AC LED Lighting Current Regulation for Low-Intensity Dimming
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Solution Overview
Problem
Existing direct drive AC LED lighting systems fail to support dimming down to very low LED current levels due to reliance on voltage drops for control, leading to unacceptable performance variations in luminance and color match at low intensity levels.
Innovation Solution
An AC lighting system utilizing a linear current regulator and field effect transistors (FETs) with a controller that rotates ON times across stages and employs bootstrap conditioning networks to maintain current uniformity, allowing dimming down to zero current without relying on LED forward conduction, and uses level shifted drives to control switches.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If LEDs are driven at very low current levels to achieve low intensity lighting, then the lighting system can reach particular points in color space with low intensity, but the variation in LED light output becomes unacceptable relative to performance requirements
Solution Approach 1:
The patent changes the control parameter from voltage-based to current-based control. By using a current regulator to directly control the forward current through each LED, the system maintains consistent current levels even at low intensity settings, thereby preserving color match consistency across the full dimming range including very low current levels.
2Ease of operation
If voltage drops across LEDs are used for control in direct drive AC systems, then the system can be powered directly from AC mains, but the system fails to support dimming down to very low LED current levels
Solution Approach 1:
The patent introduces a current regulator as an intermediary component between the AC power source and the LEDs. This current regulator actively controls the forward current through each LED, enabling precise dimming control down to very low current levels while maintaining direct AC drive capability without requiring additional power supply circuitry.
3Manufacturing precision
If LEDs are binned during manufacturing to ensure similar characteristics at moderate to high current levels, then consistency is achieved at those levels, but the LEDs exhibit much wider variation at low current levels
Solution Approach 1:
The patent employs individual current regulation for each LED that maintains precise current control across all operating levels. By using feedback-based current regulation, the system compensates for the inherent variations in LED characteristics at low current levels, ensuring consistent performance and color match even for LEDs from different bins when operated at low intensity.
Data Source
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AI summary
An AC lighting system where the intensity and/or color may be controlled by varying an output current level of a linear current regulator between a first current level and a second current level and/or varying ON times of a plurality of LED stages, respectively. When the current reaches the second current level, the output current level of the linear current regulator may be maintained at the second current level while ON times are varied is provided. Also provided is an AC lighting system where each switch may be selectively operated to provide power to a bootstrap conditioning network during the period of time when the applied voltage is insufficient to turn on the one or more LEDs corresponding to the respective switch when an LED ON time is short, such that power is provided to respective level shifted drive.