November 2010

Doc ID 17975 Rev 1

1/22

AN3276

Application note

ST solution for efficiency improvement in PFC applications,

Introduction

The challenges for modern high efficiency switching power supplies are to minimize power

losses and increase their power density without raising the cost. The goal is to reduce both

power conduction and power switching losses.

Minimization of power conduction losses is difficult to achieve without considerably affecting

the cost and power density, since more material is required (bigger active and passive

components). Unlike the conduction losses, it is easier to reduce the power switching losses

without significantly increasing the power supply cost. There are two main ways to achieve

this improvement:

Novel diodes using technologies such as SiC and GaN materials significantly reduce the

switching losses. However, their high price makes them not so attractive for applications

such as desktop server power supplies, solar inverters and µinverters.

The patented circuit [see Section 5: References, 1.], described in this Application note is

based on the soft switching method and meets market expectations since its

efficiency/cost/power, and density/EMI trade-offs are better than high voltage SiC Schottky

diodes.

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