AN2435

Sepic topology for PFC converter

9/25

∆VC1 (

Equation 17

It is useful to rewrite some quantities calculated earlier, in terms of converter output power,

generally known at the beginning of a design. Input power may be expressed as follows:

Equation 18

(F(Kv)) may be calculated as follows:

Equation 19

Equation 20

The switching frequency can be expressed as:

Equation 21

Figure 5.

Switching frequency variation vs

θ for two different input voltages

1.

V

()

∆

L

e

C1

--------

I

PK

2

2

-----------

•

ϑ

()

sin

2

V

O

2V

ac

ϑ

()

sin

•

•

+

()

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

•

=

P

in

f

L

I

PK

2

--------

2

πf

L

t

•

()

sin

1K

v

2

πf

L

t

•

()

sin

•

+

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

2V

ac

2

πf

L

t

•

()

sin

•

•

•

•

0

1

f

L

----

∫

•

dt

•

=

Fk

v

()

f

L

2

πf

L

t

•

()

sin

1k

v

2

πf

L

t

•

()

sin

•

+

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

0

1

f

L

----

∫

•

dt

•

=

2

I

PK

2P

O

•

η

2V

ac

Fk

v

()

•

•

•

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

=

f

()

η V

ac

2

•

Fk

v

()

•

P

O

L

e

•

1k

v

ϑ

()

sin

•

+

()

•

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

=