Resistor & diode in series

Discussion in 'Homework Help' started by madmartigano, Oct 29, 2010.

  1. madmartigano

    Thread Starter New Member

    Oct 29, 2010
    I'm asked to plot current vs. voltage for two circuits: one with just a constant voltage source and a forward-biased diode in series, the other with a constant voltage source, a forward-biased diode, and a resistor in series. All the information I have available for this question I've attached as a jpg. I'm basically having difficulty understanding how adding a resistor in series with a diode will affect the current of that circuit. I'm assuming it must somehow, I just don't know how to model it mathematically. My teacher apparently assumes this knowledge must be self-evident, but I still need someone to point out the obvious to me. Thanks in advance for any help.
  2. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
    A resistor limits the current that can flow through a diode.

    Roughly speaking, resistors change a voltage source into a current source.

    This is the reason resistors need to be used with LEDs, they act like 20mA fuses with a ~2V drop.
    madmartigano likes this.