LED Driver Circuitry Disconnect Switch for Flicker Elimination
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Solution Overview
Problem
Conventional LED driver circuits experience noise and flicker at very low dimming levels due to minor fluctuations in power rails, causing shimmering or flickering in the output light, which existing technologies fail to completely eliminate.
Innovation Solution
Incorporating a switch in series with the output, controlled by a decoding circuit that turns off the LED driver current to zero at a predetermined minimum dimming level, using either PWM or 0-10V control signals, to eliminate shimmering and flickering.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If conventional LED driver circuits operate at very low dimming levels, then the LED output brightness is reduced, but noise on power rails causes shimmering and flickering in the output light
Solution Approach 1:
A disconnect switch is introduced as an intermediary component between the LED driver circuit and the LED load. This switch acts as a mediator that completely interrupts the power supply to the LED when the control signal indicates a dimming level below the threshold, preventing noise-induced shimmering and flickering that would otherwise occur at very low dimming levels.
Solution Approach 2:
The system changes the operating parameter of the LED driver by introducing a threshold-based control mechanism. When the control signal falls below a predetermined threshold, the disconnect switch changes the power delivery state from continuous (allowing noise-induced fluctuations) to completely interrupted (eliminating shimmering), thus changing the operational parameter from analog dimming to binary on/off control at low levels.
2Illumination intensity
If PWM dimming is used to reduce LED brightness, then illumination intensity is reduced, but noise causes fluctuations in pulse width perceived as shimmer
Solution Approach 1:
The disconnect switch serves as an intermediary that overrides PWM control at very low dimming levels. When the control signal indicates a dimming level below the threshold, the disconnect switch completely interrupts the LED power supply, preventing noise-induced PWM pulse width fluctuations from causing shimmer, thus ensuring output stability.
Solution Approach 2:
The disconnect switch performs preliminary anti-action by preemptively cutting off power to the LED when the control signal approaches the threshold level. This prevents the harmful effect of noise-induced PWM fluctuations from occurring in the first place, rather than attempting to correct shimmer after it appears.
3Ease of operation
If analog dimming is used to maintain continuous LED current, then smooth brightness control is achieved, but 120 Hz fluctuations appear as flicker at low dimming levels
Solution Approach 1:
The disconnect switch acts as an intermediary that interrupts the continuous analog dimming current when the control signal falls below the threshold. This prevents the 120 Hz fluctuations inherent in analog dimming from causing visible flicker at very low brightness levels, while maintaining smooth brightness control at higher levels.
Solution Approach 2:
The system transitions from continuous periodic analog dimming to a periodic on/off action controlled by the disconnect switch. When the control signal is below the threshold, the disconnect switch creates a periodic interruption pattern that eliminates the harmful 120 Hz flicker associated with continuous analog dimming at low levels.
Data Source
AI summary
A circuit is described which allows an LED driver to be controlled by a control signal in such a manner that at a predetermined dimming level the output current goes to zero instead of continuing to indefinitely low dim levels, thus avoiding the possibility of flickering or shimmer at extremely low dim levels. An electronic circuit for driving an LED load with a conventional LED drive circuit has inputs connected to a power source and output terminals providing regulated output power including a load disconnect switch in series with the LED load which has a control node responsive to a control circuit; and a control input which commands varying levels of input power. The control circuit is configured to be responsive to the control input so that when the control input corresponds to a certain continuous level of dimming, the load disconnect switch is opened.