Reduced EMI noise in switched-mode power supply

摘要

A grounded capacitor in a switched-mode power supply provides AC line EMI filtering, reduced current leakage, and high voltage isolation. The capacitor is coupled between an AC rectifier circuit and the controlled switching devices of the power supply to provide the capacitor with a lower conduction angle, i.e., the grounded capacitor will only conduct a leakage current during periods when diodes within the rectifier circuit are conducting. The low impedance ground return path for the switching device output signal permits the use of a filter capacitor having a large capacitance which affords improved power supply line isolation and enhanced safety.