The main function of solid state relay is to control weak current and strong current. In simple terms, the main circuit and the main load are controlled by controllable signals. Although there are many solid-state relays on the market, they all work on similar principles. It is mainly composed of input (control) circuit, drive circuit and output (load) circuit, which can be divided into single-phase solid state relay and three-phase solid state relay.
The input circuit of the solid state relay provides a loop for the input control signal and makes it the trigger signal source of the solid state relay. The input circuit of solid state relay is mostly DC input, some are AC input, and very few are not external power supply. Dc input circuit is divided into resistive input and constant current input. The input control current of the resistive input circuit varies linearly with the input voltage. Constant current input circuit, the input voltage reaches a certain value, the current will not increase significantly with the increase of voltage.
The driving circuit of solid state relay can include isolation coupling circuit, function circuit and trigger circuit. At present, isolation coupling circuit, photoelectric coupler and high frequency transformer are mainly used. Common optocouplers are optical triode, optical bidirectional thyristor, optical diode array (photovoltaic). Transformer high-frequency coupling is a self-excited oscillation of about 10MHz under a certain input voltage, and the high-frequency signal is transmitted to the secondary transformer through the transformer core. Functional circuits can include detection and rectification, zero crossing, acceleration, maintenance, display and other functional circuits. The function of the trigger circuit is to provide a trigger signal to the output device.
The output circuit of the solid-state relay completes the on-off switch of the solid-state relay under the control of the trigger signal. The output circuit consists mainly of an output device (chip) and an absorption circuit for transient suppression, sometimes including a reaction circuit