Power Supply Filters

A power supply filter is a passive filter for linear or switching power supplies to smooth ripples or pulsations in the raw DC output. A line filter, as shown in Fig. 1, suppresses RF interference (RFI) induced into or transmitted on the AC power line or induced into or conducted from within the host product. These filters are required in products powered by switching power supplies, such as personal computers, that must comply with Federal Communications Commission (FCC) regulations limiting EMI/RFI above 10 kHz.



Figure 1 Line filter for a power supply.