COMPARATORS Integrated-Circuit (IC) Comparators : LM311
The LM311 has differential inputs, an open collector output, VCC input, VEE input, and a ground pin.
The output is taken from a bipolar transistor to allow driving a variety of loads.
A pull-up resistor connected to a positive voltage (VCC) is required to establish the output state.
There is also a strobe input pin that can be used to enable or disable the output.
If the strobe pin is left open (or connected to a positive voltage), the comparator functions normally
If the strobe pin is connected through a resistor to ground, the output assumes the open collector state (high output level) irrespective of the input.