Sepic topology for PFC converter

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Figure 3.

Sepic converter when the main switch is off

Figure 4.

Inductor L1 and inductor L2 current waveform

1.2

Sepic converter as a PFC circuit operating in transition mode

[1.]

In PFC applications, input voltage is the rectified main and it changes according to the

equation:

Equation 5

where

As switching frequency is in the range of some tenth of kHz, and thus much higher than the

line frequency, we can assume

ϑ is constant over each switching cycle.

The L6562 (see [2]) is a current mode controller dedicated to PFC applications. It is used in

this instance. It senses the MOSFET current and the input voltage of the converter (rectified

main), through a sense resistor and a resistor divider respectively. Cycle by cycle the

MOSFET is switched-off as the sensed current reaches a limit set by the controller. This limit

sinusoidal reference:

Equation 6

+

-

+

-

+

-

t

V

()

2V

ac

•ϑ

()

sin

•

=

I

() I

PK

ϑ

()

sin

•

=