doubt

Discussion in 'Physics' started by whale, Jan 14, 2009.

  1. whale

    Thread Starter Active Member

    Dec 21, 2008
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    0
    in common emitter configuration,the collector current is product of gain(β) and base current,
    from whare the factor β comes?
     
  2. mik3

    Senior Member

    Feb 4, 2008
    4,846
    63
    β is the current gain of the transistor which equals Ic/Ib
     
  3. Dave

    Retired Moderator

    Nov 17, 2003
    6,960
    145
    It is a function of the physical attributes of the transistor; namely doping concentrations in the n- and p-type semiconductor parts, physical dimensions (width, length), electron/hole diffusivity, and the minority-carrier lifetime.

    Dave
     
  4. studiot

    AAC Fanatic!

    Nov 9, 2007
    5,005
    513
    Try to think of it this simple way.

    A transistor has three legs (terminals).

    Therefore it has three terminal currents Ie , Ic, and Ib

    By Kirchoffs current law, since they all meet at a point within the transistor

    Ie+Ic+Ib = 0

    We can also define three ratios with these currents, however only two are independant, we can always get the third by cross cancelling.

    Originally the two that were chosen were called alpha and beta, after the first two letters of the Greek alphabet


    So

    alpha = Ic/Ie

    Beta = Ic/Ib

    Whatever these values turn out to be.

    The fact that these values have desireable properties makes the transistor such a valuable device.
     
  5. DickCappels

    Moderator

    Aug 21, 2008
    2,659
    632
    Everybody knows where β comes from: The datasheet!
     
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