Hybrid LED Dimming System for Wavelength Stability
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Solution Overview
Problem
Existing dimming techniques for light emitting diodes (LEDs) face limitations such as wavelength drift in constant current (CC) dimming and difficulty in achieving smooth fading to zero brightness without discontinuities in pulse-width modulation (PWM) dimming, particularly at low brightness levels.
Innovation Solution
A hybrid dimming system that combines CC and PWM control techniques, where the dimming range is partitioned into portions using both techniques jointly, with unswitched constant current, mixed CC and PWM, and PWM-only methods to adjust the duty cycle and current values, ensuring stable and smooth dimming without color shifting.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If constant current (CC) dimming is used to control LED brightness by adjusting current intensity, then brightness control is achieved, but wavelength drift occurs causing color shifting
Solution Approach 1:
The dimming range is segmented into multiple portions, with different control techniques applied to different segments. At higher brightness levels, PWM control is used to maintain constant wavelength, while at lower brightness levels, CC control is used for smooth dimming. This segmentation allows each technique to operate in its optimal range, avoiding wavelength drift at high brightness while maintaining smooth control at low brightness.
Solution Approach 2:
The system dynamically switches between PWM and CC control modes based on the desired brightness level. The control method is not fixed but adapts in real-time according to the operating conditions. This dynamic adaptation allows the system to optimize performance across the entire dimming range, combining the advantages of both PWM (wavelength stability) and CC (smooth control) techniques.
2Object-generated harmful factors
If PWM dimming is used to control LED brightness by switching current on and off, then wavelength stability is maintained, but smooth fading to zero brightness cannot be achieved without discontinuities
Solution Approach 1:
The dimming range is divided into segments where PWM control is applied to upper segments for wavelength stability, and CC control is applied to lower segments for smooth fading capability. This segmentation allows the system to achieve both wavelength stability at high brightness and smooth discontinuity-free fading at low brightness levels.
Solution Approach 2:
The patent merges PWM and CC control techniques into a unified hybrid system that operates across the entire dimming range. By combining the wavelength-stabilizing effect of PWM with the smooth-fading capability of CC control, the system achieves both objectives simultaneously, eliminating the limitations of using either technique alone.
3Object-generated harmful factors
If PWM control is used at low brightness levels, then wavelength stability is maintained, but visible discontinuities and flickering occur
Solution Approach 1:
The operating range is segmented such that CC control is applied to low brightness levels where flicker-free operation is critical, while PWM control is used at higher brightness levels where wavelength stability is more important. This segmentation ensures that each technique operates in its optimal performance range, avoiding flickering at low brightness while maintaining wavelength stability at high brightness.
Data Source
AI summary
Dimming a light source such as a LED over a dimming range (0%-100%) involves adjusting at least one of the intensity (I) and the duty-cycle (DR) of a current flowing through the light source. The dimming range includes at least one portion (L%-H%; 0%-H%) where the light source is fed with a current whose intensity (I) is switched with a given duty cycle (DR) between a non-zero on value and zero, the non-zero on value being a fraction of the rated value (Irated), whereby joint CC and PWM dimming is achieved.