Power Sources and Supplies: World Class Designs

324

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Chapter 10

So in fact, the swing  of the current or the fi

eld is the same at high input or at low input,

or in fact at any input (as long as the choke is in CCM). Since the transformer is in DCM,

its peak is equal to its swing, and so the peak too does not depend on V

IN

. Of course, the

peak switch current I

SW_PK

is the sum of the peak of the magnetization current I

M_PK

, and

the peak of the secondary-side current waveform refl ected onto the primary side, that is,

II

n

I

r

SW_PK M_PK O

 

1

1

2

⎛

⎝

⎜

⎜

⎜

⎞

⎠

⎟

⎟

⎟

⎟

⎡

⎣

⎢

⎢

⎤

⎦

⎥

⎥

(10-21)

So although the current limit of the switch must be set high enough to accommodate

I

SW

_

PK

at ...