Thermal Switch Shunting for LED Junction Temperature Protection

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Solution Overview

Problem

Existing light emitting modules lack effective thermal protection correlated to the junction temperature of semiconductor devices, as they primarily rely on resistive energy dissipation in bimetal elements rather than temperature-dependent mechanisms, which can lead to catastrophic failures due to overheating.

Innovation Solution

A light emitting module with a thermal switch arranged in parallel to the semiconductor device, utilizing high and low coefficient of thermal expansion materials to shunt current without electrical energy dissipation under normal conditions, allowing the switch to correlate with the device's temperature through radiative or conductive heating, and geometrically deform to shut off current supply before critical temperatures are reached.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a bimetal element is used for thermal protection, then the LED is protected from overheating, but the protection is not tuned to the LED junction temperature because the bimetal element operates based on its own resistive heating

Engineering Contradiction:

Improvethermal protection effectivenessVSAvoidtemperature correlation accuracy

Core Design Contradiction:

ReliabilityVSMeasurement precision

Solution Approach 1:

The patent introduces a thermal switch as an intermediary component that is thermally coupled to the LED junction but electrically isolated. This thermal switch acts as a mediator that senses the LED junction temperature through thermal conduction while preventing direct electrical heating, thereby providing accurate temperature-correlated protection without the measurement error introduced by self-heating in the protection mechanism itself

Inventive Principle:

Principle #24Intermediary (Mediator)

2Reliability

If a thermal switch is placed in series with the LED, then the LED is protected from overheating, but the current flow is interrupted causing the protection mechanism to dissipate electrical energy

Engineering Contradiction:

Improveoverheating protectionVSAvoidelectrical energy dissipation

Core Design Contradiction:

ReliabilityVSLoss of energy

Solution Approach 1:

The patent replaces the electrical series switching mechanism with a thermal coupling mechanism. Instead of using electrical switches in series that dissipate energy when opening/closing circuits, the invention uses a thermal switch that is thermally coupled to the LED junction and electrically connected in parallel, substituting thermal field interaction for electrical field interaction to achieve protection without energy loss

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Power

If multiple modules are connected in a series string, then the system provides high voltage operation, but a single module failure interrupts current flow through all modules

Engineering Contradiction:

Improvesystem operating voltageVSAvoidsystem continuity

Core Design Contradiction:

PowerVSReliability

Solution Approach 1:

The thermal switch acts as a local protective intermediary that isolates only the affected module from the rest of the series string when overheating occurs. By providing a parallel thermal protection path, it allows current to bypass the protected module and continue flowing through other modules, maintaining system operation while protecting individual components

Inventive Principle:

Principle #24Intermediary (Mediator)

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

The solution provides direct thermal protection tuned to the semiconductor device's junction temperature, preventing catastrophic failures while maintaining continuous current flow through other modules in a series string, and allows for cost-effective mass fabrication with clear visual indication of critical temperature limits.

Implementation Method 1

the thermal switch comprises a high coefficient of thermal expansion (HCTE) material with a coefficient of thermal expansion αh and a low coefficient of thermal expansion (LCTE) material with a coefficient of thermal expansion α1, and αh >α1

Methodology Applied

Scientific EffectThermal expansion: Thermal Expansion

Implementation Method 2

the (junction of the) semiconductor light emitting device heats up the former, either through radiative energy transfer or through conductive energy transfer via the constructional elements of the module

Methodology Applied

Scientific EffectThermal radiation: Thermal Radiation

Implementation Method 3

Methodology Applied

Scientific EffectThermal conduction: Conduction (thermal)

Data Source

PatentEP2225777B1Light emitting module and thermal protection method

Publication Date: 2016.09.28 KONINKLIJKE PHILIPS NV

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AI summary

Proposed is a light emitting module (1), comprising a semiconductor light emitting device (10) and a thermal switch (20). The thermal switch (20) is arranged to protect the device (10) from over heating. At elevated temperatures the junction of the device (10) may reach a critical level causing catastrophic breakdown of the device. According to the invention, the thermal switch is arranged to shunt the semiconductor light emitting device. This is especially advantageous as the thermal protection offered by the switch (20) correlates directly to the (junction) temperature of the device (10).