Re: Turn on Apple to preserve it?

["Michael J. Mahon" <mjmahon@aol.com>]

Mike Willegal wrote:
> Yes there are plenty of kinds of DC to DC converters around, but at 
> least for initial prototyping, it would be faster to put together, if I 
> didn't need to design a onboard power supply.  In any case, I also have 
> to think about ground loops.  I'm not sure if typical USB 
> implementations optically isolate the USB bus from the rest of the 
> circuit or not.

A +12v to -12v converter will have a ground in common with the +12,
which is what you want.

The USB data lines are differential, and moderately resistant to
common-mode voltages.

-michael

> Regards,
> Mike Willegal
>
> Linards Ticmanis wrote:
>
> > Mike Willegal wrote:
> >
> > > So what are the restrictions on the early Apple supplies.  I've been 
> > > thinking about the implemenation of a USB-Disk II interface.  One of 
> > > the issues is a power supply for a Disk II  (+5/-5/+12/-12).  One of 
> > > easiest solutions would be an Apple II supply, but I'm not sure if 
> > > there is enough current draw from an idle Disk II.  Any thoughts out 
> > > there?
> >
> >
> >
> > -5 is not needed at all as far as I can tell from the schematic, and 
> > -12 only to bias the differentiator in the mc3470 amplifier, so 
> > current draw should be tiny.
> >
> > Aren't there small components that can make -12 from +12?

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