LED Fixture Thermal Control Using Negative Coefficient Thermistor Array
Solution Overview
Problem
Conventional light-emitting diode fixtures face thermal stress issues due to inefficient heat dissipation, leading to reduced efficiency, shifted optical wavelengths, and potential catastrophic failure, especially in high-power applications where additional cooling means are required, increasing manufacturing costs with the need for controllers.
Innovation Solution
A light-emitting diode fixture design featuring a heat sink thermally coupled with a negative coefficient thermistor array to control a cooling device's current flow based on temperature, reducing thermal load on components and eliminating the need for a microprocessor controller.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a heat sink and cooling fan are used to dissipate thermal energy from high-power LED fixtures, then thermal control is improved, but device complexity and manufacturing cost increase due to the need for microprocessor-based controllers
Solution Approach 1:
The thermistor array automatically senses heat sink temperature and controls cooling fan operation without external control circuits. The system self-regulates by using the thermistor's temperature-dependent resistance to directly modulate fan power, eliminating the need for microprocessors or complex control logic while maintaining effective thermal management
Solution Approach 2:
The patent replaces electronic control systems (microprocessors, sensors, control circuits) with a passive thermal-responsive component (negative coefficient thermistor array). The thermistor's electrical resistance automatically changes with temperature, providing direct feedback control of the cooling fan through purely electrical-thermal coupling without mechanical or complex electronic intervention
2Temperature
If conventional thermal control systems with controllers are used, then temperature management is achieved, but manufacturing cost increases due to additional components
Solution Approach 1:
The thermistor array performs dual functions: sensing temperature and controlling cooling fan operation. This self-service approach eliminates multiple discrete components (temperature sensors, control circuits, microprocessors) that would increase assembly steps and manufacturing cost, while maintaining effective temperature management through the thermistor's inherent temperature-resistance relationship
Solution Approach 2:
The patent combines the temperature sensing function and cooling control function into a single thermistor array component. By merging these functions that would traditionally require separate sensors and control circuits, the design reduces component count, simplifies assembly, and lowers manufacturing cost while achieving effective thermal control
3Quantity of substance
If thermal energy dissipation is insufficient in high-power LED fixtures, then component density can be maintained, but thermal stress increases leading to reduced efficiency and potential failure
Solution Approach 1:
The negative coefficient thermistor array provides automatic feedback control of the cooling system. As heat sink temperature rises, the thermistor's resistance decreases, increasing power to the cooling fan to enhance heat dissipation. This closed-loop feedback mechanism dynamically adjusts cooling capacity to match thermal load, preventing thermal stress accumulation and maintaining component reliability under varying operating conditions
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 design effectively manages thermal energy dissipation, maintaining performance and reducing component stress, thereby enhancing the reliability and efficiency of high-power LED fixtures without the added complexity and cost of a microprocessor-based control system.
Implementation Method 1
A light-emitting diode and a negative coefficient thermistor array are mounted on the first printed circuit board. The negative coefficient thermistor array controls said current flow from the power supply to the cooling device based on a temperature of the heat sink
Implementation Method 2
Thermal control of light-emitting diodes involves the transfer of thermal energy from the light-emitting diode. Accordingly, one aspect of light-emitting diode fixture design involves efficiently transferring as much thermal energy as possible away from the PN junction of the light-emitting diode. This can generally be accomplished, at least in part, through the use of a heat sink.
Implementation Method 3
A cooling device is disposed within the first housing portion and is in fluid communication with the second housing portion
Data Source
AI summary
A light-emitting diode fixture comprises spaced-apart first and second housing portions. There is a cooling device disposed within the first housing portion. The cooling device is in fluid communication with the second housing portion. First and second printed circuit boards are disposed within the second housing portion. A light-emitting diode and a negative coefficient thermistor array are mounted on the first printed circuit board. The light-emitting diode and the negative coefficient thermistor array are each thermally coupled to a heat sink. A rectifier is mounted on the second printed circuit board. The rectifier is electrically connected in series with the negative coefficient thermistor array and the cooling device. Current used to power the cooling device flows from the rectifier through the negative coefficient thermistor array to the cooling device.