DC Filtering Capacitor is used to filter out a certain frequency otherwise series of frequencies from an electronic circuit is known as the filter capacitor. Generally, a capacitor filters out the signals which have a low frequency. The filter capacitor is a capacitor which filters out a certain frequency or range of frequencies from a circuit. A filter capacitor could also refer to components used in an EMI filter on the input to a power supply. The DC Filtering Capacitor is very effective.