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Homework Help: Finding R3(max) of this circuit

  1. Oct 11, 2011 #1
    1. The problem statement, all variables and given/known data
    Find R3(max)

    Resistors are in Kilo ohms unless stated otherwise like 1.8M

    http://imageshack.us/photo/my-images/265/capturesi.png/



    2. Relevant equations
    R3(max) = (V(upper rail) - V3(lowest possible value of active mode)) / I


    3. The attempt at a solution

    I know Vupperrail is 12 and I is 1mA but I do not know how to find the V3(lowest possible value of active mode).
    I have worked the whole problem except the R3(max) part
     
  2. jcsd
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