LED Driver PWM Frequency Adjustment to Eliminate Ripple Beats
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Solution Overview
Problem
Conventional pulse width modulation (PWM) techniques for LED lighting often result in visible brightness fluctuations due to low-frequency beats caused by the proximity of PWM frequency to the frequency of residual ripple in the DC voltage signal, which are not effectively addressed by existing solutions.
Innovation Solution
A method and circuit arrangement that dynamically adjusts the PWM frequency to be at least 20 Hz, preferably 30 Hz or 40 Hz, away from the frequency of the residual ripple and the power factor correction circuit, ensuring that the PWM frequency is an integral multiple of the AC voltage frequency or the frequency of the power factor correction circuit, thereby avoiding visible brightness fluctuations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the PWM frequency is set close to the residual ripple frequency or its integer multiples, then the PWM efficiency is improved, but low-frequency beats occur causing visible brightness fluctuations
Solution Approach 1:
The patent applies dynamics by making the PWM frequency adjustable rather than fixed. The control unit dynamically selects the PWM frequency based on the detected residual ripple frequency, ensuring it maintains a distance of at least 20 Hz from the ripple frequency and its harmonics. This dynamic adjustment resolves the contradiction by allowing frequency optimization while avoiding harmful beat frequencies that cause visible brightness fluctuations.
Solution Approach 2:
The patent changes the PWM frequency parameter adaptively based on the detected residual ripple conditions. By monitoring the residual ripple frequency and adjusting the PWM frequency accordingly (maintaining a minimum distance of 20 Hz), the system optimizes PWM efficiency while preventing the formation of low-frequency beats that would cause visible brightness fluctuations in the LED lighting.
2Object-affected harmful factors
If the PWM frequency is increased to avoid beats, then visibility of brightness fluctuations is reduced, but energy consumption increases
Solution Approach 1:
The patent optimizes the PWM frequency parameter by detecting the residual ripple frequency and selecting a PWM frequency that maintains at least 20 Hz distance from it. This adaptive parameter adjustment eliminates visible brightness fluctuations without unnecessarily increasing energy consumption, as the frequency is set to the lowest effective value that avoids beat frequencies.
Solution Approach 2:
The patent implements feedback by using a control unit that detects the residual ripple frequency and uses this information to adjust the PWM frequency. This closed-loop approach ensures that the PWM frequency is optimized to avoid beats and visible brightness fluctuations while minimizing energy consumption, rather than using a fixed high frequency that would waste energy.
3Device complexity
If a fixed PWM frequency is used, then the circuit complexity is reduced, but beats occur when the frequency is close to the residual ripple frequency
Solution Approach 1:
The patent introduces feedback by implementing a control unit that detects the residual ripple frequency and uses this information to adjust the PWM frequency. This feedback mechanism prevents beats and visible brightness fluctuations without requiring complex additional circuitry, as the control unit intelligently selects appropriate PWM frequencies based on real-time ripple conditions.
Solution Approach 2:
The patent applies dynamics by transitioning from a fixed PWM frequency to a dynamically adjustable frequency controlled by a microcontroller or similar device. The control unit monitors the residual ripple frequency and adjusts the PWM frequency accordingly (maintaining at least 20 Hz distance), resolving the beats issue while keeping circuit complexity manageable through software-based control rather than complex hardware circuits.
Data Source
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AI summary
The invention relates to an operating circuit for illuminants, in particular one or more LED sections (17), comprising an actively clocked PFC circuit (11), which can be supplied by an AC voltage (UAC) and optionally also a DC voltage (UDC) and the output voltage of which is directly or indirectly supplied through the illuminant (17) to a unit (19) for generating a PWM-modulated current. The operating circuit also has a control unit (16) that detects a residual ripple in the voltage (UPFC) in the supply chain before (18a), in (18b) or after (18c) the PFC circuit (11) and causes the frequency of the PWM modulation of the current through the illuminant (17) to be selected as a function of the frequency of the residual ripple.