Application information

HVLED805

20/29

Doc ID 18077 Rev 1

5.6

Voltage feedforward block

(7). Actually, the CC comparator will be affected by an internal propagation delay Td, which

will switch off the MOSFET with a peak current than higher the foreseen value.

This current overshoot will be equal to:

Equation 8

Will introduce an error on the calculated CC setpoint, depending on the input voltage.

The HVLED805 implements a Line Feedforward function, which solves the issue by

introducing an input voltage dependent offset on the current sense signal, in order to adjust

the cycle-by-cycle current limitation.

The internal schematic is shown in Figure 17.

Figure 16.

Constant current operation: Switching cycle waveforms

t

t

t

t

Q

T

R

C

V

CLED

I

−

=

CLED

I

IN

d

P

P

VT

Δ I

L

⋅

=