Common Base Amplifier

Discussion in 'Feedback and Suggestions' started by anand.gangadharan, Nov 25, 2010.

  1. anand.gangadharan

    Thread Starter New Member

    Nov 25, 2010
    1
    0
    I have this question when reading the common-base amplifier.
    http://www.allaboutcircuits.com/vol_3/chpt_4/7.html. Not sure
    if someone else will have the same question.

    Since there are no figure names in the page I am referring to
    the third circuit in the page (May be it is a good idea to name figures)
    http://www.allaboutcircuits.com/vol_3/chpt_4/7.html#03116.png


    Let us calculate the currents for this circuit.

    Assume Vin = 1.7

    Ie = Ib+Ic - (1)

    loop 1,0,2

    1.7 = .7 + R1*Ie
    1.7 = .7 + 100*Ie

    Ie = 10 mA - (2)


    loop 0,3,4,2,1

    16.7 = 5000Ic + .7 +100Ie
    16 = 5000Ic + 1
    15 = 5000Ic

    Ic = 3mA
    Ib =7mA from (1) and (2)


    I expect Ic to be much larger than Ib for a transistor because β should be
    of order of 50 or 100. Did I miss something in my calcuation?
     
  2. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
    6,357
    718
    From your first link:

    A Common base configuration has voltage gain, but negative current gain, the useful part is the low input impedance.
     
Loading...