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AN628 APPLICATION NOTE

The power transferred by the inductor in each cycle

For a given L, the twice ripple current

and its value is

.

Smaller current ripple on the inductor involves smaller noise on the rectified main bus reducing the input filter

size; but the ripple reduction will impose an increase of the boost inductor.

The high voltage, the flux density and the frequency range make the standard high frequency ferrite the most

useful material in P.F.C. applications. To avoid the core saturation, related to the high permeability materials, it

is necessary built an air-gap in order to allow an adequate magnetic force range (H+Hgap).

An easy approach, is to have an approximated minimum value of core size that could be used to perform the

conversion:

Volume

≥

where : K = specific energy constant.

L = Boost inductor value in H.

∆B swing. Practically

the suitable type will be selected with technical and economic evaluations.

Next step will be the design of the coil parameters.

The above mentioned formula

P

t

LI

Lt

I

L

∆

⋅⋅

t

on

--------------------------

=

I

L

∆

V

lt

V

O

V

lt

–

()

⋅

V

O

f

sw

L

⋅⋅

-------------------------------------

=

V

O

2

--------

I

Lmax

()

∆

V

O

4f

sw

L

⋅⋅

-----------------------

=

I

Lmax

()

∆

V

V

lpk

–

()

V

O

f

sw

L

⋅⋅

-----------------------------------------

=

K

r

I

L

∆

2I

Lpk

⋅

------------------

=

KLI

Lpk

I

Lpk

I

L

∆

2

--------

+





⋅⋅

⋅

K14

I

eff

I

gap

----------

⋅

≈

P

Ot

LI

Lt

I

L

∆

⋅⋅

t

on

--------------------------

=