Voltage regulator with alternate voltage source...

[William Donzelli]

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 . <drlegendre at gmail.com> 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 <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.
>> >
>> >
>> >
>>
>>
>> --
>> 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.
>>
>>