And Thermal Resistance Of High Power LED

The light emitting diodes have been widely used in the fields of general lighting. But the actual service life of high power LED is far less than the theoretical life in the practical application. Therefore, the reliability and durability has become the hot spot of recent research about high power LED. Junction temperature and thermal resistance are two of the most important factors affecting the reliability of LED.In order to realize the online measurement of junction temperature and thermal resistance, the paper analyzed the online measuring principle firstly. Then it designed and developed the online measuring system. On this basis, we carried out explorative study on the regular of junction temperature and thermal resistance in the process of aging of LED combining with the LED composite stress accelerated aging test system. The main work and conclusions are as follows:The paper put forward a new method which can reduce the error caused by the heat come from testing current after the analysis of traditional electric methods.The junction temperature and thermal resistance measurement system was proposed based on ARM-Cortex M3 kernel which can achieve a precise output of the current and a accurate measurement of the voltage. In this paper the embedded program consisted of the K value algorithm, the current calibration algorithm and the LED junction temperature and thermal resistance measurement algorithm have been realized. With the help of the program it was easy to switch the channel of LEDs and save the useful data. Finally, the software and hardware circuit of the system was verified through the actual results of multiple group experiments.It was able to measure the light, color, electricity and other parameters online, especially the junction temperature and thermal resistance under the over stress environment when junction temperature and thermal resistance measurement system was combined with the humidity and vibration of three integrated reliability test system.The paper carried out explorative study on the regular of junction temperature and thermal resistance in the process of aging of LED combining with the LED composite stress accelerated aging test system. The preliminary result indicated that, the junction temperature would increase gradually with the increase of time under overload current and the saltation of junction temperature and thermal resistance didn’t cause the changes in the luminous flux, color temperature and spectrum obviously.The high power LED junction temperature and thermal resistance measurement system could obtain the LED junction temperature and thermal resistance accurately in normal work conditions. It would provide a strong basis for accurate control of related process in LED industry chain and research of LED products reliability.