Adaptive Frequency Control for LED Dimming Stability
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Solution Overview
Problem
Solid state light sources, such as LEDs, experience unstable light output during dimming, particularly at low light levels and slow rate changes, due to the large granular step size of power converters/LED drivers, leading to perceptible flicker and oscillation.
Innovation Solution
Implementing adaptive frequency control in switching converters and PWM dimming signals, where the switching frequency is increased during dimming transitions to ensure the pulse width corresponds to an integral multiple of the switching period, and the PWM frequency is adjusted to synchronize with the power converter's switching cycle, thereby stabilizing the light output.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If pulse width modulation (PWM) is used to dim solid state light sources, then the light output can be controlled, but the light output becomes unstable at low light levels below 15% of total output
Solution Approach 1:
The patent applies dynamics by making the switching frequency adaptive rather than fixed. The control circuitry dynamically adjusts the switching frequency of the power converter based on the desired light output level, particularly increasing frequency during dimming transitions to ensure the pulse width corresponds to an integral multiple of the switching period, thereby eliminating unstable light output at low levels
Solution Approach 2:
The patent changes the switching frequency parameter adaptively to resolve the instability issue. By adjusting the switching frequency as a variable parameter rather than maintaining a constant frequency, the system ensures that the PWM pulse width always corresponds to an integral multiple of the switching period, eliminating flicker and oscillation at low light levels
2Device complexity
If the power converter operates at fixed switching frequency, then the system is simple to control, but the pulse width does not correspond to an integral multiple of the switching period causing granular step size and instability
Solution Approach 1:
The patent implements feedback by having the control circuitry continuously monitor the relationship between the PWM signal period and the power converter switching period. The system uses this feedback to adaptively adjust the switching frequency, ensuring that the pulse width always corresponds to an integral multiple of the switching period, thereby eliminating granular step size and light output instability
Solution Approach 2:
The system transitions from fixed frequency operation to adaptive frequency operation. The switching frequency is dynamically adjusted based on the PWM dimming signal characteristics, allowing the system to maintain stability across different light output levels without significantly increasing control complexity
3Stability of the object's composition
If the switching frequency is increased during dimming transitions, then the light output stability is improved, but the power converter operates less efficiently at higher frequencies
Solution Approach 1:
The patent applies dynamics by making the switching frequency adaptive rather than fixed. The control circuitry dynamically adjusts the switching frequency of the power converter based on the desired light output level, particularly increasing frequency during dimming transitions to ensure the pulse width corresponds to an integral multiple of the switching period, thereby eliminating unstable light output at low levels
Solution Approach 2:
The patent utilizes periodic action by synchronizing the PWM dimming signal with the power converter switching cycles. By ensuring the pulse width corresponds to an integral multiple of the switching period, the system creates a periodic relationship that eliminates instability while allowing frequency adjustment to optimize efficiency at different operating points
Data Source
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AI summary
Systems and methods to change a light output level using adaptive frequency control are provided. A switched mode power converter is configured to switch output current to a light emitting diode (LED) module, which includes an LED lighting element, at a switching frequency. Control circuitry is configured to receive a dimming control input that corresponding to a desired light output level of the LED module. The control circuitry is also configured to provide a pulse width modulation (PWM) output configured to pulse width modulate the output current, the PWM output having a pulse width, a PWM frequency, and a PWM period corresponding to the PWM frequency. The control circuitry is also configured to adjust at least one of the PWM period and the switching period in response to a change in the dimming control input, such that a light output level of the LED module is appropriately changed.