LED Driving Control Circuit for Flicker Elimination
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Solution Overview
Problem
Existing LED driving systems suffer from visible flickers due to asymmetry in valley switch operation, leading to inconsistent energy transmission and user experience issues, especially during dimming.
Innovation Solution
A control circuit and method that generates a ZCD pulse signal and a minimum turn-off time signal to control the switching device, ensuring it turns on when the feedback signal decreases to zero and the minimum turn-off time is passed, eliminating low-frequency flickers by maintaining consistent initial primary current values and introducing a latched ZCD pulse and delayed minimum turn-off time signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If the switching device is controlled to turn on at different valleys during dimming operation, then the dimming function is achieved, but visible flickers occur due to asymmetry in valley switch operation
Solution Approach 1:
The patent changes the control parameter from fixed valley switching to dynamic switching based on feedback signal characteristics. By detecting whether the feedback signal is positive or negative and selecting different switching strategies accordingly, the system maintains symmetric operation across all valleys, eliminating flickers while achieving dimming control through parameter adjustment rather than fixed timing
Solution Approach 2:
The patent introduces feedback-based control where the switching decision is based on the real-time state of the feedback signal from the transformer. The control circuit detects the polarity and magnitude of the feedback signal to determine the optimal switching moment, creating a closed-loop system that automatically adjusts switching timing to maintain symmetry and eliminate visible flickers during dimming operation
2Productivity
If the switching device turns on during dead time when feedback signal is negative, then valley switching is achieved, but initial primary current values become inconsistent causing low-frequency flickers
Solution Approach 1:
The patent dynamically changes the switching strategy based on the feedback signal parameter (positive or negative state). When feedback is negative, the system waits for the next positive feedback cycle before switching, ensuring consistent initial primary current conditions. This parameter-based decision-making ensures reliable current consistency while maintaining high switching frequency through efficient valley utilization
3Reliability
If minimum turn-off time is extended to ensure consistent switching, then reliability is improved, but switching frequency decreases and dimming performance deteriorates
Solution Approach 1:
The patent makes the turn-off time dynamic rather than fixed. The control circuit adjusts the minimum turn-off time based on the actual feedback signal characteristics and operating conditions. This dynamic adjustment allows the system to maintain reliable switching consistency when needed while achieving high switching frequencies and excellent dimming performance during normal operation, resolving the contradiction between reliability and productivity
Data Source
AI summary
The present invention discloses a control circuit, a LED driving system, and a LED driving method. The control circuit receives a feedback signal from the power converter and generate a ZCD pulse signal accordingly, indicating one or more moments when the feedback signal decreases to zero, and receives a dimming signal and generate a minimum turn-off time signal accordingly, indicating the moment when a minimum turn-off time is passed. The control circuit generates a first turn-on signal according to the ZCD pulse signal and the minimum turn-off time signal to control a switching device within the power converter to turn on when the feedback signal decreases to zero and the minimum turn-off time is passed.