What is the primary application of a diode in power supplies?

The primary application of a diode in power supplies is to change alternating current (AC) to direct current (DC). This process is known as rectification. Diodes allow current to flow in only one direction, making them essential in converting AC, which alternates direction, into DC, which flows consistently in one direction.

In power supplies that convert AC from the mains into DC for devices and circuits, diodes are used in a rectifier circuit. This typically involves a configuration of diodes that allows positive half-cycles of the AC waveform to pass through while blocking negative half-cycles. As a result, the output only contains the positive fluctuations, which can then be smoothed out to provide a steadier DC voltage.

The other options relate to different functions that are not primarily the role of a diode in power supplies. For instance, diodes do not increase voltage levels, measure circuit efficiency, or store electrical energy; those functions are generally served by other components or processes in electronic circuits.