A Technique for Improving the Precision of the Direct Measurement of Junction Temperature in Power Light-Emitting Diodes

Abstract

Extending the lifetime of power light-emitting diodes (LEDs) is achievable if proper control methods are implemented to reduce the side effects of an excessive junction temperature, TJ. The accuracy of state-of-the-art LED junction temperature monitoring techniques is negatively affected by several factors, such as the use of external sensors, calibration procedures, devices aging, and technological diversity among samples with the same part number. Here, a novel method is proposed, indeed based on the well-known technique consisting in tracking the LED forward voltage drop when a fixed forward current is imposed but exploiting the voltage variation with respect to room temperature. This method, which limits the effects of sample heterogeneity, is applied to a set of ten commercial devices. The method led to an effective reduction of the measurement error, which was below 1 °C.

A Critical Review on the Junction Temperature Measurement of Light Emitting Diodes

“…Therefore, a number of examples of FVM for T j evaluation of LED devices can be found [ 179 , 180 , 181 ]. Notably, the claimed accuracy of this method ranges from ±3 [ 62 , 82 ] to ±0.88 °C [ 182 ].…”

“…At low temperatures, deviation from the constant voltage coefficient of temperature can be explained by internal series resistance [ 184 ]. However, at low pulse durations, which ensures no T j rise [ 63 ] and falls into the exponential current interval (e.g., 1 mA), numerous perfectly linear T j – V f were reported in the literature [ 64 , 82 , 94 , 96 , 115 , 129 , 164 , 182 , 195 , 196 ].…”

An improved LED junction temperature test method based on FCM

“…It is found in the literature [10] that the test delay of this method will lose key data, and the experiment finds an abnormal heating phenomenon. In the literature [11], the use of differential voltage methods to improve equipment aging and technical heterogeneity has been proposed. According to the literature [12], the Tj is obtained by using the relationship between Tj and current.…”