NCP1012 ONSEMI [ON Semiconductor], NCP1012 Datasheet - Page 12

• Manufacturer Part Number: NCP1012
• Description: Self−Supplied Monolithic Switcher for Low Standby−Power Offline SMPS
• Manufacturer: ONSEMI [ON Semiconductor]

Lowering the Standby Power with Skip−Cycle
power by skipping unwanted cycles at light loads.
However, the recurrent frequency in skip often enters the
audible range and a high peak current obviously generates
acoustic noise in the transformer. The noise takes its origins
in the resonance of the transformer mechanical structure
Skip−cycle offers an efficient way to reduce the standby
Figure 18. A more detailed view of the NCP101X offers better insight on how to
Permanent
Figure 19. The burst frequency becomes so low that it is difficult to keep
Latch
Vclamp = 8.7 V typ.
VCC
VCC
ON
OFF
= 8.5 V
= 7.5 V
an adequate level on the auxiliary V
+
+
properly wire an auxiliary winding.
+
−
−
+
u30 ms
−
+
http://onsemi.com
+
12
I > 7.4m
(Typ.)
Startup Source
Ground
which is excited by the skipping pulses. A possible
solution, successfully implemented in the NCP1200 series,
also authorizes skip−cycle but only when the power
demand has dropped below a given level. At this time, the
peak current is reduced and no noise can be heard.
Figure 20 pictures the peak current evolution of the
NCP101X entering standby.
V
CC
Drain
+
CVcc
Rlimit
CC
. . .
+
Caux
D1
Laux