Electronic – Difference between optoisolator(optocoupler) and solid state relay


I have been looking into relays and optoisolators. I am aware that there are different optoisolators, with some having a transistor on the detector side which allows current to flow in one direction whilst there are others with triacs on the detector side to allow current to flow in both directions:

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Upon reading up on relays, I found that they work in a similar manner but using mechanical switching using electromagnets to isolate the two sides of the circuit.

I would have then expected solid state relays to be a sub category of relays, but when I looked them, by defintion they perform the same function as an optoisolator.

What is the difference between an optoisolator and a solid state relay, if any? Which is a sub category of which and what are the differences in terms of speed and applications?

Best Answer

Opto-isolators are designed to switch a small amount of current. A solid-state relay typically contains an opto-isolator along with some circuitry to switch a large amount of current in response to the small current switched by the opto-isolator.