Multicolor LED Color Stability via Dual Phototransistor Feedback
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Solution Overview
Problem
Existing systems for generating colors in automotive vehicle instrumentation panels using primary-color LEDs face issues with color consistency due to changes over time and temperature variations.
Innovation Solution
An apparatus comprising first and second differently-colored LEDs, optically coupled with phototransistors of varying spectral sensitivities, and a controller that adjusts current to maintain consistent color output by measuring and interpolating output voltages from phototransistors to achieve stable color generation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If primary-color LEDs are used to generate different colors in a vehicle instrumentation panel, then color variety is achieved, but color consistency deteriorates due to changes with age and temperature
Solution Approach 1:
The patent employs photodetectors to continuously monitor the actual color output of the LED combination and feeds this information back to a control system. The controller adjusts the drive currents to the red and green LEDs based on the feedback signal, automatically compensating for color drift caused by aging and temperature changes, thus maintaining consistent color output over time
Solution Approach 2:
The patent dynamically changes the electrical parameters (drive currents) of the LEDs based on detected color output. By adjusting the current ratios to the red and green LEDs, the system compensates for natural color shifts, maintaining a consistent perceived color despite environmental variations and aging effects
2Adaptability or versatility
If the intensity of LEDs is varied to generate different colors, then color range is improved, but color stability deteriorates due to intensity variations with temperature and aging
Solution Approach 1:
The photodetector continuously monitors the actual color output and provides feedback to the controller, which adjusts the drive currents to maintain the desired color ratio. This closed-loop control compensates for intensity variations caused by temperature and aging, ensuring stable color perception even as individual LED intensities change over time
Solution Approach 2:
The system dynamically adjusts the electrical parameters (drive currents) to the red and green LEDs based on detected color output. By changing the current ratios adaptively, the system maintains stable color perception despite variations in individual LED intensities due to temperature and aging
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
The solution ensures consistent and stable color output from the combination of LEDs, maintaining color accuracy regardless of LED aging and temperature changes, providing precise backlight illumination for vehicle dashboards.
Implementation Method 1
The first phototransistor has a first spectral sensitivity and generates an output voltage having a magnitude that varies responsive to the wavelength of light impinging on the first phototransistor from both LEDs
Implementation Method 2
The first LED generates a first nominal color having an intensity that varies responsive to the amount of current flowing through the first LED
Data Source
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AI summary
The color generated by two differently-colored LEDs (206, 208) is maintained over time and different temperatures by sensing their combined output color using two phototransistors (214, 218) having different spectral sensitivities the output voltages of which are correlated to a desired output color. As the combined output color changes, the phototransistors' output voltages will change. The currents provided to the LEDs (206, 208) can thereafter be adjusted to maintain the output voltages and thus maintain the combined output color.