Electronic switch

[gonelli]

Does anyone know of a circuit design that uses 9VAC to operate an electronic switch (something like a transistor or relay) to turn on a seperate 12VDC circuit?

[YT2095]

can`t you rectify the 9VAC to make DC instead? there`s not much in the way of "Electronics" that works on AC, it tends to prefer DC, a fullwave bridge rectifier feeding a relay will work.

Edited December 14, 2008 by YT2095

[John Cuthber]

Just a relay might work. You might need one with a coil voltage rather less than 9V because the impedance will be higher for an AC drive and you would need a relatively big relay so the switch is too big and heavy to react in the 1/100 sec or so between cycles.

[YT2095]

the above doesn`t work, you need at least 1 diode (half wave) for it to work.

try stick a paperclip to transformer

[John Cuthber]

Relays with AC coils are perfectly common and they work just fine.

http://www.maplin.co.uk/Module.aspx?ModuleNo=2567

When the current flows one way the coil becomes a magnet and atracts the armature. When the current reverses exactly the same thing happens. The reason you can't generally stick a paperclip to a magnet is that most of the flux flows round a closed loop.

[YT2095]

no one`s saying AC relays aren`t available, these are specially designed for the job and can`t be substituted with a regular relay without support circuitry (such as a diode).

 

btw, I tested your idea before I posted #4, and I assure you again, it doesn`t work, I used a 9 and 6v type, nada.

[John Cuthber]

So, what was the paperclip comment about?

[YT2095]

put DC into a transformer and it`ll stick (I tested that one that too).

 

it Would be interesting to see what would happen at a lower frequency and maybe not use a sinewave but rather a square wave?

I also expect that it may be possible to use a regular relay AC driven, if you use matched capacitors. although it would probably only work well at a given frequency.