A capacitor filter is connected directly across the load is displayed in figure. The property of a capacitor is that it permits ac component and blocks dc (direct current) component. The operation of the capacitor filter is for short the ripple to ground but leave dc (direct current) to emerge at output when it is connected across the pulsating dc voltage.
Throughout the positive half cycle, the capacitor charges equal to the peak vale of the transformer secondary voltage, Vm and will try to keep this value since the full wave input drops to zero. Capacitor will discharge via RL slowly till the transformer secondary voltage again gets increases to a value greater as compared to the capacitor voltage. The diode conducts for a period that depends upon the capacitor voltage. The diode will conduct while the transformer secondary voltage becomes much more than the diode voltage. This is termed as cut in voltage. The diode stops conducting while the transformer voltage becomes less as compared to the diode voltage. This is known as cut out voltage.