I'm designing a small module that takes power from USB and provides it to a breadboard for prototyping. My target audience will just be hobbyists so I want to include some protection. I'm more concerned about protecting the USB supply from mistakes made whilst prototyping rather than protecting the board from faulty supplies.
I'll be including a PTC resettable fuse to protect the USB supply from shorts and over overloads. One thing I am concerned about is when a higher voltage (say 12v) is accidentally connected to the 5v rail, I don't want this to be backfed to the computer or other device that is providing the 5v over USB.
Normal use of a zener diode would be to be place it after the PTC fuse, however I am thinking for my circuit it might be better to place it before the fuse. This way if a user was to accidentally connect 12v to the 5v line, it would first flow through the PTC and then the zener, hopefully tripping the PTC.
Is my thinking here correct?