In order the make transistor fully on, there must be 0V across the collector, this condition is called saturation. (from the book I read)

what is fully on?

what if there is 5V accross the collector?

Tq.

 

'Saturation' for many BJTs is chosen where the base current is 1/10 of the collector current. At that point, the collector voltage (with respect to emitter) is in the 0.1 to 0.4V range depending on the data sheet. Other transistors are specified with a saturated beta anywhere between 5 and 500 (or more?).

If there is 5V across the collector without any resistance, a lot of power is dissipated in the collector and the magic smoke comes out.

 

Although the 1 to 10 base current to collector current ratio is a good one. I tend to go by the minimum beta on the datasheet, especially if I need to save power.

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Saturation = b-e voltage > c-e voltage. . .?

 

That's a good definition of saturation.

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Carl

 

Yes, meaning that the collector-base junction is forward-biased.

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Ron

 

I've never looked at it like that but I suppose that's true.

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why dont you start a new post?
a lot of discussion and none related to my question..

 

I suggest you read the answers they have given to your question.

Most have answered the question correctly.


Its important to realise that in most transistor amplifiers/switching circuits there is a load in the collector between the voltage supply rail and the collector.
If the current flowing thru this load is high enough ALL the supply voltage will be dropped across the load, so the collector voltage will be close to 0V.

Does that help.


EDIT: added a dwg

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Eric
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When a transistor is operating in the saturation it's considered to be fully on.

Ideally the collector voltage with respect to the emitter would be zero when the transistor is in saturation but in practise we consider it to be fully on when Vbe>Vce.

The literal interpretation of what you've said doesn't make any sense.

Across the collector? With respect to what?

I can only assume you mean with respect to the emitter, i.e. Vce. To answer your question, it depends on the supply voltage, if the transistor circuit is operating from 5V then we would say it's operating in the cutoff region (fully off) but if it were running from a supply voltage of say 10V then we'd say it's operating in the active region (neither fully on or off).

http://en.wikipedia.org/wiki/Bipolar...s_of_operation

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Thank you.

 

I read it in a book!!!

 

most of them answered it correctly...with hero answer being accurate.... so i think no more fudging ovr this issue....

 

A really nice Difo!
though it is a metaphore from a book!


Muhammad89

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i think it is the better explanation.