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  1. LvW

    BJT Basics questions

    Max - just a short notice: The mentioned link is completed by a long discussion about some specific transistor features. Don`t overlook this sequence of questions and answers (understanding comes through questions and discussion).
  2. LvW

    How can I deduce the damping characteristics formula?

    I think, you must fail if you are trying to find a second-order function for a first-order circuit. The first part of your calculation is, of course, correct. Note that on page 632 of the 1st document we have two different finctions: First-order F(s) and second-order T(jw).
  3. LvW

    Negative Impedance Converter

    What is your definition for "internal resistance"? And at which point do you define the "open circuit" voltage? Well - let`s assume the "internal" resistance is the input resistance - measured at the non-inv. input terminal of the opamp. Assuming an ideal opamp (Aol infinite, input resistance...
  4. LvW

    Phase shift

    Oh - I just have realized that the wiki circuit differs from the circuit I had in mind. But it is not a problem. * The wiki circuit has a CR highpass at the non-inv. input node and the phase is phi=180 - 2*arctan(2*Pi*f*T). * Replacing the highpass by an RC lowpass (interchange of R and C) the...
  5. LvW

    Phase shift

    The circuit with three equal resistors R is given in the wiki reference. The transfer function is H(s)=(1-sT)/(1+sT) with T=RC. And the phase is phi=- 2*arctan(2*Pi*f*T). Hence, for any fixed frequency the value of T can be found for a desired phase phi. Note that -60deg is equivalent to +120deg.
  6. LvW

    Phase shift

    Why not using a simple allpass stage (one opamp only) with a phase shift of -60deg (identical to +120deg) ? https://en.wikipedia.org/wiki/All-pass_filter
  7. LvW

    need help again lrc parallel magnitude impedance

    However, Ratch, the question is if you can equalize both sides : complex expression=absolute value ? For my opinion: complex expression=magnitude*exp(j*phase).
  8. LvW

    Resistances of different lamps

    No - of course not. Each conductor has its own temperature coefficient (positive or negative). More than that, in most cases, in particular for lamps, there is specific (strong) non-linearity!.
  9. LvW

    Resistances of different lamps

    Yes - however, have you such a formula for the device under discussion?
  10. LvW

    low frequency signal amplification

    Let´s take as an example a gain of 10. Did you use the resistors as mentionmed on page 17 of the data sheet?
  11. LvW

    Switch capacitor = low pass filter ?

    In addition to Haralds answer I like to point out that a switched capacitor can mimic an ohmic resistor (within certain frequency limits, of course) only if it is operated BETWEEN two fixed voltages (one of which my be ground or opamp output). In many documents this fact is not mentioned...
  12. LvW

    Resistances of different lamps

    Of course, it is correct. Remember that the inventor of the WIEN oscillator (Hewlett) has used a tungsten lamp as a PTC resistor for stabilizing the amplitude of the oscillator. Each lamp of this type has a positive temperature coefficient which means: It is a PTC type thermistor (the...
  13. LvW

    Question about current sources - Not getting the correct current through load

    Yes - it is nothing else than a simple common emitter stage (of course, not an emitter follower) with RE feedback - and the current Ic through the "load" is considered to be the output of the current source. No magic behind the circuit.
  14. LvW

    Question about current sources - Not getting the correct current through load

    My comments are in bold. I am sorry, but this text has produced more questions to me than giving answers. Colin - perhaps I misunderstood something, but I must admit that I am really confused. It is such a simple circuit which exploits the fact that the BJT is nothing else than a...
  15. LvW

    How does an op-Amp make the inputs the same?

    You`re welcome.. I know - from personal experience - about the importance to know (a) why negative feedback is necessary for dc stabilizing purposes and (b) how negative feedback works in detail. So - I think, for you it was beneficial having asked this question.
  16. LvW

    How does an op-Amp make the inputs the same?

    What means "as required"? To answer your question, we must avoid any simplifications, which means: If the feedback factor is exactly 0.5 and the open-loop gain 1E4 the output cannot reach Vout=2V. The exact gain formula gives us Vout=Vin*[1E4/(1+0.5E4)]=1.9996001 V. Therefore: V-=0.99980004V...
  17. LvW

    How does an op-Amp make the inputs the same?

    Yes - that`s correct. And it is one of the main purposes of feedback to bring the device back to its linear amplification range. And - yes, you are also right that Vin=1V at the non-inv. input drives the opamp to positive saturation. Here we have to distinguish between two effects: 1.) After...
  18. LvW

    How does an op-Amp make the inputs the same?

    The problem is that we do not know the level of your knowledge. The opamp is a devive with a very large open-loop gain (1E5 or larger). Therefore, a small imbalance at the input (micro-Volt range) is sufficient to drive the output into saturation (out of the linear amplification range)...
  19. LvW

    How does an op-Amp make the inputs the same?

    I have tried to explain to you "the mechanics of feedback". Any further questions? Feedback factor is nothing else as it name says: It is (in most cases) a simple resistive voltage divider which couples back to the inverting terminal a certain portion (a factor below "1") of the output voltage.
  20. LvW

    How does an op-Amp make the inputs the same?

    Perhaps it helps to analyze what happens after switch-on the power supplies +/- Vs=+/-10V. Example: Non-inverting gain stage with gain of "+2". That means: Feedback factor k=0.5. 1.) Apply at t=0 an input voltage Vin=1V. The opamp is not yet working in its linear range and the output will be...
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