NCP1234 ONSEMI [ON Semiconductor], NCP1234 Datasheet - Page 13

• Manufacturer Part Number: NCP1234
• Description: Fixed Frequency Current Mode Controller for Flyback Converters
• Manufacturer: ONSEMI [ON Semiconductor]


33% of the maximum load (for a DCM design), the
switching frequency starts to decrease down to
f
helps to improve the efficiency in light load conditions.
The frequency jittering is enabled in light load
operation as well.
No load operation: When the FB voltage decreases
below V
of the maximum load, the controller enters skip mode.
By completely stopping the switching while the
feedback voltage is below V
further reduced. This allows minimizing the power
dissipation under extremely low load conditions. As the
skip mode is entered at very light loads, for which the
peak current is very small, there is no risk of audible
noise. V
V
OSC(min)
CC(min)
CC
skip(in)
. By lowering the switching losses, this feature
by the DSS, if the auxiliary winding does not
can be maintained between V
, typically corresponding to a load of 2%
skip(out)
, the losses are
CC(on)
and
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13


provide sufficient level of V
condition.
Overload: The NCP1234 features timer−based
overload detection, solely dependent on the feedback
information: as soon as the internal peak current
setpoint hits the V
count. When the timer elapses, the controller stops and
enter the protection mode, autorecovery for the B
version (the controller initiates a new start−up after
t
is released only if V
Latch−off: When the Latch input is pulled up (typically
by an over−voltage condition), or pulled down
(typically by an over−temperature condition, using the
provided current source with an NTC), the controller
latches off. The latch is released when the V
autorec
elapses), or latched for the A version (the latch
ILIM
CC
clamp, an internal timer starts to
is reset).
CC
voltage under this
CC
is reset.