Thermal Protection Circuit for Solid State Light Sources
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Solution Overview
Problem
Conventional bi-metallic thermal switches used in solid state light source modules are bulky, occupy significant space, and have a limited lifespan, making them impractical for designs where space is limited and the module's lifetime is longer than the switch's.
Innovation Solution
A thermal protection circuit comprising a temperature sensor, a variable impedance circuit, and a control circuit is implemented, which adjusts current to the solid state light sources based on temperature, using a low voltage compensation circuit to maintain operation at low dimming levels and isolate the control circuit from the variable impedance circuit when the supply voltage falls below a minimum threshold.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional bi-metallic thermal switch is used for thermal protection, then thermal shutdown function is achieved, but the device occupies significant space and has limited lifespan
Solution Approach 1:
The patent replaces the conventional bi-metallic thermal switch (mechanical system) with an electronic thermal protection circuit comprising a temperature sensor, control circuit, and variable impedance circuit. This substitution eliminates the need for bulky mechanical components while achieving the same thermal protection function through electronic means, thereby reducing space occupation and extending operational lifespan.
Solution Approach 2:
The patent employs a variable impedance circuit that dynamically adjusts its resistance based on temperature conditions. When over-temperature is detected, the control circuit modifies the impedance parameter to reduce current flow, providing thermal protection without requiring physical space-consuming mechanical switches. This parameter-based control enables compact integration while maintaining protection functionality.
2Reliability
If a conventional bi-metallic thermal switch is used for thermal protection, then thermal shutdown function is achieved, but the device has limited lifespan compared to the lighting module
Solution Approach 1:
The patent replaces the mechanical bi-metallic switch with an electronic protection circuit that has no moving parts and no wear-prone components. The electronic circuit uses a temperature sensor and control logic to manage thermal protection, eliminating the lifespan limitations inherent in mechanical switches and enabling the protection system to operate throughout the entire service life of the lighting module.
Solution Approach 2:
The electronic thermal protection circuit is designed to remain functional throughout the operating life of the lighting module without requiring replacement. The control circuit continuously monitors temperature and automatically adjusts impedance or shuts down power as needed, providing self-sustaining thermal protection that outlasts conventional mechanical switches.
3Ease of operation
If the variable impedance circuit is driven to low impedance state at low input voltage, then normal operation at low dimming levels is maintained, but the control circuit may not operate reliably below minimum supply voltage
Solution Approach 1:
The patent introduces a low voltage compensation circuit as an intermediary between the input voltage source and the control circuit. This compensation circuit includes an energy storage element (capacitor) that maintains the supply voltage to the control circuit above the minimum operating threshold even when the input voltage from the constant current source drops at low dimming levels. This intermediary ensures both reliable control circuit operation and normal operation of the solid state light sources at low light output levels.
Solution Approach 2:
The low voltage compensation circuit proactively compensates for voltage drops before they can affect control circuit reliability. By using an energy storage element to maintain voltage levels, the circuit prepares for and cushions against the potential problem of insufficient supply voltage, ensuring continuous reliable operation across the full range of dimming levels.
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
This solution effectively manages thermal protection in solid state light source modules by reducing current to prevent overheating, maintaining operation at low light output levels, and extending the lifespan of the thermal protection system, even when space is limited.
Implementation Method 1
a temperature sensor configured to sense a temperature of the plurality of solid state light sources
Implementation Method 2
The variable impedance circuit is configured to be coupled to the constant current source and the plurality of solid state light sources... the control circuit configured to drive the variable impedance circuit based on the sensed temperature to adjust the current to the plurality of solid state light sources
Implementation Method 3
The low voltage compensation circuit may include an energy storage element, e.g., a capacitor, configured to slow the decrease in the input voltage during dimming
Data Source
AI summary
A thermal protection circuit, and system and method including same, is provided. The circuit includes a variable impedance circuit configured to be coupled to a constant current source and a plurality of solid state light sources. The constant current source provides a current to the plurality of solid state light sources and provides an output voltage to establish a supply voltage for the circuit. The circuit also includes a temperature sensor configured to sense a temperature of the plurality of solid state light sources. The circuit also includes a control circuit configured to receive the supply voltage and to drive the variable impedance circuit based on the sensed temperature, to adjust the current to the plurality of solid state light sources when the supply voltage is a least a minimum supply voltage of the control circuit.