Commodore 64 Power Supply

[Roy J. Tellason]

On Friday 04 July 2008 21:40, Tony Duell wrote:
> > Roy J. Tellason wrote:
> > > 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.
> >
> > That would be ideal.  Just remember that the 18V winding will be rated
> > for half the current that a 9V winding would have been, and that still
> > applies even if you only use half the winding.  In this case I'd
>
> Now, this is more your filed than mine, but the rating of a transformer
> is determined by at least 2 things :
>
> 1) 'Copper losses' due to the resisance of the secondary winding
> 2) Ditto for the primary winding
> 3) The size of the core / the flux density in the core.
>
> Now, I think that (2) and (3) would be the same whether you used the
> whole winding or half the winding at twice the current. And for small
> transformers, the copper loss in the secondary is rarely the limiting
> factor (For example it's very rare for the seocndary to be the winding
> that fiales on a burn-out).

I'd tend to agree with this.

> Soe while I'd not try and use half the secodnary at twice the rated
> current, I think you would get away with rather more than the current you
> could draw if you used the whole winding.

Yup.

> But then again I like over-rating transformers, so I'd probably not do
> this anyway.

If I'm going to spec one,  yeah,  but more often than not if I'm building 
something from scratch I'll end up using some transformer I salvaged 
somewhere,  and mostly it works out.

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