Comparator in spice help.

Discussion in 'General Electronics Chat' started by masteropie, May 17, 2008.

  1. masteropie

    Thread Starter Member

    May 17, 2008
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    Hello, i am hoping someone can help me with LTspice. I can't seam to get comparators to work. I don't know if it is me or spice that is failing.

    The comparator is only outputting 700mV while on. It is being supplied 20 volts and should be outputting 20 volts?
     
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  2. Caveman

    Active Member

    Apr 15, 2008
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    Nope, it's working correctly. You are simply allowing the negative power supply to pull up to where the output is only 0.7V.

    Try tying your negative comparator supply input to ground instead. It'll work better.
     
  3. masteropie

    Thread Starter Member

    May 17, 2008
    26
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    Ahh yes i see. Thanks for the help with that.

    I have run into another similar problem. The bottom comparator in this file works good. The top is wired the same as the bottom comparator however it has a totally different output relative to the negative supply. I don't think it is the same problem as last time since the supply is steady. It works even worse with a single supply driving both comparators.

    I can't see what is going on, any help would be much appreciated :)
     
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  4. Audioguru

    New Member

    Dec 20, 2007
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    The top transistor has the negative supply at its collector instead of the positive supply.
     
  5. masteropie

    Thread Starter Member

    May 17, 2008
    26
    0
    Whoops, your right. Still have the same problem though. The top comparator is oscillating as well as only outputting under a volt. I guess this is caused by positive feedback?
     
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