NCP1015

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Figure 17. A Detailed View of the NCP1015 with Properly Connected Auxiliary Winding

Startup Source

Drain

+

-

-

+

+

Rlimit

+

+

CVCC

CAux

Laux

Ground

+

D1

Figure 18. The Burst Frequency becomes So Low that it is Difficult to

u30 ms

Lowering the Standby Power with Skip-cycle

Skip cycle offers an efficient way to reduce the standby

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 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 as

dropped below a given level. At this time, the peak current

is reduced and no noise can be heard. Figure 19 shows the

peak current evolution of the NCP1015 entering standby: