Study on electrical, thermal and optical properties of LED

Summary

The luminescence properties of LEDs are not only related to their electrical properties, but also to their junction temperature. Therefore, it is very important to study the heat dissipation performance and thermal management methods through actual test and simulation tools in the LED design process. In this paper, the electrical, thermal and optical properties of LEDs are studied collaboratively.

In terms of simulation, the electro-thermal simulation of a board-level system was completed; in terms of testing, the application of a thermo-optical joint test system was discussed.

1 Introduction

It is well known that the effective optical radiation (luminosity and/or radiant flux) of an LED is severely affected by its junction temperature (as shown in Figure 1, the data is derived from the Lumileds Luxeon DS25 performance data sheet).

The relationship between the effective light radiation of a group of LEDs from green to blue and white light with junction temperature

(Click on the image to view the original image)

Figure 1: The relationship between effective light radiation and junction temperature of a group of LEDs from green to blue and white.

A single LED package is often referred to as a primary LED, and an LED component with multiple LED chips mounted on the same metal substrate is often referred to as a secondary LED. When the secondary LED has high requirements on the uniformity of light, the effect of junction temperature on the luminous efficiency of the LED will be very prominent [1].

As mentioned in [2], the electrical, thermal and optical synergistic models of primary LEDs can be used to predict the electrical, thermal and optical properties of secondary LEDs. The premise is the need to accurately model the cooling environment of the LED.

In Section 2 of this article, I will discuss how to use the structure function to obtain the thermal model of the LED package, and briefly describe a new test system that we use to test. In Section 3, we first review the principles of the electro-thermal simulation tool and then extend this principle to board-level thermal simulation to help optimize the simplified thermal model of the package structure. At the end of the article we will introduce an application example.

2. Establish a simplified thermal model for the LED package

The academic community has been discussing the establishment of simplified thermal models (CTMs) for semiconductor package components for more than 10 years. Now, the DELPHI approximation processing method [3][4][5] is widely accepted for establishing boundary-condition-based steady-state simplified thermal models (CTMs) for packaging components, especially IC packages. In order to study the transient thermal performance of components, we need to extend the CTM. The extended model is called Transient Simplified Thermal Models (DCTMs). The EU has developed a method for building component DCTMs through the PROFIT project [7] and has also expanded the functionality of the thermal simulation tool [6] to enable simulation calculations of DCTM models.

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