Which device converts AC to DC?

The device that converts alternating current (AC) to direct current (DC) is known as a rectifier. Rectification is an essential process in electrical engineering, particularly in power supply systems, where it is necessary to change the AC voltage from the power grid into usable DC voltage for various applications, such as charging batteries or powering electronic devices.

A rectifier typically uses semiconductor components like diodes which allow current to flow in one direction only, effectively blocking the reverse flow of current that characterizes AC. This process results in a pulsed DC voltage, which may require further filtering to produce a steady DC output.

In contrast, a transformer alters the voltage level of AC without converting it to DC, while an inverter performs the opposite function of converting DC back to AC. A filter is used to smooth out the output of a rectifier, eliminating ripples and variations in the rectified DC voltage but does not itself convert AC to DC. Thus, the rectifier is uniquely designed for the conversion process, making it the correct choice for this question.