A relay circuit consists of a relay, which is an electromagnetic switch. It is used to control the flow of current in a secondary circuit by using a small input current to control a larger output current. The relay contains a coil of wire, which, when energized, creates a magnetic field that moves a set of contacts. These contacts can either open or close, depending on the design of the relay, and thereby control the flow of current through a connected circuit.

    At its core, a relay operates as a mechanical switch, with the additional benefit of being controlled electrically. This means that a relay can turn on or off a high-voltage circuit using a low-voltage control signal, offering electrical isolation between the control and the output circuits. This feature is particularly useful in situations where low-voltage devices need to control high-voltage equipment, such as in industrial automation systems or home appliances.