For solid state relays, read this article is enough

Solid state relay

SSR for short. It is a non-contact switching device with relay characteristics, using semiconductor devices instead of traditional electrical contacts as switching devices. The single-phase solid-state relay is a four-terminal active device in which two input control terminals and two output terminals are optically isolated between the input and output terminals. After the DC or pulse signal is applied to the input terminal to reach a certain current value, the output terminal can change from off state to on state.

Where can solid state relays be used?

At present, solid state relay has been widely used in computer peripheral interface equipment, electric furnace heating constant temperature system, NUMERICAL control machinery, remote control system and industrial automation equipment. Signal lamp, scintillator, lighting stage lighting control system; Instruments, medical instruments, photocopiers, automatic washing machines; Automatic fire protection, security system and power capacitor switch as power factor compensation are widely used in chemical industry, coal mine and other places that need explosion-proof, moisture-proof and corrosion protection.

What are the types of solid state relays?

According to the switching mode, AC solid state relay can be divided into voltage zero-crossing conduction type (referred to as zero-crossing type) and random conduction type (referred to as random type). According to the output switching elements, there are bidirectional thyristor output type (common type) and unidirectional thyristor inverse parallel type (enhanced type); Depending on the method of installation, there are two types: pin-in for printed circuit boards (natural cooling without heat sink) and mounted on metal substrates (heat sink cooling). In addition, there are wide input range (DC3-32V) constant current source type and input series resistance current limiting type.

The difference between zero-crossing SSR and random SSR

When an effective control signal was applied to the input, the output of the random SSR turned on immediately (at a speed of microseconds), while the zero-crossing SSR did not turn on until the load voltage crossed the zero-crossing region (about 15 V). When the control signal is withdrawn at the input, both zero-crossing SSR and random SSR turn off while keeping the current below this value. Although zero-crossing SSR may cause more than half cycle delay, it reduces the impact on the load and the rf interference, making it an ideal switching device and widely used in "SPDT" switching applications. The random solid-state relay has the characteristics of fast response speed and can control the phase-shifting trigger pulse to change the AC power grid voltage conveniently. Therefore, it can be used for precision temperature and light adjustment of resistive loads and some inductive loads.

Zero-crossing SSR is used for "switch" switching (from the "switch" switching function, it is equivalent to ordinary relay or Contactor), and most of the solid-state relays we usually call are zero-crossing SSR(zero-crossing SSR can only "switch" but not "voltage regulation").