NCP1380 ON Semiconductor, NCP1380 Datasheet - Page 14

• Manufacturer Part Number: NCP1380
• Description: Quasi-Resonant Current Mode Controller
• Manufacturer: ON Semiconductor

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voltage of the auxiliary winding of the transformer. A
valley is detected when the voltage on pin 1 crosses
down the 55 mV internal threshold. When a valley is
The valley detection is done by monitoring the
La ux
ZCD
FB
Ct
VDD
Rpullup
ICt
10 V
ES D
DRV
VDD
Figure 26. Operating Valley According to FB Voltage
Ct setpoint
Vth
VALLEY DETECTION AND SELECTION
+
−
3 us puls e
Figure 27. Valley Detection Circuit
leakage
blanking
+
−
Discharge
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Ct
V FB
V FBth
14
detected, an internal counter is incremented. The
operating valley (1
the FB voltage as shown by Figure 26.
de m a g
LOGIC BLOCK
Tim e Out
VDD
st
, 2
nd
CS comparator
, 3
rd
or 4
th
) is determined by
R
S
Q
Q
DRV