Filter circuit for removing HF parasitics from mains supply - uses notch filter to reduce earth leakage currents through shunt branch of filter

摘要

The filter circuit seeks to reduce the high level of earth currents set up by the need to use a large value shunt capacitor in the filter to reduce the value of the series inductance so as to reduce the voltage drop over the inductance. The addition of a second inductor (5) connected in parallel with the capacitor forms a notch filter circuit, which has a higher impedance at all but the notch frequency, reducing the earth currents. An additional series capacitor (6) (with a non-electrolytic shunt capacitor (7) if an electrolytic capacitor is used) further limits the current, with the added shunt capacitor (7) shunting frequencies at which an electrolytic capacitor (6) has high leakage.