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2 1
2
ENABLE _ th(max)
VINS VINS
AC( on ) ENABLE _th(max) F _ BRIDGE
VINS
R R
V VINS V
=
- -
2
1 2
IN _ RMS
VINS
VINS VINS
V
P
R R
=
+
2
2
1 2
0 9
CVIN _ dschg
VINS
BROWNOUT _th(min)
VINS
VINS
IN _ RMS(min)
VINS VINS
t
C
VINS
R n
R
. V ( )
R R
-
=
é ù
ê ú
ê ú
ê ú
ê ú
+
ë û
l
2
half _ cycles
CVINS _ dschrg
LINE(min)
N
t
f
=
UCC28019
SLUS755B – APRIL 2007 – REVISED DECEMBER 2007
First, select R
VINS1
based on the the highest reasonable resistance value available for typical applications.
Then select R
VINS2
based on this value:
Where V
F_Bridge
is the forward voltage drop across the ac rectifier bridge.
Power dissipated in the resistor network is:
The filter capacitor, C
VINS
, has two functions. First, to attenuate the voltage ripple to levels between the enable
and brown-out thresholds which will prevent the ripple on VINS from falsely triggering IBOP when the converter
is operating at low line. Second, C
VINS
delays the brown-out protection operation for a desired number of line
half-cycle periods while still having a good response to an actual brown-out event.
The capacitor is chosen so that it will discharge to the VINS
BROWNOUT_th
level after N number of half line cycles of
delay to accommodate line dropouts.
Where:
and V
IN_RMS(min)
is the lowest normal operating RMS input voltage.
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Product Folder Link(s): UCC28019