Adaptive Bleeder Circuit for Stable TRIAC Dimming
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Solution Overview
Problem
Conventional dimmable lighting circuits using TRIACs face instability and flickering issues due to insufficient holding current, especially when the load current is low, leading to inconsistent LED lighting.
Innovation Solution
A control circuit comprising a voltage divider, controller, and adaptive bleeder that generates a dimming signal and control signal to draw a bleeder current from the input terminal, ensuring the sum of bleeder and load currents exceeds the minimum holding current of the TRIAC, thereby maintaining a stable ON state and preventing flickering.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If the load current is reduced to achieve dimming, then the lighting intensity is reduced, but the TRIAC holding current requirement is not met causing flickering
Solution Approach 1:
The patent introduces a bleeder circuit as an intermediary component that draws additional current from the TRIAC to supplement the load current. This mediator ensures the total current through the TRIAC exceeds the holding current threshold, maintaining TRIAC stability while allowing the actual load current to be reduced for dimming purposes.
Solution Approach 2:
The patent dynamically adjusts the bleeder current parameter based on the dimming level. As the load current decreases during dimming, the bleeder circuit compensates by increasing its current draw to maintain the total current above the TRIAC holding current requirement, thus preserving reliability across different illumination levels.
2Reliability
If a fixed bleeder resistor is used to maintain TRIAC holding current, then the TRIAC stability is improved, but the power consumption increases
Solution Approach 1:
The patent replaces the fixed bleeder resistor with a dynamic bleeder circuit controlled by an additional PWM signal. This allows the bleeder current to vary dynamically - being higher when dimming is active (to maintain TRIAC stability) and lower or zero when full brightness is required (to minimize power consumption), thus resolving the contradiction between reliability and energy loss.
Solution Approach 2:
The bleeder circuit operates periodically in sync with the dimming control cycle. During the dimming phase, the bleeder current is activated to ensure TRIAC holding current is met. During non-dimming phases, the bleeder current is reduced or eliminated, minimizing unnecessary power consumption while maintaining TRIAC stability when needed.
Data Source
AI summary
The present invention provides a control circuit for dimming LED lighting. The control circuit comprises a voltage divider, a controller and an adaptive bleeder. The voltage divider receives an input voltage from an input terminal to generate a dimming signal. The controller generates a switching signal in response to the dimming signal. The controller further generates a control signal in response to the input voltage. The adaptive bleeder receives the control signal and draws a bleeder current from the input terminal in response to the control signal.