Method and apparatus for reducing audio noise in a switching regulator

摘要

A switching regulator 139 utilizing on/off control that reduces audio noise at light loads by adjusting the current limit of the switching regulator. In one embodiment, a switching regulator includes a state machine 301 that adjust the current limit 305 of the switching regulator 139 based on a pattern of feedback signal values from the output of the power supply for a preceding N cycles of the drive signal. The state machine 301 adjusts the current limit lower at light loads such that cycles are not skipped to reduce the operating frequency of the switching regulator 139 into the audio frequency range until the flux density through the transformer is sufficiently low to reduce the generation of audio noise.