Estimation of LED Junction Temperature Based on Forward Voltage Method for Digital Hardware Implementation

Abstract

In contrast to classical light bulbs, LEDs used for lighting applications achieve greater energy efficiency. Nevertheless, LEDs are not lossless; power loss generates heat in the semiconductor junctions as well as in the light conversion material. High temperature significantly impairs the luminescent material and results in degeneration of the luminescent encapsulation material whereby its transparency is reduced. Avoiding high temperatures of an LED extends the live span and guarantees light quality. Therefore, temperatures of the p-n junction has to be measured and controlled by the LED driver. One considered constraint for implementing a temperature controller in the LED driver is the use of a hardware description language for the digital part to limit design complexity. Common temperature estimation methods are either mathematical to complex to be implemented into the LED driver or not accurate enough to protect p-n junctions against high temperatures. This paper describes a less complex mathematical approach to determine the p-n junction temperature based on the forward-voltage method. The related calculations are of moderate complexity allowing integration into a small size custom IC.