🚀 go-pugleaf

maestro@cix.co.uk wrote in message
<76977j$2r6$2@plutonium.compulink.co.uk>...
>TRANSISTORS
>I don't really understand HOW, but the device has 3 terminals called
>emitter, base and collector.


Bill J,
Not wishing to steal your thunder; it was a very good article,
but like yourself, I didn't really understand transistors and got
very frustrated with a series of text-books that described WHAT
happens, but not HOW it happens.

About 3 years ago, I enjoyed a valuable discourse in this NG with
a guy from Virginia Tech who, in his turn, had experienced these
same difficulties. After all, if you are trained to have the enquiring
mind of an engineer, WHAT is not as satisfying to you as HOW.

SO, in my turn at passing on the true gospel......

First of all, I must ask you, the reader, to find out how a semiconductor
diode works; it will help our purposes if you do this by the BOND model
and not the BAND model, although they are two facets of the same
working. This is definitely the coward's way out for me; but the textbooks
are usually quite good on the diode, it's only on the (BJT) transistor that
they become all vague and mumbly.

Secondly, in the operation of a diode, you need to be aware that charge
carriers, be they holes or electrons, travel a short distance across the
diode boundary before they recombine - elementary text books will have
you believe that this happens right at the junction, and this is true enough
for diodes; however, for transistors, this transit distance is critical.

Thirdly, to make a BJT, you essentially have two diodes back-to-back, but
with the central semiconductor (P in NPN) being one piece, and so thin that
it is comparable with the transit distance mentioned above.

Fourthly, here goes.....

The Collector-Base junction is reversed biased; the emitter-base junction
is forward biased.

Now, imagine that in an NPN transistor, one electron is torn from the base
by the bias. To do this exercise, we must consider the base current to be
so small that we can talk in terms of single electrons. Because the base
is so thin, and is just as much part of the C-B diode as it is part of the
E-B diode, the built-in reverse-bias potential of the C-B diode is no
longer completely reverse biased, because one electron has been
removed from it.

What now happens is that one electron passes from E to B to make up the
loss. BUT BUT BUT, because of randomness, it may not hit the hole which
has been created, and provided the base is thin enough to be smaller than
the recombination distance, will carry on over into the Collector circuit,
because that reverse bias is still disturbed. So,......another electron
starts
to whizz across. This carries on until one of the whizzers happens to hit
the
hole, and so restores the reverse bias. Nothing happens further until
another
electron is torn from the base as part of the base current.

Now, the whole operation is rather random and statistical in operation,
because
the FIRST electron might plug that gap! BUT, taken on average, the number
of whizzers that pass before the hole is filled up again is the current
gain,
or Beta!

Voila! Zat is Cointreau!