Switching Power Supply Control Circuit for Audible Noise Reduction
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Solution Overview
Problem
Flyback-type switching power supply systems experience varying power supply operation frequencies when subjected to different AC input voltages, leading to inconsistent vibration isolation requirements and potential audible noise due to transformer vibration.
Innovation Solution
A control circuit that detects AC input voltage levels and adjusts the frequency decreasing gain characteristics to maintain consistent power supply operation frequency characteristics across different load factors, eliminating the need for individual vibration isolation measures based on AC input voltage magnitude.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the switching frequency is decreased under light-load condition to reduce switching loss, then the efficiency is improved, but the power supply operation frequency enters the audible region causing transformer vibration and noise
Solution Approach 1:
The patent applies dynamics by making the switching frequency adjustable rather than fixed. The control circuit dynamically changes the switching frequency based on detected AC input voltage levels and load conditions. For high AC input voltages, the frequency is maintained higher to avoid audible noise, while for low AC input voltages, the frequency can be decreased to reduce switching loss, optimizing both efficiency and noise performance across different operating conditions
Solution Approach 2:
The patent changes the switching frequency parameter based on AC input voltage detection. The control circuit detects the AC input voltage level and adjusts the switching frequency accordingly - maintaining higher frequencies for high voltage inputs (100V/120V systems) to prevent audible noise, and allowing lower frequencies for low voltage inputs (200V/230V systems) to reduce switching loss, thus resolving the contradiction between efficiency and noise
2Object-generated harmful factors
If different vibration isolation measures are implemented for different AC input voltage systems, then the audible noise is reduced, but the device complexity increases
Solution Approach 1:
The patent implements a universal vibration isolation structure that functions across different AC input voltage systems (100V/120V and 200V/230V). The vibration isolation measure is designed with universal applicability, and the control circuit automatically adapts the switching frequency to match the appropriate system type, eliminating the need for separate vibration isolation designs for different voltage systems while maintaining noise reduction effectiveness
Data Source
AI summary
An input voltage detection unit detects whether an AC input voltage is the voltage of a 100V system or of a 200V system. In response, a frequency decreasing gain setting unit switches between frequency decreasing gain characteristics relative to load factors. The frequency decreasing gain characteristics are established so that the initiation of a decrease in a feed back signal in the 100V system is earlier than that in the 200V system. By switching the frequency decreasing gain characteristics based on an AC input signal, the characteristics, in which a decrease in a feed back signal in the 200V system is earlier than that in the 100V system, are cancelled to allow load factors, at each of which a power supply operation frequency reaches the audible region, to be approximately the same to enable a vibration isolating measure to be independent of the AC input voltage.