What is a Solid State Relay

What is a Solid State Relay (SSR)

Three types of solid state relays

Solid state relay (also known as SSR, SS relay, SSR relay or SSR switch, solid state contactor, power electronic switch, automotive relay, electronic power relay, electrical signal contactor) is a compact integrated non-contact electronic switching device composed of Composed of integrated circuits (ICs) and discrete components. Depending on the switching characteristics of electronic components (such as switching transistors, triacs, etc.), SSRs are able to switch the load's "ON" and "OFF" states very quickly through electronic circuits, just like the function of traditional mechanical relays. Compared with the previous "coil-reed contact" relay, the electromechanical relay (EMR), there is no moving mechanical part inside the SSR, and there is no mechanical action during the switching process of the SSR. Therefore, solid state relays are also called "non-contact switches".

The structural features of SSR switches make them superior to EMRs. The main advantages of solid state relays are as follows:

● As the switch of the relay, the semiconductor element has small volume (small volume) and long life (long life).

● Better electromagnetic compatibility than EMR - anti-radio frequency interference (RFI) and electromagnetic interference (EMI), low electromagnetic interference, low electromagnetic radiation.

● No moving parts, no mechanical wear, no action noise, no mechanical failure, high reliability.

● No spark, no arc, no burning, no contact bounce, no wear between contacts.

● With "zero voltage switching, zero current shutdown" function, easy to achieve "zero voltage" switching.

● Fast switching speed (SSR switching speed is 100 times that of general EMR) and high operating frequency.

● High sensitivity, low level control signal (SSR can directly drive high current load through small current control signal), compatible with logic circuit (TTL, CMOS, DTL, HTL circuit), easy to realize various functions.

● Generally encapsulated with insulating materials, it has good moisture-proof, mildew-proof, corrosion-proof, vibration-proof, mechanical shock-proof and explosion-proof performance.

Solid State Relays vs Electromechanical Relays

In addition, the amplification and driving functions of solid state relays are ideal for driving high power actuators and are more reliable than electromagnetic relays (EMRs). The control switches of solid state relays require very low power, so low control currents can be used to control high load currents. In addition, solid-state relays use mature and reliable photoelectric isolation technology between the input and output terminals. This technology allows the output signal of the low-power device to be directly connected to the input control terminal of the solid-state relay, and the high-power device is controlled at the output of the solid-state relay, without the need for an additional protection circuit to protect the low-current device, because the "small control current device" (connected to the SSR) input terminal) and the "large control power supply" (connected to the SSR output terminal) have been galvanically isolated. In addition, the AC solid state relay adopts the "zero-crossing detector" technology to safely apply the AC-SSR to the output interface of the computer, without causing a series of disturbances or even serious failures to the computer. And these functions are beyond the reach of EMR.

Due to the inherent characteristics of solid state relays and the above advantages, SSR has been widely used in various fields since its inception in 1974, completely replacing electromagnetic relays in many fields where electromagnetic relays cannot be applied. Especially in the field of computer automatic control systems, since solid-state relays have very low requirements for driving power and are compatible with logic circuits, they can also directly drive output circuits without additional intermediate digital buffers.

Solid State Relay (SSR) applications.

At present, solid state relays perform well in military, chemical, industrial automation control devices, electric mobile, telecommunications, civil electronic control equipment, and security and instrumentation applications, such as electric furnace heating systems, computer numerical control machine tools (CNC machines), remote control machinery, electromagnetic Valves, medical equipment, lighting control systems (such as traffic lights, flashers, stage lighting control systems), household appliances (such as washing machines, electric stoves, ovens, refrigerators, air conditioners), office equipment (such as copiers, printers, fax machines and multifunction printers), fire safety systems, electric vehicle charging systems, etc. All in all, solid state relays can be used for any

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