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problem with the integration of DC analysis

Discussion in 'General Electronics Discussion' started by sairam.chappidi, Mar 9, 2015.

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  1. sairam.chappidi

    sairam.chappidi

    1
    0
    Mar 9, 2015
    I am working on circuit to convert micro ampere current into voltage. For this purpose, I am using an integrator circuit using LMC6001 as the op-amp. I want to convert DC current in the micro ampere range into voltage. My circuit output for AC analysis matches with the simulation results, where the input is a sine wave or a square wave. Unfortunately, I get no circuit output for DC analysis, when the SPICE simulation software gives the correct output as calculated mathematically. I am using a feedback capacitor of 2nf and a resistor of 10M ohms as feedback resistance in the Integrator circuit. I am using these values of capacitance and resistor so that my integrator circuit can work with in a frequency range of 8-20 Hz.

    In DC analysis, for discharging the capacitor I am using a JFET (2N4117) that has to be given a clock pulse with a period of 50ms and the JFET will be switched off for 1msec. I want my capacitor to discharge in this 1ms and then start integrating once again for the next 49ms. For the rest of the 49ms, the JFET will not be working as it will be in open circuit. I am placing this JFET in such a way that the source and drain are across the feedback resistor and capacitor in the circuit. I am providing the gate with a clock pulse of amplitude of -5V for 49ms. This for the off condition and 0V for the rest of 1msec : this is the on condition for the JFET.

    The main problem in this circuit is that the switching action of the JFET works fine in AC analysis, but not in the DC analysis.

    I would be grateful for any help / suggestions.

    P.S : Do you think that it’s because of testing this micro ampere- range circuit on a breadboard ?

    Does any precaution needs to be taken for the circuit testing ? Any design changes that need to be done
     
  2. Arouse1973

    Arouse1973 Adam

    5,165
    1,087
    Dec 18, 2013
    Can you post the circuit diagram please?
    Adam
     
  3. LvW

    LvW

    604
    146
    Apr 12, 2014
    The main problem in this circuit is that the switching action of the JFET works fine in AC analysis, but not in the DC analysis.

    Yes - a circuit diagram would be very helpful. However, one question: Do you expect to see any "switching action" in a DC analysis?
     
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