NCP1246 ONSEMI [ON Semiconductor], NCP1246 Datasheet - Page 26

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

Low Load Operation Modes: Frequency Foldback
Mode (FFM) and Skip Mode
the frequency of the internal oscillator is linearly reduced
from its nominal value down to f
foldback starts when the voltage on FB pin goes below
V
The maximum onïtime duration control is kept during the
skip mode is activated: the driver stops, and the internal
consumption of the controller is decreased. While V
FB(foldS)
In order to improve the efficiency in light load conditions,
When the FB voltage reaches V
, and is complete when V
Figure 58. Current Setpoint Dependency on the Feedback Pin Voltage
OSC(min)
Figure 57. Frequency Foldback Mode Characteristic
skip(in)
FB
reaches V
while decreasing,
. This frequency
FB(foldE)
http://onsemi.com
FB
NCP1246
is
.
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frequency foldback mode to provide the natural transformer
core antiïsaturation protection. The frequency jittering is
still active while the oscillator frequency decreases as well.
The current setpoint is fixed to 300 mV in the frequency
foldback mode if the feedback voltage decreases below the
V
light loads conditions as well.
below V
soon as V
starts to pulse again.
FB(freeze)
skip(out)
FB
level. This feature increases efficiency under the
crosses the skip out threshold, the DRV pin
, the controller remains in this state; but as