Abstract
Thermal transient testing is widely used for LED characterization, derivation of compact models, and calibration of 3D finite element models. The traditional analysis of transient thermal measurements yields a thermal model for a single heat source. However, it appears that secondary heat sources are typically present in LED packages and significantly limit the model’s precision. In this paper, we reveal inaccuracies of thermal transient measurements interpretation associated with the secondary heat sources related to the light trapped in an optical encapsulant and phosphor light conversion losses. We show that both have a significant impact on the transient response for mid-power LED packages. We present a novel methodology of a derivation and calibration of thermal models for LEDs with multiple heat sources. It can be applied not only to monochromatic LEDs but particularly also to LEDs with phosphor light conversion. The methodology enables a separate characterization of the primary pn junction thermal power source and the secondary heat sources in an LED package.
Highlights
The market of solid-state lighting has rapidly expanded over the past decades
Phosphor-related thermal losses PhD can be estimated as high as 50% of Ph if we consider an light emitting diodes (LEDs) that has 65% phosphor light conversion efficiency [14] driven with current correspondent to 75% internal quantum efficiency (IQE)
We propose a possible extraction procedure for the parameters of this compact thermal model in Appendix
Summary
Due to commoditization of light emitting diodes (LEDs), the expansion sets a need for accurate thermal modeling of LEDs to ensure highly reliable end products. Compact thermal modeling is an approach that enables fast and reliable thermal simulations of the devices of interest without disclosing confidential information from LED suppliers. Compact thermal models (CTMs) are widely used in modern production and in optimization processes ( in the semiconductor industry) [1,2,3]. One of the goals of our European Union project Delphi4LED [4,5] is the standardization of the CTMs for LEDs. CTMs are traditionally either directly generated based on measurement data of thermal transients or are extracted by model order reduction [1] from detailed full-3D finite element thermal models [6]
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