2017-06-15, 16:20
(2017-06-14, 23:12)kevinmcc Wrote: I still think they should add a protection diode to the 3.3 V rail.
Can't use a series diode, it would drop to much voltage in forward mode.
Parrallel zener? Maybe but it has to have a high enough voltage such that an "enthusiastic" nominal 3.3 V supply doesn't cause it to conduct but low enough that it'll conduct before the nominal 3.3 V components get fried. The +5 V regulator is a nominal 250 mA device but has a typical short circuit current of 500 mA, so this 3.5 V has to dissipate 1.75 W or more...
Best not to fiddle with the power jumpers with the unit powered up. B-)