1. If Edison is OFF and +5V USB is plugged in. That will turn ON Q1.1 and turn OFF Q2.1 resulting in logic high for PWRBTN# on Edison. Basically that will do nothing for Edison and it will stay OFF.
2. Note that since the Edison module is OFF, the gate of p-channel FET Q1.2 is 0 volts and the pin 2 of R4 is at VBAT while pin 1 of R4 is ground because Q1.1 is ON.
3. Now removing the +5V USB will make the gate of Q2.1 to VBAT thereby turning it ON. This will pull down PWRBTN# pin on Edison module.
4. Once Edison is turned on, net V3P3_Edison will become 3.3V turning OFF p-channel FET Q1.2. This will lead to the gate of Q2.1 pull down to GND by R5. This will bring back the PWRBTN# of Edison high.
5. Note that once Edison is turned on, if you insert +5V USB, nothing will happen.
Stop breadboarding and soldering – start making immediately! Adafruit’s Circuit Playground is jam-packed with LEDs, sensors, buttons, alligator clip pads and more. Build projects with Circuit Playground in a few minutes with the drag-and-drop MakeCode programming site, learn computer science using the CS Discoveries class on code.org, jump into CircuitPython to learn Python and hardware together, TinyGO, or even use the Arduino IDE. Circuit Playground Express is the newest and best Circuit Playground board, with support for CircuitPython, MakeCode, and Arduino. It has a powerful processor, 10 NeoPixels, mini speaker, InfraRed receive and transmit, two buttons, a switch, 14 alligator clip pads, and lots of sensors: capacitive touch, IR proximity, temperature, light, motion and sound. A whole wide world of electronics and coding is waiting for you, and it fits in the palm of your hand.