K-factor calibration issues of high power LEDs

Operation of LEDs is highly affected by their junction temperature. However, for proper thermal characterisation a well fitted K-factor function is needed within its validity range. Correction for the parallel thermal resistance during thermal transient testing also needs special care. This paper focuses on the issues of applying a correct K-factor value or higher polynomial fit to the temperature dependent forward voltage characteristics of the tested LEDs. Our work is based on JEDEC's LED thermal testing standards, and the outcome is a set of practical recommendations beyond the well established guidelines for thermal characterization. These new recommendations are easy to implement in an automated way.