"...if you leave the unregulated rail _unattached_ and put +5 switcher straight onto the regulated +5 rail..."
My error, I read that as "attached". In any event, just lift both the 7805 IN and OUT pins, and then supply known-solid +5DC between the OUT and GND pads on the board. No, you can't feed the IN pin with +5V, for as others have mentioned, the 7805 has a minimum dropout of 2V or so. On Thu, Apr 7, 2016 at 4:03 PM, William Donzelli <[email protected]> wrote: > Per his description, the 7805's input will be open. It will not try to > source any current, as it will have none to give. > > I suppose there might be a little leakage. > > -- > Will > > On Thu, Apr 7, 2016 at 4:58 PM, drlegendre . <[email protected]> wrote: > > 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 > > do. > > > > On Thu, Apr 7, 2016 at 3:41 PM, wulfman <[email protected]> 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. > >> > > >> > > >> > > >> > >> > >> -- > >> The contents of this e-mail and any attachments are intended solely for > >> the use of the named > >> addressee(s) and may contain confidential and/or privileged information. > >> Any unauthorized use, > >> copying, disclosure, or distribution of the contents of this e-mail is > >> strictly prohibited by > >> the sender and may be unlawful. If you are not the intended recipient, > >> please notify the sender > >> immediately and delete this e-mail. > >> > >> >
