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  1. LvW

    Transistors

    Didn´t we invent the "displacement current" (I hope it is the correct english term) with the aim to fill the gap (between the plates)?
  2. LvW

    Oscillator circuit - possibly Wien Bridge Oscillator?

    @TFahey: In case you need further help it would be good (in fact: necessary) to tell us what you really want to design. I assume, you want to create a linear oscillator with a sinusoidal output? Correct ? Which frequency? Tunable about what range? Amplitude?
  3. LvW

    Transistors

    It´s OK - no problem. LvW
  4. LvW

    Transistors

    Yes - you are right. I didn´t explain the "fundamental physics" of the BE junction (minorities, majorities, diffusion, recombination,...) I am not a specialist for this. For my opinion (and for the purpose of this thread) , it was sufficient to see the relationsip to the pn junction of a diode -...
  5. LvW

    Transistors

    I think, it´s time to find a summary. Let me try it (my view): * As a stand-alone element and with an appropriate C-E voltage the transistor (BJT) can deliver a collector current that undoubtly is controlled by a voltage that exist across the B-E junction. That means: The BJT can be seen as a...
  6. LvW

    Transistors

    Of course not (between base and emitter). Or did you expect another answer (I am not a beginner) ? In each of my contributions I have mentioned the necessity of having dc negative feedback (as you know - because of tolerances and temperature stability).
  7. LvW

    Transistors

    Hi Bob - please read my response to Steve´s post - I suppose, there is the same misunderstanding between us regarding the term "control". Nevertheless, thank you for your answer.
  8. LvW

    Transistors

    Hi Steve, I am afraid, there is a deep misunderstanding between us. Nevertheless, at first, I will answer your question: 1.) As you know, the voltage V1 should be in the range 0.6...0.7 Volts. However, this biasing scheme makes absolutely no sense because the transfer function Ic=f(Vbe) has very...
  9. LvW

    Transistors

    Bob - may I ask you: At which design step? Again, I like to refer to my post#65 which lists a typical design procedure for a common emitter amplifier. I cannot see any step in which the designer "treats the BJT" as current-controlled device. Am I wrong? And this is excactly the point which...
  10. LvW

    Transistors

    Your last sentence would apply to 100% in case I could know the exact Vbe value which belongs to the desired current.. However, as we all know this is not the case and, therefore, we apply negative feedback in practice. It is easy to show that in this case, it practically does not matter if I...
  11. LvW

    Op-Amp input signal question? idk

    feelsguy - have you an idea about the maximum possible output amplitude?
  12. LvW

    Transistors

    Useless? Hello Bob - and what about the design steps I have listed in my post#65? Anything wrong?
  13. LvW

    Transistors

    OK - I have expressed my opinion and I do not want to repeat my arguments. However, I have made up my mind a bit (yes - that´s possible from time to time) and I arrived at a rule that could be something like a "natural" rule: I have the feeling (at the time being it is not more) that, in...
  14. LvW

    Transistors

    Sure I did. I know - and I have used this knowledge - that a suitable voltage Vbe allows a current Ic that is stabilized by negative voltage feedback. Exactly THIS is the point I do not understand: Everybody knows that he needs a voltage Vbe that allows a certain current Ic. But the cause of an...
  15. LvW

    Transistors

    Here is - in short - the typical process of designing a common emitter amplifier: * Choose a suitable DC operating point (Ic and Vce) * Calculate corresponding resistors Rc and Re (negative feedback to cope for temperature and BJT uncertainties) * Calculate two resistors for proper base DC...
  16. LvW

    Transistors

    Agreed. On the other hand, the data sheets contain a graph Ic=f(Vbe) and the slope of this graph is the most fundamental parameter for BJT amplifiers (transconductance gm). I am afraid, those people feel lost without knowing the meaning of this fundamental graph. And we should not forget: Also...
  17. LvW

    Transistors

    I like to contribute some general thoughts to the subject under discussin (current vs. voltage control). For my opinion, it is really a funny (?) story which has started long time ago. Let me explain: I suppose, all students and newcomer in electronics know that for a pn diode there is an...
  18. LvW

    Transistors

    Yes - of course, everybody can try to find the best explanation of the BJT´s behaviour. I think, this applies, In particular, during the process of designng a circuit. Nevertheless, there are some applications which - for my opinion - cannot be explained based on current-control, for example...
  19. LvW

    Transistors

    Yes - I agree. Therefore, I did point to the fact that during design we assume that Ib controls Ic. It was only my intention to remind the interested readers to the physical facts. By the way - the well known feedback using an emitter resistor works only because of the voltage-control feature of...
  20. LvW

    Transistors

    May I add a short comment for clarification? During design of a transistor amplifier we very often make use of the relation Ic=Ib*beta. However, this does not mean that the BJT would be "current-driven". In fact, the BJT is a voltage-controlled device (Ic=Io*exp(Vbe/Vt). A voltage Vbe between...
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