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NCP1240G Datasheet, PDF (28/44 Pages) ON Semiconductor – Fixed Frequency Current Mode Controller for Flyback Converters
NCP1240G
Figure 57. HV Pin ac Input Timing Diagram with X2 Capacitor Discharge Sequence When the Application is
Unplugged Under High Line Condition
The Low Consumption Off Mode
There was implemented the low consumption off mode
allowing to reach extremely low no load input power as
described in previous chapters. If the voltage at feedback pin
decreases below the 0.6 V the controller enters the off mode.
The internal VCC is turned−off, the IC consumes extremely
low VCC current and only the voltage at external VCC
capacitor is maintained by the Self−Supply circuit. The
Self−Supply circuit keeps the VCC voltage at the VCC(reg)
level. The supply for the FB pin watch dog circuitry and FB
pin bias is provided via the low consumption current sources
from the external VCC capacitor. The controller can only
start, if the FB pin voltage increases above the 2.2 V level.
See Figure 58 for timing diagrams.
Only the X2 cap discharge and Self−Supply features is
enabled in the low consumption off mode. The X2 cap
discharging feature is enable due the safety reasons and the
Self−Supply is enabled to keep the VCC supply, but only
very low VCC consumption appears in this mode. Any other
features are disabled in this mode.
The information about the latch status of the device is kept
in the low consumption off mode and this mode is used for
the TSD protection as well. The protection timer
GoToOffMode tGTOM is used to protect the application
against the false activation of the low consumption off mode
by the fast drop outs of the FB pin voltage below the 0.6 V
level. E.g. in case when is present high FB pin voltage ripple
during the skip mode.
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