First LM393 comparator circuit issues

Discussion in 'General Electronics Chat' started by fishygurl, Dec 16, 2011.

  1. fishygurl

    Thread Starter New Member

    Dec 16, 2011
    2
    0
    I have a LM393 hook up to turn an LED on when the Vin voltage is higher than the Vref voltage. The Vcc of the LM393 is connected to 12V. The Vef voltage is sitting at 11.5V (volt divider with a pot to tune this). My Vin is sitting at 11.8V, which mean my output LED should be on (pulled up using 1K). The LED however won't turn on....If i change the Vef down to 10.8V, the LED (output high) will turn on. This tell me that I have a problem with an offset...I'm just not sure if that problem is with the offset between the vin and vref or if it has sometime to do with 11.8 being so close to 12V?
    Not sure what the trouble is?
    Thanks
     
  2. MrChips

    Moderator

    Oct 2, 2009
    12,435
    3,360
    Check the spec sheet. The input common mode voltage range is Vcc - 1.5V.
     
  3. fishygurl

    Thread Starter New Member

    Dec 16, 2011
    2
    0
    o i see thanks..so i need to either change my range or find a different comparator chip...
     
  4. bertus

    Administrator

    Apr 5, 2008
    15,647
    2,346
    Hello,

    No need to change the comparator.
    Just lower the reference voltage and adopt the to be checked voltage to it with a voltage divider.

    Bertus
     
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