HVLED805

Application information

Doc ID 18077 Rev 1

21/29

During MOSFET’s ON-time the current sourced from DMG pin is mirrored inside the

Such “feedforward 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 feedforward compensation will be:

Equation 11

Equation 12

Figure 17.

Feedforward compensation: internal schematic

.

CC

Block

Aux

Rdmg

Rfb

IFF

Rsense

RFF

CC

Feedforward

Logic

PWM

LOGIC

DMG

DRAIN

SO URCE

dmg

IN

FF

R

m

V

I

⋅

=

(

)

(-)

SENSE D

FF

FF

SENSE

V= R

I +I

R +R

⋅⋅

()

SENSE

FF

dmg

IN

OFFSET

R

R

R

m

V

V

+

⋅

⋅

=

dmg

FF

IN

OFFSET

R

m

R

V

V

⋅

⋅

=