Commodore 64 Power Supply

[Roy J. Tellason]

On Monday 30 June 2008 20:52, Eric Smith wrote:
> I wote:
> > Why does it require isolation between the 9VAC and the +5V DC?  It's not
> > obvious to me from the schematic.
>
> Roy wrote:
> > The 9VAC supply is fed into a voltage doubler to derive the regulated
> > +12V and a separate +5VDC supply,  and I don't think that either of those
> > 9VAC lines can be grounded.
>
> Neither side needs to be grounded.

Well,  if you were trying to operate the 9VAC and the regulator for the +5VDC 
off the same winding,  you'd run into some trouble there,  I think...

> The C64 *already* has a bridge rectifier and 5V linear regulator powered
> by the 9VAC input to produce an auxiliary 5V supply, so I don't see why
> building an external power supply using a transformer with a single 9VAC
> secondary, and a bridge rectifier and 5V regulator (linear or switching)
> would be a problem.

Because they really need to have those two +5VDC supplies separate and 
independent of each other.  That's the way the thing was designed,  and as 
much as that company was into cost-cutting and shaving wherever they could, 
to the extent possible,  I think that if they could have omitted that somehow 
they would have.

> However, I haven't tried it, and don't accept any responsibility for
> anyone else trying it.

:-)

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