Voltage regulator with alternate voltage source...

drlegendre . drlegendre at gmail.com
Thu Apr 7 15:58:32 CDT 2016

Err.. unless the voltage of the switcher is identical to that of the 7805,
then one device will source current, and the other will sink it.

Like putting two 6V batteries in parallel, where one is fresh and the other
weak. Current will flow until the potentials are equalized. But with two
regulated circuits, I don't see how equality can be achieved.

Not saying it's going to smoke-out, but it does seem like a wonky thing to

On Thu, Apr 7, 2016 at 3:41 PM, wulfman <wulfman at wulfman.com> wrote:

> You should be just fine.
> On 4/7/2016 1:38 PM, Bill Sudbrink wrote:
> > If you have a circuit which is normally designed to
> > operate with an unregulated supply, through a regulator...
> > say unregulated +8 through a 7805 to a regulated +5 and
> > you want to test it independent of the +8 supply, if
> > you leave the unregulated rail unattached and put +5
> > switcher straight onto the regulated +5 rail, will you
> > damage the 7805?  Clearly the VIN is open, but the ground
> > pin will still be attached.  Would this push voltage
> > back through and screw things up?
> >
> > Thanks,
> > Bill S.
> >
> >
> >
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