# Transistors - making me ill

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

1. ### Keith R. WilliamsGuest

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).

2. ### R. Steve WalzGuest

---------------
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: