Hi all, I need to build a circuit that will switch a low voltage signal when a high voltage (240VAC RMS) is detected. Basically I have an existing circuit as below:

|----------/-------------|
| |
AC LOAD
| |
|------------------------|

where the '/' is a switch on the active line. (sorry for the crappy drawing . Once that switch is closed I need to close a circuit between an input and a 5V rail but I am unsure how to accomplish this. The best way I can think of doing it is to wire in a step down transformer/rectifier/filter to drive a relay but this seems overly complicated for the outcome I need to achieve. The other way is to use the 240V switch to connect the 5V rail to the input but I will need someway to isolate the high voltage portion of the circuit.

Can anyone suggest the best way to do this?

Cheers

Mick

 

Hi,

How about a relay with a 240 volt coil?

 

Why would rectifier and filter be needed to drive a relay? A small transformer should be all that's needed for driving a relay.

 

hmm...yeah in hindsight that was stupid, of course a relay coil could be driving off AC..silly me, however I had a bit of a look around and could not find a relay with a 240V coil. Every 240v relay I found was rated to 240v on the contacts but not the coil...

 

Howdy, welcome aboard! Potter-Brumfield/Tyco make small relays with 240 VAC coils with up to four "C form" contacts and NTE probably does, too. Check with Google.

 

cool thanks! ill check it out

 

Check Digikey...

http://www.digikey.com/scripts/DkSearch/dksus.dll?Criteria?Ref=96566&Site=US&Cat=33817707

That link is for SS relays.

Just change the filter to 240VAC and, you will get a bunch.