• State TI Thinks Resolved
  • Locked Locked
  • Replies 4 replies
  • Answers 1 answer
  • Subscribers 46 subscribers
  • Views 1212 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

LM741: Device not functioning as expected.

Kim Rogers
Prodigy 70 points
Part Number: LM741
Other Parts Discussed in Thread: LM35,

I created a voltage comparator to monitor temerature and to trip a relay when the temperature exceeded a set point.
I used and LM35 as the sensor,   I used what I thought was a standard configuration.  When powered up with the sensor voltage below the set point the output should be low.  But it's not.  It is at the rail.
This is not how a non inverting comparator should work.  It works in simulators but not real life.  I have attached tthe schematic for review.  any help is greatly apprecaiated.8233.HV Switch.pdf

  • Former Member
    0 Former Member

    Hello Kim,

    The LM741 will not work reliably with a 5V supply as this because it is below the rated supply voltage of the amplifier.  I would also recommend switching to a part that is a dedicated comparator instead of using an op amp, such as the LM741.  Here is a link to the comparator search tool.

    The circuit may have worked in simulation because the model does not verify whether or not the supply voltage is in an acceptable range.  I would imagine that when the supply voltage is out of its intended region, the output operation becomes unpredictable and cannot be modeled.

    Please let me know if you need any further help.

    Regards,
    Daniel

  • 0 in reply to Former Member
    Prodigy 70 points

    Hmm.  I thought that was good. I never really looked at it cause the example circuit I found was using a 9v single ended supply.
      Could you suggest a Pin compatible part that would be low cost that could run from a single 5V supply or maybe a 9V?  I see so many options but
    I don't want to overspec the part for this simple circuit.  I apprecaite your input.  I can't believe I made such a bone headed move.  I guess I trusted the sim
    to give me accurate results given I used the actual parts.  I just grabbed a pn I was familiar with by memory and when the sim showed it working correctly
    I assumed everything was good to go.

    I look forward to your reply.

  • Former Member
    0 Former Member in reply to Kim Rogers

    Kim,

    Not a problem and a mistake we all make from time to time.  Would you share the package you are using?  Once we determine that, I can split this off into a new thread so the comparators team can make a suggestion.

    Regards,
    Daniel

  • Former Member
    0 Former Member

    Hi Kim,

    Thanks for the information.  I have split this thread into a new one so the proper team can recommend a part.

    Here's the new thread.  I will close this one for now, but feel free to comment here again if you have any type of issue.

    Regards,
    Daniel