Soft-Burst Circuit for Switched-Mode Power Supply Noise
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Solution Overview
Problem
Switched-mode power supplies often generate undesirable audible noise, particularly in high-efficiency power supplies using pulse-skipping techniques during light load conditions, which is difficult and costly to mitigate effectively.
Innovation Solution
A soft-burst circuit is introduced to control the switching frequency of output transistors, utilizing a control signal to discharge a storage device and minimize audible noise by adjusting the operating frequency, incorporating a bipolar transistor and resistors to manage capacitor charging and discharging, thereby regulating the converter's gain and reducing noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If pulse-skipping techniques are used to turn off output transistors at light load levels, then efficiency is improved, but audible noise increases
Solution Approach 1:
The patent applies periodic action by using burst-mode operation where the power converter operates in periodic bursts rather than continuous operation. The controller enables the power converter to operate in a first mode during light load conditions and transitions to a second mode when the control signal reaches a threshold level, creating periodic on-off cycles that maintain efficiency while controlling noise through regulated frequency transitions
Solution Approach 2:
The patent employs parameter changes by dynamically adjusting the operating frequency of the power converter. The controller monitors a control signal and transitions between operating modes based on threshold levels, thereby changing the frequency parameter to move switching operations out of the audible range while maintaining efficient light-load operation
2Measurement precision
If switching frequency is varied to regulate output voltage, then voltage regulation is improved, but audible noise occurs when frequency enters audible range
Solution Approach 1:
The patent implements feedback by continuously monitoring the control signal level and using this information to determine when to transition between operating modes. The controller compares the control signal against a threshold level and adjusts the operating frequency accordingly, creating a closed-loop system that maintains voltage regulation while preventing audible noise through frequency management
Solution Approach 2:
The patent applies dynamics by making the operating frequency adaptive rather than fixed. The controller dynamically adjusts the switching frequency based on real-time monitoring of the control signal, allowing the system to transition smoothly between different operating modes and keep the switching frequency out of the audible range while maintaining precise voltage regulation
Data Source
AI summary
A switched-mode power supply includes a soft-burst circuit to minimize or prevent distracting audible noise. The power supply includes a control circuit for controlling switching of an output transistor to deliver a regulated output voltage to a load. The control circuit adjusts the operating frequency of the power supply based on a control signal. The soft-burst circuit discharges a storage device to minimize or prevent audible noise when the control signal reaches a particular level.