Light-Emitting Diode Junction-Temperature Sensing using Various Voltage/Current Measurement Techniques

Abstract

Given the temperature dependence of various aspects of light-emitting diode (LED) performance, LED temperature sensing is becoming increasingly important in solid-state lighting applications. This thesis presents an electrical technique for junction-temperature sensing based on the measurement of the forward voltage and current of an LED at two bias points. This technique is inspired by techniques commonly used in temperature sensors based on bipolar transistors. While it leads to higher temperature errors than existing electrical techniques, which use the linear relationship between voltage and temperature at a fixed current, the proposed technique has the potential to significantly reduce calibration costs, as it requires calibration at only one temperature instead of two for existing techniques. Measurements of commercial high-power LEDs show that temperature errors can be reduced by using differential measurements around a fixed voltage-bias point instead of the more commonly used fixed current-bias point.