LED Lamp Thermal Properties - App Brief

In the vast majority of customer applications, LED lamps are soldered directly on a printed circuit board. Lamp data sheets provide a conservative power or current derating based on maximum ambient temperature. In virtually any application, an understanding of the thermal properties of LED lamps is useful for several reasons: 1. Avoid over-stressing the LED, which lowers its reliability. 2. Allow the LED to be operated at the highest drive current (and highest light output) possible. 3. In some cases, allow the LED to be driven at conditions beyond the maximum ratings. LED lamps are usually constructed by encapsulating an LED chip in an epoxy package. The LED chip is attached to a metal pin with electrically conductive epoxy. The top of the LED chip is connected to another pin with a gold wire. Because of different rates of thermal expansion, the gold wire is deformed slightly when the lamp is subjected to large temperature extremes. Even though gold is a very ductile metal, the gold wire can break after large number of temperature cycles, causing the LED to fail as an open circuit. Avago Technologies LED lamps are capable of withstanding thousands of temperature cycles over the temperature range of -55/100°C, non operating.