LM311 comparator simple question

Discussion in 'The Projects Forum' started by bobsuper, May 29, 2013.

  1. bobsuper

    Thread Starter New Member

    Mar 14, 2011
    I am building a simple comparator circuit as a test ground for another project.
    The comparator is LM311N.
    The LED lights up when the V+ input is above 6.3 volts, but it doesn't go out until the V+ input goes down to around 0.5 volts....shouldn't it turn off as soon as V+ gets under 6.3 volts???
    I looked at datasheet examples and all, but can't really seem to figure out why it doesn't work as intended.
    Pins 5 and 6 are tied together, and pin 4 (V-) I left unconnected, as the circuit wouldn't work at all with it connected to ground.
    Also, the datasheet mentions it doesn't need a dual power supply, so what should I do with pin 4 (V-)


    Thanks for any input!
    Last edited: May 29, 2013
  2. absf

    AAC Fanatic!

    Dec 29, 2010
    Pin 4 is Vee should be connected to GND. Also put a 10K resistor from output of LM311 to the Battery positive. The LM311 output is open-collector.

  3. bobsuper

    Thread Starter New Member

    Mar 14, 2011
    Thanks Allen, that did the trick!