Vivanco UNIVERSAL SWITCHMODE AC TO DC MAINS ADAPTERS WITH USB CHARGING FUNCTION Guia do Utilizador descarregar pdf (Página 15)

Introduction

FIGURE 1-4: BLOCK DIAGRAM OF THE COMPONENTS FOR POWER FACTOR CORRECTION

1.2.1.2 PFC TOPOLOGIES

The Power Factor can be achieved with various basic topologies such as Buck, Boost

and Buck/Boost.

1.2.1.2.1 Buck PFC Circuit

In a Buck PFC circuit, the output DC voltage is less than the input rectified voltage.

Large filters are needed to suppress switching ripples and this circuit produces

considerable Power Factor improvement. The switch (MOSFET) is rated to V

IN in this

case. Figure 1-5 shows the circuit for the Buck PFC stage. Figure 1-6 shows the Buck

PFC input current shape.

FIGURE 1-5: BUCK PFC

Rectifier Chopper

Rectified Voltage

Bus Current

DC Voltage

dsPIC

Digital Signal Controller (DSC)

Load

AC Input

Switching pulses

1 2 ... 10 11 12 13 14 15 16 17 18 19 20 ... 117 118

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Vivanco UNIVERSAL SWITCHMODE AC TO DC MAINS ADAPTERS WITH USB CHARGING FUNCTION Guia do Utilizador Página 15