Constant current sources

Discussion in 'Homework Help' started by Steve1992, Dec 14, 2011.

  1. Steve1992

    Thread Starter Senior Member

    Apr 7, 2006
  2. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
    From the article:

    K needs to change to ensure transistor is in the working area of the transistor, which can be found on the datasheet for your current (Ic). Typically I_B=0.1 x Ic
    Steve1992 likes this.
  3. jimkeith

    Active Member

    Oct 26, 2011
    In the middle of the page is this statement:
    "where K = 1.2 to 2 (so that R1 is low enough to ensure adequate IB)"
    It appears that K is simply a fudge factor that accommodates a wide range of Hfe's.
    Minimum base current = Ib and Maximum base current = K*Ib

    Another take could be designing for a 'starved' base drive circuit--this might be OK for battery operated devices, but generally a poor design practice.

    K and Hfe may be ignored under this condition: Iz = 10* Ib
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