Transient response of integrator circuit from t = 0

Discussion in 'Homework Help' started by Muhammad Danyal, Jan 3, 2015.

  1. Muhammad Danyal

    Thread Starter New Member

    Jan 3, 2015
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    I am new to the forum. I want to ask my first question. What is the output of an integrator during transient when a switch (connected to dc 1.5V) is closed at time t=0?
    I guess the input is a ramp function and the output will be a parabolic function.
     
  2. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    Welcome. The moderators will likely move your question to its own thread. This looks like homework?

    You are guessing wrong. Let me ask you this: What is the current in R1 after the switch closes? Once you know the current, the output voltage is the simple integral of that current.
     
  3. Muhammad Danyal

    Thread Starter New Member

    Jan 3, 2015
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    yes it is a question from exercise. The current through the resistor is 0A due to infinite input resistance. so what is the output?
     
  4. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    No it is not. Write a KCL equation for the inverting input of the opamp.
     
  5. crutschow

    Expert

    Mar 14, 2008
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    What resistance do you think is infinite?
     
  6. MrAl

    Well-Known Member

    Jun 17, 2014
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    Hi,

    The input resistance to the OP AMP is often considered infinite for basic calculations, but the input resistance to the CIRCUIT is not infinite because the inverting input is considered a 'virtual ground' and so current flows from the battery though the resistor and then to the virtual ground.

    The output is the time integral of the input voltage times a constant. If R=1 and C=1 that constant would be equal to 1, but in this case R and C are not 1 so it is a different constant that you have to find.

    If the input voltage was really a ramp input and not the constant voltage battery then the output would be parabolic, but the input is not a ramp here it's a constant.

    What techniques did you use in the past so far, and what kind of math have you had already?
     
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