Precise measurement of junction temperature by thermal analysis of light-emitting diode operated at high environmental temperature

摘要

Light-emitting diodes (LEDs) have become a promising solid-state light source in numerous applications. During operation, they are often exposed to high environmental temperatures, resulting in performance and reliability degradation. It is thus important to monitor the temperature at the junction, which is a primary lighting and heat source, especially for an LED operated under a high-temperature environment. In this study, the temperatures at the junction, phosphor, and thermal pad of the LED operated at high temperatures (up to 107.2 degrees C) are measured and analyzed. The junction temperature is measured by a transient thermal tester at known environmental temperatures and input currents. Moreover, the temperatures at the phosphor and thermal pad are simultaneously measured by using an infrared (IR) thermometer and a thermocouple, respectively. A single highly linear temperature correlation (R-2 = 0.997) is found between the junction and phosphor temperatures regardless of the operating conditions. This could aid in precisely estimating the junction temperature by simply measuring the surface temperature of phosphor. On the other hand, the correlation between the junction and thermal pad temperature that is often treated as a single correlation exhibits dependence on the input current over the tested temperature range. The structural thermal analysis on the thermal resistance of the LED package supports the experimental results along with the numerical analysis. The obtained results in this study could provide a set of guidelines for the precise prediction of junction temperature and thermal management of LEDs, which are operated under high-temperature environments.