1 Jul
2008
1 Jul
'08
4:07 a.m.
Eric Smith wrote:
I wote:
If I'm reading the C64 schematic (Sam's photofact version) correctly, the
ground-side diodes of the two bridges (the original low-current one in the
C64 and the new/main one in the power supply) would end up in parallel
(or almost in parallel: there's a noise suppression inductor, fuse, etc.
involved), so one may have unpredictable behaviour as to which diodes take
the current and/or issues with unintended current flow in some supply paths.
I haven't looked at what the low-current bridge diodes are rated for,
perhaps it would work for the currents involved, but I think it looks bad
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.
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.
However, I haven't tried it, and don't accept any responsibility for
anyone else trying it.
Eric from a 'design principles' perspective.
If one were willing to modify the C64 you could open the ground lead of the
existing bridge (so that you have two half-bridges for the two positive sides,
and one half-bridge for the ground side).
Or perhaps the ground-side diodes of the bridge in the C64 would just go poof and
effectively open the ground lead for you :)