Commodore 64 Power Supply
dkelvey at hotmail.com
Wed Jul 2 22:50:28 CDT 2008
> From: rtellason at verizon.net
> On Wednesday 02 July 2008 02:32, Seth Morabito wrote:
>> On Mon, Jun 30, 2008 at 1:48 PM, Philip Belben wrote:
>>> Roy J. Tellason wrote:
>>>> 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
>> 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"!)
> Which chapter depends on what edition of the handbook. :-)
> If you're talking about a full-wave (4-diode) bridge across a 9V winding you
> can get the same result by using two diodes with an 18V winding. For the
> other, where what you want is only 9VAC, you can use half the winding,
> just one end and the center tap and not use the other end.
I thought I might mention that one could get a 12v transformer and remove
some turns. The easiest ones are the double bobin types used now days
for isolation. These are usually easiest to unwind.
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