Does this warning assume that there is something on Vin, and not open? With a quick look at the internal schematic of an old-school 7805, it seems like what Bill suggests (leaving Vin open) will not actually do much. -- Will

On Thu, Apr 7, 2016 at 7:23 PM, John Robertson <jrr at flippers.com> wrote: > On 04/07/2016 2:18 PM, Bill Sudbrink wrote: >> drlegendre wrote: >>> Not saying it's going to smoke-out, but it does >>> seem like a wonky thing to do. >> I disagree about "wonky" let me try with more >> diagram and less English: >> >> (+8) >> | >> VIN| ceramic cap >> |-----][----- >> ___|____ | >> | 7805 |----------GROUND >> -------- | >> | | >> VOUT|(+5) | >> | | >> ___|____ | >> | LOAD |-------| >> -------- >> >> +8 is not currently available (no pun intended). >> I would like to test LOAD without removing 7805 >> as it is soldered in place. Is damage to 7805 >> likely if alternative regulated current is applied >> at (+5) and (+8) is left open? >> >> Bill S. >> >> >> > Yes, you can damage the 7805 - READ the data sheets... > > Raising the Output Voltage above the Input Voltage: > > Since the output of the device does not sink current, forcing > > LM340/LM78MXX Series 3-Terminal Positive Regulators LM340/LM78MXX Series > 3-Terminal Positive Regulators > > the output high can cause damage to internal low current paths in a manner > similar to that just described in the ?Short- ing the Regulator Input? > section. > > > LM340/LM78MXX Series 3-Terminal Positive Regulato John :-#(#