Power Electronics, transistors

[jas1991]

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

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[rude man]

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 ...

 

[rude man]

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.