LED Dimming Circuit Synchronizes PWM with AC Voltage
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Solution Overview
Problem
Existing LED lighting devices using PWM dimming often experience flicker or shimmer due to unsynchronized PWM signal frequencies with rectified AC voltage frequencies, posing potential human health concerns.
Innovation Solution
An LED lighting device incorporating a luminescent circuit, adjustable current source, detecting circuit, and dimming control circuit that synchronizes the PWM signal frequency with the rectified AC voltage by using a comparator and PWM signal generator to adjust the duty cycle of the LED current, ensuring synchronized turn-on periods with the rising or falling edge of the AC voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If PWM dimming is implemented by periodically switching LED current according to a PWM signal, then the LED luminance can be adjusted to save energy or provide different brightness levels, but the waveform of the LED current may vary during different cycles of the rectified AC voltage, causing flicker or shimmer
Solution Approach 1:
The patent employs a feedback mechanism where the PWM signal generator receives feedback from the rectified AC voltage frequency detection circuit. This feedback loop continuously monitors the frequency of the rectified AC voltage and adjusts the PWM signal frequency accordingly, ensuring synchronization between the two frequencies to eliminate flicker and shimmer while maintaining dimming control capability
Solution Approach 2:
The patent dynamically changes the frequency parameter of the PWM signal to match the frequency of the rectified AC voltage. By adjusting the PWM frequency parameter in response to changes in the AC voltage frequency, the system maintains synchronization and prevents waveform variations that cause flicker, while still allowing luminance adjustment through duty cycle modulation
2Object-affected harmful factors
If the frequency of the PWM signal is not synchronized with the frequency of the rectified AC voltage, then the LED current waveform varies during different cycles, but synchronizing the frequencies eliminates flicker and shimmer
Solution Approach 1:
The synchronization is achieved through a feedback mechanism where the PWM signal generator continuously monitors the frequency of the rectified AC voltage via the frequency detection circuit and adjusts its own frequency accordingly. This closed-loop feedback system automatically maintains frequency synchronization without requiring complex manual adjustment mechanisms
Solution Approach 2:
The system performs self-synchronization by using the rectified AC voltage frequency information to automatically adjust the PWM signal frequency. The feedback mechanism enables the system to self-regulate and maintain synchronization without external intervention, reducing the need for complex external synchronization control circuits
Data Source
AI summary
An LED lighting device includes a luminescent circuit, a detecting circuit, an adjustable current source and a dimming control circuit. The luminescent circuit is driven by a rectified AC voltage for providing light. The detecting circuit is configured to detect a rising edge or a falling edge of the LED current associated with a frequency of the rectified AC voltage. The dimming current regulator is configured to vary a duty cycle of the LED current according to a PWM signal. The dimming control circuit is configured to generate the PWM signal and synchronize a frequency of the PWM signal with the frequency of the rectified AC voltage at the detected rising edge or the falling edge of the rectified AC voltage.