PWM Dimming Noise Control via Dynamic Frequency Adjustment
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Solution Overview
Problem
Pulse width modulation (PWM) dimming in driver circuits for lighting can cause audible noise due to mechanical vibrations, particularly at frequencies between 1 kHz and 4 kHz, which is challenging to identify and costly to mitigate.
Innovation Solution
An apparatus and method that generate a PWM signal with a control circuit assigning a duty cycle and period based on dimming values, increasing frequency only at high dimming levels to reduce noise, allowing the driver circuit to operate at lower frequencies otherwise, and using a control switch or interface to set thresholds for noise reduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If PWM frequency is increased to reduce audible noise, then noise reduction is achieved, but operational costs and device complexity increase
Solution Approach 1:
The patent applies dynamics by making the PWM frequency adjustable rather than fixed. The control circuit dynamically changes the PWM frequency based on the dimming level detected from the illuminant output. At high dimming levels where audible noise occurs, the frequency is increased to shift it above the audible range. At lower dimming levels, the frequency is reduced to minimize operational costs and reduce device complexity. This dynamic adaptation resolves the contradiction between noise reduction and device complexity.
Solution Approach 2:
The patent changes the PWM frequency parameter adaptively based on operating conditions. Instead of using a constant high frequency to eliminate noise, the system monitors the dimming level and adjusts the frequency parameter accordingly. When noise is detected at high dimming levels, frequency is increased; when operating at lower dimming levels, frequency is decreased. This parameter change approach achieves noise reduction only when necessary, avoiding the continuous overhead of high-frequency operation.
2Object-affected harmful factors
If PWM frequency is increased to prevent noise, then noise is reduced, but operational costs increase
Solution Approach 1:
The system dynamically adjusts PWM frequency based on actual noise conditions and dimming levels rather than operating continuously at high frequency. The control circuit monitors the dimming level and only increases frequency when audible noise is detected at high dimming levels. This dynamic approach eliminates noise when necessary while minimizing energy consumption during normal operation at lower dimming levels.
Solution Approach 2:
The patent implements parameter changes by adaptively modifying the PWM frequency based on operating conditions. The control circuit changes the frequency parameter from a constant high value to a variable value that increases only when needed for noise reduction. This reduces the average energy consumption while maintaining noise reduction effectiveness when required.
3Object-affected harmful factors
If general increase in PWM frequency is applied, then noise is reduced, but device complexity and cost increase
Solution Approach 1:
The patent applies local quality by targeting noise reduction specifically at the problematic operating condition (high dimming levels) rather than applying a general frequency increase across all operating conditions. The control circuit identifies when the illuminant operates at high brightness levels and only then increases PWM frequency. This localized approach reduces noise where it occurs without unnecessarily complicating the device for conditions where it is not needed.
Solution Approach 2:
The system dynamically adapts PWM frequency to match actual noise generation conditions. The control circuit continuously monitors dimming levels and adjusts frequency in real-time based on when noise is likely to occur. This dynamic, condition-based approach avoids the device complexity of a general frequency increase while maintaining effective noise reduction at problematic operating points.
Data Source
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AI summary
The present invention relates to an apparatus for generating a PWM signal for controlling output power of at least one illuminant based on a dimming signal. The apparatus comprises a control circuit (9) configured to assign, to a dimming value indicated by the dimming signal, a duty cycle of the PWM signal and a period of the duty cycle, wherein the period decreases continuously or discontinuously with an increase of the duty cycle.