What are relays?

A relay is a switch powered by a relatively small electric current that can turn a much larger electric current on or off. Essentially, relays are power-switching solutions that can be used to allocate power without manually opening or closing a switch. To switch power on and off, a relay simply requires a small electrical signal. The ability to have low-power control over a high-power signal makes relays a major component throughout the history of electronics.

The purpose of a relay is to enable or interrupt the electrical connection between two or more circuits. Relays act as switches that can be remotely controlled or triggered by an electrical signal. When the relay receives the input signal, it either opens or closes its contacts, allowing or blocking the current flow in the controlled circuit.

Relays come in a wide variety of styles and types, from large relays with high-current contacts that control motors, to small reed relays that systems employ for low-voltage, low-current signals.

There are two major classes of relays that are commonly used in printed circuit boards: electromechanical relays and solid-state relays.