temperature circuit not working on breadboard

Discussion in 'Homework Help' started by ali8tor, Apr 29, 2015.

  1. ali8tor

    Thread Starter Member

    May 29, 2012
    43
    0
    Hi

    Im following this circuit i made on multisim it basically turns on if the temperature is to low or to high. the problem im having is that when i make it on breadboard both leds are on, Im using an LM35 temperature sensor and LM741 as my comparator.

    im getting all my calculated values on the inverting and non inverting pins.

    any help
     
  2. OBW0549

    Well-Known Member

    Mar 2, 2015
    1,328
    890
    Your circuit doesn't work because you are attempting to operate the LM741 with its inputs outside their common-mode input voltage range, and you are attempting to operate it at a lower supply voltage than it's capable of working at. The 741 isn't suited for 5V single-supply operation.

    Read the data sheet: http://www.ti.com/lit/ds/snosc25c/snosc25c.pdf

    You would be better off using an opamp capable of low-voltage, single-supply operation, like the LM358 (dual) or LM324 (quad). Even better would be a proper comparator IC such as the LM339 (datasheet at http://www.ti.com/lit/ds/symlink/lm339-n.pdf).
     
    ali8tor likes this.
  3. MikeML

    AAC Fanatic!

    Oct 2, 2009
    5,450
    1,066
    All of which says that the Multisim '741 model isn't worth a crap!
     
  4. ali8tor

    Thread Starter Member

    May 29, 2012
    43
    0
    i replaced the IC and it works well with LM324 thank you!
     
  5. OBW0549

    Well-Known Member

    Mar 2, 2015
    1,328
    890
    Excellent!
     
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