What device is primarily used to convert alternating current (AC) to direct current (DC)?

The device that is primarily used to convert alternating current (AC) to direct current (DC) is a rectifier. A rectifier functions by allowing current to flow only in one direction, effectively blocking the reverse direction of the AC waveform. This process transforms the fluctuating AC voltage into a steadier DC voltage, which is essential for many electronic devices that require direct current for operation.

Rectifiers can take different forms, such as half-wave rectifiers, which utilize only one half of the AC waveform, and full-wave rectifiers, which use both halves, resulting in a smoother DC output. The rectification process is crucial in power supply systems where devices must run on DC but are supplied with AC power from the electrical grid.

The other options, while related to electrical conversion, serve different purposes. An inverter, for example, is used to convert DC to AC, hence it operates in the opposite direction. A transformer is used to change the voltage level of AC and does not convert it to DC. The term converter is a broader category that can refer to any system that changes one form of electrical energy to another, but specifically converting AC to DC falls under the role of a rectifier.