What component is commonly added to a rectifier circuit to filter varying DC?

A capacitor is commonly added to a rectifier circuit to filter varying DC. In a rectifier circuit, the output voltage tends to fluctuate due to the conversion of alternating current (AC) to direct current (DC). This fluctuation, known as ripple, is not suitable for many applications that require a stable DC voltage.

When a capacitor is placed across the output of the rectifier, it charges up to the peak voltage of the rectified signal during the voltage peaks and discharges during the valleys. This charging and discharging action helps smooth out the variations in the voltage, reducing the ripple and producing a more stable DC voltage. The effectiveness of the capacitor as a filter depends on its value; larger capacitors generally provide better filtering by allowing more charge to be stored and released.

Other components listed, like resistors and inductors, do not perform the filtering function as effectively as capacitors in this context. A transformer, while crucial in some rectifier circuits for stepping up or stepping down voltage, does not serve the purpose of filtering the varying DC output.