Thermal impedance of AC LEDs

This paper aims at providing a rigorous description of the thermal impedance of AC LEDs, especially of retrofit LED lamps which are directly driven from the mains supply. The paper gives an overview of the different representations of the thermal impedance then provides estimates of the AC power of LEDs for two extreme cases (voltage and current driven situations). The high harmonic content of the AC power is calculated for these cases and real measurement results are presented for a practical situation. Suggested setup for actual measurement of the AC thermal impedance and the junction temperature of LEDs under AC conditions is also shown.