Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Estimating Is and Rs values

  1. Sep 18, 2011 #1
    1. The problem statement, all variables and given/known data
    A) If a certain current source supplies i=.46A at v=10v, and i=.4A at v=25v, estimate is and Rs??

    (B) What current would this source supply at v=15v, and v=-15v?

    2. Relevant equations
    possibly v=iR ?

    3. The attempt at a solution

    Pretty much lost on the way to start this problem, Would appreciate some help.
    Thank you
  2. jcsd
  3. Sep 19, 2011 #2


    User Avatar

    Staff: Mentor

    Hi Eric08, welcome to PF.

    First you might want to draw the equivalent circuit for the source and its internal resistance so that you have an idea of what is occurring in terms of the interplay of voltages and currents when the supply is loaded (an attached load draws current). How does the internal resistance for a current supply usually present itself in the equivalent circuit of a non-ideal source?

    Next, consider drawing what is called a Load Line. On Cartesian exes, put voltage on the Y axis and current on the X axis. Then plot your two given points and join them with a straight line. You can find the equation for that line and hence predict the voltage vs current for other points along the line.

    If the output is short circuited so that output voltage is zero, all the current Is will flow through that short circuit. From your load line, what's that current going to be?
    When no load current is being drawn, where must the ideal current supply Is be flowing? What voltage appears at the output? What's producing that potential difference?
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook