hysterisis in a comparator circuit

Discussion in 'The Projects Forum' started by pona, Apr 11, 2011.

  1. pona

    Thread Starter New Member

    Jun 21, 2010
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    I have attached a comparator circuit. I want to add hysterisis on non-inverting input. How can I do that?
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
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  3. wayneh

    Expert

    Sep 9, 2010
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    Welcome to the forums.

    When you post a circuit, we'd appreciate a picture file - such as png, pdf, pict, etc. - as opposed to a Word doc. It's much faster to take a peek.

    Have you read the datasheet for a comparator, such as LM339? They will usually include an example of applying hysteresis
     
  4. pona

    Thread Starter New Member

    Jun 21, 2010
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    thanks alot
     
  5. pona

    Thread Starter New Member

    Jun 21, 2010
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    How can i increase the switching speed of this circuit?
     
  6. wayneh

    Expert

    Sep 9, 2010
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    Feed it a faster signal?

    You need to supply a LOT more info for anyone to help you. You haven't specified any parts or circuit details. How do you know you need faster switching? What are you really trying to do?
     
  7. SgtWookie

    Expert

    Jul 17, 2007
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    Increase the speed of WHICH circuit? You need to post a schematic of which circuit you are talking about, preferably in .PNG format.
     
  8. pona

    Thread Starter New Member

    Jun 21, 2010
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    Sorry. I have attached the circuit now. The inverting input changes at a slow rate and the output of opamp changes in the form of ramp. I want to decrease the time it takes to change levels.
     
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  9. SgtWookie

    Expert

    Jul 17, 2007
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    Try it like this instead.

    See the attached.
     
  10. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    Also using a dedicated comparator(393 or 339) will do away with the ramp on the output. Output will be a square wave, and will work with a single rail supply.
     
  11. SgtWookie

    Expert

    Jul 17, 2007
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    Those comparators require a pull-up resistor, as their outputs are open-collector.

    Pull-up Ohms ~= Vcc/4mA
     
  12. pona

    Thread Starter New Member

    Jun 21, 2010
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    thanks a lot for the help
     
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