Voltage regulator with alternate voltage source...

[Brent Hilpert]

On 2016-Apr-08, at 11:27 AM, Mouse wrote:

>> I archive all data sheets I run across and I found this information
>> on both TI and Fairchild data sheets for the 78H05, LM340 and LM78XX
>> devices - it is usually under a heading called Application Hints and
>> for some reason Fairchild have removed these Hints from the sheets
>> you quote.
> 
>> In ALL cases the manufacturers caution that putting voltage to the
>> output when the input is not powered CAN DAMAGE THE CHIP.
> 
> I have the datasheet PDF for the On Semiconductor version, and I have
> been unable to find anything of the sort in it.


http://www.ti.com/lit/ds/symlink/lm340-n.pdf
page 11

I suspect it would be OK if VIN and VOUT were shorted during the procedure (and VIN was otherwise open or has just a small cap to gnd) as that likely takes care of reverse current and reverse bias situations being set up on internal junctions, but one doesn't know for sure unless you examine the internal schematic adequately or test the device.