照明應用中led結溫的計算

　　操作LED超過制造商推薦的最高溫度可以降低設備的效率和光輸出，并可能導致過早失效。LED的熱點被定義為形成二極管的p型和n型半導體之間的結。本文使用一個示例照明應用程序來說明如何計算LED的結溫，并確定它是否有可能超過指定的上限。

　　LED結溫的計算

　　一個LED通過將電荷載體（電子和空穴）重新連接到LED連接處，將電能轉換成光（圖1）。不幸的是，即使發光二極管相對有效，大約65至75%的電能消耗仍然產生熱量，而不是光，提高芯片的溫度。

　　Figure 1： Charge carriers combine at the junction of an LED to generate some light and a lot of heat.

　　But just how hot can a high-brightness LED get？ Let‘s look at how to determine junction temperature using a simple calculation.

　　The maximum junction temperature （Tj） attained with a given power input is determined by three factors： ambient temperature， thermal resistance between the LED junction and its surroundings， and the power dissipated by the chip.1

　　For ease of calculation， let’s assume an ambient temperature （Ta） of 23 degrees Celsius （°C）。 （Note that a comprehensive design calculation should consider the worst case scenario of the maximum ambient temperature that the LED will experience in normal operation.） Lower ambient temperatures will decrease the junction temperature and prolong the life of the LED. This makes LED lighting a good choice for certain applications， such as chilled food display cabinets.