Hi, I wonder if I am correct that the subsystem on the 5V Arduinos that controls how power is applied affects basically between the barrel connector/VIN and the USBVCC power path, not the 5V pin. So if sufficient voltage is applied to either the barrel connector or VIN the comparator shuts the USBVCC path with a mosfet. The 5V pin is unaffected by this, is that correct?
This means that one could make a regulated low power idle system (say 3-500 mA) for a 5V Arduino feeded via USB that kicks in a bigger PSU to VIN when needed for peripherals for example? The Aduino could wake that PSU up from an output pin that opens a triac, SSR or a mosfet controlled relay? An I dont have to bother about disconnecting the USBVCC feed.