P1012AP13 datasheet(13/25 Pages) ONSEMI

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NCP1010, NCP1011, NCP1012, NCP1013, NCP1014

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Figure 22. Low Peak Current Skip−Cycle Guarantees Noise−Free Operation

100%

Peak current

at nominal power

25%

Skip−cycle

current limit

Full power operation involves the nominal switching

frequency and thus avoids any noise when running.

Experiments carried on a 5.0 W universal mains board

unveiled a standby power of 300 mW @ 230 Vac with the

DSS activated and dropped to less than 100 mW when an

auxiliary winding is connected.

Frequency Jittering for Improved EMI Signature

By sweeping the switching frequency around its nominal

value, it spreads the energy content on adjacent frequencies

rather than keeping it centered in one single ray. This offers

the benefit to artificially reduce the measurement noise on

a standard EMI receiver and pass the tests more easily. The

EMI sweep is implemented by routing the VCC ripple

(induced by the DSS activity) to the internal oscillator. As a

result, the switching frequency moves up and down to the

DSS rhythm. Typical deviation is

"3.3% of the nominal

frequency. With a 1.0 V peak−to−peak ripple, the frequency

will equal 65 kHz in the middle of the ripple and will

increase as VCC rises or decrease as VCC ramps down.

Figure 23 portrays the behavior we have adopted.

Figure 23. The VCC ripple is used to introduce a frequency jittering on the internal oscillator sawtooth.

Here, a 65 kHz version was selected.

VCC Ripple

VCCOFF

67.15 kHz

65 kHz

62.85 kHz

VCCON

Internal Sawtooth

P1012AP13 데이터시트(PDF) 13 Page - ON Semiconductor