1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
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: A diode with a resistor in parallel and in series.

  1. May 8, 2012 #1
    I have a diode with a resistor in parallel(R2), but also diode resistor circuit has a resistor in series with it(R1). I have uploaded a drawing as well but I think it takes a bit of time for them to be authorised.
    The values of the circuit are
    Vs = 20v
    R1 = 3kΩ
    R2 = 470Ω
    Diode = Has a Volt drop of 2v

    I've found the formula Vo-Vd/Rl = I for a diode in series in a resistor but am not sure how this relates if the diode also has resistor in parallel with it. I'm guessing from what I've read that the diode does not have a resistance as such but only 'consumes' 2v, so can I use 18v along with the resistance in the remainder of the circuit to calculate It ? Or am I heading down the wrong path entirely. This is my second night on this question so could really do with some help. Thankyou

    Attached Files:

  2. jcsd
  3. May 9, 2012 #2


    User Avatar

    Staff: Mentor

    My .doc viewer isn't working, but I think I can see the circuit. That would be a zener diode, and, yes, it leaves 18V across R1.

    Knowing the voltage across R2, you can calculate the current through R2.
  4. May 9, 2012 #3
    Thank you so much. I think I was mis understanding that the voltage drop stated was the same as the voltage shown across, when that twigged today I got it, what a feeling :) Thank you for your help and time :)
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook