NCP1237 ONSEMI [ON Semiconductor], NCP1237 Datasheet - Page 11

• Manufacturer Part Number: NCP1237
• Description: Fixed Frequency Current Mode Controller for Flyback Converters
• Manufacturer: ONSEMI [ON Semiconductor]

the HV pin is higher than V
reaches V
V
high enough to ensure a proper startup, i.e. when V
reaches V
time V
between V
CC(min)
At startup, the current source turns on when the voltage on
Even though the DSS is able to maintain the V
CC
. This sequence repeats until the input voltage is
reaches V
HV(start)
CC(on)
CC(on)
. It turns on again when V
and V
. The switching actually starts the next
V
V
CC(on)
V
V
CC(inhibit)
HV(start)
V
HV(min)
CC(min)
CC(min)
CC(on)
DRV
, as shown in Figure 5.
V
HV(min)
V
CC
HV
by turning the HV startup
, and turns off when V
Figure 5. Startup Timing Diagram
source =
current
I
CC
HV
start1
CC
reaches
voltage
http://onsemi.com
HV
CC
11
current source on and off, it can only be used in light load
conditions, otherwise the power dissipation on the die would
be too high. As a result, an auxiliary voltage source is needed
to supply V
switching pulses are delivered, e.g. in a brown−out
condition, or to prevent the controller from stopping during
load transients when the V
The DSS is useful to keep the controller alive when no
source =
current
I
HV
start2
CC
during normal operation.
starting
before
V
Waits
next
CC(on)
CC
might drop below V
time
time
time
CC(off)
.