What component converts alternating current into direct current?

A rectifier converts alternating current into direct current.

Alternating current periodically reverses direction, while direct current flows in one direction. A rectifier performs this conversion by allowing current to pass more readily in the desired direction. Modern rectifiers most commonly use semiconductor diodes, whose one-way electrical behavior makes them suitable for the task.

A single diode can provide half-wave rectification, using only one half of an AC cycle. A bridge rectifier uses four diodes to provide full-wave rectification, using both halves of the cycle. The resulting output still has ripples, so power supplies usually add capacitors and voltage-regulation circuits.

A transformer can change AC voltage but does not itself convert AC to DC. Rectifiers appear in phone chargers, computers, radios, battery chargers, and many laboratory power supplies.