Transistor Confusion

[Nigel Goodwin]

why does it feel more like an argument, then?

Perhaps because you're losing?

Perhaps one thing I think we can agree upon is that political correctness is a pox upon civilization.

VERY true!.

 

[philba]

I dunno, sure looks like the lady doth protest too much.

 

[raybo]

A TRANSISTOR IS COMPOSED OF TWO DIODE it maybe PNP or NPN the interaction is caused by doping some minority carriers. meaning put a current into the base it will react with the other diode. Now some of these people before me got personal about and never explained anything to you. a transistor is a voltage amplifier as opposed an old tube which is a current amplifier. the best way to learn is read specs on transistor and other devices

 

[dknguyen]

Npn & Pnp

NPN & PNP: For BJT-type transistors that is.

 

[philba]

Odd, I though a bipolar tansistor was a current amplifier.

 

[dknguyen]

Is

It is isn't it? A current amplifier? Rings a bell. All the alpha and beta equations for BJTs only have curent in them, no voltage.

 

[napos]

BJT can amplify both voltage and current, it depends where you take the output (from BJT). NPN common emitter amplifies voltage, Common collector (emitter follower) amplifies current.

Here is a good reading of BJT **broken link removed**

The thing is that BJT is driven with current (you have to get some current to base to make transistor to open), but FET transitors need voltage to open (there is no current in FET gate). So all the equation with BJT are based on the base current. But this does NOT mean that they can only amplify current.

 

[grittinjames]

normally transister indecate bjt .which is maid up of silicon or germaniun,
it is a current controlled device, it having a parameter called beta .ur collecter current will multiplier of base current & beta upto the saturation of ur device

 

[philba]

my point was in response to the comment that a bjt is a voltage amplifier. it is basically a current amplifier - that's what Hfe is all about. you don't calculate the gain in terms of voltage, you use Ic = Hfe*Ib. I'm not making this up, you know. what you do with that current decides whether you see voltage vary or current.

that link doesn't open but I prefer the Art of Electronic, Horowitz and Hill. I suggest people read that for a good explanation of this effect.

 

[headinthemicrowave]

Thanks for all the help. I understand it somewhat better now. I was just confused all around, but there's some clarity there now.