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  1. LvW

    Assistance with Transistor Theory

    Although I have learnd that the forum moderation does not want to continue this thread (https://www.electronicspoint.com/threads/question-about-transistor.272142/#post-1637925) I think it is important to understand the position of the "current-control party". Laplace - therefore, I kindly ask...
  2. LvW

    Assistance with Transistor Theory

    "I can see two reasons why it's helpful to describe it that way: (a) VBE causes IB and (b) IC is approximately proportional to IB and is not approximately proportional to VBE." Hi Kris, I do not want to explain things again - however, I am afraid you are a "victim" of a deep misunderstanding...
  3. LvW

    Question about Transistor

    I think, the reason simply is that it is common to use (at least in circuit diagrams) POSITIVE supply voltages appearing on the top of the diagram. There are no "electrical" reasons. For npn: VCE>0 For pnp: VEC>0 (VCE<0)
  4. LvW

    Assistance with Transistor Theory

    Hi Kris, I do not intend to answer from the charged carrier point of view. Instead, I just observe and try to explain the BJT`s behaviour: 1.) Let the collector unconnected and treat the pn junction of the B-E path like a simple diode. There will be acurrent IE if the voltage is in the...
  5. LvW

    Assistance with Transistor Theory

    I think, a good visualization is the following: Using the classical base biasing scheme, we have a voltage divider consisting of a resistor (R1) and the parallel combination of R2 and the B-E path. If we drop R2 we still have a voltage division between R1 (of course, with another value) and the...
  6. LvW

    Bipolar transistor SPICE modeling book

    Hi Ian, I have sent you a PM (Inbox).
  7. LvW

    Assistance with Transistor Theory

    Perhaps not too important, however: In order to be one small step more exact: ....consists of charge movement of any polarity. (The carriers move very slowly). More than that, I agree, of course, to Ian Getreu`s contribution.
  8. LvW

    Assistance with Transistor Theory

    I rather would say that this applies only to the very specific (theoretical) example you have mentioned (current source for biasing). I think, in most cases, linear BJT amplfier stages are biased with a VOLTAGE (via a low-resistive voltage divider). At least, it is the goal to create a "stiff"...
  9. LvW

    Assistance with Transistor Theory

    It was my only point to say that - in fact - we are buiding a voltage divider - as you said: Producing the "natural value" for Vbe. We shouldn`t deviate too much from our main theme (physical mechanism which detrmines Ic), do you agree? PS: I`ve just realized, that - up to now - I didn`t get...
  10. LvW

    Assistance with Transistor Theory

    Merlin - I think you are touching the question of dc feedback. Why? Because you mention a FIXED Vbe value. It would be a very poor design to use fixed Vbe value because (a) we do not know the exact value for a certain Ic (do you know the exact value for Ib? NO!), and (b) because of the...
  11. LvW

    Assistance with Transistor Theory

    Hi laplace - I think it is important to note that there is no current source in practice. We always are using a voltage source with a large series resistance Rs. And what happens if we connect these two elements to the base? We have realized a simple voltage divider with one fixed resistor Rs...
  12. LvW

    Assistance with Transistor Theory

    I like it too. Much better (and clearer) than "current gain". Do you know that we find the term "current gain" also in some FET datasheets? Crazy...
  13. LvW

    Assistance with Transistor Theory

    . ---would not work? OK - it is not pratical to connect a battery with 0.65234 voltas across the B-E path. However, we would have a corresponding Ic, or not?
  14. LvW

    Assistance with Transistor Theory

    Transconductance gm is the slope of the curve Ic=f(Vbe). As such, it is of course a small-signal parameter and not a fixed value but depending on the DC value for Ic. The non-linearity for large-signal operation can be observed, in particular, for class A-B and class B operation. However, this...
  15. LvW

    Assistance with Transistor Theory

    OK -but. in fact, it is a wasted current (see Barrie Gilberts term "defect" current)
  16. LvW

    Assistance with Transistor Theory

    However, please note that on page 79 we read: "Clearly, our transistor model is incomplete and needs to be modified ......Our ...transconductance model will be accurate enough for the remainder of this book." And on the same page (chapter 2.10): "But to understand diff. amplifiers...
  17. LvW

    Assistance with Transistor Theory

    Yes - I agree, of course. In particular the term "waste current". That`s what it really is: A current that exist and cannot be avoided. (And which is the source of a lot of misinterpretations because of the misnomer "current gain").
  18. LvW

    Assistance with Transistor Theory

    Which textbook are you referring to? Different textbooks offer different descriptions. By the way - here is a slide created by the Barrie Gilbert:
  19. LvW

    Assistance with Transistor Theory

    I don`t think that this is the case. We cannot "forget about Vbe" . For calculation of the resistor necessary to allow a certain current Ib you need the voltage difference V(source)-V(base). And V(base) dpends on the desired Vbe.
  20. LvW

    Assistance with Transistor Theory

    OK Adam - thank you for the example. Some comments: * The shown circuit does not contain any voltage source with base resistor (POT) but an ideal current source that does not exist in practice. Thus, it is not a real-world application. And - as far as I understood you - it was your goal to...
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