1. Not finding help here? Sign up for a free 30min 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!

Common collector

  1. Oct 30, 2012 #1
    1. The problem statement, all variables and given/known data

    for the common collector configuration shown i need to find the voltage gain.
    The voltage gain formula is AV = (β+1)(roll RE)/(rπ+(β+1)(roll RE)
    But in the circuit RE is absent . So how do we consider it ??
    Nothing is given about the current source.

    from the circuit theory i know that the internal impedance of a current source is very high (am i correct ?).

    So in this case how do we relate it ?
    2. Relevant equations



    3. The attempt at a solution
     

    Attached Files:

    • co.jpg
      co.jpg
      File size:
      5 KB
      Views:
      87
    Last edited: Oct 30, 2012
  2. jcsd
  3. Oct 30, 2012 #2

    CWatters

    User Avatar
    Science Advisor
    Homework Helper

    Yes the impedance of an ideal current source is infinite.
     
  4. Oct 31, 2012 #3
    Since resistance attached to the output of the transistor is infinite you can't ignore the output resistance of the transistor itself. You've no doubt been ignoring it in most of your circuits but this could only be done because Ro (of the transistor) >> than anything attached to the transistor output and it was connected in parallel to anything attached at the output.
     
    Last edited: Oct 31, 2012
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook