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.pdf
Notice LM311 output is open collector, it's either conducting to ground or high Z.
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.pdf
Notice LM311 output is open collector, it's either conducting to ground or high Z.