了解LED内部热阻

　　了解LED内部热阻

　　尽管与传统照明相比，其卓越的功效，LED仍然得到热。由于过多的热量是不希望的影响，如色度移位或更糟，灾难性故障的原因，热管理是固态照明（SSL）设计的一个重要方面。

　　对于一组给定的操作条件下，LED的内部热阻主要决定了该设备将如何热，以及如何将很快达到峰值温度。更大的内部热阻导致更快的温度上升和更高的峰值温度。

　　本文着眼于LED的内部热阻的定义及其对商业产品的结温的影响。

　　The importance of thermal management

　　The primary source of heat in an LED comes from the junction between the p-type and n-type semiconductor material making up the device. This heat is a by-product of the recombination of electrons and holes at or near the junction. Ideally， recombinations result in photons that exit the LED and contribute to the overall illumination， but often the photon is reabsorbed in the die， generating heat. Tiny vibrations of the LED’s crystal lattice that occur while the device is operating also raise the temperature. Despite the high efficacy of LEDs compared to conventional light sources， some 70 to 80 percent of the electrical energy applied to the device is still converted to heat rather than light.

　　Because the LED junction is small， the energy density is high and the temperature rises rapidly. It is not uncommon for the junction temperature （TJ） of modern chips to rise to 100oC and above， and although contemporary LEDs are far more robust than older devices， prolonged operation at high temperatures is undesirable. Limiting junction temperature reduces chromaticity drift and prolongs life. （See the TechZone articles “Thermal Effects on White LED Chromaticity” and “Understanding the Cause of Fading in High-Brightness LEDs.”）