NCP1246 ONSEMI [ON Semiconductor], NCP1246 Datasheet - Page 28

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

instance, not all the energy stored during the on time is
transferred to the output during the off time, even if the on
time duration is at its minimum (imposed by the propagation
delay of the detector added to the LEB duration). As a result,
the current sense voltage keeps on increasing above V
because the controller is blind during the LEB blanking
time. Dangerously high current can grow in the system if
nothing is done to stop the controller. That’s what the
additional comparator, that senses when the current sense
voltage on CS pin reaches V
as soon as this comparator toggles, the controller
immediately enters the protection mode.
Under some conditions, like a winding shortïcircuit for
CS(stop)
( = 1.5 x V
Figure 60. SoftïStart Feature
ILIM
), does:
http://onsemi.com
ILIM
NCP1246
,
28
duty cycle above 50%, the fixed slope compensation is
internally applied to the currentïmode control. The slope
appearing on the internal voltage setpoint for the PWM
comparator is ï32.5 mV/ms typical for the 65 kHz version,
and ï50 mV/ms for the 100 kHz version. The slope
compensation can be observable as a value of the peak
current at CS pin.
signal synchronized with the internal oscillator is subtracted
from the FB voltage divided by K
In order to allow the NCP1246 to operate in CCM with a
The internal slope compensation circuitry uses a sawtooth
FB
.