Transistor,help me to check the answer

Discussion in 'Homework Help' started by xx123321, May 10, 2011.

  1. xx123321

    Thread Starter New Member

    Apr 27, 2011
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    hi,every guys,please help me to check the answer.
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  2. xx123321

    Thread Starter New Member

    Apr 27, 2011
    15
    0
    can any one help? urgent...
     
  3. jegues

    Well-Known Member

    Sep 13, 2010
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    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: May 10, 2011
  4. Jony130

    AAC Fanatic!

    Feb 17, 2009
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    Yours answers look good except question number 3. And jegues has done the good job to show you the right solution.
     
  5. xx123321

    Thread Starter New Member

    Apr 27, 2011
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    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?
     
  6. Jony130

    AAC Fanatic!

    Feb 17, 2009
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    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
    But which value for Ie your Professor will be preferred.
    The exact one, or approximate value ?
     
    Last edited: May 12, 2011
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  7. jegues

    Well-Known Member

    Sep 13, 2010
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    Rin(base) means the input resistance looking into the base.

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

    Well-Known Member

    Sep 13, 2010
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    I'm not sure where your book is getting that, I would lean more towards my solution.

    KVL has no if/ands/or/buts, in this situation atleast!
     
    Last edited: May 11, 2011
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  9. Jony130

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    Feb 17, 2009
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    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: May 12, 2011
  10. jegues

    Well-Known Member

    Sep 13, 2010
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    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.
     
  11. t_n_k

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    Mar 6, 2009
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    Are you sure you don't mean ....??

    R1||R2||(β+1)Re
     
  12. Jony130

    AAC Fanatic!

    Feb 17, 2009
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    Yes, my mistake.
    And thanks for correct my stupid mistake
     
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