NCP1246 ONSEMI [ON Semiconductor], NCP1246 Datasheet - Page 19

• Manufacturer Part Number: NCP1246
• Description: Fixed Frequency Current Mode Controller for Flyback Converters
• Manufacturer: ONSEMI [ON Semiconductor]

V
case the V
failure, or external pullïdown on V
controller). There is only one condition for which the current
source doesn’t turn on when V
voltage on HV pin is too low (below V
HV Sensing of Rectified AC Voltage
monitoring circuitry. It includes a minimum startïup
can start immediately. When it crosses V
CC
For safety reasons, the startïup current is lowered when
The NCP1246 features on its HV pin a true ac line
When V
is below V
CC
HV
V
V
HV stop
V
pin is shorted to GND (in case of V
HV(start)
V
HV(stop)
CC(min)
crosses the V
CC(on)
CC(inhibit)
DRV
V
V
CC
HV
, to reduce the power dissipation in
HV(start)
CC
reaches V
threshold, the controller
Figure 49. Ac Line Dropïout Timing Diagram
HV(min)
t
CC
HV
HV(stop)
to disable the
CC(inhibit)
).
CC
, it triggers
capacitor
http://onsemi.com
: the
HV timer elapsed
NCP1246
Brown-out
detected
Internal Latch
19
Brown-out
resets the
condition
threshold and an autorecovery brownïout protection; both
of them independent of the ripple on the input voltage. It is
allowed only to work with an unfiltered, rectified ac input to
ensure the X2 capapacitor discharge function as well, which
is described in following. The brownïout protection
thresholds are fixed, but they are designed to fit most of the
standard acïdc conversion applications.
brownïout condition is detected, and the controller stops.
The HV current source maintains V
the input voltage is back above V
a timer of duration t
doesn’t stop in case of line cycle dropïout.
VccON before
When the input voltage goes below V
Waits next
starting
HV
, this ensures that the controller
HV(start)
CC
at V
time
time
time
time
.
CC(min)
HV(stop)
level until
, a