Техническая Спецификация для STMicroelectronics 19 V - 75 W SMPS using the L6563 and the L6566A EVL6566A-75WES4 EVL6566A-75WES4
Модели
EVL6566A-75WES4
Application information
L6563S
26/43
Doc ID 16116 Rev 4
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, will be:
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
the time constant R
FF
•
C
FF
below which improper activation of the VFF fast discharge may
occur. In fact, the twice-mains-frequency ripple across CFF under steady state conditions
must be lower than the minimum line drop detection threshold (V
must be lower than the minimum line drop detection threshold (V
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 37.
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