LED Dimming via PWM Dithering to Eliminate Acoustic Noise
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Solution Overview
Problem
Traditional lighting systems, such as incandescent and fluorescent bulbs, suffer from short lifespan, low energy efficiency, and color degradation over time, while LED-based systems face challenges in tunable color temperature and rendering index adjustments, especially when multiple LEDs are coupled, and exhibit undesirable acoustic effects due to PWM signals.
Innovation Solution
The development of firmware and circuit techniques that allow for precise control of LED brightness through pulse width modulation (PWM) and shunting, enabling smooth dimming from maximum to near-extinction levels, and dithering of PWM signals to mitigate acoustic effects by converting them into white noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If PWM signals are used to control LED brightness, then precise brightness control is achieved, but acoustic noise is generated due to resonant frequencies
Solution Approach 1:
The patent applies periodic action by using pulse width modulation (PWM) to control LED brightness through periodic switching of current pulses. The PWM technique varies the duty cycle of periodic pulses to achieve precise brightness control while maintaining the periodic nature of the signal to avoid acoustic resonance issues.
Solution Approach 2:
The patent changes the frequency parameter of the PWM signal to operate outside the human hearing range (above 20 kHz), thereby eliminating acoustic noise while maintaining precise brightness control. This parameter change transforms the harmful audible frequency into an inaudible ultrasonic frequency.
2Quantity of substance
If multiple LED-based lighting systems are coupled together, then lighting coverage is increased, but color consistency and tuning responsiveness deteriorate
Solution Approach 1:
The patent implements feedback mechanisms where each LED module includes sensors that detect the actual color output and provide feedback to the control system. This allows the controller to adjust the PWM signals to maintain color consistency across multiple coupled LED systems, compensating for variations in individual module characteristics.
Solution Approach 2:
The patent creates a universal control protocol that can be applied across multiple LED modules of the same type, allowing them to be coupled together while maintaining consistent color rendering. The standardized interface and control methodology enable multi-functionality across the expanded lighting system.
3Use of energy by stationary object
If fixed white LEDs are used in LED-based lighting systems, then energy efficiency and lifespan are improved, but color tunability is limited
Solution Approach 1:
The patent transitions from static fixed-color LEDs to dynamic color-tunable LED modules by incorporating multiple LED types (different color temperatures) within each module and using PWM to dynamically adjust the contribution of each LED type. This allows the system to adapt color output while maintaining the energy efficiency of LED technology.
Solution Approach 2:
The patent segments the color rendering function by separating different color temperature LEDs into distinct modules or channels within each lighting unit. This segmentation allows independent control of each color channel through PWM, enabling precise color mixing and tunability while maintaining overall system energy efficiency.
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 precise control of LED brightness with seamless transitions and significant reduction in acoustic noise, maintaining high energy efficiency and color accuracy across varying brightness levels without noticeable flickering or gaps.
Implementation Method 1
The development of firmware and circuit techniques that allow for precise control of LED brightness through pulse width modulation (PWM)
Implementation Method 2
dithering of PWM signals to mitigate acoustic effects by converting them into white noise
Implementation Method 3
PCBAs with LEDs often exhibit undesirable acoustic effects when the PCBAs are driven at particular (e.g., resonant) frequencies in the human hearing range
Data Source
AI summary
Various embodiments are described herein that relate to systems and methods for selectively providing current to power LEDs. The techniques introduced here can enable smooth dimming of the LEDs from maximum brightness down to “actual extinction” or “pseudo-extinction.” More specifically, the LEDs can be dimmed to extinction without any significant gaps in the levels of brightness (i.e., a noticeable drop rather than a smooth transition between brightness levels). Various pulse width modulation (PWM) and shunting techniques may be used to control the power provided to each color channel of an LED board. Conventionally, PWM often causes LEDs to produce an undesirable acoustic effect. However, by dithering the PWM signals between multiple predetermined positions once the frequency enters the audible range (e.g., below 25 kHz), the cumulative acoustic effect instead becomes white noise.