Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Diode Circuit Problem

  1. Oct 18, 2007 #1
    1. The problem statement, all variables and given/known data
    See attachment


    2. Relevant equations
    We are to assume the voltage drop across diodes is .7v (don't use the diode equation!).


    3. The attempt at a solution

    I first was assuming that both diodes were "on". Then my work is as follows:

    V1 is the voltage directly above diode D1 (the left most diode)...



    [tex]I+ \frac{V_{1}-.7-(-5)}{5k\Omega}=\frac{5-V_{1}}{10k\Omega}[/tex]

    [tex]I+ \frac{.7-.7+5}{5k\Omega}=\frac{5-.7}{10k\Omega}[/tex]

    [tex]I=-.57mA[/tex]

    Now since I is negative, one of my assumptions is wrong? So now I assume the rightmost one is "off" (D2).


    So.. then
    Solving for I
    [tex]I = \frac{5-.7}{10k\Omega}[/tex]

    [tex]I = .43 mA[/tex]

    Solving for V
    Well.. since theres no current, v=-5?



    Am I approaching this correctly?
     

    Attached Files:

    Last edited: Oct 18, 2007
  2. jcsd
  3. Oct 20, 2007 #2

    Gokul43201

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    You're on your way. In this second case, what would be the value of V1? Does this agree with your assumption?
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook