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How to determine the breakdown voltage of a diode?

  1. Feb 16, 2016 #1
    1. The problem statement, all variables and given/known data
    The question is posted below.

    2. Relevant equations


    3. The attempt at a solution
    I don't know how to solve this question.Does the breakdown voltage of a diode depends on the voltage source near the diode?For example,breakdown voltage of D1 in (a) is 30V?

    Also, I don't know how to determine the Vo either.If D2 in (a) is forward biasing,what is the value of Vo?
    Thanks!
     

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  3. Feb 16, 2016 #2

    phyzguy

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    Science Advisor

    It says "Assume ideal diode". Do you know what this means? Did you discuss the properties of an ideal diode in your class or your textbook?
     
  4. Feb 18, 2016 #3
    Could you answer my questions directly?
    I do have studied the properties of a diode!
    However,I do not know whether the D1 in (a) is parallel to the 30V voltage source.
    So I don't know if the breakdown voltage is 30 for D1.
     
  5. Feb 18, 2016 #4

    gneill

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    Staff: Mentor

    haha1234, I suspect that you are not using the terminology correctly.

    Breakdown voltage is an inherent property of a diode. It does not depend upon external factors like voltage supplies. To determine the breakdown voltage of a real diode one either looks it up on the manufacturer's datasheet to find the guaranteed safe value, or takes several of them from a single manufacturing batch and tests them to determine a typical value.

    An ideal diode has defined characteristics. This includes forward bias voltage ("turn-on" voltage) and maximum reverse bias ("breakdown voltage"). What are these for an ideal diode?

    Whether or not a diode experiences breakdown does, of course, depend on the conditions in the circuit at any given instant. If the potential across the diode exceeds the diode's breakdown voltage then it will fail and very likely destroy the diode.
     
  6. Feb 18, 2016 #5
    Thank you for clarifying my wrong concepts.
    But I still cannot understand that will D1 conduct if the Vi is less than 30V.
    Also, how to determine Vo in (b)?
    I don't know how to determine V1 I defined in (b) as the 100ohm resistor consumes some voltage.
    And is Vo is equal to V1?
    Thanks
     
  7. Feb 18, 2016 #6

    gneill

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    Staff: Mentor

    You'll need to come up with a strategy to analyze the circuit, try it, and draw conclusions. If you post your work we can critique it and point out any issues. We can't just tell you the solution: that is against the forum rules.

    Here's a suggestion: One approach is to consider all combinations of conducting/not-conducting for the diodes, analyze the circuit in each case and look for contradictions to eliminate the incorrect choices. Use the given source voltages to pick likely values for Vin that you can try (for example, suppose Vin is just less than 30 V, or just greater than 30 V).

    Diode circuits can require a lot of trial and error to analyze because they are non-linear components; you can't write a single set of equations to analyze the circuit all at once. Experience will help you make educated guesses as to behavior and let you choose the important scenarios to test more quickly. Until you gain that experience, exhaustive search and elimination is the way to proceed.
     
  8. Feb 18, 2016 #7

    phyzguy

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    I was trying to point you in the right direction. Apparently you don't know what is meant by an "ideal diode". An ideal diode has an infinite breakdown voltage. It is an open circuit when reverse biased (no matter how high the voltage), and a short circuit when forward biased.
     
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