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AN829

APPLICATION NOTE

November 2003

BOOST CIRCUIT OPTIMIZATION PARAMETERS

Among the available topologies, a boost circuit operating in continuous current mode is the only topology which

enables the RFI noise across the input capacitor to be limited, and consequently a lower cost filter is required.

Also, the boost inductor stores only a part of the transferred energy, because the mains still supplies energy

during the demagnetization phase of the boost inductor - so the magnetic part required is smaller than needed

with any other topology. Therefore the boost topology leads to the cheapest solution. Figure 1 shows the general

topology of a boost PFC. Its optimization requires careful adjustment of the following parameters:

– the parasitic capacitances of the boost inductor and power semiconductors, including those associ-

ated with the heatsink

– the operating frequency and also the frequency modulation technique.

Figure 1. Semiconductor Kit for PFC Schematic.

+

C1

Lb

STH80N05

STE30NA50-DK

Lp1

1/KY

7

6

13

14

VREF

Lp5

Lp2

X

Lp3

Lp4

A

+

-

FREQ. MODUL.(B)

SYNCHRON. (A)

89

10

5

+

20

FULL

PROTECTION

ONE CHIP

L4981A/B

CONTROLLER

4

any

compensation

1

D95IN252A

by J.M. Borgeous

SEMICONDUCTOR KIT FOR

POWER FACTOR CORRECTOR

This paper present a new line of P.F.C. dedicated products. Both silicon and packaging have been op-

timized to reduce system cost, including filtering. The products shown here are offered as a kit for power

factor correction.