This may be the wrong forum to ask this, but any reason why the output of a 5v LDO regulator can't be connected to the output of a 3v LDO regulator? Both having 12v on their inputs? The purpose would be for a jumper to provide an option of 5 volt to all circuitry with jumper on, and only 3 volt with jumper off to part of the circuit with 5v going to another part of the circuit. Would obviously be best to connect 5v out to 3v reg-in with jumper, but I'd like to use only one jumper yet have option to power either both 5 and 3 to different parts of the circuit, or only 5 volts to everywhere. I'm thinking the output diode in the 3v LDO would block any current backwards into it from the high voltage as long as it had a high input.
Ideas?
No, that would be bad.
Why not just have a 3-pin header with +5 on one end, circuit power in the middle, 3v at the other end.
Then your 2-pin jumper connects either 5v or 3v to the circuit.
Yours,
TonyWilk
Thanks Tony. Here's a pic of what I tried. Can you explain why it would be bad, even though it had "seemed" to me at first it would be too? With what I tried I saw no extra current flow, or any extra heat on either LDO. Disconnect the 3 and LED dims and 3.3v on output (of course). Connect 5v with 3v and LED brighter and 5v on output. No extra current flow or heat anywhere.
edited: should have read: "Disconnect the 5V and LED dims and 3.3v. . ."
With what I tried I saw no extra current flow, or any extra heat on either LDO.
So you can "see inside" the regulator can you?
Connecting two power outputs together is a stupid thing to do. It is not only heat that kills an IC.
