What does a transistor do?

[asfastasdark]

Yeah... I've been trying to figure this out. Tried Google, Wikipedia, even searching here, but I can't find a decent explanation of what they do/how to use them. And what do all the base/emitter/collector 's do, etc.? I know it's a pretty noob question but there's a first try for everything... right? 

[R.G.]

Go read: http://geofex.com/Article_Folders/How_It_Works/hiw.htm

[petemoore]

  Switch DC voltage, Amplify AC signals, and they have diodes so can do some diode tricks, to name a few.

[Mark Hammer]

You know those fancy lathes that will trace an object with some kind of physical or other sensor, and then recreate the object?  Better yet, perhaps as a kid you may have had some sort of cool drawing gadget that let you trace a drawing with a pen that was hooked up to another drawing implement via some series of brackets, and you could redraw the original picture even bigger than it originally was, simply by tracing it.

Transistors are sort of like that in some ways.  People think that the transistor itself takes in a signal and makes the signal itself bigger, the way you might get a balloon as a shrivelled thing and blow into it to make the balloon itself bigger.  But really, what the transistor does is supply current to the output from a source somewhere.  The base is sort of like the hand on the faucet connected to the garden hose, and the input signal is the person who tells the faucet hodler how much to turn the faucet up or down, and for how long.  The signal that arrives at the base essentially "instructs" the transistor to allow current to flow from the current source as if the transistor were "tracing" the original signal.  What the transistor is doing is kind of like making a larger scale copy of the original signal.  All the various components around the transistor, whether biasing at the base, or emitter and collector components, dictate the scale of that copy, and the extent to which it builds in kinds of "errors" in that copy.

That's more or less what goes on at a conceptual level.  I'll let the tech-types translate that into something more precise.

[sean k]

I always image how a tube works when I think of amplifying devices because I started on them and all because theres lots more descriptions out there around the discovery of the first diode and then the triode. So when I look at any transistor I see a triode. Theres also the fact that the tube works by shifting electrons through free space, inside the vacuum of the tube, that makes it all a lot easier to imagine.

[Sir H C]

Easiest way to view it is a voltage controlled current source.  A voltage across the base and emitter causes a current from the collector emitter (base = gate, source=emitter, drain = collector for FETs). 

[petemoore]

  Jfets bias a lot like a tube triode stage.
  Bipolars require a different biasing than Jfets, Mosfets...they all produce more output than input [and of course require DC supply to do so], but they each do it in different ways, each is a course of study.