Teensy usb powered + External power at same time?


Well-known member

So I've been reading some things on here and I don't quite understand some of it.
Is it possible to have my teensy powered from a regulated 5V source (VIN), and then I plug on a usb cable to update it?
Is it possible to do this OK without cutting the trace?

I've done this with arduino nanos and got away with it, what's the issue with teensy?

Teensy 3.6
if your external source voltage backfires to your PC port, it may or may not work, however, if the voltage of the external psu is higher you can blow out the PC usb port. Secondly some arduinos switch to the external power instead of USB if the power if both are applied, they have a circuit for that, not sure on the nanos, however, the VIN on teensies is tied to both external and USB, thats why a trace is there to be cut or not.

you can also use a data-only usb cable as well instead of cutting the trace, this will allow you to reprogram teensy while plugged into the external source without cutting the trace. But realistically, you’d want to remember that later on in future you don’t use wrong usb cables or forget you didnt cut the trace, etc.
OK. I saw that circuit, and I'm still thinking of an easier way,

So backfeeding is a concern, OK i hear that.
Will it still be a problem if i put a diode after my regulator to drop the voltage to 4.3V, would that still backfeed into the usb 5v power?
OK just heard from Paul,
he mentioned that even though having a 4.3V from regulated power and 5V from usb will probably work,
it won't when the PC power drops to 0 (completely turns off) and at that point it's possible for voltage to flow into the PC.