The English name of solid state relay (also known as solid state relay) is SSR. The input and output of the SSR device can be changed from two input contacts to the active state by switching the input and output contacts of the SSR to two input and output terminals.

The solid state relay has the advantages of reliable operation, long service life, no noise, no spark, no electromagnetic interference, fast switching speed, strong anti-interference ability, small size, impact resistance, vibration resistance, explosion-proof, moisture-proof, corrosion-proof, compatible with TTL, DTL, HTL and other logic circuits, and can directly drive large current load with small control signal. The main disadvantages are the on state voltage drop (corresponding heat dissipation measures are required), the off state leakage current, the common use of AC and DC, the small number of contact groups, and the poor index of over-current, over-voltage, voltage rise rate and current rise rate.