Re: transistors: so confusing!!

Andrew,

Something that has been confusing me no-end, and I just cant seem to
grasp, is how a TRANSISTOR works!!!

You are not alone!

Try this, it is much closer to the truth although, as with most
explanations, an over-simplification.

++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

The base and emitter form a diode.

Put a forward voltage across that diode and electrons will flow
out of the emitter into the base (i.e. in a NPN transistor).

Now the base region is narrow and the base/collector junction is
biased so as to attract electrons to it.

So, on the way to the base terminal, more than 90% of them are
kidnapped by the collector and never get there. It acts like a
narrow pipe with a big hole in it.

More voltage on the base, more emitter current and so more of it
available to be diverted.

++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

There are two hang-ups that can cause confusion -

1). Current flow in the collector is caused by a smaller current
flow in the base.

But what causes that base current in the first place? It is of
course the base to emitter voltage.

Essentially then, a transistor is a voltage (not a current)
operated device although when working out biasing, it is
convenient to stay with the 'current' model.

2). The collector-base region is reverse-biased.

Yes it is, but only for electrons trying to flow in from the
collector. For the electrons in the base trying to get into the
collector it is forward-biased.


Cheers - Joe



.

Loading