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Old 5th September 2003, 08:30 PM   #1
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Default Here's a good problem for you (non-audio related)

I am trying to find a circuit to replace a relay with a 120VAC coil. The relay was used to sink a DC signal to ground. I need to find a solid state circuit to replace the relay, with a cost limit of around $10- $15 US. Here's the catch: the AC line must be isolated from the DC, and it must be reversable, in case the outlet is wired wrong. I have gone over and over this, but the only circuits I can come up with will always turn on and stay on when the AC line is reversed. I was thinking of using a mosfet to sink the DC, but you can't isolate the supply, or there is no reference for the mosfet gate-source voltage! This is like a dog chasing it's tail. I thought it was an interesting problem. Maybe someone here can come up with something. Right now, I am thinking of finding a very small PC mount tranformer to supply an isolated AC signal (doesn't need to source any current- just need the voltage).
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Old 5th September 2003, 08:33 PM   #2
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Have you considered using an optocoupler?
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Old 5th September 2003, 08:58 PM   #3
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Yes, but I don't want to have to re-design a pcb in a few years because an opto went obsolete. I guess I forgot to mention that it should use easily replaceable parts.
I will probably stick with the relay, because it's cheap and easy (and this is for work).
Good suggestion.
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Old 5th September 2003, 09:11 PM   #4
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There are almost always lots of good deals to be had on used Solid State Relays.

http://www.mpja.com/productview.asp?product=12808+RL

OOPS thats backwards from your application...
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Old 5th September 2003, 09:18 PM   #5
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Default Perhaps a little closer:

How much current did you need to sink?

Will this work:

http://www.mpja.com/productview.asp?product=14578+RL

This one might be a little closer:

http://www.mpja.com/productview.asp?product=7936+RL
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