auto-sensing voltage switch

Dec 14, 2005 4 Replies

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440roadrunner 20 years ago

I need to find or design a circuit that detects the input line voltage (it will be either 110vac or 24vac), and then toggle a switch (or relay) to the output path to the proper circuit.

The logic of the circuit would be something like:

If line-in voltage is 110v then switch position A If line-in voltage is 24v then switch position B

Unit should handle 2amp max current draw.

Is anything like this commercially available? If not, any ideas?

I know this is probably something quite simple for you guys...

Thanks!

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ehsjr 20 years ago

It's a 120 VAC relay. When 24 VAC is applied to its coil, nothing happens, and the relay stays de-energized. When

120 VAC is applied to its coil, the relay is energized, and the contacts transfer. +------Normally Open | | +------ Common | | o o o------ Normally Closed ----- | | | Vin ------|Relay| | | | ------|Coil | |> |

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Rich Grise 20 years ago

I saw a guy do this to switch from 120V to 240V mains, but he added a diode and a cap for some reason, and every time I plugged one in to 240 to test, I kinda cringed expecting an explosion. It did seem to work OK, however. :-)

Cheers! Rich

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Pooh Bear 20 years ago

SGS-Thomson once made an IC specifically to do this ( except it was 120/240V ). One important thing to note is that the status needs to be latched once detected or you may get a loud band under brown-out recovery conditions !

formatting link

Graham

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Jasen Betts 20 years ago

~~~~~~~~~~~ like Deep Purple -

Smoke Upon the Water

(sorry)

Bye. Jasen

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