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In this letter, the thermal evaluation of high-power LED packages at pulse conditions was reported. A theoretical calculation model was proposed based on the analogy between the thermal and electrical RC circuits. The thermal performance of LED packages driven by pulse input was calculated using the RC network extracted from transient thermal measurement. The junction temperature fluctuation band decreases with the frequency at certain duty cycles. The saturated average junction temperature rise linearly increases with the duty cycle at certain frequencies. These predictions were verified by the real-time junction temperature measurement using the peak shift method at pulse conditions. The theoretical model was found to be effective and applicable to the evaluation of the thermal performance of LEDs working at pulse conditions. [ABSTRACT FROM AUTHOR]

This is the first report on the direct measurement of the junction temperature and on the determination of thermal resistance of a commercial amorphous silicon (a-Si) solar cell package under real operating conditions. Thermal transient method was utilized for the thermal characterization. Irradiation of sunlight to the solar cell package was found to induce significant heat generation inside the solar cell package. It was shown that the driving of the solar cell package with a sun power of 1 sun (100 mW/cm² and 1.5 AM) resulted in a junction temperature of about 113 °C. Surprisingly, the temperature difference between the junction and the case surface of the solar cell package was as high as 43 °C. The efficiency drop was observed with the increase of junction temperature in the solar cell package. Thermal resistance was determined under various operating conditions. [ABSTRACT FROM AUTHOR]

In this letter, we present our thermal study results of GaN-based heterojunction field effect transistors (HFETs). In thermal computation, PAMICE code was used to calculate temperatures in a three-dimension (3-D) model. In the rmal measurement, nematic liquid crystal thermography was employed to determine the peak temperature on the surface of the device chip. The calculated and directly measured temperatures agree well. These methods are valuable in predicting the thermal performance of GaN-based HFET devices, in particular the power devices. [ABSTRACT FROM AUTHOR]