Flicker Resisting MOSFET for LED Dimming
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Solution Overview
Problem
Phase-cut dimmers for LED lighting often produce perceptible flicker or shimmer, especially at lower light levels, due to current variations caused by AC line transients and dimmer instability, which existing ripple reduction circuits fail to address efficiently, wasting energy by filtering both low and high load ripples.
Innovation Solution
A system using a flicker resisting MOSFET operated in linear mode at low light levels to reduce flicker and in saturation mode at high light levels, allowing full power to the LED, with a controller adjusting the MOSFET's impedance to minimize power loss and reduce undershoot and overshoot during dimming transitions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a ripple reduction circuit is used to reduce flicker and shimmer at low light levels, then flicker and shimmer are reduced, but energy is wasted by filtering both low and high load ripples
Solution Approach 1:
The circuit dynamically switches between two operational modes based on load conditions: a first circuit configuration is used when load current is below a threshold level to reduce flicker, and a second circuit configuration is used when load current is at or above the threshold level to eliminate energy waste. This dynamic adaptation resolves the contradiction by applying flicker reduction only when necessary.
Solution Approach 2:
The circuit changes its electrical parameters (impedance, filtering characteristics) based on the load current level. At low current levels, the circuit parameters are adjusted to provide flicker reduction; at high current levels, the parameters are changed to bypass the filtering function, thereby eliminating energy waste while maintaining efficiency.
2Object-affected harmful factors
If a ripple reduction circuit filters out low light shimmer and flicker, then flicker is reduced, but normal output current ripple at higher loads is also filtered out causing energy waste
Solution Approach 1:
The ripple reduction function is segmented into two distinct circuit paths: one path handles low load currents with flicker reduction filtering, while the other path handles high load currents with minimal filtering. This segmentation allows the system to apply appropriate filtering only when needed, avoiding energy waste at high loads.
Solution Approach 2:
The circuit is designed with multi-functionality to handle both flicker reduction and efficient power delivery. The same circuit structure can operate in two functional modes: flicker attenuation mode for low loads and efficient power transmission mode for high loads, making it universally applicable across different operating conditions without energy waste.
3Ease of operation
If phase-cut dimming is used for LED lighting, then dimming control is achieved, but perceptible flicker or shimmer occurs especially at lower light levels
Solution Approach 1:
An intermediary circuit is introduced between the phase-cut dimmer and the LED load. This intermediary circuit detects the dimming level and applies appropriate filtering or correction to eliminate flicker and shimmer caused by phase-cut dimming, while preserving the dimming control functionality. The intermediary acts as a mediator that reconciles the conflicting requirements of dimming control and flicker elimination.
Data Source
AI summary
Systems, devices, and methods for dimming of solid state lighting reduce ripple and flicker at low load dimming levels (low LED current, lower light levels) yet provide full power to the load at high load dimming levels (high LED current, higher light levels) thereby reducing power loss compared to conventional dimming techniques. When dimming to lower light levels a flicker resisting metal oxide semiconductor field effect transistor (MOSFET) connected to the LED operates in linear mode such that the relationship of its drain-source voltage to the LED current is resistive to provide flicker reduction. Conversely, at higher light levels the flicker resisting MOSFET is operated in saturation mode such that full power is supplied to the LED as flicker reduction is less needed. The disclosed techniques also reduce undershoot and overshoot of the LED voltage during transitions in dimming control from high to low and low to high respectively.