[sdiy] Transistor help

[Ian Fritz]

At 09:05 PM 4/26/05, Bob Weigel wrote:
>But the way suggested is more proper since it takes into account the 
>actual things which are going to affect the performance of the circuits in 
>question usually. -Bob

Well, we've been around on that one many times here.  If the mismatch 
between two units is due to different mesa areas (say) then the temperature 
dependences will cancel properly and the mismatch will not matter (just an 
unimportant current ratioing).  So the standard method could give false 
negatives.

OTOH, if the differences are due to, say, defects, then these would also 
affect hFE.  I think that is why I have observed very good correlation 
between Vbe and hFE.  And why I think simply matching hFE makes sense.

   Ian