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Homework Help: Power Electronics, transistors

  1. Aug 31, 2011 #1
    Hi,

    I'd need some help regarding some parts of an exercise (attached below). The question is that they make me assume that the tranistors is working as a chopper, so then I have many things to calculate. The question is, which kind of chopper should I assume?

    Thanks in advance.

    http://img854.imageshack.us/img854/331/powerelectronics.png [Broken]

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    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
     
    Last edited by a moderator: May 5, 2017
  2. jcsd
  3. Sep 1, 2011 #2

    rude man

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    A. You can't compute the power loss without knowing the frequency f or duty cycle d. f isn't mentioned until part B and d in part D.

    The ENERGY lost per cycle is just E = ∫Vidt. Use Fig. 1 to compute that integral (there are five regions of integration; add 'em up).

    B. P = E/T where T = 1/f

    C. Once the inductor current is constant, what is the voltage across the load? The current? Ergo, the resistive load?

    D. This also requires several integrations. Power is almost d*Vd*I0 but not quite.

    E. (P in load - P lost in switch)/(P in load)

    F. Look at fig. 1 and think about the two things you must have to generate switching losses.

    Try to go from there ...
     
  4. Sep 1, 2011 #3

    rude man

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    I didn't answer your question, did I.

    But that's because you don't need to know what kind. All you need is fig. 1 (and I guess fig.2, though it's a crummy equivalent ckt IMHO.
     
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