NCP1234 ONSEMI [ON Semiconductor], NCP1234 Datasheet - Page 26

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

Frequency Foldback
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
Skip Cycle Mode
skip mode is activated: the driver stops, and the internal
consumption of the controller is decreased. While V
In order to improve the efficiency in light load conditions,
When the FB voltage reaches V
Nominal f
FB
CS
f
OSC(min)
OSC
f
OSC
Figure 43. Frequency Foldback when the FB Voltage Decreases
OSC(min)
skip(in)
blanking
Skip
t
K
LEB
FB
V
while decreasing,
. This frequency
skip(in)
Figure 44. Skip Cycle Schematic
V
LOW LOAD OPERATION
+
FB(foldE)
http://onsemi.com
V
skip
FB
+
−
+
−
V
is
FB(foldS)
26
V
whatever the nominal switching frequency option is. The
current−mode control is still active while the oscillator
frequency decreases. Note that the frequency foldback is
disabled if the controller runs at its maximum duty cycle.
below V
soon as V
starts to pulse again.
FB(foldS)
skip(out)
, and is complete before V
FB
crosses the skip out threshold, the DRV pin
, the controller remains in this state; but as
S
R
Q
DRV stage
FB
reaches V
FB
skip(in)
,