Hello from UK

@DaveE, & @ robotBuilder..Indeed, with out getting to far into the weeds over how the transistor really works..I refer to the Bell lab inventors in 1947,

Etymology

Bell Telephone Laboratories needed a generic name for the new invention: "Semiconductor Triode", "Surface States Triode", "Crystal Triode", "Solid Triode" and "Iotatron" were all considered, but "Transistor," coined by John R. Pierce, was the clear winner of an internal ballot (owing in part to the affinity that Bell engineers had developed for the suffix "-istor").^[20][21] The rationale for the name is described in the following extract from the company's Technical Memorandum calling for votes:

Transistor. This is an abbreviated combination of the words "transconductance" or "transfer", and "varistor". The device logically belongs in the varistor family, and has the transconductance or transfer impedance of a device having gain, so that this combination is descriptive.

The following document explains the Electron/Holes flow theory better than I could ever do...a snipet for the document on page 7 says it all...

As the semiconductor material
is heated further, more electrons are freed to drift through
the crystal lattice in response to an applied electric field, and the
conductivity of the material increases (resistance decreases).
Quite apart from heat action, electrons in some semiconductors
may also be dislodged from the valence bonds at ordinary temperatures
by the action of light shining upon the material. This
photoelectric action is utilized in the selenium photocell of the
photographic exposure meter. Bombardment by other forms of
radiation likewise has been observed to release electrons in semiconductors.

and with that , I shall retire from this discussion to ponder other problems such as putting together a robot car what will arrive Monday, and how to make it work with my new Huskylens camera I have been playing with...lol

Take care, both of you.. Regards,

LouisR

Transistors-Theory-and-Practice-Rufus-Turner.pdf

 

I think I have discerned the main point requiring clarification. the current multiplier model is the most manageable, as the ratio is constant while all else varies. With a Beta of 200, 1 mA BE allows 200 mA CE.

To know the specific voltage drop / resistance at any point between cutoff and activation, you have to read it off the curve - but when employed as an amplifier, the specific values are irrelevant, largely, as long as you don't toast the transistor, lol.

@binaryrhyme 

The reason I laboured the point was because it really messed with my mind until the penny dropped and I understood what was really happening. I felt mislead by the glib statement that the base current controls the resistance. True I am not the sharpest knife in the kitchen but even a not so bright self taught hobbyist can aspire to have some clearer understanding if possible.

The point is: The transistor collector to emitter cannot be used as a potentiometer, the position (value) of which you can select with a base current of some value. A real potentiometer would behave very differently in series with a variable resistive load. Yes,  if the resistive collector load is constant then the resistance between the collector to emitter will change in step with the base current and appear to be determined by the base current.

The cool thing I remember at the time (decades ago) was discovering that this property meant you could make a constant current source. A battery being a constant voltage source (in series with some internal resistor value).

I shall now also retire from this discussion and get back to my true love programming my robot.

@Binaryrhyme, No, I think you have the gist of it..In saturation, no further collector current will flow with additional base current, or in  the case of the cut-off region, current ceases to flow.. The point is transistors are in the class with Varistors, and you can call it trans-conductance or variable resistance, makes no difference as far as the equations are concerned. The modeling used in analysis of common emitter circuitry does use the internal resistance of the base-emitter : rEE

for Silicon rEE ≅ 0.026V/IE = 26mV/IE 

While normally, we usually don't concern ourselves with that level of detail, it is however good to know that there are other things going on in the transistor that affect our expected performance in initial circuit design.

@daveE mentioned methodology and terminology can be somewhat confusing.. but in real world, practical knowledge and understanding helps with these seemingly contradictory ideals.. I'm a hands on type of guy..so the theory was only useful to understand how it was suppose to work.. in the field, it's entirely a different animal...lol

Posted by: @edlee

@inst-tech "warning!  the math is a killer for those that may be math impaired..lol"

Well, I'm not scared of numbers even though I'm not very good with them, but always willing to learn. 😎 

... you had no idea what you were unleashing when you said that, did you? 😉

Posted by: @binaryrhyme

... you had no idea what you were unleashing when you said that, did you? 😉

I think I will abide by the old adage, "be careful what you wish for". , in future.

I think this discussion should be closed now. lol

If you are really interested in this stuff the H Parameter analysis isnt that difficult once you have gotten you head around it and it clears up all the confusion.

I will see If I can remember a good clear textbook.

Thanks Mark.