Linear Bypass Circuit for LED String Color Control
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional LED dimming methods suffer from efficiency penalties, electromagnetic interference, and inability to mimic the color temperature change of incandescent bulbs, resulting in suboptimal light quality and increased component costs.
Innovation Solution
An electrical circuit with linear mode transistors and bypass transistors is used to drive LED strings, allowing for fine-tuning of color temperature by controlling current ratios between white and color LEDs, eliminating the need for inductors and minimizing EMI, while operating from a standard TRIAC dimmable constant current power supply.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If duty cycling LED strings at high frequency is used to modulate light intensity, then color control and dimming function are achieved, but electromagnetic interference increases and efficiency decreases
Solution Approach 1:
The patent replaces the switching-based mechanical control system with a linear mode transistor system that continuously adjusts current without abrupt on/off transitions, eliminating the mechanical switching action that generates EMI while maintaining color and intensity control capabilities
Solution Approach 2:
The patent changes the operating parameter from binary switching (on/off) to continuous linear modulation by controlling transistor gate voltages, allowing smooth adjustment of LED current and light output without the harmful effects of high-frequency switching
2Ease of operation
If duty cycling LED strings at high frequency is used to modulate light intensity, then color control and dimming function are achieved, but power efficiency decreases
Solution Approach 1:
The patent maintains continuous current flow through the LED strings controlled by linear mode transistors, eliminating the intermittent duty cycling approach. This continuous operation at adjusted current levels is more efficient than switching at full current, as it avoids the efficiency penalties of high-frequency switching and allows for smoother, more energy-effective dimming control
3Loss of energy
If LED current is reduced for dimming, then power efficiency improves, but color temperature does not shift as expected
Solution Approach 1:
The patent segments the LED load into multiple parallel strings with different color characteristics (e.g., warm white and cool white LEDs). By independently controlling the current through each segment using linear mode transistors, the system can adjust the mix of color temperatures while maintaining overall dimming control, achieving both efficiency and expected color temperature shifts
Solution Approach 2:
The patent applies different control characteristics to different LED strings based on their local color properties. Each LED string is controlled by its own linear mode transistor with adjusted gate voltage, allowing local optimization of current distribution to achieve desired color temperature mixing while maintaining overall system efficiency
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 optimizes power efficiency, adjusts intensity and color characteristics, and mimics the color temperature change of incandescent bulbs, improving light quality and reducing component costs by minimizing EMI and eliminating the need for inductors.
Implementation Method 1
A light-emitting diode (LED) emits incoherent narrow-spectrum light when the diode is electrically biased in the forward direction of the p-n junction inside of the diode
Implementation Method 2
LEDs typically have higher luminous efficacy, i.e. lumens per watt, than conventional light sources
Implementation Method 3
The bypass transistor is coupled to one of the color strings. The bypass transistor is operating in a linear mode
Data Source
AI summary
An electrical circuit is described that comprises a first string and second LED string coupled in parallel, a first and second transistor, at least one bypass transistor, and a controller. The first transistor is coupled to the first LED string at a first terminal of the first transistor. The second LED string includes multiple LED color strings coupled in series. The second transistor is coupled to the second LED string at a first terminal of the second transistor. The bypass transistor is coupled to one of the color strings. A first terminal of the bypass transistor is coupled to a first terminal of the color string. The second terminal of the bypass transistor is coupled to a second terminal of the color string. The controller controls a gate voltage of the first and second transistors and the bypass transistor to operate all transistors in linear modes.