Analysis of thermal effects on high power LEDs

• Main Authors: Jian-Sin Chen, 陳建欣
• Other Authors: Chia-Ching Chuang
• Format: Others
• Language: zh-TW
• Published: 2009
• Online Access: http://ndltd.ncl.edu.tw/handle/57686704337534213813

碩士 === 和春技術學院 === 電機工程研究所 === 97 === Abstract Today, as everyone knows, high power LEDs possess the commercial potential to replace the traditional light source with the features of long-term reliability, environmental friendliness and low power consumption. In fact, they have been viewed as a promising alternative for future lighting. However, the rate of heat generation increases with the illumination intensity. Generally, the LED has 15%~30% visible light and heat generated from the remainder. The purpose of this study is to find available ways to improve the heat dissipation to increase the efficiency of the LED. A finite element analysis software, COMSOL Multiphysics 3.2, had been used to simulate the thermal behavior of the high power LEDs (white, green, blue, and red), at several different operating conditions, including different output wattages (P=1W, 3W, and 5W), different surrounding temperatures ( ~ ), and different heat sink areas ( ~ ). At low power, 1W, the waste heat produced from the chip was removed well by the heat sink plate even under . Therefore, the variation in chip temperature was almost equal to that in surroundings, and the slope of their relationship approximated to 1. However, when the output power was increased above 5W, the accumulated waste heat can not be removed from heat sink plate and results in high junction temperature. But higher junction temperature also results in more heat generation and finally damages the LED. This phenomenon will be extremely obvious in the red light LED. At 5W, Tj is 475.6K for white light but 652.4K for red light at with heat sink plate. Taking as the criterion for normal working of the chips, the white light LED needs a heat sink with 2100 mm2 at least but 3000 mm2 for red light LED as P= 5W. And as P= 5W, required heat sink areas reduce to 1600 mm2 and 2100 mm2 for white light and red light, respectively.