Power supply unit with noise reduction capability

摘要

Embodiments of the present invention provide a power supply unit capable of achieving noise reduction while maintaining efficiency under the light load state. A FET driver controls switching elements in either one of a Pulse Width Modulation (PWM) mode, an intermittent mode having a lower operating frequency than that in the PWM mode, and a noise-free mode having a higher operating frequency than an audible frequency range. The FET driver operates first in the intermittent mode under the light load state. A microphone collects noise generated from the surroundings of a power supply unit. When the level of an audio signal collected by the microphone exceeds a predetermined level, the FET driver transitions from the intermittent mode to the noise-free mode. In accordance with such an embodiment, the FET driver operates in the noise-free mode only when noise is actually generated.