Arbitrary Pulse Alignment for LED Flicker Reduction
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Solution Overview
Problem
LED flicker occurs in systems using pulse width modulation (PWM) for dimming, which can discourage consumer adoption and is detrimental to the environment due to the inefficiency and toxicity of alternative lighting technologies.
Innovation Solution
An LED system with a PWM controller that generates pulses with an arbitrary alignment, where the leading and trailing portions of the pulse width are varied across successive pulses to suppress flicker by incrementing or decrementing the m % on a pulse-by-pulse basis when switching between head and tail alignment modes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If conventional PWM dimming is used, then linear dimming profile and constant color temperature are achieved, but LED flicker occurs
Solution Approach 1:
The patent dynamically adjusts the pulse alignment mode (head, tail, or center) based on the duty cycle range. The controller switches between different alignment modes as the duty cycle varies, allowing the system to adapt to different operating conditions and eliminate flicker while maintaining linear dimming and constant color temperature.
Solution Approach 2:
The patent changes the pulse alignment parameter (m%) based on the duty cycle range. By adjusting the alignment mode according to the duty cycle value, the system maintains optimal performance across different brightness levels, preventing flicker while preserving the linear dimming characteristic and color temperature stability.
2Adaptability or versatility
If pulse alignment mode is switched between head and tail alignment, then different dimming characteristics are achieved, but undesirable flicker occurs during mode transition
Solution Approach 1:
The patent introduces a center alignment mode as an intermediate step when transitioning between head and tail alignment modes. This preliminary center alignment phase ensures smooth transition and eliminates flicker by avoiding direct switching between head and tail modes, while still providing the flexibility to achieve different dimming characteristics.
Solution Approach 2:
The center alignment mode acts as an intermediary between head and tail alignment modes. When switching between head and tail modes, the system first transitions to center alignment and then to the target mode, using this intermediate state to bridge the transition and prevent flicker while maintaining adaptability.
3Reliability
If arbitrary pulse alignment is used, then flicker is eliminated, but pulse timing complexity increases
Solution Approach 1:
The patent segments the pulse alignment control into distinct modes (head alignment, tail alignment, and center alignment) based on duty cycle ranges. Each mode has a specific alignment percentage (m%), and the controller selects the appropriate mode based on the current duty cycle, simplifying the timing control logic while eliminating flicker.
Solution Approach 2:
The patent uses dynamic mode selection based on the duty cycle range to manage pulse timing complexity. The controller automatically adjusts the alignment mode according to the operating conditions, providing flicker-free operation while keeping the control logic manageable through structured decision-making based on duty cycle thresholds.
Data Source
AI summary
An arbitrary alignment is provided for a series of pulses controlling a switch that in turn controls a current in an LED. Each pulse is generated according to a target time responsive to a reference time in a corresponding cycle of a synchronization clock. Each pulse has a leading portion that precedes its target time and a trailing portion subsequent to its target time. The arbitrary alignment defines the relative size of the leading portion to the trailing portion such that these relative sizes are incrementally changed across successive ones of the pulses.