LED Driver Circuit for Dissimilar Color String Lengths
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Solution Overview
Problem
Current methods for driving LEDs in dissimilar color string lengths and with different colors suffer from efficiency penalties due to the need to regulate current across varying voltage drops, leading to inefficient power conversion and reduced LED efficiency.
Innovation Solution
An electrical circuit that couples color strings in series, using bypass switches and passive storage elements to shunt power and control current distribution among strings, allowing for efficient power supply voltage conversion and maintaining high LED efficiency by adjusting power delivery based on coordinated duty cycles and frequencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If current is regulated using a Buck regulator from a common bus voltage source to each LED string, then complete color control is achieved, but efficiency penalty increases due to disproportionate voltage drops across strings of different lengths
Solution Approach 1:
The patent divides the LED driver circuit into separate current sources for each color string, allowing independent current regulation without requiring a common bus voltage source. This segmentation eliminates the efficiency penalty caused by regulating different voltage drops to a common bus, while maintaining the ability to independently control each color string's current for complete color control.
2Device complexity
If duty cycling is used to modulate LED string output, then simple current regulation is achieved, but efficiency decreases due to full current rating operation and switching losses
Solution Approach 1:
The patent employs continuous PWM dimming control that maintains steady-state operation of LED strings without duty cycling on and off. This continuous operation eliminates the efficiency losses associated with switching and allows for smooth dimming control, achieving both simple regulation and high efficiency by operating LEDs continuously at optimized current levels rather than cycling at full current rating.
3Adaptability or versatility
If bus voltage is sized to the longest LED string, then all strings can be powered from a common source, but shorter strings suffer from disproportionately greater voltage drops and reduced efficiency
Solution Approach 1:
The patent eliminates the common bus voltage source architecture and instead provides separate current sources for each LED string. This segmentation allows each string to operate at its optimal voltage and current independently, eliminating the efficiency penalty suffered by shorter strings when powered from a bus sized for the longest string, while still enabling all strings to be controlled from a single controller.
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 achieves high electrical efficiency by optimizing power distribution among LEDs of different colors and lengths, reducing dissipative losses and maintaining stable current while varying power is shunted, thus enhancing overall LED performance and energy efficiency.
Implementation Method 1
a switch coupled in parallel with one of the color strings is configured to shunt power away from the color string to a power supply or to one or more other color strings
Implementation Method 2
passive storage elements are utilized to store shunted power
Implementation Method 3
a current injector is configured to inject or remove current from a node adjacent to a color string
Implementation Method 4
A light-emitting diode (LED) is a semiconductor diode that emits incoherent narrow-spectrum light when electrically biased in the forward direction of the p-n junction
Data Source
AI summary
An electrical circuit is disclosed. The electrical circuit comprises a plurality of color strings coupled in series, where each color string has at least one lamp, preferably a light emitting diode. The color strings may be of dissimilar length and may contain light emitting diodes of different colors. In one embodiment, a switch coupled in parallel with one of the color strings is configured to shunt power away from the color string to a power supply. In another embodiment, a switch coupled in parallel with one of the color strings is configured to shunt power away from the color string to one or more other color strings. In several embodiments, passive storage elements are utilized to store shunted power. In another embodiment, a current injector is configured to inject or remove current from a node adjacent to a color string. In several embodiments the invention is implemented as a light emitting diode driver integrated circuit or chip. Methods are disclosed for producing a desired light output utilizing color strings that may be of dissimilar length and that may contain light emitting diodes of different colors.