Commodore 64 Power Supply
Roy J. Tellason
rtellason at verizon.net
Mon Jun 30 20:02:23 CDT 2008
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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