LED Backlight Color Control via PWM Phase Shift
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Solution Overview
Problem
LCD backlights with RGB LEDs face non-uniformity in brightness and colorfulness due to variations in LED characteristics and temperature differences, requiring complex and costly feedback systems with multiple sensors for uniformity.
Innovation Solution
A method and system where each LED strip in an LED backlight is adjusted using pulse width modulation (PWM) with time delays or phase shifts to match desired chromaticity and brightness coordinates, utilizing a lookup table to store reference values and adjust duty cycles or amplitudes of PWM currents for RGB LEDs to achieve uniform light output.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If multi-color sensors or temperature sensors are used to monitor LED areas, then uniformity of brightness and colorfulness is improved, but device complexity and cost increase
Solution Approach 1:
The patent extracts only the necessary measurement function by using a single photodetector that measures total light intensity, removing the need for complex multi-color sensors or temperature sensors. The chromaticity information is obtained indirectly through PWM duty cycle relationships rather than direct measurement, simplifying the sensing system while maintaining uniformity control.
Solution Approach 2:
The patent introduces PWM duty cycle as an intermediary parameter to represent chromaticity information. Instead of directly measuring chromaticity coordinates, the system uses the PWM duty cycle ratio between different LED types as a mediator to control and match chromaticity, reducing the need for complex sensors and control circuitry.
2Manufacturing precision
If PWM driving current is adjusted to control chromaticity coordinates, then color uniformity is improved, but control circuitry complexity increases
Solution Approach 1:
The patent implements a feedback control system where the measured light intensity from each LED strip is fed back to adjust the PWM driving current. The controller continuously monitors the intensity values and adjusts the PWM duty cycles to maintain desired chromaticity coordinates, achieving color uniformity through closed-loop control rather than complex open-loop circuitry.
Solution Approach 2:
The patent controls chromaticity by changing the PWM duty cycle parameter of the driving current supplied to different LED strips. By adjusting this single parameter, the system can control the effective contribution of each LED type to the overall light output, thereby achieving desired chromaticity coordinates without complex control circuitry.
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 approach ensures uniform chromaticity and brightness across the LED backlight without the need for multi-color or temperature sensors, simplifying control circuitry and reducing costs while maintaining desired color and brightness standards.
Implementation Method 1
An LCD backlight typically includes a plurality of red, green and blue (RGB) LEDs, regularly arranged to form a number of LED areas, and driven electrically to produce various colors of light including white light
Implementation Method 2
One known feedback system includes a plurality of photo-sensors. Each photo-sensor is configured to individually monitor the chromaticity of the light emitted from a corresponding LED area
Data Source
AI summary
The present invention relates to a light emitting diode (LED) backlight having a plurality of LED strips, in which driving current supplied to each of the plurality of LED strips is adjusted according to measured differences in chromaticity coordinates between the actual light chromaticity and brightness output by each LED strip and a desired light chromaticity and brightness of each LED so that the LED backlight generates light of a desired color with a uniform brightness, and methods of operating the same.