How solid state relay works?
Answer:
Solid state relays switch electric current on and off using a semiconductor device similar to a transistor. They can control voltages and currents that are significantly higher than the signal voltage that is applied to cause them to turn on and removed to tell them to turn off.
Relays are switches that are operated by an electromagnet.
When power is sent to the coil the relay changes its state and has a set on or off state.
They use an optically coupled triac.
The control input (what would be the 'coil' of the relay) current lights a light emitting diode (LED). The light from the LED shines on the photoreceptor portion of a triac.
A triac is a semiconductor device that will breakdown and conduct current when a small control current is injected into its 'gate' input -- only in this case instead of DC current it is current produced by the light from the LED that turns on the triac. The triac will conduct current in both directions so you can connect AC sources and loads to it (just as the contacts on a relay would pass both DC and AC).
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