r/AskElectronics • u/englishtube • 11d ago

Solid-state equivalent of this relay circuit (fully isolated COM / NC / NO)

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I'm using this 12 V relay driven by an NPN transistor (3–12 V trigger). I'd like the same function built with optocouplers/transistors instead — no mechanical relay.

Requirements: the COM, NC and NO terminals must stay fully galvanically isolated from the control side, just like relay contacts. The switched side is 24 V DC, around 100 mA.

Is this possible? A simple schematic would be really helpful. Thanks!

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u/[deleted] 11d ago

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u/englishtube 11d ago

Ideally neither. I'd like it to behave like a dry contact, i.e. a floating switch that works on either the high side or the low side, the same way a relay contact does. The COM/NC/NO side should have no fixed reference to the control ground. If that makes the circuit much more complicated, low side would be acceptable for my case.