Apparatus for Measurement of Thermal Impedance of High-Power Light-Emitting Diodes and LED Assemblies

Measurement results of thermal impedance of powerful light-emitting diode assemblies are described. The measurements were performed with the help of a frequency method that involves heating the object under test by varying power harmonically. A pulse sequence of heating current, with the pulse length varying harmonically, is passed through the device under test. The p-n junction temperature is determined through measuring a temperature-sensitive parameter, which is forward voltage drop on the p-n junction between heating pulses at low measuring current. The first harmonic of the p-n junction temperature is determined by the discrete Fourier transform, which allows determination of thermal impedance module and phase at the modulation frequency of heating power. Analysis of the dependence of thermal impedance on modulation frequency allows determination of thermal impedance components corresponding to the structural elements of the object under test.