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Thermal Analysis of High Power LEDs at Dynamic Conditions
Keywords: Thermal analysis, high power LEDs, dynamic condition
High power LEDs exhibit a prominent future in general illumination with the merits of high luminous efficiency and significant energy saving. One critical issue of high power LEDs is thermal management since high junction temperature decreases light output, leads to a color shift, and reduces device lifetime. The thermal behavior of DC driven LEDs has been extensively investigated by both experimental and numerical methods. However, no systematic thermal analysis of the high power LEDs at dynamic conditions has been reported yet. The performance of high power LEDs can be improved by driving LEDs at either AC or periodic pulse signal instead of conventional DC signal. AC-drive LEDs can have higher wall-plug efficiency than both periodic pulse signal and DC signal because of a higher power factor. Pulse-driven LEDs can realize brightness control in a wide range at lower power consumption. Computational fluid dynamics analysis was employed to investigate the thermal behaviors of high power LEDs driven at AC, DC and periodic pulse conditions. Under both AC and periodic pulse conditions, the junction temperature increases in an oscillation fashion initially and then reaches a steady state at which both the average junction temperature and the oscillation band remain stable with the operating time. The time to reach steady state and the average junction temperature in both AC and pulse cases are the same. It is found that the steady-state junction temperature of LEDs driven at DC signal is around 6 higher than that of LEDs driven at AC and periodic pulse signals, demonstrating the effectiveness of heat removal under dynamic signal modes.
Bohan Yan, Student
University of California, Irvine
Irvine, CA

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