transistor saturation calculation

Discussion in 'General Electronics Chat' started by jut, Jan 21, 2010.

  1. jut

    Thread Starter Senior Member

    Aug 25, 2007
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    2
    On page 38 of this document, http://focus.ti.com/lit/an/slod006b/slod006b.pdf , could someone tell me how they got equation 2-28?

    I see how to do a KVL loop on the input side of the BJT: Vin = RbIb + Vbe
    But why do they say RbIb < Vin - Vbe ?
     
  2. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    214
    It is Ohm's Law in action. R = V/I.

    hgmjr
     
  3. jut

    Thread Starter Senior Member

    Aug 25, 2007
    224
    2
    Yeah, but why the "<" ?
     
  4. Jony130

    AAC Fanatic!

    Feb 17, 2009
    3,957
    1,097
    The lower RB the greater Ib is.
    So decrease RB we become independent of hfe variation and make sure proper saturation.
    So it is a safety margin.
     
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