V(AVG) of a sine, again

Discussion in 'Homework Help' started by Agonche, Aug 21, 2012.

  1. Agonche

    Thread Starter Member

    Aug 26, 2011
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    0
    Hey, it's a similar question again.
    This time, I think my teacher got a wrong answer.
    Here's the problem:
    _________________________________________________________

    Draw the output voltage waveform, and find V_{AVG}.
    The diode is considered ideal.

    [​IMG]

    V_i=30sin\omega t
    _________________________________________________________

    Diode is ON when V_i>-11.3V, in this case V_o=-11.3V
    Diode is OFF when V_i<-11.3V, in this case V_o=V_i

    V_o waveform:

    [​IMG]

    \theta_1=\pi + arcsin \frac{-11.3}{-30}
    \theta_2=2\pi - arcsin \frac{-11.3}{-30}

    OK, here's what I've done. I pushed the waveform up +11.3.

    V_{AVG}=\frac {1}{2\pi}[\int_{\theta_1}^{\theta_2}18.7sin\theta \cdot d\theta]-11.3
    V_{AVG}=-16.8V

    The teachers answer is -15.8. I don't know how he got there but can anyone confirm that I'm right.
     
  2. The Electrician

    AAC Fanatic!

    Oct 9, 2007
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    If the diode is considered ideal doesn't that mean that the forward voltage drop is zero? That's what you assumed in your previous thread, wasn't it?
     
  3. Agonche

    Thread Starter Member

    Aug 26, 2011
    30
    0
    Im sorry, the diode has the .7V barrier. It seems I was looking somewhere else when I wrote ideal.
    Anyway, thank you for the very clear explanation. I didn't really catch the easy way, with the MIN function. (Im not that good at math :/).

    btw, can you tell me what software are you using to display the function graph, and these integrals.
     
  4. The Electrician

    AAC Fanatic!

    Oct 9, 2007
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    I'm using Mathematica. There are several similar programs that you have to pay for such as Maple, Mathcad, Matlab and there are some free ones that can also solve integrals. I think t_n_k can tell you what they are.
     
  5. MrChips

    Moderator

    Oct 2, 2009
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  6. The Electrician

    AAC Fanatic!

    Oct 9, 2007
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  7. Agonche

    Thread Starter Member

    Aug 26, 2011
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    0
    I tried some of these programs. I found Wolfram Mathematica is the best for me (got used to it pretty quickly). Thanks everyone.
     
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