High Power LED Junction Temperature Measurement And ANSYS Simulation Analysis

LED(light emitting diode, light emitting diode) is a kind of semiconductor device which can convert electrical energy into light energy. In this article, we focused on the junction temperature heat issues that could cause the problems of LED’s photoelectrical properties. The main article proposed the indirect LED junction temperature testing program and ANSYS simulation analysis.The indirect-type mainly used the basic principle of the method of voltage. Firstly, this article derive the approximately linear relationship existing between the forward voltage of the LED and the LED junction temperature with the semiconductor I-V characteristics and the relationship of reverse saturation current, which is called the theoretical derivation of the voltage method. Based on this principle, we worked out the factor K under the small current with the method of least square linear fitting. And then we got the LED junction temperature. We found that the same batch of the same type same manufacturing leds have a similar factor K by experiment, the maximum minimum K-factor error is only 5.7%. Then we elaborated the shortcomings of the small current K-factor method. At the same time, we put forward the large current testing program. The large current LED junction temperature testing program is mainly based on the LED transient thermal equations, we calculated the initial voltage the under large current according to the transient thermal equations. Then we got the K-factor, and calculated the LED working junction temperature. Finally, we do experiments on a group of six power LED samples separately with small current junction temperature testing, high current junction temperature testing and Infrared temperature measurement, through a comparative analysis of the testing results confirming the feasibility of high-current test program.ANSYS simulation analysis mainly combine the powerful modeling Pro/E with pefect thermal analysis ability of ANSYS simulating the temperature distribution of LED module. We determined the value of ANSYS thermal simulation of air convection coefficient according to the shell temperature of the LED devices measured by platinum resistor, which made the simulation results more accurate. Comparing the results of this method with the results of standard voltage method and the results of infrared thermal testing we found that the testing results of these three methods have a good Consistency. It confirmed that ANSYS simulation analysis can be used as an effective non-contact engineering approach LED junction temperature analysis. At the same time, we used ANSYS finite element thermal simulation analyzing the temperature distribution of the multi-chip COB package LED, and confirmed that with the growing distance between the chips, the three-chip surface temperature distribute more evenly in the rage of transparent silicone, and the highest chip junction temperature becomes smaller with the growing.