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  1. LvW

    Question about B-E voltage.

    I hope I can answer your question: The keyword ids "feedback". Because we do not know the exact Vbe value for the desired current Ic we are applying negative feedback. One of the many advantages of negative feedback is a sensitivity reduction of circuit parameters upon (uncertain) parameters of...
  2. LvW

    Question about B-E voltage.

    You do not care? Bob - unfortunately, you didn`t respond to my questions to you (see my post#12). May I repeat one of my question (see my post#12): * How do you choose the resistors for the resistive voltage divider at the base? * Don`t you follow the rule "as low as possible with respect to...
  3. LvW

    Question about B-E voltage.

    Yes - that`s true. On the other hand, I think the real working principle of a BJT should be clear as it was discussed also in this forum already some time ago (although some persons are still denying physical facts). For participating in THIS discussion, my only intention is to reveal the...
  4. LvW

    Question about B-E voltage.

    Everybody uses beta. And - everybody uses Vbe=0.65...0.7 V for calculating this resitor RB. So - what does this proove? Nothing. (Read my post#15). . This is, certainly, not a chicken-egg question. The voltage is always first; no current without driving voltage.
  5. LvW

    Oscillator CR amp op

    The condition of oscillation is a general condition. It does not depend on the specific circuit topology. If you want to analyze and/or construct an oscillator the first task is to understand WHY and under which conditions a system is able to oscillate. These fundamental things cannot and should...
  6. LvW

    Question about B-E voltage.

    OK - I think, that is one of two possible interpretations (assuming that such thing like a current source does exist).. Another explanation/interpretation is as follows: "Feeding a current into the base" means nothing else than to calculate a resistor RB which is part of a non-linear voltage...
  7. LvW

    Question about B-E voltage.

    1.) Of course, you can write a function between two or more parameters in several different forms. But this writing has no meaning at all while discussing physical properties. However, in the following I don`t want to stress again the physical working principle of the BJT. To me, this is clear...
  8. LvW

    Question about B-E voltage.

    Good luck! Steve, I should add the following: As we all know - RE-feedback increases the signal input resistance at the base node. And from feedback theory it is known that such an increase is possible only if the feedback signal is a VOLTAGE.
  9. LvW

    Question about B-E voltage.

    How do you know? Perhaps it is shocking news for you - but I was teaching analog electronics for more than 25 years. Colin - since a long time I know your position in this question, but it is never too late to take into consideration positions and explanations from other sources - even "crazy...
  10. LvW

    Question about B-E voltage.

    I rather think that the base-emitter voltage Vbe is of primary concern because it controls the collector current Ic. Remember Shockleys function Ic=f(Vbe/Vt). It is a common misconception (to be found even in some textbooks) to believe that Ic would be "controlled" by Ib. The current into the...
  11. LvW

    Op Amp LM358 somehow doesn't work

    While reading in a forum that a simple opamp based amplifier is not working, I always assume at first that a single supply voltage is used - also in this case. For my opinion, everybody who is trying to become familiar with opamps should at least know why classical (basic) opamp applications...
  12. LvW

    RL low pass filter, Voltage across inductor at 100hz

    A voltage is to be measured BETWEEN two points - how can you detect a voltage at one side of the inductor? Referenced to which node? More than that - if you are asking me why I would "need to take a measurement "across" the inductor at 100hz" my answer is: I do not need such a measurement. The...
  13. LvW

    RL low pass filter, Voltage across inductor at 100hz

    I really don`t know what your problem is. What is the question? How can a voltage exist "across either end of the inductor"? What do you mean ? Voltage across the inductor? In the headline you speak about a lowpass. How do you know if it is a lowpass?
  14. LvW

    RL low pass filter, Voltage across inductor at 100hz

    As I can read - you have an RL circuit, whatever this may be. Perhaps you have rough drawing, because there is not only one single alternative to connect both parts.
  15. LvW

    Les Paul

    Well, I rememeber Les Paul and Mary Ford: The world is waiting for the sunrise...
  16. LvW

    LTspice 4 Trouble With Transient Simulation Reults

    Doing a TRAN analysis the most important parameter is the specufied (minimum) time step (time resolution). I always would suggest to use AT LEAST 1000 points within the simulation time. So - for a simulation time of 1 sec I recommend a minimum step of 1msec. What was your choice?
  17. LvW

    need help with an amplifier

  18. LvW

    need help with an amplifier

    As I understand the task, the amplifier should work in the quasi-linear range with a gain of 100. Hence, the transistor is neither turned (switched) ON nor OFF.
  19. LvW

    need help with an amplifier

    Toffetan - are you aware that your resistance values (Rc and RE) are rather low? So you need a lot of milli-Amps as DC current through the transistor. Why not in the lower kOhm range? Example: Ic=1mA (2mA) and Rc=6 kohms (3kOhms). The stabilizing resistor RE could be app. 5...10% of Rc...
  20. LvW

    need help with an amplifier

    I suppose it should read: 0.707 mV (rms). Toffetan: Did you perform an AC or a TRAN analysis? In any case, I would do a TRAN analysis in order to check the waveform (distortions).
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