Transistor,help me to check the answer

jegues

Joined Sep 13, 2010
733
Your answers for the first page are correct.

I will continue to look at the others and edit this post accordingly.

EDIT:

The answers on the 2nd page are also correct.

EDIT:

For question number 3,

After using the thevenin equivalent we can write a KVL in the base-emitter loop,

\(-V_{th} + I_{b}R_{in(base)} + 0.7 + I_{e}R_{e} = 0\)

\(\rightarrow I_{c} = \frac{V_{th} - 0.7}{\frac{R_{in(base)}}{\beta} + \frac{R_{e}}{\alpha}}\) where \(\alpha = \frac{\beta}{\beta + 1}\)

This gives me,

\(I_{c} = 1.37 mA\)

The rest follows from here.

I haven't studied MOSFETS yet, but perhaps I'll take a look and get back to you.

EDIT: For question 4,

This is the typical arrangement for biasing using a drain-to-gate feedback resistor. The large feedback resistance forces the DC voltage at the gate to be equal to that at the drain (Ig = 0).

Thus,

\(V_{gs} = V_{ds} = V_{dd} - R_{d}I_{d}\)

If V1 is non zero(as you've indicated) then certainly Id is nonzero as well.

Hope this helps!
 
Last edited:

Jony130

Joined Feb 17, 2009
5,487
Yours answers look good except question number 3. And jegues has done the good job to show you the right solution.
 

Thread Starter

xx123321

Joined Apr 27, 2011
15
first,thanks jegues and Jony130 very much for helping me !
I have some questions about Rin(base) in question 3.
1-Does Rin(base) mean R(th) ?
2-In my study book,it shows me that if the following condition be ture,it will take the approximation.
"If βRE>>RTH, then IE=(VTH-VBE)/RE"
so, does my answer still be wrong?
 

Jony130

Joined Feb 17, 2009
5,487
1-Does Rin(base) mean R(th) ?
Well, i don't know, maybe yes or maybe not.
I don't have your book.
Maybe they define Rin(base) as
Rin(base) = R(th)|| (β+1)*Re = 103.83KΩ

Rin(base) = R(th) = R1||R2 = 2.83KΩ
2-In my study book,it shows me that if the following condition be ture,it will take the approximation.
"If βRE>>RTH, then IE=(VTH-VBE)/RE"
so, does my answer still be wrong?
But which value for Ie your Professor will be preferred.
The exact one, or approximate value ?
 
Last edited:

jegues

Joined Sep 13, 2010
733
first,thanks jegues and Jony130 very much for helping me !
I have some questions about Rin(base) in question 3.
1-Does Rin(base) mean R(th) ?
2-In my study book,it shows me that if the following condition be ture,it will take the approximation.
"If βRE>>RTH, then IE=(VTH-VBE)/RE"
so, does my answer still be wrong?

Rin(base) means the input resistance looking into the base.

I believe it turns out to be what you have called Rth.
 

Jony130

Joined Feb 17, 2009
5,487
Rin(base) means the input resistance looking into the base.

I believe it turns out to be what you have called Rth.
Maybe I'm pick on but if you looking into the base.
Then for sure you will see R1||R2 || (β+1)Re.
 
Last edited:

jegues

Joined Sep 13, 2010
733
Maybe I'm pick on but if you looking into the base.
Then for sure you will see R1||R2 + (β+1)Re.
Hmmm... I'm not sure what you would call it then, but I'm fairly sure the intention was for it to be R1//R2.

This resistance value is commonly denoted as RBB in certain textbooks, and likewise the resulting thevenin source, VBB.
 
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