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Homework Help: Diodes in series and parallel

  1. Nov 3, 2011 #1
    1. The problem statement, all variables and given/known data

    The reverse saturation currents of a Schottky diode and pn-junction diode at T = 300K are 5*10^-8 and 10^-12 A, respectively. The diodes are connected in parallel and are driven by a constant current of 0.5 mA.

    (i) Determine the current in each diode.
    (ii) Determine the voltage in each diode.
    (iii) Repeat the previous two parts if the diodes are connected in series.

    2. Relevant equations

    Not sure. Maybe...

    Ideal diode equation

    Id = Is * [exp(Vd/Vt) - 1]

    I.d is the current through the diode
    V.d is the voltage across the diode
    I.s is the reverse saturation current
    V.t is the thermal voltage (0.0259)
    (not sure if I can use the equation for a Schottky diode)

    3. The attempt at a solution

    Things that are given:

    Reverse saturation current
    Thermal voltage
    constant current of 0.5mA, however, I'm not sure if I would plug
    this value in for the "current through the diode", due to the diodes
    being in parallel.

    I don't know what to do because we have not covered analysis of diodes in my circuits class, but they are asking this in my device physics class. Is the voltage drop across both diodes going to be the same? Am I suppose to divide the constant current up? Would this ideal diode equation work for both pn-junction diodes and Schottky diodes? Not sure where to start...
  2. jcsd
  3. Nov 3, 2011 #2


    User Avatar

    Staff: Mentor

    Using the same equation for both diodes should yield a pretty good approximation. The saturation current determines the "turn-on" voltage knee, and yields values in the right ballpark for both diode types.

    Yes, being connected in parallel the applied current will be divided between the two, and they will both share the same potential drop.
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