LED Dimming Control Unit for Flicker-Free Low-Light Operation
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Solution Overview
Problem
Existing LED dimming technologies face challenges in achieving stable dimming control, especially at lower dimming levels, due to variations in V-I characteristics of LED elements and the difficulty in controlling pulse width to prevent flickering.
Innovation Solution
A lighting apparatus with a dimming control unit that adjusts the supply power and the number of lit LED elements in response to dimming ratios, using both DC and PWM dimming processes, along with a selective dimming process to maintain luminance continuity and prevent excessive luminance decrease.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If DC dimming process is used to dim the LED load by adjusting the magnitude of current, then the LED load can be controlled at higher luminance levels, but it becomes difficult to dim the LED load at lowered dimming levels due to individual V-I characteristics variations
Solution Approach 1:
The patent divides the dimming control into two distinct processes: DC dimming for higher luminance levels and PWM dimming for lowered luminance levels. This segmentation allows each process to operate in its optimal range, with DC dimming handling the upper range where current magnitude adjustment is effective, and PWM dimming handling the lower range where pulse width modulation provides stable control without the limitations of DC dimming at low currents.
2Illumination intensity
If PWM dimming process is used to dim the LED load by adjusting the duty ratio of pulse current, then the LED load can be dimmed at lowered dimming levels, but it becomes difficult to stably control the LED load because small changes in pulse width cause flickering
Solution Approach 1:
The patent dynamically switches between DC dimming and PWM dimming processes based on the desired dimming level. The dimming control unit determines which process to use, enabling the system to adapt its control method to the operating conditions. This dynamic approach allows stable control at low dimming levels by using PWM when needed while avoiding the flickering issues that would occur with pure PWM control across the entire range.
3Illumination intensity
If the pulse width is narrowed to achieve lower dimming levels in PWM dimming, then the LED load can be dimmed further, but the control becomes unstable and flickering occurs
Solution Approach 1:
The patent segments the dimming control strategy so that PWM dimming with narrowed pulse widths is only applied in the lowered dimming level range where it provides stable control. For higher dimming levels, DC dimming is used instead. This segmentation prevents the control instability and flickering that would result from using narrow pulse widths across the entire dimming range, as the system selectively applies PWM only where its advantages are needed.
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
Enables successful dimming control at lower dimming levels, including ratios less than 1%, by varying the number of lit LEDs and adjusting current magnitude and duty ratio, thereby stabilizing LED output and preventing flickering.
Implementation Method 1
a light source (a plurality of light emitting elements) which emits light in response to DC power
Data Source
AI summary
The lighting apparatus in accordance with the present invention includes a dimming control unit configured to control, in accordance with a dimming ratio, a light source including a plurality of light emitting elements designed to emit light in response to DC power. The dimming control unit is configured to, when the dimming ratio falls within a first dimming range, vary supply power to the light source in accordance with the dimming ratio. The dimming control unit is configured to, when the dimming ratio falls within a second dimming range different from the first dimming range, vary, in accordance with the dimming ratio, a lighting number defined as the number of the light emitting elements to be lit.