How relays work

How does a relay work? Working principle of relay varies depending on the type, mainly including the following: the working principle of electromagnetic relay electromagnetic relay based on the electromagnetic induction law of 5. Main working process of the following five: initial state: no electricity, no excitation coil current, magnetic core without magnetic field, contact in a specific position, normally closed contact closure, normally open contacts disconnect. Magnetic fields generated by excitation coil, the process of electricity: current, magnetic core into a temporary magnet. And process: core appeal, when magnetic field is strong enough, contact the attraction, normally closed contacts disconnect, normally open contact closure. Power process: power excitation coil, core magnetic field gradually disappear, contact under the action of the spring back to the initial position, normally closed contacts closed, normally open contacts disconnect.。

Solid-state relay

A solid state relay is a contactless switching device composed entirely of solid state electronic components. The main working principle is as follows:
Input circuit: Provides a control signal for the solid-state relay, which can be a DC voltage, current, or digital logic level. The input circuit usually uses a photoelectric coupler or transformer coupling, etc., to isolate the input signal from the output circuit.
Trigger circuit: Under the control of the input signal, the trigger circuit generates the required trigger signal, which is used to drive the switching circuit. For AC solid-state relays, in order to prevent radio frequency interference and pollution to the power grid, there is usually a zero-crossing control circuit to ensure that the AC voltage is switched on when the AC voltage is zero, and after the AC voltage is zero, wait for the junction point of the positive and negative half weeks of the AC current (zero potential) to be turned off.
Switching circuit: composed of high-power transistor transistor, unidirectional thyristor, bidirectional thyristor, power field effect tube, insulated gate bipolar transistor and other semiconductor devices, under the control of trigger signal, to achieve the load circuit on and off control.
Absorption circuit: used to prevent the impact and interference of the peak and surge voltage from the power supply to the switching device, generally using R-C series absorption circuit or nonlinear resistor (varistor).

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