> I didn't put in a diode because of the forward voltage drop

Voltage drop does depend on current and diode rating.

Schottkys -

BAT46 100uA 250mV, 10mA 450mV, 250mA 1000mV
1N582x 100mA 220mV, 500mA 275mA, 3000mA 450mV

So for your envisaged 500mA, a 1N5820 would probably do
to make Vcc > 4.7V

Silicon diodes (1N4148, 1N400x etc) start at ~0.6V. If you
want to compensate for a silicon diode drop you can jack up
the regulator to 5.6V output. Similarly with a Schottky drop

A PFET is good for high-current circuit protection in the +ve
rail or an NFET in the ground rail can be used, generally if the
circuit is self-contained (eg has no external connection to other
equipment that can pass ground current which would get around
the FET)

You can work out what Ron with V =3D IR. eg 0.25V drop at 500mA
=3D> 500 milliohms. A power FET will typically have an Ron of a few
milliohms

Joe


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