NTC Thermistor Current Limiting for LED CCT Stability
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Solution Overview
Problem
LED light engines face challenges in maintaining consistent color correlated temperature (CCT) during startup, as LEDs initially produce undesirable colors due to temperature variations, and existing solutions like PWM and PTC thermistors are complex or inefficient.
Innovation Solution
A light engine design featuring an array of LEDs with a control circuit that includes a temperature variable resistance component and a switch, selectively connecting an NTC component to limit current during initial energization, ensuring consistent CCT by adjusting current distribution between LED strings as they heat up.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If PWM control is implemented to adjust LED current based on temperature, then CCT consistency is improved, but device complexity increases
Solution Approach 1:
The patent employs a temperature-dependent resistor (thermistor) that automatically adjusts current distribution to LED strings based on temperature without requiring external control circuits. The thermistor's resistance changes with temperature, naturally compensating for CCT shifts as LEDs warm up, eliminating the need for complex PWM control circuitry while maintaining CCT consistency.
Solution Approach 2:
The patent introduces a temperature-dependent resistor as an intermediary component between the power supply and LED strings. This intermediary automatically modulates current distribution based on temperature, serving as a passive mediator that simplifies the control system while achieving the desired CCT stability.
2Stability of the object's composition
If PTC thermistor is used to shunt current, then CCT consistency is improved, but energy efficiency deteriorates due to power consumption
Solution Approach 1:
Instead of using a PTC thermistor that shunts current (wasting energy), the patent inverts the approach by using an NTC thermistor in series with LED strings. The NTC thermistor's decreasing resistance with temperature naturally increases current to the strings as they warm up, compensating for their decreased light output without dissipating significant power.
Solution Approach 2:
The patent converts the harmful effect of LED light output decreasing with temperature into a beneficial control mechanism. By using an NTC thermistor whose resistance decreases with temperature, the system automatically increases current to the LED strings as they warm up, turning the temperature-induced performance degradation into a self-correcting feature that maintains CCT consistency while minimizing energy loss.
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 reduces variations in CCT over time, providing a consistent color output from startup to steady-state operation, improving user perception and reducing energy losses associated with PTC thermistors.
Implementation Method 1
The control circuit includes a temperature variable resistance component and a switch selectively connecting an NTC component to limit current during initial energization
Implementation Method 2
The array of LEDs comprises at least one first string of first LEDs connected in series which, when energized, output light having a first wavelength range
Data Source
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AI summary
An array of LEDs having output light in different wavelength ranges. A control circuit connected to the array includes a temperature variable resistance component and a switch selectively connecting the component to the array. The control circuit limits the current applied to at least some of the LEDs during initial energization of the LEDs prior to steady-state operation of the LEDs. Variations over time of a color correlated temperature (CCT) of output light of the energized array are reduced.