Dual Feedback Loop Controller for Flicker-Free Dimmable LED Lighting
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Solution Overview
Problem
Dimmable LED lighting systems experience visible flicker due to slow reaction times and fluctuations in electrical current, particularly at low dimming levels, as the optical output of LEDs responds quickly to changes in electrical input, making existing phase-cut dimmer systems inadequate for stabilizing light output.
Innovation Solution
A controller with a power converter and a controllable constant current source, featuring a first feedback circuit to adjust the power converter and a second feedback circuit to control a supplementary output load in parallel, which absorbs transient variations and provides finer resolution control, reducing or eliminating visible flicker by adjusting the output load faster than the power converter.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single feedback circuit controls the power converter in phase-cut dimmer systems, then the system structure remains simple, but visible flicker occurs due to slow reaction time and coarse resolution control
Solution Approach 1:
The single feedback circuit is segmented into two independent feedback circuits: a first feedback circuit for coarse control of the power converter and a second feedback circuit for fine control of the supplementary output load. This segmentation allows each circuit to operate with optimized response characteristics, eliminating visible flicker while maintaining system stability.
Solution Approach 2:
A supplementary output load is introduced as an intermediary element between the power converter and the LED lighting circuit. This intermediary absorbs transient power variations and provides an additional control degree of freedom, enabling the second feedback circuit to compensate for fluctuations that the first feedback circuit cannot address quickly enough.
2Reliability
If the feedback circuit operates with coarse resolution to maintain simple control, then device complexity is reduced, but visible flicker persists at low dimming levels
Solution Approach 1:
The control function is segmented between two feedback circuits with different resolution characteristics. The first feedback circuit provides coarse control for overall power management, while the second feedback circuit provides fine resolution control for suppressing visible flicker, particularly at low dimming levels where precision is most critical.
Solution Approach 2:
The second feedback circuit applies excessive control action specifically targeted at flicker suppression. By dedicating this circuit solely to detecting and correcting small fluctuations in LED current, the system achieves finer resolution control where needed without requiring the entire control system to operate at high resolution.
3Reliability
If the power converter is controlled to provide stable power, then energy conversion is efficient, but transient variations cause visible flicker due to slow response time
Solution Approach 1:
The supplementary output load acts as a buffer intermediary that absorbs transient power variations before they reach the LED lighting circuit. This allows the power converter to operate efficiently with slower response characteristics while the supplementary load compensates for transient fluctuations, maintaining both efficiency and fast transient response.
Solution Approach 2:
The supplementary output load provides beforehand cushioning by being pre-configured to absorb transient power variations. This cushioning effect prevents fluctuations from propagating to the LED circuit, compensating for the power converter's slower response time without requiring the converter itself to respond faster.
Data Source
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AI summary
A controller for a for a dimmable LED lighting circuit is disclosed, the controller comprising: an LED current controller configured to set a current of a constant current source In dependence on a conduction angle of the phase-cut dimmer; a first feedback circuit configured to control the circuit's power converter in dependence on the constant current source by adjusting an output of the power converter; and a second feedback circuit configured to control a supplementary output load arranged In parallel with the series arrangement of the constant current source and plurality of LEDs, wherein the second feedback circuit Is operable to adjust the supplementary output load faster than the first feedback circuit adjusts the output of the power convertor. A driver and lighting circuit also disclosed, as is a method for controlling a dimmable lighting circuit.