1 Jul
2008
1 Jul
'08
11:32 p.m.
On Mon, Jun 30, 2008 at 1:48 PM, Philip Belben <philip at axeside.co.uk> wrote:
Roy J. Tellason wrote:
Oddly enough, whereas two 9V secondary windings seem common in the UK,
I'm having a VERY difficult time finding one in the US. I suppose
it's got something to do with the fact that UK/European transformers
are stepping down from 230V mains, where the North American ones are
stepping down from 110-120V mains.
I have been able to find transformers with a 115 V primary winding and
two 18 V secondary windings with center taps. I assume I can use the
center taps, but honestly I'm not sure. Time to consult some higher
authorities! (i.e., Chapter 6 of "The Art of Electronics" and Chapter
17 of "The ARRL Handbook"!)
-Seth
The 9VAC has to be a separate transformer winding
from the one that
provides the +5VDC eventually, because of how it's used...
There are plenty of transformers around with two 9V secondaries. I'd reckon
on using on of at least 20VA rating even if you have a switching regulator.