This is in regards to the Arduino Mega 2560.
I’m close to fully understanding the circuit for powering the Arduino - power jack, USB, and when both are plugged in.
When both are plugged in, the LM358D acting as a comparator gives powering priority to the USB if the jack is < +6.6V. Then, the FDN304V mosfet is turned on, allowing the USB voltage to get regulated to +3.3V via the LP2985-33DBVR. The +5.0V from the USB also now is referenced by “5V” on the schematic.
When both are plugged in but the jack is >= 6.6V, the mosfet stays “closed”, and the voltage from the jack goes to the MC33269ST-5.0T3 regulator for the +5.0V.
In both scenarios though, the MC33269ST-5.0T3 regulates +5.0V (unless it doesn’t for some reason?)
My question is this: which voltage does the +5V reference on the schematic refer to when the USB is powering the board? Fundamentals of electricity may come in to play here, so forgive me.