NCP1341 Datasheet, PDF (26/41 Pages) ON Semiconductor – High-Voltage, Quasi-Resonant, Controller Featuring Valley Lock-Out Switching

NCP1341
is acknowledged initiating an X2 capacitor discharge cycle,
and the controller is disabled.
If V_CC is above V_CC(on), it is first discharged to V_CC(on).
A second timer, t_{line(discharge)} (typically 32 ms), is used for
the time limiting of the discharge phase to protect the device
against overheating. Once the discharge phase is complete,
t_{line(discharge)} is reused while the device checks to see if the
line voltage is reapplied. During the discharge phase, if V_CC
drops to V_CC(on), it is quickly recharged to V_{CC(X2_reg)}. The
discharging process is cyclic and continues until the ac line
is detected again or the voltage across the X2 capacitor is
lower than V_{HV(discharge)} (30 V maximum). This feature
allows the device to discharge large X2 capacitors in the
input line filter to a safe level.
It is important to note that the HV pin cannot be
connected to any dc voltage due to this feature, i.e.
directly to the bulk capacitor.
X2 Capacitor
Discharge
V_HV
V_{BO (start )}
V_{BO (stop )}
AC Line Unplug
X2 Capacitor
Discharge
V_{HV(discharge )}
Timer
t_{line(removal )}
t_{line(discharge /detect )}
AC
Timer
Starts
AC
Timer
Restarts
DRV
t_{line(removal )}
AC
Timer
Expires
No AC Detection
t_{line(discharge )}
t_{line(detect )}
t_{line(discharge )}
time
X2 Discharge
Current
I_{start 2}
I_CC
I_{CC(discharge )}
I_CC3
I_{start 2}
V_CC
V_{CC (X2_reg )}
V_{CC (on )}
Device is stopped
X2 Discharge
X2 Discharge
time
Figure 23. Line Removal Timing
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