AN2761 datasheet(21/36 Pages) STMICROELECTRONICS

21 / 36 page

AN2761

Designing a TM PFC

Doc ID 14690 Rev 2

21/36

Because the internal current sense clamping sets the maximum current that can flow in the

inductor, the maximum peak of the inductor current is calculated considering the maximum

voltage Vcsmax allowed on the L6562A (in the datasheet):

The calculated ILpkx is the limit at which the boost inductor saturates and it is used for

calculating the inductor number of turns and air gap length.

The power dissipated in Rs is given by:

According to the result two parallel resistors of 0.68

Ω with 0.25 W of power rating have

been selected.

●

Pin 3 (MULT): The MULT pin is the second multiplier input. It is connected, through a

resistive divider, to the rectified mains to get a sinusoidal voltage reference. The

multiplier can be described by the relationship:

where:

–VCS (multiplier output) is the reference for the current sense

–

k = 0.38 (typ) is the multiplier gain

–VCOMP is the voltage on pin 2 (E/A output)

–VMULT is the voltage on pin 3

(58)

(59)

(60)

max

pkx

Vcs

pkx

rms

ISW

⋅

(

)

⋅

MULT

COMP

)

(

⋅

−

⋅

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