STMicroelectronics LED815 Evaluation Boards EVALHVLED815W15 EVALHVLED815W15 Fiche De Données

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Doc ID 023409 Rev 4

During MOSFET's ON-time the current sourced from DMG pin is mirrored inside the "Feed-
forward Logic" block in order to provide a feed-forward current, I

FF

.

Such "feed-forward current" is proportional to the input voltage according to the formula:

Where m is the primary-to-auxiliary turns ratio.

According to the schematic, the voltage on the non-inverting comparator will be:

The offset introduced by feed-forward compensation will be:

As R

FF

>>R

SENS

E, the previous one can be simplified as:

This offset is proportional to VIN and it is used to compensate the current overshoot, 
according to the following formula:

AM13569v1

CS

.

IFF

Feedforward
Logic

+

-

CC

Rff

Rsense

PWM

LOGIC

DMG

CC 

Block

Aux

Rfb

Rdmg

SOURCE

DRAIN