does comparator depends on current?

Discussion in 'General Electronics Chat' started by electron_prince, Feb 19, 2013.

  1. electron_prince

    Thread Starter Member

    Sep 19, 2012
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    initially there was one preset for each IR sensor. I am making two IR sensors on a single board and i want to use only one preset. The current to the input terminals of comparators will obviously decrease. does it affect my circuit? i know that op-amps have very high input impedance so very little current flows into them, but still i don't want to take any risk by making a circuit without consulting people on this forum.
     
  2. praondevou

    AAC Fanatic!

    Jul 9, 2011
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  3. electron_prince

    Thread Starter Member

    Sep 19, 2012
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    oh gosh, i was using LM358p (http://www.alldatasheet.com/datasheet-pdf/pdf/158154/TI/LM358P.html) as a comparator. I don't remember who told me about this IC but it worked for my last 10-15 IR sensors which i have designed and i didn't get any fault in my sensors. I just had looked at the datasheet and found my IC is a operational amplifier (not a comparator). would you like to suggest some other IC?
     
  4. Brownout

    Well-Known Member

    Jan 10, 2012
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    An Op-amp can be used as a comparator, and is often used that way. However, you can run into problems for rapidly changing signals, as op-amps are slow, comparatively speaking. As long as your opamp has sufficient bandwidth and slew rate for your signal, you are OK. If not, then use a faster comparator.
     
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  5. ramancini8

    Member

    Jul 18, 2012
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    A comparator uses a very fast output stage that can recover from saturation quickly. An op amp uses a linear output stage, and the designer doesn't worry about recovery from saturation because it is assumed that op amps aren't used in the saturated mode. Aside saturation recovery op amps function fine as comparators as long as speed isn't a concern. An LM324 from TI might recover is 300Ns while one from a competitor might recover in 3 Us. This means that op amps don't function well as high speed comparators, but they are fine in low speed applications like sensing switch closures, IR sensing in the Us range, and other mechanical tasks. PS- I wouldn't put a lot of faith in SLOA67 from TI.
     
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