Measure the junction temperature of alternating current light-emitting diodes.

• Main Authors: Chen-hung Yang, 楊振泓
• Other Authors: Jyh-Chen Chen
• Format: Others
• Language: zh-TW
• Published: 2010
• Online Access: http://ndltd.ncl.edu.tw/handle/08228895585706802499

碩士 === 國立中央大學 === 機械工程研究所 === 98 === There are several methods employed to measure junction temperature using Micro-Raman spectroscopy, electroluminescence, photoluminescence, noncontact method, and forward voltage method. The forward voltage method is most popularly used today because it is easy to operate and has the better accuracy. Forward voltage method can be easily used in DC LED device due to the constant current input, but it is very difficult to be extended for measuring the junction temperature of AC LED because the AC LED device is driven by a time varying voltage. The condition of heat generation in AC LED for AC operation is different from that in DC LED for constant DC input. But little investigation on the measurement of junction temperature for AC LED was proposed. In this study, the method for measuring the junction temperature of AC LED is proposed. The linear relationship between the temperature and the input current is derived from the Shockley equation. The variation of threshold current with temperature under the threshold voltage is performed experimentally to confirm this linear relation. The average and maximum junction temperature of AC LED at the quasi-steady state can be determined by using the linear temperature dependence of the threshold current and measuring the threshold currents at both initial and quasi-steady states. The thermal resistance of AC LED and the effective input power are defined in this study. The accurate of the average junction temperature measurement can be verified by the thermal resistance of AC LED. Finally, the relation between maximum junction temperature and the effective input power can be used to calculate the junction temperature vary with time.