Two-Stage Negative Feedback

Discussion in 'Homework Help' started by newbie2019, May 31, 2019.

  1. The Electrician

    AAC Fanatic!

    Oct 9, 2007
    2,682
    474
    newbie2019, are you still working on this?
     
  2. newbie2019

    Thread Starter Member

    Apr 5, 2019
    95
    2
    Yes dude.
     
  3. The Electrician

    AAC Fanatic!

    Oct 9, 2007
    2,682
    474
    Where are you in the process? What are you trying to do now?
     
  4. newbie2019

    Thread Starter Member

    Apr 5, 2019
    95
    2
    The last part of my study involves computing the ac voltages and currents for
    the configuration with negative feedback. The feedback loop obviously
    complicates things and I cannot figure it out.
     
    Last edited: Jun 13, 2019
  5. newbie2019

    Thread Starter Member

    Apr 5, 2019
    95
    2
    I think that I have the dc analysis of the two-stage amplifier with and without negative feedback
    figured out. I have created a new post with regard to the ac analysis of same.

    Mod: Merged the two Threads.
     
    Last edited by a moderator: Jun 13, 2019
  6. Zeeus

    Member

    Apr 17, 2019
    304
    10
    no..please teach us
     
  7. Jony130

    AAC Fanatic!

    Feb 17, 2009
    4,848
    1,360
    https://www.allaboutcircuits.com/textbook/direct-current/chpt-10/what-is-network-analysis/

    Do you know any of a circuit/network analysis techniques?

    Also, what is the point of doing all those analyze and find AOL and ACL. If now you want to solve the circuit with the negative feedback directly? Without involving the "feedback theory" (without AOL ACL and feedback factor)?

    We use a feedback theory to get approximation result without the need for direct analysis of a whole circuit.
     
  8. newbie2019

    Thread Starter Member

    Apr 5, 2019
    95
    2
    First I had the circuit with no feedback and I was able to analyze the ac current and voltages.

    Now that I have the same circuit but with negative feedback, the ac currents and voltages are different.
    If I didn't have LTSpice how would I predict these new currents and voltages?
     
  9. The Electrician

    AAC Fanatic!

    Oct 9, 2007
    2,682
    474
    jony130, I sent you a PM.
     
  10. The Electrician

    AAC Fanatic!

    Oct 9, 2007
    2,682
    474
    You and newbie2019 are apparently using the same text book. Have you learned standard network analysis techniques, such as nodal, mesh, loop?
     
  11. Jony130

    AAC Fanatic!

    Feb 17, 2009
    4,848
    1,360
    You have to analyze the whole circuit one more time from the beginning. And it will be a hardcore job to do if you want the symbolic solution.
    untitled.PNG
    Good luck with that.
     
    Last edited: Jun 13, 2019
  12. Zeeus

    Member

    Apr 17, 2019
    304
    10
    nope..don't have his textbook

    https://forum.allaboutcircuits.com/threads/two-stage-bjt-amplifier-with-feedback.26710/
    yeah learned little of them but did not learn you and Jony's advanced method or advanced members I agree

    but think this your circuit, RFB is positive feedback...Emitter of Q2 is negative with respect to Vbe...RFB is reducing emitter voltage and therefore increasing Vbe

    if not then guess need re-read my book

    Edit : oh sorry, see you said it is positive feedback
     
    Last edited: Jun 13, 2019
  13. The Electrician

    AAC Fanatic!

    Oct 9, 2007
    2,682
    474
    Are required to use some particular technique to analyze your circuit, such as with concepts like loop gain, factors like Av / (1 + (Av * β)), etc., or can you use any technique you choose?
     
  14. Zeeus

    Member

    Apr 17, 2019
    304
    10
  15. The Electrician

    AAC Fanatic!

    Oct 9, 2007
    2,682
    474
    Assuming that newbie2019 will be back here eventually, and that he can use any technique, my next question for him will be this: do you have access to any mathematical software that can do symbolic linear algebra such as Matlab, Mathcad, Mathematica, Maple, or Macsyma?

    If that answer to that question is yes, then the next thing to do is to watch this video:

    That will help to understand what is going on in this thread: https://forum.allaboutcircuits.com/threads/two-stage-bjt-amplifier-with-feedback.26710/
     
Loading...