Digital Hardware Implementation of LED Temperature Measurement Based on Forward Voltage Method

High junction temperature of LEDs can significantly decrease their lifespan. The colour and light intensity can also change by LED overheating. Therefore, a thermal management has to be implemented into the LED driver to prevent over heating and to realize long lifetimes of LEDs. Measuring or good estimation of the temperature of the LED junction is fundamental to develop a thermal management. Current LED driver often use external resistors attached to the LED to get an approximated temperature of the LED, but this approach does not provide the LED junction temperature. Another drawback is, that the method cannot detect short temperature pikes because of the thermal low-pass filter behaviour of the LED structure. Furthermore, changes in the mechanical structure like solder and change of LED structure are difficult to consider. In this paper, the forward-voltage of LEDs is used to calculate the core temperature of an LED, because the detected voltage provides fairly good temperature data. For the necessary data processing a fast mathematical approach is discussed. The on-chip implementation is performed using VHDL to be able to realize an optimized ASIC device. The developed approach can be integrated into small size LED drivers.