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Homework Help: A problem with zener limtting output voltage

  1. Nov 15, 2013 #1
    hello guys !!

    i know that in zener diode limitting circuit
    there are three types : 1-limitting Positive peak 2-limitting Negative peak 3-limtting both peaks

    and i know that output voltage for
    limitting positive peak =VZ+0.7v
    limitting negative peak= -VZ-0.7v
    but i don't know what will happen if the input voltage is changed ?!!
    i mean is there a relationship between input voltage and VZ ??

    in this photo i understand that in


    (a) Positive peak output = 5.1v+0.7v=5.8v
    Negative peak output =-3.3v-0.7=-4.0v
    (b) Positive peak output =6.2v+0.7v=6.9v
    Negative peak output = -15v-0.7v=-15.7v

    but in related problem i don't know if the output voltage will change if the input voltage is changed ?!!
    i think it will not change but iam not sure about that ..so help me guys !!!

    Thank you :)
  2. jcsd
  3. Nov 15, 2013 #2


    User Avatar

    Staff: Mentor

    The zener characteristics are nearly independent of the input voltage. I say nearly because "real-life" zeners do have a small resistance value that will make the zener voltage vary a bit when its current changes (the same holds true for all diodes). Do a web search for zener characteristic curve and zener equivalent model.
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