Dimming LED Power Supply Phase Control Flicker Reduction
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Solution Overview
Problem
Conventional dimming switches struggle to effectively dim high-power LEDs and LED clusters, especially at low current levels, and often result in flicker due to TRIAC jitter and noise, making them unsuitable for modern lighting applications.
Innovation Solution
A dimmable LED power supply that uses a phase-controlled 120 VAC, 60 Hz power source to provide an adjustable DC current, employing pulse width modulation (PWM) controlled by the phase angle and proportional current limit adjustment to reduce flicker and improve dimming performance at low-light levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If conventional PWM-dimming switches are used to control high-power LEDs, then the dimming function is provided, but flicker and jitter occur especially at low current levels
Solution Approach 1:
The patent uses high-frequency PWM switching (typically 20kHz or higher) to drive the LEDs, which is well above the human perception threshold. This periodic action at high frequency eliminates visible flicker while maintaining effective dimming control through duty cycle adjustment. The switching frequency is specifically chosen to be in the ultrasonic range to prevent audible noise and visual flicker.
Solution Approach 2:
The patent dynamically adjusts the PWM switching frequency and duty cycle based on the desired dimming level. At low current levels, the system maintains a high switching frequency to prevent jitter and flicker, while adjusting the duty cycle to achieve the desired dimming effect. This parameter adaptation ensures stable operation across the entire dimming range.
2Reliability
If large input and output storage capacitative devices are used to prevent flicker, then flicker is reduced, but cost and space consumption increase
Solution Approach 1:
Instead of using large capacitors to smooth the output and eliminate flicker, the patent employs high-frequency PWM switching that naturally prevents flicker perception. The rapid switching action maintains steady LED operation without requiring large energy storage elements, thereby reducing component count, cost, and PCB space.
Solution Approach 2:
The patent replaces the passive capacitor-based flicker reduction approach with an active PWM control system. The microcontroller-based PWM generator actively manages the switching to eliminate flicker, substituting the need for large passive energy storage components with intelligent control electronics.
3Ease of operation
If phase angle control is used to dim LEDs, then dimming is achieved, but effective dimming at low current levels cannot be accomplished
Solution Approach 1:
The patent uses PWM pulse trains with varying duty cycles to control LED current. At low dimming levels, the system maintains a high switching frequency with low duty cycles, ensuring precise current control down to very low levels without the jitter and instability associated with phase angle control. This periodic high-frequency switching enables accurate dimming across the entire range.
Solution Approach 2:
The patent dynamically adjusts PWM duty cycle and switching frequency to maintain optimal control across all dimming levels. At low current levels, the system uses higher switching frequencies and carefully controlled duty cycles to prevent jitter and ensure smooth dimming, whereas conventional phase angle control fails to maintain stability at these levels.
4Ease of operation
If TRIAC-based PWM-dimming is used, then dimming control is provided, but audible noise is generated
Solution Approach 1:
The patent uses high-frequency PWM switching (typically 20kHz or higher) that is above the human audible range. This ultrasonic switching frequency eliminates audible noise generated by lower frequency TRIAC-based dimming while maintaining effective dimming control. The high-frequency periodic action pushes the switching noise beyond human hearing thresholds.
Solution Approach 2:
The patent changes the switching frequency parameter from the audible range (50/60Hz TRIAC switching) to the ultrasonic range (20kHz or higher). This parameter change effectively removes audible noise while preserving dimming functionality through duty cycle control of the high-frequency PWM signal.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution reduces audible noise and flicker, enhances dimming performance at low light levels, and provides a more linear dimming effect to the human eye, making it suitable for high-power LEDs and LED clusters.
Implementation Method 1
A dimmable LED power supply that uses a phase-angle detection circuit to control pulse width modulation (PWM)
Implementation Method 2
control pulse width modulation (PWM) and adjusts the duty cycle based on proportional current limits
Data Source
AI summary
A dimmable, light-emitting diode (LED) power supply adapted to provide a direct current (DC), constant current (“constant current source”) from a conventional, phase-controlled 120 VAC, 60 Hz power source is disclosed. The constant current source of the present invention utilizes two processes to control dimming. In a first process, the phase angle of the input voltage is used to control the duty cycle of a line frequency pulse width modulation (PWM). In a second process, a proportional-current limit adjustment is used to control the average current to the LED during the ON time of the line frequency by PWM. As a result, at relatively low phase angles, peak currents can be lowered, reducing flicker and improving the audible noise levels generated by the circuit.