AN1606 APPLICATION NOTE

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Description of "Bridgeless PFC Configuration" Topology

The conventional boost topology is the most efficient for PFC applications. It uses a dedicated diode bridge to

rectify the AC input voltage to DC, which is then followed by the boost section. See Figure 2.

This approach is good for a low to medium power range. As the power level increases, the diode bridge begins

to become an important part of the application and it is necessary for the designer to deal with the problem of

how to dissipate the heat in limited surface area. The dissipated power is important from an efficiency point of

view.

Figure 2.

The bridgeless configuration topology presented in this paper avoids the need for the rectifier input bridge yet

maintains the classic boost topology.

This is easily done by making use of the intrinsic body diode connected between drain and source of PowerMOS

switches.

A simplified schematic of the bridgeless PFC configuration is shown in Figure 3.

Figure 3.

Load

L

A

controller

Rs

V_Rs

Mains

M

D

Inductor

Controller

Mains

Load

L

O

A

D

Inductor

M1

M2

D1

D2