AN3112

Designing a fixed-off-time PFC

Doc ID 16820 Rev 3

11/36

4.2

Operating condition

The first step is to define the main parameters of the circuit, using the specification points

given in

Section 4.1 on page 9:

Rated DC output current:

Equation 8

Maximum input power:

Equation 9

Referring to the main currents shown in

Figure 1, the following formula expresses the

maximum value of current circulating in the boost cell which means at minimum line voltage

of the selected range:

RMS input current:

Equation 10

It is important to define the following ratios in order to continue describing the energetic

relationships in the PFC:

Equation 11

Equation 12

From

Equation 11 and Equation 12:

Line peak current:

Equation 13

Inductor Ripple-

∆ILpk:

out

out

out

V

P

I

=

A

00

.

1

V

400

W

400

I

out

=

=

η

in

P

P

W

44

.

444

100

90

W

400

=

⋅

=

PF

VAC

P

I

min

out

in

⋅

=

A

99

.

4

99

.

0

Vac

90

W

400

I

in

=

⋅

=

out

min

min

V

VAC

2

k

=

32

.

0

V

400

Vac

90

2

=

=

out

max

max

V

VAC

2

k

=

94

.

0

V

400

Vac

265

2

k

max

=

=

out

min

in

max

PK

V

k

P

2

I

⋅

⋅

=

A

98

.

6

V

400

32

.

0

W

44

.

444

2

I

max

PK

=

⋅

⋅

=