Non-Invasive LED Junction Temperature Measurement via Spectral Shift

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Solution Overview

Problem

Current methods for testing junction temperature in LEDs and laser diodes are invasive, destructive, and difficult to separate the effect of series resistance, making them inefficient for high-powered devices.

Innovation Solution

A non-invasive optical method measuring junction temperature by observing the shift in peak wavelength of the LED's spectrum as a function of temperature, using a heat chamber and spectrometer to determine the relationship between wavelength and temperature, allowing for quick and non-destructive testing.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If the forward voltage temperature coefficient method is used to measure junction temperature, then the measurement can be performed, but the method is invasive, destructive, and difficult to separate the effect of series resistance

Engineering Contradiction:

Improvejunction temperature measurement accuracyVSAvoidinvasive and destructive testing

Core Design Contradiction:

Measurement precisionVSObject-affected harmful factors

Solution Approach 1:

The patent replaces the electrical measurement method (forward voltage temperature coefficient) with an optical measurement method (peak wavelength temperature coefficient). This substitution eliminates the need for invasive electrical testing and destructive separation of series resistance effects, allowing non-contact measurement of junction temperature through spectral analysis of the LED's light output

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent introduces the peak wavelength of the LED's emission spectrum as an intermediary parameter to measure junction temperature. Instead of directly measuring temperature through invasive electrical methods, the optical spectrum serves as a mediator that reflects temperature changes without requiring direct contact or destructive testing of the diode

Inventive Principle:

Principle #24Intermediary (Mediator)

2Measurement precision

If the forward voltage temperature coefficient method is used, then junction temperature can be measured, but the effect of series resistance must be separated which is difficult to do

Engineering Contradiction:

Improvejunction temperature measurement accuracyVSAvoidcomplexity of separating series resistance effect

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent substitutes the complex electrical analysis required to separate series resistance effects with a straightforward optical measurement. By measuring the peak wavelength shift of the LED spectrum, the method directly captures temperature information without requiring decomposition of multiple electrical parameters or complex data processing to isolate series resistance contributions

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Measurement precision

If traditional testing methods are used for high powered LEDs, then junction temperature can be measured, but the testing process is time-consuming and complex

Engineering Contradiction:

Improvejunction temperature measurementVSAvoidtesting speed and efficiency

Core Design Contradiction:

Measurement precisionVSProductivity

Solution Approach 1:

The patent replaces slow, complex electrical testing procedures with rapid optical spectroscopy. The peak wavelength measurement can be performed quickly without requiring extensive data collection and processing, significantly improving testing throughput for high-powered LED devices while maintaining measurement accuracy

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

Enables accurate, non-invasive measurement of junction temperature and its variations, simplifying the testing process and reducing costs by using spectral shift measurements, which can estimate failure rates and degradation rates of LEDs.

Implementation Method 1

measuring the output wavelength of the LED as a function of temperature... the peak wavelength of the spectrum of the LED depends on the junction temperature... When the junction temperature increases with constant concentration of the injected carrier, the peak wavelength will move to longer wavelengths

Methodology Applied

Scientific EffectWavelength shift with temperature:

Data Source

PatentUS7651268B2Method and testing equipment for LEDs and laser diodes

Publication Date: 2010.01.26 ENNOSTAR CORP

AI summary

The present invention is a non-invasive method and associated apparatus for determining the junction temperature for an LED or laser diode (collectively “LED”). First a sample LED is placed in a heat chamber and the change of the LED's peak wavelength is recorded over time, as is the change in the temperature in the heat chamber. Since the heat chamber supplies the major component to the junction temperature, dwarfing the other components, it is a reasonable proxy for true junction temperature. The data is compiled to determine change of peak wavelength as a function of temperature and that function can then be used to determine junction temperature of similar LEDs that are installed in a system or manufactured. The invention may also be used to measure other useful data, such as power, output power changing with the junction temperature and intensity of the LED over time and may be used to estimate failure rate.