Very Simple Diode Question

Discussion in 'Homework Help' started by jegues, Mar 1, 2011.

  1. jegues

    Thread Starter Well-Known Member

    Sep 13, 2010
    I'm confused as to how I can check why the diodes are non-conducting/cut off when vi is postive. (See figure)

    For the diodes to be cut off the voltage across the diodes must be negative.

    I don't see how I can check this.

    I'm looking at the first diode and trying to find vd1, and it looks like the voltage across it is,

    v_{D1} = \text{floating voltage?} - v_{I}

    Can someone clarify this for me?
  2. Georacer


    Nov 25, 2009
    If you want to be sure that the diode is not conducting, you can assume that it is, and replace it with a voltage source of 0.7V. This clearly shows you that it is not forward biased.

    If you wonder about the actual voltage, maybe you could replace the open-circuit with a very large resistor and say that you have half the Vi dropped in each diode. A simulation would be enlightening. A second opinion too.