A solid state relay circuit has following main components −
Input Circuit Components
Control Circuit Components
Output Circuit Components
The input circuit of solid state relay (SSR) is part to which the control circuit is connected and the control voltage is applied to this circuit. The input circuit of SSR performs the same function as the coil of an electromechanical relay. The input control voltage of a solid state relay is controlled by means of mechanical switches, transistors, logic gates, low-voltage signals etc. The input circuit is activated by applying an input control voltage to the SSR that being higher than the specified pickup voltage of the solid state relay.
The control circuit of solid state relay has the components that determines when the output circuit being switched on or off. It acts as the interface between the input and output circuit of the SSR.
The control circuit consists of electronic circuitry inside the SSR and the switching method of this control circuit depends upon the type of SSR viz. zero switching SSR, instant on SSR, peak switching SSR or analog switching. When the input control voltage is applied to the SSR, the control circuit responds depending on the type of the relay.
The output circuit of a solid state relay (SSR) performs the function of switching the load. The most solid state relays use SCR, TRIAC, transistor, anti-parallel SCRs or SCRs in a diode bridge depending upon whether the load is AC or DC.