definition

An electromagnetic induction device used to alter the voltage of an alternating current.

A transformer consists of two electromagnetically coupled coils; an alternating current flowing through one coil (known as the "primary side") generates a changing magnetic field, which in turn induces a current in the other coil (known as the "secondary side"). Typically, the two coils are linked by an iron or ferrite core, although high-frequency devices can also operate without a core.

Transformers perform two main functions: voltage transformation and isolation.

The secondary voltage can be higher or lower than the primary voltage, determined by the turns ratio of the two coils.

Since the coils are coupled via a magnetic field, they can share different common grounds, thereby providing isolation.

Key applications include power and signal isolation/impedance transformation.

An autotransformer is a transformer featuring a single magnetic core that generates an induced voltage via a central "tap"; this type of transformer does not provide electrical isolation.

Transformer capacity is expressed in kilovolt-amperes (kVA): Volts × Amperes / 1000.