LED Driver PWM Synchronization to Eliminate Flicker
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Solution Overview
Problem
PWM dimming techniques in lighting systems often result in flicker and strobing issues, particularly at frequencies below 100 Hz, which can be problematic for LED lighting systems, and existing solutions like high PWM frequencies or spread-spectrum modulation come with drawbacks such as reduced dimming range, increased cost, or reduced efficiency.
Innovation Solution
Synchronizing the PWM frequency with the line frequency and using randomized phase angles on a cycle-to-cycle basis or across multiple PWM drivers to eliminate or reduce flicker and strobing, without requiring significant additional hardware, by implementing a phase-lock-loop circuit and microcontroller-generated quasi-random delay times.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If PWM dimming is used to control LED brightness, then brightness control is achieved, but flicker and strobing occur at frequencies below 100 Hz
Solution Approach 1:
The patent applies periodic action by synchronizing the PWM frequency to an integer multiple of the line frequency (e.g., 4x or 8x synchronization). This creates a periodic modulation pattern where the PWM cycles are locked to the AC mains frequency, ensuring that the LED turns on and off in sync with the power supply cycles. This periodic synchronization eliminates sub-harmonic modulation and prevents flicker perception while maintaining effective brightness control through duty cycle adjustment.
2Object-affected harmful factors
If high PWM frequency is used to eliminate flicker, then flicker is reduced, but dimming range is reduced
Solution Approach 1:
By synchronizing PWM to line frequency multiples, the patent creates a periodic structure that pushes flicker components to higher frequencies (above 100 Hz) where they are not perceptible to the human eye. This allows the system to maintain a moderate PWM frequency while achieving flicker-free operation, thereby preserving the full dimming range from 0% to 100% without the limitations imposed by simply increasing PWM frequency.
Solution Approach 2:
The patent changes the parameter of PWM frequency synchronization by locking it to integer multiples of the line frequency (4x, 8x, etc.) rather than using fixed high frequencies. This parameter change allows the system to adapt to different line frequencies (50 Hz or 60 Hz) and maintain optimal performance across varying operating conditions while preserving both flicker elimination and full dimming range capability.
3Object-affected harmful factors
If spread-spectrum modulation is used to reduce flicker, then flicker is reduced, but system complexity and cost increase
Solution Approach 1:
The patent employs periodic synchronization of PWM to line frequency multiples, which is implemented using standard microcontroller timer/counter hardware and software. This approach achieves flicker and strobing elimination through frequency locking and phase synchronization without requiring complex spread-spectrum modulation circuits, special hardware components, or sophisticated signal processing algorithms, thereby maintaining low system complexity and cost.
4Object-affected harmful factors
If multiple PWM drivers with different phase angles are used to eliminate strobing, then strobing is reduced, but device complexity increases
Solution Approach 1:
The patent eliminates strobing by synchronizing a single PWM driver to integer multiples of the line frequency, creating a periodic pattern where the LED modulation is locked to the power supply cycles. This single-driver synchronization approach achieves strobing elimination without requiring multiple PWM drivers with different phase angles, thereby maintaining simple device architecture while effectively preventing the translation of temporal light modulation into spatial modulation through motion.
Data Source
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AI summary
PWM-based dimming techniques are provided for lighting systems. The techniques can be used to eliminate or otherwise reduce the potential for strobing and flickering, and may be implemented, for example, in a driver suitable for powering LED lighting systems, but can be used with other suitable light sources as well. In an example embodiment, the potential for line frequency induced flicker, or even line disturbances that are periodic with the line frequency, can be eliminated or reduced by synchronizing the PWM frequency to the line frequency or so-called mains frequency, and the potential for strobing can be eliminated or reduced by either using a randomized phase angle on a cycle-to-cycle basis or by using multiple PWM LED drive circuits all having constant cycle-to-cycle phase angle but a different phase angle from drive circuit to drive circuit.