The working principle of solid-state relays is based on the characteristics of electronic components to achieve contactless switch control.

Taking the common optoelectronic coupling type solid-state relay as an example, its working principle is roughly as follows:

The input circuit receives control signals, usually a small voltage or current. After processing, this input signal drives the light emitting diode (LED) to emit light.

The light emitted by LEDs is received by optoelectronic devices such as phototransistors or photo controlled thyristors. Due to the irradiation of light, the conductivity characteristics of optoelectronic devices change, thereby achieving electrical isolation and signal transmission.

The power semiconductor devices (such as thyristors, transistors, etc.) in the output circuit control the on/off of the load circuit based on the conduction state of the optoelectronic devices. When the optoelectronic device conducts, the power device in the output circuit also conducts, allowing current to pass through the load; When the photoelectric device is turned off, the power device in the output circuit is also turned off, and the load current is cut off.

In summary, solid-state relays convert input control signals into the on-off of power devices in the output circuit through optical coupling, thereby achieving load control. They have the advantages of fast response speed, contactless operation, and long lifespan.