Synchronized PWM Dimming Circuit Eliminates LED Flicker
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing dimmable LED lighting systems experience visible flicker at low dimming levels due to frequency differences between PWM and switch mode converter frequencies, leading to beat frequencies and flicker issues.
Innovation Solution
A lighting circuit with a switch mode power converter delivering a triangular current waveform, where the PWM pulse is delayed until a predetermined current level is reached, ensuring synchronization with the switch mode power converter's timing, thereby preventing beat frequencies and flicker.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If PWM dimming control is applied to LED lighting with switch mode power converter, then dimming capability is improved, but visible flicker occurs at low dimming levels due to frequency mismatch between PWM and converter switching frequencies
Solution Approach 1:
The patent uses a synchronization mechanism where the PWM controller detects the switching frequency of the power converter and adjusts its own switching frequency to match. This feedback-based frequency synchronization eliminates the frequency mismatch that causes beat frequencies and visible flicker during dimming operations.
Solution Approach 2:
The PWM switching frequency is made dynamic rather than fixed. The system automatically adjusts the PWM frequency to match the power converter's switching frequency, which may vary with operating conditions. This dynamic adaptation ensures continuous synchronization and prevents flicker across different dimming levels.
2Illumination intensity
If deep dimming levels are achieved using PWM control, then light output control range is improved, but PWM pulse duration approaches or drops below buck converter switching cycle period causing under sampling and beat frequencies
Solution Approach 1:
The system changes the PWM frequency parameter dynamically to match the power converter switching frequency. By adjusting this critical parameter, the system ensures that PWM pulse duration remains sufficient to properly sample the converter output even at deep dimming levels, preventing under-sampling artifacts and maintaining consistent light output.
Solution Approach 2:
The synchronization mechanism provides real-time feedback about the converter's switching frequency to the PWM controller. This allows the PWM system to adapt its pulse width and frequency to ensure adequate sampling of the converter output, maintaining reliable and consistent light output across the full dimming range.
3Device complexity
If fixed frequency PWM control is used, then control simplicity is improved, but frequency mismatch with variable switching frequency converter causes beat frequencies and flicker
Solution Approach 1:
The system introduces a synchronization mechanism where the PWM controller receives feedback about the power converter's actual switching frequency and adjusts its own frequency to match. This feedback loop adds minimal complexity while effectively eliminating beat frequencies and flicker caused by frequency mismatch.
Solution Approach 2:
The system performs preliminary frequency detection and synchronization before PWM dimming control is applied. By pre-synchronizing the PWM frequency with the converter switching frequency, the system prevents beat frequencies from occurring during subsequent dimming operations.
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
A lighting circuit makes use of a switch mode power converter to drive a solid state lighting arrangement having a lighting unit and a lighting control switch. A pulse width modulation control signal is applied to the lighting control switch for dimming control with an activation pulse during which the lighting unit is activated. The power converter delivers a triangular current waveform and the activation pulse is delayed until a predetermined point within the triangular current waveform. This ensures that the PWM pulse during which the lighting arrangement is turned on has timing which is synchronized with the timing of the switch mode power converter. The prevents beat frequencies so that visible flicker is avoided.