A Bipolar-Pulse Voltage Method for Junction Temperature Measurement of Alternating Current Light-Emitting Diodes

We introduce a new method for measuring the junction temperature of alternating current light-emitting diodes. This method employs a periodic bipolar voltage pulse signal as the input, and utilizes the amplitude of corresponding output current as the temperature sensitive parameter (TSP), of which a linear temperature dependence is proven in a prior experiment in this paper. On the basis of the TSP, we devise a detailed procedure-first, measure the thermal resistance of the package of ac-LEDs, which further contributes to the calculation of junction temperatures under various power inputs. Comparisons between values calculated by using this method and those obtained directly from a thermocouple indicate a decent accuracy of the former. The advantage of this method benefits from the stability of thermal resistance under different driving conditions that one could immediately obtain the junction temperature by measuring the electric and optical powers.