Constant current sources

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

  1. Steve1992

    Thread Starter Senior Member

    Apr 7, 2006
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  2. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    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
     
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  3. jimkeith

    Active Member

    Oct 26, 2011
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    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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