The Study Of Measurement Of LED Junction Temperature

LED meets the requirements of low-carbon economy because of their high energy saving efficiency, long life-time and high reliability, and it is widely used in many fields especially the fields of semiconductor lighting. However, the test of thermal performance and heat dissipation is still a prominent problem. In order to obtain stable light output and maintain normal lifetime of the devices, how to keep the junction temperature within the allowable range? This is still a burning question at present.On the basis of making enough investigation on the measuring methods of LED junction temperature, this text mainly studies the K coefficient measuring method which can reduce the measurement noise and the effect. Meanwhile, it also studies a new method - the pulse current method which can measure the junction temperature and thermal capacity of LED device at the same time. By injecting constant narrow pulse of square-wave current to the LED devices, it will obtain the sensitivity coefficient dVF/dT of forward voltage and the temperature under a certain current. Then, by measuring the forward junction voltage under the rated current, users can use the sensitivity coefficient to obtain the junction temperature. Through the study of 12μs , 24μs and 50μs and other pulses whit different pulse width, it is concluded that in order to achieve the effect of pulse current on junction temperature measuring accuracy lower than 1℃, the pulse width should be controlled from a few to a dozenμs. This text also makes primary exploration of the pulse current method on the thermal capacity measurement of LED devices.Based on the experimental demonstration, this text offers a prototype structure of LED junction temperature measuring instruments with pulse current method. Hope it will contribute to the measurement of LED junction temperature.