Ac solid-state relay is a contactless on-off electronic switch, in which the two terminals are input control terminals, the other two terminals are output control terminals, the three phase is six terminals, three in three out, photoelectric isolation is used in the middle, as the input and output between the photoelectric coupling. By adding a DC or pulse signal to the input, the output can switch from the off state to the on state (the blocking state when there is no signal), thus controlling the heavy load. The whole device has no moving parts and contacts, and can achieve the same function as the common mechanical electromagnetic relay.

Solid-state relay is a contactless switching element composed of solid elements, so compared with electromagnetic relay, it has the characteristics of reliable operation, fast switching speed, no noise, long life, small size, no spark, corrosion, explosion, vibration resistance and so on. For interference small, compatible with logic circuit, strong anti-interference ability, fast switching speed and easy to use, and a series of advantages, thus has a wide application field, has the potential of gradually replacing the traditional electromagnetic relay, and can be further extended to the application of computer in areas such as traditional electromagnetic relay, at present has been widely used in computer peripheral interface equipment, constant temperature electric heating equipment; CNC machinery, remote control system, industrial automation equipment; Signal lights, traffic lights, lighting stage lighting control equipment; Instruments, medical equipment, duplicator, color expander, rubber and plastic machinery, automatic washing machine; In addition, it is widely used in explosion-proof, wet-proof and anticorrosive situations in chemical industry, coal mine, etc., and has become an ideal replacement product for relay family (EMR).