transistor: active, cut-off, saturation, and pinch off!

[PG1995]

Hi

I was searching if a transistor is linear device or not. A linear device has a linear relationship between current and voltage (Ohm's law). I'm a beginner in this electricity and electronic stuff. So, please keep your reply simple. Thanks.

While searching I found this:
We will operate transistor mainly in 4 regions, namely active , cut-off, saturation and pinch off region, depending on the type of biasing. If it is under active region then transistor is a linear device (linearity in the sense if the output is proportional to input then it is said to be linear).


So far I only know that a transistor has a collector, base, and emitter points.

It would be extremely nice of you if you could explain it a bit. I would be much grateful.

Regards
PG

 

[MikeMl]

For a bipolar (NPN or PNP) transisto biased into the active (linear) region, the collector current is proportional to the base current.

 

[carbonzit]

Good question, deserves good answer.

Just for starters, here's a curve you want to become familiar with for transistors, known as the "load line" (it's a plot of Vce--collector-emitter voltage--vs. Ic, collector current):

**broken link removed**

Saturation is at upper left, cutoff is at lower right. Saturation, as the term implies, means "can't do no more!". Cutoff means that no current flows.

More to come later ...

 

[PG1995]

Thanks a lot, MikeMl, carbonzit.

I was reading that a transistor is an active component. How is it one? It doesn't produce any power. We feed 'power' to it. It is just like a resistor which is a passive component. Could you please explain this to me in simple words? It would extremely nice of you.

 

[Ratchit]

PG1995

I was reading that a transistor is an active component. How is it one? It doesn't produce any power. We feed 'power' to it. It is just like a resistor which is a passive component. Could you please explain this to me in simple words? It would extremely nice of you.

Electronic component - Wikipedia, the free encyclopedia

Ratch

 

[carbonzit]

I was reading that a transistor is an active component. How is it one? It doesn't produce any power. We feed 'power' to it. It is just like a resistor which is a passive component. Could you please explain this to me in simple words? It would extremely nice of you.

Excellent question. Not sure I can come up with an excellent answer ...

By the way, the hell with Wikipedia, the "encyclopedia" that any pimple-faced 11-year-old can edit. Their definition in this case sucks, as is so often the case. Replies on forums like this that merely toss Wikipedia articles at you should be ignored.

Having said that, the best I can come up with is this: It's true that even "active" components are passive in the sense that they don't actually produce any power. However, they can modify that power (voltage, current or both) in ways that passives cannot. This includes many functions, the most obvious of which are amplification and switching. Look at amplification: this is something no passive resistor, capacitor, etc., can do, which is to multiply its input either linearly or nonlinearly to produce a higher (or lower, but at least modified) output.

Now that you've asked this, I would like to find a more rigorous definition of active and passive. I'll have to scour the electronics textbooks I have. If anyone else can find a good definition online (not from Wikipedia!), I'd like to see it.

 

[Ratchit]

carbonzit,

Excellent question. Not sure I can come up with an excellent answer ...

Well, Wikipedia did.

By the way, the hell with Wikipedia, the "encyclopedia" that any pimple-faced 11-year-old can edit. Their definition in this case sucks, as is so often the case. Replies on forums like this that merely toss Wikipedia articles at you should be ignored.

In this case, a pimple faced 11 year old did not write or edit the article. You can tell from the way it is written. You never said what is wrong with its description of "passive". I don't think it contradicts anything you said about the word as it applied to electronic components. Making a blanket rejection of Wikipedia cuts you off from a lot of good information that can be obtained quickly.

Ratchit

 

[MikeMl]

...
In this case, a pimple faced 11 year old did not write or edit the article. You can tell from the way it is written. You never said what is wrong with its description of "passive". I don't think it contradicts anything you said about the word as it applied to electronic components. Making a blanket rejection of Wikipedia cuts you off from a lot of good information that can be obtained quickly.

Especially when this comes from a person who signs on with "ZIT" in the their username...