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Transistors - making me ill

Discussion in 'Electronic Basics' started by Jon, Jan 28, 2004.

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  1. Strange! First of all, look at the footnote for these three specs.
    Hfe, Vce(sat), and Vbe(sat) are specified with a 300uS pulse at 2% duty
    cycle. Exceed these limits and all bets are off (including package
    integrity ;-).

    Now the Vce(sat) spec calls for 3A Ic with Ib=.375A and is 1.2V. I
    *assume* this goes with the Vbe(sat) of 1.8V at IC=3A (consistent so
    far). So you have 1.8V Vbe and 1.2V Vce, so the base-collector
    junction is forward biased by .6V. Ok, that's saturation. Don't do
    this for more than 300uS though. The magic smoke is near!

    What I don't understand is the Vbe(sat) condition of Vce=4V (it was
    1.2V with this collector current in the line above). The transistor is
    *not* in saturation with Vce=4V and Vbe=1.8V (Base-collector junction
    is reverse biased by 2.2V).

    Other comments?
     
  2. ---------------
    First, stop trying to find a formula. Not that there aren't any,
    but that they AREN'T NECESSARY!! Use a pot and simply dial in
    your desired result state in the collector path:

    Read these:
    ftp://ftp.armory.com/pub/user/rstevew/TUTS/tranxstr.txt
    ftp://ftp.armory.com/pub/user/rstevew/TUTS/xstr-bjt.txt

    -Steve
     
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