Cascade LED Driver PWM Control for Color Mixing Efficiency
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Solution Overview
Problem
Current methods for modulating light output from multiple-color LED systems, such as those used in high-power applications, suffer from efficiency penalties due to the need to regulate current across different-colored LED strings, leading to inefficient voltage regulation and reduced overall efficiency.
Innovation Solution
A circuit system utilizing digitally-timed waveform signals and a digital waveform generator to precisely control the current to each LED string, allowing for precise 'quanta' of delivered current and enabling the coexistence of lower power LEDs with higher power LEDs in series, while using a microprocessor to manage the LED strings and optimize efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If current modulation is used to control light output from different-colored LED strings, then color control is achieved, but efficiency penalty increases due to disproportionate voltage drops
Solution Approach 1:
The patent applies pulse-width modulation (PWM) to periodically switch LED strings on and off at different duty cycles. This allows precise control of average current to each LED string without continuous voltage regulation, eliminating the efficiency penalty of regulating different voltage drops while maintaining color control capability.
Solution Approach 2:
The patent segments the LED control system into independent PWM-controlled channels for different colored LED strings. Each string can be controlled independently with its own duty cycle, allowing efficient current delivery without the need for a common regulated current source that would suffer from voltage mismatch losses.
2Adaptability or versatility
If duty cycling is used to modulate LED output, then color control is achieved, but LED efficiency decreases due to full current rating operation
Solution Approach 1:
The patent changes the operating parameters by using PWM duty cycles less than 100%, allowing LEDs to operate at reduced average current while maintaining peak current capability. This optimizes LED efficiency by avoiding continuous operation at full current rating while still achieving the desired color mixing and dimming through temporal modulation.
3Device complexity
If bus voltage is sized to the longest LED string, then voltage regulation is simplified, but shorter strings suffer disproportionate voltage drops
Solution Approach 1:
By using PWM switching, the system can apply full bus voltage to each LED string periodically without requiring continuous voltage regulation. The switching nature of PWM allows the bus voltage to be sized for the highest voltage requirement without penalty, as each LED string receives full voltage during its on-period, eliminating the continuous voltage drop losses in shorter strings.
4Illumination intensity
If multiple different-color LED strings are used to achieve high CRI, then color rendering is improved, but overall efficiency penalty increases
Solution Approach 1:
The patent uses PWM to control multiple different-color LED strings (white, amber, red, green) with independent duty cycles. This allows high CRI to be achieved by mixing lights from multiple strings while maintaining high efficiency, as each string operates from the same voltage bus without continuous regulation losses, and the overall output is controlled through temporal modulation rather than resistive voltage matching.
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 achieves high-fidelity color rendering and tunable white light with significantly improved system efficiency by allowing each LED string to operate at continuous, arbitrary precise current levels, reducing energy loss and enhancing LED efficacy.
Implementation Method 1
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
Implementation Method 2
A light-emitting diode (LED) is a semiconductor diode that emits incoherent narrow-spectrum light when electrically biased
Data Source
AI summary
An electrical circuit is disclosed and methods for controlling the same. The electrical circuit may comprises a plurality of color strings coupled in series, where each color string has at least one lamp, preferably a light emitting diode. Improved efficiency may be accomplished in some embodiments using certain of the disclosed systems and methods.