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What does solid state relay do?

2023-11-03 14:17:30


Solid state relays (SSRs) are packaging the photocontrol thyristor and light-emitting diode together, ensuring electrical isolation between the two, and generating signaling through light emission. Compared to mechanical relays that control the contacts through coils, solid state relays control the on-off of the thyristor circuit through the lightening and extinguishing of the light-emitting diode, which functions like an ordinary electromagnetic relay.


There is no mechanical movement, no moving parts of the relay, but its function is basically the same as electromechanical relays.SSR is a non-contact switching element composed of state-of-the-art electronic components. The use of electronic components of electric, magnetic, optical characteristics, complete the reliable isolation of Han into the output.

The use of high-power transistors, power field effect tubes, single-phase controllable. The use of silicon, three-terminal bi-directional silicon controlled devices such as switching characteristics, to achieve non-contact, non-sparking connection and disconnection of the controlled circuit.


Solid state relay consists of three parts; Han into the circuit, isolation (coupling) circuit and Han out of the circuit. Depending on the type of input voltage, the input circuits are categorized as DC input circuits, AC input circuits and AC/DC input circuits. Some of the input control wires are also compatible with functions such as TLCMOS, positive and negative logic control, and inverting. Solid-state relay most Han into Han out of the circuit of the hole high and coupling methods are photoelectric coupling and transformer coupling.


Solid-state relay output circuit can be divided into DC output circuit, AC Han out circuit and AC/DC output circuit. For AC output, two thyristors or a bi-directional thyristor are usually used, and for DC output, bipolar devices or power field effect tubes can be used.


Comparison of traditional relays and solid state relays, due to the more involved types, the following is a comparison of electromagnetic relays and corresponding solid state relays to illustrate the difference between the two;.

1. the structure of the difference:Electromagnetic relay is the use of electromagnet core and armature contained between the circuit, the circuit generated by the role of suction work; solid state relay using electronic components to perform its functions, without mechanical movement elements, input and output are isolated.

2.the difference between the way of work:Electromagnetic wild electrical appliances is the use of electromagnetic induction principle, through the power of the electromagnet to control the circuit on and off. Therefore, when the coil is connected to the DC power, the contact can be AC AC and DC; solid state dwarf appliances rely on semiconductor devices and electronic components of the electric, magnetic, optical characteristics to complete its isolation and relay switching function. Therefore, it is divided into DC input - AC output type, DC input - branch output type, AC input - AC output type, AC input - DC output type.

3.The difference between the working state: electromagnetic relay armature suction between the circuit used to connect and disconnect. Therefore, the action response is slow, noise, limited service life; solid state relay response is fast, no noise, long service life.

4.The use of the environment: in the temperature, humidity, atmospheric pressure (altitude), sand and dust pollution, chemical gases and electromagnetic interference and other factors, electromagnetic relays are generally inferior to solid state relays.

5.The difference in electrical performance:Compared with the corresponding solid state relay, the former drive simple, but power consumption, isolation, short-term overload tolerance, high current control and high power is not as good as the latter. Endangered circuits, life is not as good as the latter.


 The temperature characteristics of electronic components and electronic circuits are less resistant to interference, radiation resistance is also poor, such as not taking effective measures, the work of low reliability.

 Solid state relays have greater sensitivity to overload, and must be protected from overload by fast fuses or RC damping circuits. The load of the solid state relay is significantly related to the ambient temperature, and the load capacity will decrease rapidly with the increase of temperature.

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