Compact modeling of power LEDs

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Dr. Poppe András
Department of Electron Devices

This document provides a short overview of power LEDs and their development trend. It describes the basics of thermal characterisation of packaged semiconductor devices, especially of power LED-s. As a part of that it shows the method of thermal transient based semiconductor measurement and gives a condensed explanation of theory of the so called structure function derived from the thermal transient of the junction temperature (response to a unit-height heating power step) as the thermal network model of the junction to ambient heat-flow path. The paper discusses the so called transient dual interface method which by using thermal transient measurements provides accurate and highly repeatable means to determine the so called junction-to-case thermal resistance or the junction-to-case thermal impedance of a package – an important input for generating the so called compact network thermal model (thermal RC network model) of the package aimed at thermal simulations.

In my thesis I touch upon the importance of calibration measurements. I also discuss how to chose proper values for the most important measurement parameters (such as times, voltage ranges and the level of the heating and measurement currents). During thermal characterisation of LEDs knowledge of the emitted optical power (radiant flux) is important. The final purpose of my work is to generate LED models aimed at system (luminaire) level thermal simulations which would allow predicting the luminous flux of LEDs at operating temperatures (hot lumen prediction). Therefore I describe the main aspects of combined thermal and radiometric/photometric measurements on LEDs.

Detailed documentation on measuring four power LED types is attached to the thesis in which I describe the proper process of performing the tests, the difficulties arisen and the solutions to them. Description of methods of generating compact LED models aimed at thermal simulators software is also a part of the documentation.


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