I need to power my Pi 3A+ via the pins (not the onboard micro USB) so I can put the power connector anywhere I want in my custom box. I have a separate micro USB female connector connected via two wires to the first 5V pin and one of the ground pins on the Pi. Using the same power adapter that works very well with the onboard connector, I often get under-voltages, and so I worry about regulating the voltage.
I've read hats-master and it says that it's fine to do things that way, as long as I "implement a duplicate power safety diode", and it also provides this diagram:
Seems to me that this diagram shows not one but two diodes, plus a polyfuse. I could solder these on the 5V input (between my own micro USB female connector and Pi's pins) but I don't understand what kind of diodes I need, and what polyfuse.
I would appreciate some simple answers telling me what components I should buy, and if it's fine to just solder them as per the diagram above.