Transistor modes and maybe mosfets.

[jrz126]

I'm studying for a test in my microelectronics class, and I'm having some difficulty remembering what the tests are to see if the transistor is in Forward Active Mode or Saturation mode.
For both cases ib > 0A, (or else it is cut off).
In my notes I have:
Vcb > -0.4V for npn and Vcb <-0.4V for pnp in F.A.M.
Is this correct? My friend who took the course last year said that it should be Vc<Vb for a pnp. So I'm confused?? If i do use the -0.4V, where does that value come from?

Now for Saturation mode, am I just checking to see if the calulated Beta (by using a ratio of the currents, like Ic/Ib) is less than the given Beta?
Where would I use the Vce(sat)=0.2V that is given to me?

Once I get to studying the MOSFET stuff, I may add a post about them as well.

Thanks for the help

 

[TheOne]

Here's my 2 cents;

For a transistor to operate normally the base should be reversed biased with respect to the collector and forward biased against the emitter. So for a NPN, base less positive than collector. For a PNP just the opposite, base less negative than collector. I am not sure where the 0.4v fits in, 0.6 or 0.7 I know :?

 

[Russlk]

Vcb > -0.4V for npn and Vcb <-0.4V for pnp in F.A.M.
This implies that Vce(sat) is 0.2 volts, which is not universly true. In the active mode, the Vcb is usually positive.

You are correct that in the saturated mode, the base current is higher than in the active mode.

 

[samcheetah]

Cutoff - emitter base junction reverse biased and collector base junction reverse biased

Active - emitter base junction forward biased and collector base junction reverse biased

Saturation - emitter base junction forward biased and collector base junction forward biased


this is written on page 223 in your pillow :lol:

 

[jrz126]

:lol: :lol:
We must have different pillows, because my pg 223 is the questions at the end of chapter 3, diodes...speaking of the end of the chapter questions, what idiot wrote these sections, figures all over the place and they dont seem to be in any order. Then the answers in the back are so inconsistant, you can't even check yourself (either wrong or not there). they tend to skip over large groups of problems for these answers as well. grrrrrrr :evil: :x

Had to vent a bit, the test is in 15 minutes :roll: I feel confident about it (not a good sign)
Hopefully it all goes well :?
Thanks for your help.

 

[samcheetah]

:lol:

i have the fourth edition of the book. which edition do you have?

about the problems, well i get really mad with the problems section too. just keep on doing the problems no matter what the answer is :lol:

and good luck with your exam

 

[jrz126]

I have the 5th edition brand spanking new this year, (they like to screw us by using new books every year or 2)

And my exam went very well...One of my co-workers took this class last year and he had his old tests, lets just say that the prof used the same concepts on this test. :wink:

 

[samcheetah]

oh okay. i only have the 5th chapter of the 5th edition which can be downloaded free from sedra's website. anyway i have attatched the table which shows the modes of operation of BJTs.

and hey its always a good idea to have a look at the test papers from last year. and especially if its the same teacher!!!!!!!