On 15/05/2014 15:57, gareth wrote:
After studying (mainly BJTs, but with FETs in the final year) at Uni,
I was conversant with all the models, Hybrid-Pi, etc, and the use
of various matrical parameters, h, y, s, etc, for describing and predicting
transistor behaviour in circuit, but was puzzled on how it actually worked,
by which I mean, how did the base current control the collector current?

(So many of the textbooks just glibly say that the part of the emitter
current
divides off to become the base current, but this does not describe the
low-level controlling action)

I found the answer about 18 years ago in these NG (ISTR sci.electronics
before its unnecessary split), but I wonder whether anyone else puzzled
over this, and what was their answer?

It does rather depend on the depth you wish to go to and the model you
wish to utilise as all of them. To a certain extent all the explanations
have flaws and, IMHO, you don't need to know how it works to use it. All
you need is and analogy and the transfer functions and hfe etc to bias
and use it.

Once you get to the quantum models it all gets a bit silly and
confusing to be honest. The quantum model was my limit. I stayed away
from quantum models in physics and stuck to engineering physics.

Transistor theory is like the explanation how a wing works - a lot the
explanations are designed to give people an explanation that they are
comfortable with so that they can get on with actually using it.

Andy