Voltage-temperature coefficient analysis and testing of high power light-emitting diodes

Forward voltage method is commonly used and easy to implement in various measuring methods of LED´s thermal characteristic. Considering the determination of voltage-temperature coefficient is the key for the forward voltage method, this parameter is worth studying and has a big effect on application. In the junction temperature measurement, static method has advantages of being more convenient and on a continuous basis compared with the commonly used dynamic method. The goal of the letter is to study voltage-temperature coefficient versus current because the static method can only be used on the premise of getting the voltage-temperature under large current. In theoretical analysis, there is a relation between the temperature coefficient of the forward voltage and the current. A negative logarithmic relationship exists between them in the small current region and a linear relationship exits between them in the large current region. Experimentally, the voltage-temperature coefficient of red (AlGaInP), green (GaInN), blue (GaInN), UV (GaInN) and two white (GaInN) high power light-emitting diodes under different current is measured. The test current ranges from 0.1 mA to 350 mA for 1 watt LEDs and from 0.1mA to 1000mA for 3 watt LEDs. The pulse current width is set 10μs which can´t generate heat by the device itself. The LED chips have different material, structure and bonding technology. Commendable agreement between the theoretical and experimental relation between voltage-temperature coefficient and forward current is found.