AN2761 datasheet(22/36 Pages) STMICROELECTRONICS

22 / 36 page

Designing a TM PFC

AN2761

22/36

Doc ID 14690 Rev 2

Figure 11.

Multiplier characteristics family

A complete description is given in Figure 11, which shows the typical multiplier

characteristics family. The linear operation of the multiplier is guaranteed within the range 0

to 3 V of VMULT and the range 0 to 1.16 V (typ) of Vcs, while the minimum guaranteed value

of the maximum slope of the characteristics family (typ) is:

Taking this into account, the following is the suggested procedure to properly set the

operating point of the multiplier.

First, the maximum peak value for VMULT, VMULTmax is selected. This value, which occurs at

maximum mains voltage, should be 3 V or nearly so in wide-range mains and less in case of

single mains. The sense resistor selected is Rs = 0.34 Ω and it is described in the paragraph

concerning pin 4 of this section. The maximum peak value, occurring at maximum mains

voltage is:

where ILpk and Rs have been already calculated, and 1.1 V/V is the multiplier maximum

slope reported in the datasheet.

From (62) the maximum required divider ratio is calculated as:

(61)

(62)

(63)

Multiplier characteristic

-0.1

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

1.1

1.2

0.0 0.2 0.40.6 0.81.0 1.2 1.4 1.61.8 2.02.2 2.4 2.6 2.83.0

VMULT (pin3) (V)

V COMP (pin2) (V)

Upper Volt. Clamp

2.5 V

3 V

3.5V

4 V

5.75 V

4.5V

5 V

MULT

min

max

VAC

VMULT

⋅

Vac

265

VMULTmax

⋅

max

MULT

Vac

265

VAC

−

⋅

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