HVLED807PFTR datasheet(24/36 Pages) STMICROELECTRONICS

Part #	HVLED807PFTR

Description	Offline LED driver with primary-sensing and high power factor up to 7 W

PDF	36 Pages

Scroll/Zoom	100%

Manufacturer	STMICROELECTRONICS [STMicroelectronics]

Direct Link	http://www.st.com

Logo

24 / 36 page

Device description

HVLED807PF

24/36

Doc ID 023464 Rev 5

Figure 19.

Feed-forward compensation: internal schematic

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, IFF.

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

Equation 9

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

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

Equation 10

The offset introduced by feed-forward compensation will be:

Equation 11

As RFF>>RSENSE, the previous one can be simplified as:

Equation 12

This offset is proportional to VIN and it is used to compensate the current overshoot,

according to the following formula:

AM13569v1

IFF

Feedforward

Logic

Rff

Rsense

PWM

LOGIC

DMG

Block

Aux

Rfb

Rdmg

SOURCE

DRAIN

HVLED807PFTR Datasheet(PDF) 24 Page - STMicroelectronics