Thermal Characterization Of Power LEDs And LED Assemblies
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Date
2012-06
Authors
Permal, Anithambigai
Journal Title
Journal ISSN
Volume Title
Publisher
Universiti Sains Malaysia
Abstract
As the technology of light emitting diode (LED) improves, the amount of heat generated becomes a bottleneck to the technology that affects the reliability, stability and lifetime of the device. Therefore, to sustain the performance of a product, thermal management of power LEDs has become very significant. Both junction temperature (TJ) as well as thermal resistance (Rth) are the key evaluation parameters in the study of thermal management. The goal of this research is to understand the thermal characteristics of power LEDs under various conditions which could enhance the understanding towards better thermal management. Utilization of still air chamber revealed that it is necessary to control the environment to ensure the cooling of the devices only takes place through natural convection generated by the package under test. Employing JEDEC JESD51-14, the junction to board thermal resistance of 3W blue LED was 10.84 K/W at 700 mA compared to the datasheet value which was 17.0 K/W. Water flow reduced the total junction to ambient thermal resistance as much as 55.6% where the total Rth achieved was 11.89K/W compared to 26.78 K/W achieved in still air chamber. This study revealed that partial Rth of a package is always the most important parameter of a device; stating the best performance limit under the best cooling conditions. The primary difference between single chip cool and warm white LEDs were due to the phosphor concentration in the material of the chip. Cool white LEDs achieved a TJ difference of 1.62% less compared to warm white LEDs. This suggest a defined reason for lighting industry to focus more on cool white and neutral white application. It was also found that multi chip achieves less Rth and TJ compared to single chip LEDs.
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Keywords
Thermal characterization of power LEDs , and LED assemblies