照明應(yīng)用中led結(jié)溫的計(jì)算

　　操作LED超過(guò)制造商推薦的最高溫度可以降低設(shè)備的效率和光輸出，并可能導(dǎo)致過(guò)早失效。LED的熱點(diǎn)被定義為形成二極管的p型和n型半導(dǎo)體之間的結(jié)。本文使用一個(gè)示例照明應(yīng)用程序來(lái)說(shuō)明如何計(jì)算LED的結(jié)溫，并確定它是否有可能超過(guò)指定的上限。

　　LED結(jié)溫的計(jì)算

　　一個(gè)LED通過(guò)將電荷載體（電子和空穴）重新連接到LED連接處，將電能轉(zhuǎn)換成光（圖1）。不幸的是，即使發(fā)光二極管相對(duì)有效，大約65至75%的電能消耗仍然產(chǎn)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.