Windo comparator using LM311 to compare between 3.3v to -24vdc

Discussion in 'General Electronics Chat' started by Sigamani, Feb 13, 2014.

  1. Sigamani

    Thread Starter New Member

    Apr 6, 2012
    5
    0
    Dear Sirs,

    Using NI Multisim version 13.0, windo comparators works fine when comparing voltages between 9 to 24Vdc.
    However it fails when comparing 3.3 to -24vdc.
    Will the comparator, LM311 able to compare the 3.3 to -24vdc?

    Any help in this would be very much appreciated.
     
  2. #12

    Expert

    Nov 30, 2010
    16,261
    6,774
    Only if you give it the right power supply voltages.
     
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  3. crutschow

    Expert

    Mar 14, 2008
    13,000
    3,229
    The LM311 can't compare voltages below it's negative supply voltage.

    Post your circuit diagram.
     
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  4. Sigamani

    Thread Starter New Member

    Apr 6, 2012
    5
    0
    Hi Thanks for the help.

    1. I have given the right voltage supply (in MultiSim) still no luck.

    2. Supply voltage is +/- 18 volts. The upper and lower limys are 3.3v and -24volts. Sensing voltage is -10v.

    I will post the drawing tonight (Sorry at work now)


    Thanks
     
  5. Sigamani

    Thread Starter New Member

    Apr 6, 2012
    5
    0
    Hi I have attached the drawing.

    please help.

    Thanks
    Mani
     
  6. tindel

    Active Member

    Sep 16, 2012
    568
    193
    It looks like your supply is negative and you've given it a '-18V'... that's a double negative, making a positive. Change the polarity of your negative voltage or remove the '-' from the voltage level... not both. Then your sim should work.
     
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  7. Sigamani

    Thread Starter New Member

    Apr 6, 2012
    5
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    Hi tindel et al, thanks for the help.
    I have sorted supply voltages and the simulation is working fine now.
     
  8. crutschow

    Expert

    Mar 14, 2008
    13,000
    3,229
    Note that ±18V is the absolute maximum supply voltage allowed for the LM311. You should keep it no greater than ±15V for reliability. Also the worst-case input voltage range is 13V to -14.5V. If you need to detect input voltages higher then that, you can use resistive voltage dividers (bridge circuit) on the inputs.
     
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  9. Sigamani

    Thread Starter New Member

    Apr 6, 2012
    5
    0
    Hi crustchow, many thanks for the info. It was a great help.
    very much appreciated. Thanks.
     
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