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39DC-DC Converter Design and Magnetics

Note also, that for any topology, a high duty cycle corresponds to a low input voltage,

and a lo

w duty cycle is equivalent to a high input. So increasing D amounts to decreasing

the input voltage (its magnitude) in all cases. Therefore, in a boost or buck-boost, if the

difference between the input and output voltages is large, we get the highest DC inductor

current.

Finally, with the DC and AC components known, we can calculate the peak current using

III

I

I

PK AC DC L

 



2

(3-9)

3.5 Defi ning the “ Worst-case ” Input Voltage

So far, we have been implicitly assuming a fi xed ...