NCP1339 Datasheet, PDF (18/31 Pages) ON Semiconductor – High-Voltage, Quasi-Resonant Controller featuring Valley Lock-Out

NCP1339
ǒ Ǔ _{tstart2 +}
V_CC(on) * V_CC(inhibit) C_Vcc
IC2
(eq. 2)
Assuming a 100−mF V_CC capacitor is selected and replacing
IC1, IC2, V_CC(inhibit) and V_CC(on) by their typical values, it
comes:
t_start1
+
1
V 100
500 mA
mF
+
200
ms
(eq. 3)
(15 * 1) 100 mF
t_start2 +
10 mA
+ 140 ms
t_start + t_start1 ) t_start2 + 340 ms
V_CC(on)
V_CC(inhibit)
t_start1
t_start2
Figure 44. V_cc at Start−up is made of Two Segments given the
Short−circuit Protection Implemented on the HV Source
If the V_CC capacitor is first dimensioned to supply the
controller for the traditional 5 to 50 ms until the auxiliary
winding takes over, no−load standby requirements usually
cause it to be larger. The HV start−up current source is then
a key feature since it allows keeping short start−up times
with large V_CC capacitors (the total start−up sequence
duration is often required to be less than 1 s).
Brown−out Circuitry
For the vast majority of controllers, input line sensing is
performed via a resistive network monitoring the bulk
voltage or the incoming ac signal. When in the quest of low
standby power, the external network adds a consumption
burden and deteriorates the standby power performance of
the power supply. Owing to its proprietary high−voltage
technology, ON Semiconductor now offers onboard line
sensing without using an external sensing network. The
brown−out thresholds are fixed (101 V line rising, 93 V
falling, typically). Respectively correponding to about 72 V
rms and 66 V rms, these levels are designed to fit most of
standard ac−dc converter applications. The simplified
internal schematic appears in Figure 45 while typical
operating waveforms are drawn in Figure 46.
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