NCP1012 ONSEMI [ON Semiconductor], NCP1012 Datasheet - Page 13

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

frequency and thus avoids any noise when running.
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
value, it spreads the energy content on adjacent frequencies
rather than keeping it centered in one single ray. This offers
Full power operation involves the nominal switching
Experiments carried on a 5.0 W universal mains board
By sweeping the switching frequency around its nominal
Figure 21. The V
Figure 20. Low Peak Current Skip−Cycle Guarantees Noise−Free Operation
CC
ripple is used to introduce a frequency jittering on the internal oscillator sawtooth.
VCC
62.85 kHz
100%
ON
V
CC
Here, a 65 kHz version was selected.
Ripple
Peak current
at nominal power
65 kHz
http://onsemi.com
VCC
25%
OFF
13
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 V
(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 V
Figure 21 portrays the behavior we have adopted.
67.15 kHz
Internal Sawtooth
Skip−cycle
current limit
CC
rises or decrease as V
CC
ramps down.
CC
ripple