LM331 hystersis resistor

Discussion in 'The Projects Forum' started by hasanferoz, Mar 27, 2011.

  1. hasanferoz

    Thread Starter New Member

    Mar 8, 2011
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    wat is the function of 47 ohms resistor imean how is it helping in improving the linearity i am talking abt the lm331 figure 3
     
  2. wayneh

    Expert

    Sep 9, 2010
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    Different mfgs publish different datasheets, and change them over time. You'll need to post the specific circuit or pdf you are looking at.
     
  3. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    The 47Ω resistor causes a square wave to appear across it as the internal current source switches on and off. For example, if the reference current is 100uA (Rref=1.9V/100uA=19kΩ), then the hysteresis will be
    Vhys=100uA*47Ω=4.7mV.
    This ensures that the comparator switches crisply when the internal current source switches.
     
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  4. hasanferoz

    Thread Starter New Member

    Mar 8, 2011
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    i have one confusion is to why we want 4.7 mv as the hystersis voltage and what will happen if i increase or decrease i mean an i calculate the value of this resistor then wat parameter should i take into consideration
     
  5. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    I suspect that the exact amount of hysteresis is not critical, so long as you keep it well below the minimum input voltage. I think that a few millivolts hysteresis would be adequate. More might cause inaccuracies. I don't have real hardware experience with this part.
     
  6. hasanferoz

    Thread Starter New Member

    Mar 8, 2011
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    wat abt my ckt and the output waveform which is continoulsy fluctuating
     
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