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  1. LvW

    what is this Circuit ?

    On the output? The 157k resistor is the ac input to the filter circuit. It is one of the well-known filter topologies - however, I wonder where it is used with this dimensioning (extremly low dc gain).
  2. LvW

    what is this Circuit ?

    Gentlemen - it is one of the most applied lowpass filter circuits in multi-feedback topology: MFB lowpass filter in single-supply configuration.The R10-R4 circuitry is for bias purposes only. And - of course - the low-resistive opamp output serves as filter output. A rough calculation shows that...
  3. LvW

    RC oscillator and Quartz frequencies

    And tell us which type of RC oscillator you are using.
  4. LvW

    Wein bridge vs. Phase shift oscillator

    What menas "better"? There are many different parameters which have to be considered: Frequency range, amplizudes, tunability, THD, price, parts count, ....?
  5. LvW

    How Transistors Work

    Oh - I forget to mention that the main question was "How transistors work" and not "What is the most simple method for designing a BJT stage". PS: Sorry, but I have to stop the conversation at this point because of a jouney starting tomorrow morning.
  6. LvW

    How Transistors Work

    Hi Steve, I think we are pretty close together - only some "minor" differences: All of us assume a VBE value while designing an amplifier stage, do we not? And what about IB? No tolerances/uncertainties for IB=IC/B ? I don´t think I have to "describe" the change in VBE separately. I have...
  7. LvW

    How Transistors Work

    Hi Adam - for my opinion you didn´t really met "my point". Let me explain: As the result of your contribution we have two formulas which - for my opinion - cannot be compared to each other. That means: They cannot reveal any differences between both approaches. The first equation describes the...
  8. LvW

    How Transistors Work

    Steve - I cannot see where I have used a current to "control" something. Of course, there is a current IB and, therefore, we must consider its influence; and, thus, we consider and calculate the voltage "loss" at the resistor RB caused by this current IB. But all this only to allow the...
  9. LvW

    How Transistors Work

    Hi Steve, Every time I read a statement like this (..far less useful in practice..) I ask myself: How can you design a simple transistor stage without using the voltage-control property of the BJT? It is simply not true that "base current controlling collector current almost always allows you...
  10. LvW

    Op Amp

    Sorry - I didn´t know too much about the intentions of the questioner. I was of the opinion, he wants to find a proper bias point for some further experiments.
  11. LvW

    Op Amp

    1.) It is not clear which current you are speaking of. For checking the gain it is much more meaningful to measure input and output voltages. 2.) For linear amplification it is necessary to bias the opamp in its linear range. Normally, this is done using dual supply voltages with negative...
  12. LvW

    zener circuit

    The current must not be larger than (25.8-3.3)/120k=0.1875mA to allow a voltage of 3.3V across the zener.. That means: I don´t think that you can reach the breakpoint at 3.3V with such a small current.
  13. LvW

    Thermistor model for Spice?

    Some years ago I have created a model for a thermistor, see here: http://www.spectrum-soft.com/news/fall98/therm.shtm
  14. LvW

    Slight Instability at start on active phase shift circuit

    Yes - that´s what I have tried to explain in my former post.
  15. LvW

    Slight Instability at start on active phase shift circuit

    The output shows a ggod portion of triangular distortions caused by insufficient slew rate. Is this a problem for you? This is no indication of instrability. It is, rather, a normal transient behaviour as a result of the inpiut signal switch-on event. No reactive circuit is able to reach its...
  16. LvW

    Slight Instability at start on active phase shift circuit

    I think, it is a classical allpass cicuit: Constant amplitude and frequency-dependent phase shift. But I don`t understand the problem. Where do you see some kind of instability? Sinus in and sinus out - where is the problem?
  17. LvW

    Slight Instability at start on active phase shift circuit

    pgiles, the LT6210 is a current-feedback amplifier which requires a certain feedback resistor (lower limit). You should check if you are complying with the specification. More than that, your circuit description is not clear - please provide a circuit diagram. Furthermore, a "slight instability...
  18. LvW

    Op Amp Power Supply

    Surprising idea. What do you expect when operating an npn transistor with a negative VDS voltage?
  19. LvW

    LM2903N differential op-amp

    Mike, I´ve got the impression that you are using a single supply voltage. Correct? And - at the same time - you expect an output as low as 0 volts? In any case, it would be best to show us your circuit including supply voltages. The we can try to solve your problem.
  20. LvW

    Integrator circuit using single resistor gain"ad620" op amp?

    Yes - but the problem is: It is not possible to realize an (ideal) integrator. It always will be a low pass filter (however, with a rather small corber frequency).
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