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  1. LvW

    Assistance with Transistor Theory

    Adam - there is one point which I agree with you upon (wording correct?): We have to define the term "control". According to my understanding - as far as the BJT is concerned - this term defines the electrical quantity at the input port of the BJT (base-emitter path) which determines the current...
  2. LvW

    Assistance with Transistor Theory

    Why? It is my experience that such a discussion - if it is a fair and technically oriented sequence of questions and answers - is the best method to improve the knowledge. It always widens the horizon.
  3. LvW

    Assistance with Transistor Theory

    Laplace - are you aware that you are repeating a claim - nothing else? Can you present one single justification for your claim (we speak about the BJT alone - not about a test circuit)? Of course, in a test circuit even an opamp (undoubtly, voltage-controlled?) can act as a current-to-voltage...
  4. LvW

    Assistance with Transistor Theory

    Hi Laplace, sorry - but contains your contribution more than just a claim without any justification? In my post#17 I have presented two effects which can be measured/evaluated and which - I am convinced - can explain WHY the BJT is voltage-controlled. Why don`t you comment on this? If I am wrong...
  5. LvW

    Assistance with Transistor Theory

    Hi Bob - I am afraid you have overlooked something. For calculation of the gain, Adam has used the quantitty re which is nothing else than the inverse transconductance gm=1/re. Do you know the meaning of gm? It is the inverse slope of the curve Ic=f(Vbe). Are you aware what happens without...
  6. LvW

    Assistance with Transistor Theory

    Adam - thank you providing this numeric example. What I do not understand is the following: Why you don`t consider this as the "voltage-control" method? This the main question: At which design step did you implement any idea of current-control? In contrary, you follow exactly the list of steps I...
  7. LvW

    Assistance with Transistor Theory

    Not only from physics! It is not a problem to show by test&measurement that it is the voltage Vbe only that determines the current Ic (see my reply#17)
  8. LvW

    Assistance with Transistor Theory

    To all participants of this thread: Merry Christmas and a healthy New Year. Again I like to mention my hope that somebody is willing and able to follow Adams recommendation in post#35 (Maybe someone else can have ago using their own method and we can see how it compares.). I think, it would be...
  9. LvW

    Assistance with Transistor Theory

    To be honest - I am not sure about that. Didn`t I list the sequence in my former reply? I think, it is up to another person to show HIS steps for designing an amplifier stage showing - in contrast to me - where he uses the control-control principle.
  10. LvW

    Assistance with Transistor Theory

    Laplace - just one comment to your "conclusion" (not usable in practice): Do you really not understand the meaning of the second quote above? I cannot believe. It is simply an argument in favour of dc feedback - that`s all. And the sentence directly after the quoted sentence says: "You will see...
  11. LvW

    Assistance with Transistor Theory

    Some recent quotes: *Either model works, voltage(ebers moll) or current, but the current is easier to use generally. *In summary: the current-model is roughly correct, while the voltage-model is not usable in practice. *LvW believes the OP should be introduced to concepts necessary for...
  12. LvW

    Assistance with Transistor Theory

    Kj6EAD - thank you for the interpretation. Answer to Bob: As I have mentioned in my post#15 - I do not speak about models and not about design steps. Should the BJT be the only part that allows two different explanations how they work? No - of course not. Perhaps the following excerpt from...
  13. LvW

    Assistance with Transistor Theory

    Bob - I must confess that I do not understand your reply (due to my limited knowledge of your language). Is it an anlogy?
  14. LvW

    Assistance with Transistor Theory

    Ahh - I see, may be that both of use have a different understanding of the term "control". I am using this term as it is used and defined in classical closed-loop control systems. That means (my explanation): Of course, I can vary the base current (using a so-called "current source", in fact a...
  15. LvW

    Assistance with Transistor Theory

    Quote Merlin:"The only reason I did not like your original post was that you insist people must use the voltage model. People use the current model because it helps them design & understand circuits. Does the voltage model do that? I cannot see how it helps the average person at all. What you...
  16. LvW

    Assistance with Transistor Theory

    Merlin - thank you for your reply. I understand what you mean (and, please, excuse my bad english while explaining my view), but there is one point I cannot agree with you: For my opinion, we should strictly discriminate between a MODEL (which can be good or bad) and a desription of the PHYSICAL...
  17. LvW

    LM324N active bandpass filter

    Lifeng, here is one simple set of design formulas for your circuit (figure 44): C1=C2=C; |A|=R6/R5 . R1=R3=R4=R; Rp=R1||R3||R4=R/3 ; R2=k2*R, Center frequency wc=1/[RC*SQRT(3/k2)] , Q=SQRT(3*k2)/(2-|A|*k2) , Band pass gain (center) Ac=k2/(2-|A|*k2) . Hope it helps. LvW
  18. LvW

    Assistance with Transistor Theory

    Laywah - I must confess that I hesitate a little to write the following (because in the past I had some - bad and disappointing - experiences with similar discussions, even personal attacks! ), nevertheless: If you really want to understand the working principle of a bipolar junction transistor...
  19. LvW

    LM324N active bandpass filter

    Lifeng, you should know that a second-order filter is described not only by its pole frequency but also by the corresponding pole Q (which, for example, detrmines the bandwidth of the bandpass output of this filter). Here is one set of possible design equations (can be found in each relevant...
  20. LvW

    Bandpass filter help

    I do not see a high pass filter. Rather I see a rectification circuit (function of the diode).
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