op-amp circuits

Discussion in 'Homework Help' started by neiji, Jan 29, 2008.

  1. neiji

    Thread Starter Member

    Jul 25, 2007
    19
    0
    I need help to understand the schematics which has been attached. I know that the first op amp is an integral cct which discharges through the 100Kohn in parallel with the capacitor.

    It is the second op amp that i am having difficulty. I don't know how to derive the gain and to explain how it converts the triangular waveform from the 1st op amp to triangular waveform of larger time
     
  2. rwmoekoe

    Active Member

    Mar 1, 2007
    172
    0
    first of all, i don't understand the practical use of this circuit.
    the first opamp is a low pass filter at about 16Hz.
    the second one is a triangle wave generator at a smaller period of time compared to the cycle period of the 16Hz or lower input signal. there is the hysteresis threshold formed by the positive feedback 100k res.
    the gain is 1 but the voltage divider that forms the hysteresis threshold is reducing the gain to 0.33 times.
    so the total gain is -0.33 times. and the output waveform would be like a low-pass-filtered signal, formed by higher frequency sawtooth waves.
    what is this circuit for, for the sake of curiosity?
     
  3. neiji

    Thread Starter Member

    Jul 25, 2007
    19
    0
    this circuit is used a pulse controller for a dc motor with a feedback. the signal gen is used to implement the feedback. actually i would like to know, how the second op amp is a triangle wave generator. on simulation both generate triangle wave but the second one has a LARGER time period than the the first op amp cct. any information about this type of circuit will be useful.
     
  4. rwmoekoe

    Active Member

    Mar 1, 2007
    172
    0
    it creates a near triangle waveform while charging or discharging the 0.22uF cap through the 200k res.
    it is the neg feedback loop, right? only, it has a very slow slew rate, created by that cap and res.
    what makes it a triangle gen further is the positive feedback loop (100k res to the + input) that creates a schmidt threshold. you know, like a schmidt trigger?
    these two things make the opamp work its way in an everlasting pursue of the + input and thus the oscillation.
     
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