Color-Balanced LED Backlight Using Single Photodetector Feedback
Solution Overview
Problem
Existing backlights for avionics LCD screens, particularly those using fluorescent tubes, face challenges such as high voltage requirements, fragility, low efficiency at low temperatures, and difficulty in maintaining color balance across varying brightness levels, which are addressed by transitioning to LED-based solutions but require complex adjustments to maintain color balance.
Innovation Solution
A color-balanced LED backlight system utilizing feedback loops for each color, with a single photodetector and measurement modulation to isolate and control the brightness of individual color groups, allowing for precise color balance over a wide range of illumination without the need for multiple photodetectors or color filters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple photodetectors with color filters are used to measure each color separately, then color balance measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The patent combines multiple color measurement functions into a single photodetector by using sequential LED activation. The microcontroller activates red, green, and blue LEDs separately in time-division multiplexing, allowing one photodetector to measure all three color components through sequential sampling, thereby eliminating the need for multiple photodetectors and color filters while maintaining measurement precision
Solution Approach 2:
The system uses periodic activation of different colored LEDs in sequence, with each color group being activated during specific time periods. This periodic action allows a single photodetector to distinguish between different colors by measuring light intensity during the respective activation periods, achieving color separation without physical filters
2Adaptability or versatility
If the brightness of each color LED is controlled independently over a wide range, then illumination adaptability is improved, but maintaining color balance becomes more difficult
Solution Approach 1:
The patent implements feedback control by continuously measuring the actual light output of each color LED group using the photodetector and comparing it with target values. The microcontroller adjusts the current to each LED group based on the measurement feedback, automatically maintaining accurate color balance across the entire brightness range without requiring complex manual calibration
Solution Approach 2:
The system dynamically adjusts the brightness of each color LED group in real-time based on feedback measurements. Rather than using fixed ratios, the control system continuously adapts the current to each LED group to maintain optimal color balance as operating conditions change, enabling wide illumination adaptability while simplifying color balance maintenance
3Illumination intensity
If fluorescent tubes are used for backlighting, then broad color spectrum output is achieved, but reliability and durability worsen due to fragility and unexpected failures
Solution Approach 1:
The patent replaces the mechanical fluorescent tube system with solid-state LED technology. The fluorescent tube (a fragile mechanical component requiring high voltage) is substituted with robust LED chips that convert electrical energy directly to light through electroluminescence, eliminating the mechanical fragility and high voltage requirements while maintaining broad color spectrum output through red, green, and blue LED combinations
4Illumination intensity
If high voltage power supply is used for fluorescent tubes, then sufficient illumination output is achieved, but safety and reliability worsen due to high voltage requirements
Solution Approach 1:
The patent replaces the high voltage power supply system with low-voltage LED driver circuits. Instead of using high voltage to excite fluorescent gas, the system uses low-voltage electrical current to directly excite LED semiconductor materials, producing the same illumination output without the harmful high voltage, thereby improving safety and reliability
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 enables a wide range of illumination with precise color balance, simplifying the design and reducing costs by using a single photodetector and minimizing the need for calibration, while maintaining color accuracy across varying brightness levels and temperatures.
Implementation Method 1
A single photodetector senses light output for each feedback loop
Implementation Method 2
a set of groups of solid state lamps, the lamps of each group providing a different color of light
Data Source
AI summary
A color balanced solid-state backlight provides feedback control of each color using a single photodetector by imposing a modulation pattern on the solid-state lamps revealing individual colors to the photodetector. The photodetector signal provides feedback controlling color balance over a small range of instantaneous brightness less than larger range of average brightness of the display to provide for accurate color balance throughout a large range of average brightnesses.