On Sat, 30 Jul 2005 13:17:59 +1000, Groups wrote:

>...<
> I was also thinking that maybe I could print a transformer on the PCB. ie.
> Place a resistor in series with a track to develop
> a mA or 2 in the primary and pick up a small portion magnetically (bit like
> a directional coupler). The current limiting then allows
> the low impedance track to be used without shunting the motor (The circuit
> is to have 3 inputs that monitor the voltage
> across motors).  A 270 V MOV would be placed across the input for transient
> protection.
> 
> What are your thoughts ?

The isolation requirements would mean that you're unlikely to be able to do this in a 25x25mm space.  Using a 
transformer with the mains side pins on the edge of the PCB gives you some "automatic" clearance by the 
transformer's own size, and putting a slot in the PCB can increase this, but you can't do that with a printed 
coil - it, its current-limiting resistors, and the MOV are all live so you need clearance all round, and it 
sounds like you don't have the space.  I'd go for a "proper" transformer and as you've found, Jinx has some 
experience of these, and has made a lot of the mistakes for you!  :-)

Cheers,


Howard Winter  G1BYY
St.Albans, England

-- 
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist