Analysis of three different junction temperature estimation methods for AC LEDs

• AC LED junction temperature is measured using three methods and analyzed.
• Results from voltage drop and peak wavelength methods for AC LEDs agree.
• The temperature at different phase angles within the first AC power cycle is measured.
• Accuracy of the rms current method improves when the first half cycle heating is included.

Light-emitting diodes (LEDs) operating on alternating current (AC) are gaining popularity in lighting applications. The junction temperature of an LED significantly influences the performance and reliability of the product. Although there are many proven methods for estimating the junction temperature of direct current (DC) LEDs, only a few methods have been proposed for AC LEDs. Two recently proposed methods, the voltage drop method for AC LEDs and the rms current recovery method, indicated different thermal resistance values for the identical LED package. This discrepancy in thermal resistance values is due to the junction temperature rise in the first half cycle that is not accounted for in the rms current recovery method. The peak emission wavelength shift is another approach used in DC LEDs to estimate junction temperature. This method was used to estimate junction temperature for AC LEDs. The measured junction temperature results were compared to results obtained using the voltage drop method for AC LEDs. The junction temperature estimated using the two approaches agree.