Time Division Multiplexing for Solid State Lighting Color Control
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Solution Overview
Problem
Existing PWM illumination control systems for solid state lighting devices impose a non-uniform load on power supplies, leading to inefficiency and require expensive feedback control mechanisms with narrow spectral detectors for accurate color adjustment.
Innovation Solution
A solid state lighting system using time division multiplexing with a constant current power source and a R/G/B switch to cycle energy among red, green, and blue channels, suppressing flicker and allowing a broadband photo sensor to measure light output for feedback control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If PWM control is used to independently control multiple LED channels, then color and intensity control is achieved, but power supply load becomes highly non-uniform causing stress and requiring large power supply capacity
Solution Approach 1:
The patent applies periodic action by cycling through different LED color channels in sequential time slots rather than simultaneously. Each channel receives power in alternating periods, creating a periodic power delivery pattern that maintains constant average power while achieving color mixing through temporal separation. This resolves the power supply stress issue while preserving color control capability.
Solution Approach 2:
The patent transitions from spatial simultaneous activation of multiple channels to temporal sequential activation. By adding the time dimension to the control strategy, channels are activated at different time slots rather than simultaneously, transforming the power delivery pattern from fluctuating to constant while maintaining the ability to produce various colors through temporal multiplexing.
2Adaptability or versatility
If PWM control is used with rapid power cycling, then color adjustment is achieved, but power supply must be large enough to supply full power even though it is consumed only part of the time
Solution Approach 1:
The system uses periodic cycling through color channels where each channel is activated in sequential time slots. This periodic activation pattern ensures that the power supply delivers constant power continuously rather than fluctuating between 0% and 100%, allowing the power supply to be sized for the average power requirement rather than peak power, reducing overall capacity needs.
Solution Approach 2:
The patent maintains continuous useful action by ensuring the power supply operates at constant power level throughout operation rather than cycling on and off. The temporal multiplexing of channels ensures that while individual channels are activated periodically, the power supply itself operates continuously at a steady level, eliminating waste and optimizing power supply utilization.
3Measurement precision
If three different narrow spectral light sensors are used for feedback control of RGB channels, then accurate color measurement is achieved, but system cost increases significantly
Solution Approach 1:
The patent applies universality by using a single broadband photosensor that can detect all color channels (red, green, blue) rather than requiring separate specialized sensors for each channel. The temporal separation of channel activation allows one sensor to sequentially measure all channels, making the sensor multi-functional and eliminating the need for three separate narrowband sensors, thereby reducing system cost while maintaining measurement capability.
Solution Approach 2:
The feedback measurement uses periodic action by cycling the single broadband sensor through measurements of different color channels during their respective time slots. The sensor sequentially measures red, green, and blue channels as they are activated in different periods, achieving complete color feedback with one sensor instead of requiring simultaneous three-sensor measurement systems.
4Reliability
If current is diverted through dummy load resistors to avoid power variations during PWM, then power cycling is avoided, but power efficiency decreases substantially
Solution Approach 1:
The patent uses periodic action to cycle through different LED channels in sequential time slots, allowing the power supply to deliver constant power to whichever channel is currently active. This eliminates the need for dummy load resistors because the power supply naturally maintains constant output by switching between channels periodically, achieving both power stability and efficiency without energy-wasting diversion paths.
Solution Approach 2:
The system maintains continuous useful action by ensuring that constant power from the power supply is always converted into useful light output through temporal multiplexing of channels. Unlike dummy load approaches where power is wasted in resistors, this method ensures continuous productive conversion of electrical power to light, maintaining high efficiency while achieving power supply stability.
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 reduces power supply stress, enhances efficiency by maintaining a constant current, and allows for cost-effective, accurate color control with a single broadband sensor, improving power management and color consistency.
Implementation Method 1
Solid state lighting devices include light emitting diodes (LEDs)
Data Source
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AI summary
A multi-channel light source has different channels for generating illumination of different channel colors corresponding to the different channels. An electrical power supply selectively energizes the channels using time division multiplexing to generate illumination of a selected time-averaged color.