NCP1246 ONSEMI [ON Semiconductor], NCP1246 Datasheet - Page 18

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

Autorecovery) is kept during the low consumption off mode
due the safety reason. The reason is not to allow unlatch the
device by the remote control being in off mode.
Startïup of the Controller
on the HV pin is higher than V
V
V
proper startïup, i.e. when V
controller actually starts the next time V
The controller then delivers pulses, starting with a softïstart
period t
increases before the currentïmode control takes over.
CC
CC(min)
The information about the fault (permanent Latch or
At startïup, the current source turns on when the voltage
reaches V
SSTART
, until the input voltage is high enough to ensure a
CC(on)
V
V
V
V
CC(inhibit)
during which the peak current linearly
V
HV(start)
CC(min)
HV(min)
DRV
CC(on)
V
, then turns on again when V
V
HV
CC
HV
HV(min)
reaches V
source = I
HV current
, and turns off when
CC
Figure 48. V
reaches V
HV(start)
start1
CC
reaches
http://onsemi.com
CC(on)
CC
. The
Startïup Timing Diagram
NCP1246
.
18
the V
the HV startïup current source on and off, it can only be used
in light load condition, otherwise the power dissipation on
the die would be too much. As a result, an auxiliary voltage
source is needed to supply V
alive when no switching pulses are delivered, e.g. in
brownïout condition, or to prevent the controller from
stopping during load transients when the V
The NCP1246 accepts a supply voltage as high as 28 V, with
an overvoltage threshold V
off.
source = I
Even though the Dynamic SelfïSupply is able to maintain
The Dynamic SelfïSupply is useful to keep the controller
HV current
CC
voltage between V
start2
Waits next
before starting
CC(ovp)
CC(on)
CC
during normal operation.
that latches the controller
and V
V
time
time
time
CC(on)
CC(min)
CC
might drop.
by turning