12v also feeds the input of the lm317 and puts out 5.3v regulated voltage on the output, according to the resistor feedback circuit.
R3 and R4 form a voltage divider that puts 4.86v on the non-inverting input of the amplifier when the reference voltage placed on the positive plate of the capacitor is fed into the inverting input.
...allowing current o flow from the drain of the MOSFET and out of the collector to charge the capacitor.
...and at the same time turns on the PNP transistor Q2 lighting the Green LED...
Actually, Q2 should be an NPN transistor. Unless the idea is to use the BE junction as a Zener, but then, there would be no inversion, so the LED would light when Q1 is ON, not when it's OFF.
... nut isnt Q2s base normally pulled high by 10k resistor and only when the output of the amplifier is LOW can it be activated?
The base of Q2 is pulled LOW by pin 7 of U2-A, turning OFF Q1 and the LED.http://www.ti.com/lit/ds/symlink/lm311.pdfNotice LM311 output is open collector, it's either conducting to ground or high Z.