Electronic circuits and components
Transformers are used to couple a.c. power or signals from one circuit to another. Voltage may be stepped-up (secondary voltage greater than primary voltage) or stepped-down (secondary voltage less than primary voltage). Since no increase in power is possible (transformers are passive components like resistors, capacitors, and inductors) an increase in secondary voltage can only be achieved at the expense of a corresponding reduction in secondary current, and vice versa. In fact, the secondary output power will be slightly less than the primary input power due to iron and copper losses within the transformer.
Typical applications for transformers include stepping-up or stepping-down mains voltages in power supplies, coupling signals in AF amplifiers to achieve impedance matching and to isolate d.c. potentials associated with active components.