What is the role of solid state relays?

The input circuit of the solid state relay is to provide a loop for the input control signal, making it the trigger signal source of the solid state relay. The input circuit of the solid state relay is mostly DC input, and some are AC input. The DC input circuit is further divided into resistance input and constant current input. The input control current of the resistive input circuit varies linearly and positively with the input voltage. In the constant current input circuit, when the input voltage reaches a certain value, the current will no longer increase significantly with the increase of the voltage. The relay can be applied to a wide range of input voltages.

The output circuit of the solid state relay is controlled by the trigger signal to realize the on-off switching of the solid state relay. The output circuit is mainly composed of an output device (chip) and an absorption loop that acts as a transient suppressor, and sometimes a feedback circuit is also included.

The advantages of solid state relays:

(1) Long life and high reliability: SSR has no mechanical parts and has solid-state devices to complete the contact function. With no moving parts, it can be used in high shock and vibration environments. Solid state relays have long life and high reliability due to the inherent characteristics of the components that make up solid state relays.

(2) High sensitivity, low control power, and good electromagnetic compatibility: solid-state relays have a wide input voltage range and low driving power, and are compatible with most logic integrated circuits that do not require buffers or drivers.

(3) Fast switching: Since the solid-state relay adopts solid-state devices, its switching speed can be from several milliseconds to several microseconds.

(4) Small electromagnetic interference: The solid state relay has no input "coil", which does not trigger arcs and rebounds, thereby reducing electromagnetic interference. Most AC output solid state relays are zero voltage switches, conducting at zero voltage and closing at zero current, reducing sudden interruptions in the current waveform, thereby reducing switching transient effects.