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.