Voltage Comparator in Multisim 10

Discussion in 'General Electronics Chat' started by yoppy, Mar 16, 2010.

  1. yoppy

    Thread Starter New Member

    Mar 16, 2010

    I'm trying simulate voltage comparator using Multisim 10.
    I use LM741 (as in "Circuit LM741.jpg"). The output is not limited to V+ or V-. Instead, it's going over kilovolt.
    Why? Can you explain to me?

    Then, I replace LM741 with 741 op-amp. The result is as expected (V+ or V-).

    What is the difference between LM741 and 741 ?

    Thx for helping .... [​IMG]
  2. retched

    AAC Fanatic!

    Dec 5, 2009
    Five bucks says it wont do that in practice. (for long)
  3. NatashaB

    New Member

    Feb 4, 2009
    Hi there,

    I think you have come across one of the simplified opamp models in the database. Some of the opamps have only 3-pins modeled (ie. inputs, and output - no power supplies). The models work properly in closed-loop configuration, but in open-loop (as seen here), they will not clip.

    Here's someone who had a similar issue on the Multisim forum: http://forums.ni.com/ni/board/message?board.id=370&message.id=6762&query.id=3269420#M6762

    My suggestion is to replace the model with one that has the power supplies modeled. There is a National Semiconductor model attached to the same component that has all pins modeled. To replace the model:

    1. Double-click on the component
    2. Click on Replace
    3. In the model field for the LM741H, select the National/LM741_3 model

    Let me know if you're still having trouble.
  4. yoppy

    Thread Starter New Member

    Mar 16, 2010

    Thank you so much... Your suggestion is very helpful. May be next time I will ask you again. may I know your email / YM ID? Mine is <snip>
    Last edited by a moderator: Mar 17, 2010