question about npn clipping from art of electronics book

Discussion in 'General Electronics Chat' started by tpny, Oct 17, 2016.

  1. tpny

    Thread Starter Member

    May 6, 2012
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    Hi please see pic of page 67 enclosed, I don't understand why the npn clips when input voltage is less than -5v. Please illuminate, thank you!
     
  2. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    In order for the output voltage to go lower and lower, the transistor has to conduct less and less. It is the emitter resistor that "pulls" the output down to -10 V. However, the load is another 1 K resistor to ground. When the transistor is completely turned off, the two resistors form a simple voltage divider between GND and -10 V. If the two resistors are of equal value, the middle node is half the total voltage, -5 V. If the load were 111 ohms, the clipping level would be -1 V (-0.999 V).

    ak
     
    Last edited: Oct 18, 2016
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  3. wayneh

    Expert

    Sep 9, 2010
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    The text says it clips at an output voltage of -5V, not input. But neither makes sense to me.

    Gaaa, AK beat me to it and even got it right. I had missed he ground symbol which is not the same as -10V. I wish they'd use 0V instead.
     
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  4. tpny

    Thread Starter Member

    May 6, 2012
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    I also didn't see the ground symbol. second you on using 0v insteadl

    Hi ak, thanks for illuminating duly. But you said if load were 111 ohms, the clipping would be 1v, did you mean -1v? thank you!!
     
  5. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    Either that was a test and you passed, or my beloved, clicky Focus keyboard is failing.

    ak
     
  6. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    **even**?

    And, in this unschooled, wild west internet age, they *even* got the ground symbol pointing in the correct direction. even.

    ak
     
  7. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    I don't. 0 V and GND are not interchangeable symbols or concepts.

    ak
     
  8. Jony130

    AAC Fanatic!

    Feb 17, 2009
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  9. wayneh

    Expert

    Sep 9, 2010
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    You're right, but I think in the example the important thing we both missed was that the point marked with the ground symbol was at 0V. That's our bad, but explicit labelling of that point as 0V might have prevented the miscommunication.
     
  10. wayneh

    Expert

    Sep 9, 2010
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    All I meant by that is that you were both faster and correct, not just one or the other. I could have used "also".
     
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