Study Of Non-contact Methods For Determining Junction Temperature Of LEDs And Design Of The Measurement System

With the development of the semiconductor material technology, solid-state lighting (LED, Light Emitting Diode) are playing a more and more important role in general lighting area. At present, the high junction temperature limits the development of the high power LED, so it's necessary to determine the junction temperature to help chip design, package and heat sink design. As to LED lighting system or LED display screen, the forward voltage method is not available because the pins of LED can't be contacted as for the system encapsulation. Hence it's important to develop a non-contact method to determine the junction temperature of LEDs in order to evaluate the system design and forecast the life time of LEDs. A new non-contact method is proposed to determine the junction temperature of LEDs in this thesis.In the first part, a new non-contact method based on relative radiation intensity is proposed, which is suitable for one single LED or the average junction temperature of LED array. A measurement system is set up based on high-speed data acquire card and LabVIEW. The junction temperature of LEDs with different power, packaging materials and colors is measured, which is compared with the result obtained by the forward voltage method. The result is analyzed and the system error is determined.In the second part, a high-speed non-contact method of junction-temperature distribution measurement of LED array is proposed and which is based on digital image processing. The measurement system is developed on visual C++ development platform and utilizing an industrial digital camera. Junction temperature distribution of a LED array is measured and the system error is analyzed.At the end of the thesis, a summary analysis of factors influencing measurement precision is discussed, and some methods to improve measurement precision of the measurement system are suggested.