Solid-state relays use light-emitting diodes and light-sensitive semiconductors to turn on and off outgoing power. Usually, a lower voltage switching circuit controls a higher voltage output. Solid-state relays are used in a variety of industrial switches where a simple mechanical switch cannot handle the current.
Solid-state relays allow lower voltage switches to control higher voltage outputs to various equipment. Industrial equipment often requires voltages exceeding the capacity of normal switches, but that equipment still needs to be cycled on and off. Solid-state relays allow small direct current or alternating current loads to control this larger current. When signal power from a lower voltage switch reaches a solid-state relay, a light-emitting diode is activated. This diode in turn triggers a light-sensitive semiconductor which then allows power to pass through it. Solid-state relays lack the moving parts of electromechanical relays, which employ a magnetized physical switch, and offer a variety of advantages over electromechanical relays. As there are no moving parts, solid-state relays are usually more reliable and have longer working lives than electromechanical relays. Solid-state relays also provide switching with almost no delay. The ability to cycle on and off quickly and reliably makes solid-state relays an ideal choice for any application where frequent switching is necessary such as controlling the heating element in a kiln.