Power factor section

AN3973

6/24

Doc ID 022164 Rev 1

2.1

PFC section design

The first step is to define the converter specifications that the user must set for the new PFC

boost topology project.

At switching frequency, the inductor current is a triangle shape and the average value is half

of the peak of triangle. The resulting inductor current is shown in Figure 3, where it is also

shown that, by geometric relationships, the average value is the peak of sinewave input

current. The system operates the boundary between continuous and discontinuous

(transition mode current):

Figure 3.

Inductor and input current waveform. MOSFET timing

Therefore the main operating conditions are:

●

RMS input current

●

Peak inductor current

●

RMS inductor current

Table 1.

Converter specification data and fixed parameters

Name

Symbol

Value

Input voltage range

180 Vac to 264 Vac

Nominal output voltage

400 V

Nominal output power

60 W

Target efficiency

n

∼ 90%

Minimum switching frequency

35 kHz

Expected power factor

PF

0.99

AM10586v1

 

A

374

.

0

PF

V

*

P

PF

V

P

I

min

AC

out

min

AC

in

in

=

η

=

=

 

in

pk

I

2

2

IL

=

 

in

RMS

I

3

2

IL

=