Commodore 64 Power Supply

[Eric Smith]

Brent wrote:
> so one may have unpredictable behaviour as to which diodes take
> the current and/or issues with unintended current flow in some supply
> paths.

It generally won't matter that much which bridge is providing
the ground return path.  It will provide the necessary reference
voltage.

If the lower-rated diode happens to have a slightly lower forward
drop at low current, it will start carrying more current, but that
will make its forward drop rise, and the higher-rated diode will
then start conducting more.  (Unless the forward ratings of the
two bridges are significantly different.)

> 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
> from a 'design principles' perspective.

I won't claim that it's great, but I've seen it done in many pieces
of equipment, and haven't ever actually seen a problem result from
it.

> 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).

That will cause a worse problem than the one you're trying to solve.

Eric