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how exactly do transistors work? in detail.? Answered

 i need to know about how applying a positive charge to the base allows electrons to flow through it to the emmiter. npn


There's a little man who lives inside the transistor.  He watches the base current, and he adjusts a little rheostat (variable resistor) so that the collector current is always β times the base current.  A picture of this is attached.

Picture source:
Horowitz and Hill. pp 64-65. The Art of Electronics. 2nd Ed. Cambridge University Press. 1989.

Google Books link to this book:


Better grab an actual copy of H&H. They give more than one explanation of the transistor, each in increasing complexity, where each one is very different than the last.

The one shown above is the ultra simple "current amplifier" explanation. Fine for beginners, as long as you treat transistors as Black Boxes and have no wish to look inside and find out how "transisting" can occur.

Next they get into the guts of the silicon: the Ebers-Moll explanation where transistors are controlled by Vbe voltage. But still that only works for DC and low frequency.

Later they introduce far more detail: charge storage and variable capacitance; high frequency effects and nonlinearity.

Analogy from physics: first we learn that atoms are just like little solar systems, but with e-field force instead of gravity. Next we learn that that's actually wrong. Instead the electrons "orbit" in clouds with fuzzy geometrical shapes. Then we learn that that's actually wrong. Instead the electrons are not objects with position and velocity, they are strange entities which obey flabbergasting quantum mechanical rules with electrons more like standing waves than like tiny billiard balls.

What? You mean transistor-man isn't real, and instead the inner workings of a BJT has something to do with a microscopically thin layer of atoms that can change from insulating  to conducting under the influence of an applied electric field?

And what's this you're saying about atoms NOT resembling little star systems?  Have you seen the official flag of the IAEA? Um, here:

You see that?  Those are hard sphere-like electrons in Keplerian elliptical orbits, around another little sphere, which I guess represents the nucleus.

Probably the next thing you're going to try and tell me is that it's not really Santa Claus who puts presents under Christmas trees, and that instead it's actually everyone's parents who are buying presents for them, or something crazy like that.

Seriously though, I appreciate the effort you put into your reply.  Also it is kinda neat that I just "got schooled" by the Bill Beaty of amasci.com.    I mean you're famous, man!  At least on the internet. 

Be careful what you ask for. "In detail" semiconductor theory is a term's worth of work at MIT. (If you really want that level of detail, the class notes are probably available on MIT's "Open Courseware" system.)

A term ? We had a whole ^%$%£^&£& year of it when I studied EE !


This _is_ MIT. And that's just the basics -- enough to design a simple IC (which is the final project, if I remember correctly). But I'm assuming that this is already tremendously more detail than anyone who asks the question here really wants.

Which is the point. "Exactly" can be a life's study. "In detail" can be a career. The querant either needs to simplify the question, or go someplace where the supposedly desired level of detail is appropriate. Instructables really ain't it.

In detail: Start with Band Theory, then Google "How transistors work"