Application information HVLED805
20/29 Doc ID 18077 Rev 1
5.6 Voltage feedforward block
The current control structure uses the voltage V
C
to define the output current, according to
(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
I
P
Is
Q
IC
T
R
C
V
CLED
I −=
CLED
I
IN d
P
P
VT
Δ I
L
=
