I have a power supply (original Raspberry Pi power supply, datasheet) with 5.1 V which delivers up to 3 A. In case of a short-circuit or if more than ~ 3.4 A is drawn, the power supply will change to a short-circuit state.
This behaviour is used for a simple reverse voltage protection. A Schottky diode is placed anti-parallel and therefore will cause a short-circuit in case of reversed polarity. It will draw all the current and cause a high voltage drop below 0.3 V and so will protect the circuit.
The question though is, how many amperes do I need for the Schottky diode considering that the power supply will switch to a short-circuit state in that case? I consider that the diode will only get the ~ 3.4 A for milliseconds. Will I really need a diode with >= 3 A or isn't a diode with 1 A also be enough?