How to make a comparator circuit

Discussion in 'Homework Help' started by paulepc, May 8, 2014.

  1. paulepc

    Thread Starter Member

    Apr 2, 2014
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    The comparator output needs to be 0 volts or -12 volts. I have the +12 volt or zero working but can't get the -12 to work.
    Thanks
     
  2. WBahn

    Moderator

    Mar 31, 2012
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    4,800
    What does the -15V on the output mean?
     
  3. paulepc

    Thread Starter Member

    Apr 2, 2014
    55
    0
    The -15 is the result I get on the circuit simulator, don't know why.
    The simulator switches the output from +12 to -12 volt.

    Basically what I trying to solve is if the voltage going into the op amp drop below 1.2 volts

    I need to disable the circuit. I thought I would pass the 1.2 to 3.2 into an op amp which would give me a maximum volts of approx +10 and a minimum as close to zero as I can get it.

    then put that through a comparator that would shut the voltage down if the input drops below 1 volt.
     
  4. WBahn

    Moderator

    Mar 31, 2012
    17,757
    4,800
    I'm totally confused. You say that the -15V is the output from the simulator and then immediately say that the simulator is switching the output from +12V to -12V. So which is it?

    What do you mean by "shut down the voltage"? You have a comparator that is powered by +12V and -12V rails, so if the differential input voltage is positive, you should get something approaching +12V out and if the differential voltage is negative you should get an output approaching -12V. Why do you think that the voltage would be "shut down" and what does that even mean?

    Perhaps you might start with a concise description of what you are trying to do. You have some input from somewhere and you need to produce some output in response. What is the that relationship supposed to be.
     
  5. paulepc

    Thread Starter Member

    Apr 2, 2014
    55
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    Thanks for the comments, I will post a complete circuit tomorrow if that's ok I really need some import this the last part of the project.
    The forum has been a big help. Really glad I joined.
     
  6. paulepc

    Thread Starter Member

    Apr 2, 2014
    55
    0
    The project receives a PWM signal that goes through a u/Controller which outputs .5 volts to 3 volts this needs to be converted to +/- 10 volts to drive a motion controller driving servo motors. my circuit simulates what I need.

    My problem is if there is no signal coming out of the u/controller I need the output to be zero volts, this makes sure the motion controller cannot move therefore safe.

    So what I need is to disable the circuit or switch off the output and pull it to ground if the input drops below .5 volts

    I am stuck on this I would really appreciate some help.

    Paul
     
  7. paulepc

    Thread Starter Member

    Apr 2, 2014
    55
    0
    This is posted in the wrong forum it's now in the projects forum.
    Thanks
     
  8. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    5,801
    1,105
    How about this?
     
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