1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Simple Transistor

  1. Mar 19, 2014 #1
    .......
     
    Last edited: Mar 19, 2014
  2. jcsd
  3. Mar 19, 2014 #2
    Your answer is not correct. You forget about 150K resistor.

    Maybe this circuit will be easy for you to solve, you can even use nodal analysis.

    attachment.php?attachmentid=67808&stc=1&d=1395236790.png

    Also notice that I1 = (Ib + I2)

    Or you can replace voltage divider with his thevenin equivalent circuit.
     

    Attached Files:

    • re2.PNG
      re2.PNG
      File size:
      4.2 KB
      Views:
      88
  4. Mar 19, 2014 #3
    Here is a revised version of the solving for VB using KVL
    This is question 2(a).

    Thank you for any help that you can offer.

    Did I answer the question correctly and thoroughly? Can you please find any errors, and point them out to me so that I can fix them?

    1. The problem statement, all variables and given/known data

    2(a): Calculate VB including loading of the bias network by the BJT

    2. Relevant equations

    IE = IC + IB
    ...............................................................
    VCC-(IB)(RB) -(IE)(RE)-(VBE) = 0
    ....................................................................................................


    3. The attempt at a solution


    https://scontent-b.xx.fbcdn.net/hphotos-frc1/t1.0-9/1964876_10151943479145919_1107480603_n.jpg


    Is the answer correct for V(B)? If not, where are the errors located?

    Thanks again for your help.
     
  5. Mar 19, 2014 #4
    You have error already in the the second expression. Are you sure that this is correct KVL/KCL for this circuit? Can you tell me where do you see RB resistor in this circuit ?
    The KCL for VB node is I1 = I2 + Ib

    Or why you don't try to use thevenin's theorem and replace R1 and R2 and Vcc with his equivalent circuit (Rth and Eth)?
     
  6. Mar 19, 2014 #5
    Could Rb= Rb1||Rb2?
     
  7. Mar 19, 2014 #6

    How many loops do you have with KVL?
     
  8. Mar 19, 2014 #7
    Two loops:
    First loop
    Vcc = I1*R1 + I2*R2
    And the second one
    I2*R2 = ??

    Or we can use nodal equation

    (15V - Vb)/130k = Vb/150k + Ib

    Where Ib = ??

    Yes, but what about Vcc ?
     
    Last edited: Mar 19, 2014
  9. Mar 19, 2014 #8

    I don't understand,

    Wouldn't it be :

    Vcc - Ib(R1||R2) - IeRe - Vbe = 0

    and
    Vcc = I1*R1 + I2*R2
     
  10. Mar 19, 2014 #9
    No this is incorrect because Ib current flows only through R1 resistor.
    But we can use Rb = R1||R2 if you replace R1 and R2 voltage divider with his thevenin's equivalent circuit.
     
  11. Mar 19, 2014 #10

    berkeman

    User Avatar

    Staff: Mentor

    Do *NOT* remove content from your posts. Check your PMs.
     
  12. Mar 19, 2014 #11
    you please just tell me the KVL for this circuit again. I cannot obtain an official answer anywhere. I've been working on this problem for four days and it's only worth two points. I don't get it, and I need it to be laid out without anymore theory, on math.

    You've been a big help. Could you show me both of the KVLs for this circuit

    thank you
     
  13. Mar 19, 2014 #12
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: Simple Transistor
Loading...