LED Driver Circuit Synchronization for Flicker-Free Dimming
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Solution Overview
Problem
Conventional LED dimming control systems using switching converters face limitations in achieving very low duty cycles, leading to visible flicker effects and brightness variations due to random delays between PWM control signals and clock signals, especially at low brightness levels.
Innovation Solution
The proposed solution involves an LED driver circuit with a control unit that includes a current control unit, logic circuit, and RS-flip-flop to generate a gate signal independent of the clock signal's phase, ensuring synchronized activation of the switching converter at the beginning of each duty cycle, thereby minimizing random delays and flicker.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the duty cycle is reduced to achieve very low brightness levels, then the brightness control range is improved, but random delay between PWM control signal and LED current increases causing visible flicker
Solution Approach 1:
The patent applies preliminary action by synchronizing the switching converter's activation with the PWM control signal's rising edge before the random delay can cause flicker. The logic circuit ensures the switching converter is activated at the precise moment the PWM signal transitions high, eliminating the random delay effect and enabling very low duty cycles without visible flicker.
2Reliability
If the minimum on-time is increased to avoid flicker, then flicker-free operation is improved, but the minimum duty cycle increases limiting brightness control range
Solution Approach 1:
The patent extracts the timing synchronization function from the clock signal-based control mechanism. By using a logic circuit that directly synchronizes with the PWM control signal's rising edge rather than relying on clock signal phases, the system eliminates the minimum on-time constraint and achieves very low duty cycles without flicker.
3Reliability
If the switching converter is activated at the beginning of each duty cycle independently of clock phase, then random delay is reduced, but control circuit complexity increases
Solution Approach 1:
The patent introduces a logic circuit as an intermediary between the PWM control signal and the switching converter's activation. This logic circuit receives the PWM control signal and generates a synchronized activation signal that triggers the switching converter at the precise moment needed, eliminating random delay while adding minimal circuit complexity.
Data Source
AI summary
A system for supplying current to a load is disclosed. One embodiment provides a switching converter for providing a load current to the load. The switching regulator includes a switching circuit. A current control unit generates a modulated current control signal representing a desired load current. The switching circuit is driven dependent on the modulated current control signal. A logic circuit receives a pulse-width-modulated control signal representing a desired dimming ratio and is configured to generate a gate signal for driving the switching circuit dependent on the current control signal during a duty cycle of the pulse-width-modulated control signal. The logic circuit is configured to activate the switching converter, independent on the state of the current control signal, at the beginning of the duty cycle of the pulse-width-modulated control signal.