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RC Circuit from Voltage equation

Discussion in 'Electronics Homework Help' started by Thelair, Mar 2, 2013.

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  1. Thelair


    Mar 2, 2013
    Hey there, I've got a little problem with my electronics homework and I can't really find any hints over the internet nor in my notes.
    We were given a table showing time and voltage values and we are to create a proper one-capacitor circuit from it.
    So far I managed to create an equation showing the voltage in given t-time:
    U(t) = 1.84 + 5.765 * e (-t/T)
    Also, during the process, I got few variables which may be useful later:
    T = 2,8s
    U(5T) = 1.84V (5T = 14s)
    Uinput = 10V

    So far it was somehow clean math, but the question is how to transform voltage equation into a single-capacitor-single-resistor circuit.
    I don't really want an answer, rather a hint, I really like that "process of creation", but I tried everything I know ( t-to-s domain transformation, time-dependant circuit builds, math ) but I get too many unknowns as I calculate and it goes to nowhere so far.

    I hope someone can help me with this one a bit :)
    Last edited: Mar 3, 2013
  2. Laplace


    Apr 4, 2010
    Compare the given discharge equation to a common RC discharge equation. How does the variable 'T' compare to the RC time constant 'tau'? There are many different values of R and C that will give the required value for 'tau'.
  3. Thelair


    Mar 2, 2013
    T is the time constant, same as tau, just easier to write on the forum :)
    I'm gonna go and look for this common discharge equation, I think I have seen it somewhere, maybe it will be much more useful than I thought.
    Last edited: Mar 3, 2013
  4. Thelair


    Mar 2, 2013
    Ok, so far I noticed that/and why whole excersise is about discharging ( I've drawn the function ). And I've noticed that after being discharged the capacitor leaves 1,84V inside the circuit. I therefor belive that I should start with such circuit:
    I did some calculations and the result shown that R1 = 4,434R2.
    Now I think I'll try to fit a capacitor on the line between voltmeter node-clips.
    Am I going the right path?
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