STMicroelectronics EVAL BOARD FOR L6563 EVL6563H-250W EVL6563H-250W Data Sheet
Product codes
EVL6563H-250W
L6563H
Application information
Doc ID 16047 Rev 3
27/49
The twice-mains-frequency (2
•
f
L
) ripple appearing across C
FF
is triangular with a peak-to-
peak amplitude that, with good approximation, is given by:
where f
L
is the line frequency. The amount of 3rd harmonic distortion introduced by this
ripple, related to the amplitude of its 2
•
f
L
component, is:
shows a diagram that helps choose the time constant R
FF
·C
FF
based on the
amount of maximum desired 3rd harmonic distortion.
Note that there is a minimum value for the time constant R
FF
·C
FF
below which improper
activation of the V
FF
fast discharge may occur. In fact, the twice-mains-frequency ripple
across C
FF
under steady state conditions must be lower than the minimum line drop
detection threshold (
ΔV
VFF_min
= 40 mV). Therefore:
Always connect R
FF
and C
FF
to the pin, the IC will not work properly if the pin is either left
floating or connected directly to ground.
Figure 40.
R
FF
·C
FF
as a function of 3rd harmonic distortion introduced in the input
current
FF
FF
L
MULTpk
FF
C
R
f
4
1
V
2
V
+
=
Δ
FF
FF
L
3
C
R
f
2
100
%
D
π
=
min
_
L
min
_
VFF
max
_
MULTpk
FF
FF
f
4
1
V
V
2
C
R
−
Δ
>
⋅
D %
3
0.1
1
10
0.01
0.1
1
10
f = 50 Hz
L
f = 60 Hz
L
R · C [s]
FF
FF