Switching Regulator Control Circuit for Audio Noise Elimination
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Solution Overview
Problem
Switching regulators face audio noise issues when the frequency of the switching control signal drops into the audio range during light loaded or unloaded conditions, as they typically reduce the on/off frequency to minimize power loss, leading to intermittent control circuit operation.
Innovation Solution
A control circuit for a switching regulator that generates a switching control signal with constant on time in a first mode and decreasing on time in a second mode, using a set pulse generator, reset pulse generator, and logic circuit to maintain a constant duty cycle and avoid audio noise by adjusting the time interval between reset and set pulses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the on/off frequency of the power switch is reduced to minimize power loss during light loaded or unloaded conditions, then power loss is reduced, but audio noise is generated when the frequency drops into the audio range
Solution Approach 1:
The patent applies dynamics by making the on-time of the power switch variable rather than fixed. The control circuit dynamically adjusts the on-time based on the operating mode: in normal mode, a fixed on-time is used, but in light-loaded or unloaded conditions, the on-time is shortened to increase switching frequency and eliminate audio noise while maintaining reduced power loss
Solution Approach 2:
The patent changes the parameter of switching frequency by adjusting the on-time of the power switch. During light-loaded or unloaded conditions, the control circuit shortens the on-time, which increases the switching frequency above the audio range, thereby eliminating audio noise while maintaining the benefit of reduced power loss through intermittent operation
2Loss of energy
If the switching control signal frequency is reduced during light loaded conditions, then power loss is minimized, but the switching frequency drops into the audio range causing audio noise
Solution Approach 1:
The control circuit dynamically adjusts the switching frequency based on load conditions. In light-loaded or unloaded modes, it shortens the on-time to increase frequency above the audio range, while in normal mode it uses a longer on-time for lower frequency operation, optimizing the trade-off between power loss and frequency
3Device complexity
If the on time of the power switch is maintained as constant, then the control is simple, but audio noise occurs when the switching frequency drops into the audio range during light loaded conditions
Solution Approach 1:
The patent introduces dynamic control where the on-time is no longer constant but varies based on operating mode. The control circuit determines whether the system is in normal mode or light-loaded/unloaded mode and adjusts the on-time accordingly, adding complexity only when necessary to eliminate audio noise
Data Source
AI summary
Disclosed are a switching regulator and a control circuit and a control method therefor. In one embodiment, a switching control signal with decreasing on time is generated to control a power switch in a second mode so that audio noise can be avoided when the switching regulator operates in a light loaded or unloaded condition.