ncp1230a ON Semiconductor, ncp1230a Datasheet - Page 19

• Manufacturer Part Number: ncp1230a
• Description: Low?standby Power Soft Skip Mode Controller
• Manufacturer: ON Semiconductor

Frequency Jittering
signature by spreading out the average switching energy
around the controller operating switching frequency. The
NCP1230A offers a nominal ±6.4% deviation of the
Thermal Protection
integrated circuit in the event that the maximum junction
temperature is exceeded. When activated (165 °C typically)
the controller turns off the PWM Drive Output. When this
occurs, Vcc will drop (the rate is dependent on the
NCP1230A loading and the size of the Vcc capacitor)
because the controller is no longer delivering drive pulses to
the auxiliary winding charging up the Vcc capacitor. When
Frequency jittering is a method used to soften the EMI
An internal Thermal Shutdown is provided to protect the
Figure 42. An Internal Ramp is used to Introduce Frequency Jittering on the Oscillator Saw Tooth
62.4 kHz
Internal Ramp
65 kHz
http://onsemi.com
5 ms
19
67.6 kHz
nominal switching frequency. The sweep sawtooth is
internally generated and modulates the clock up and down
with a 5 ms period. Figure 42 illustrates the NCP1230A
behavior:
Vcc drops below 4.0 volts and the Vccreset circuit is
activated, the controller will restart. If the user is using a
fixed bias supply (the bias supply is provided from a source
other than from an auxiliary winding, refer to the typical
application ) and Vcc is not allow to drop below 4.0 volts
under a thermal shutdown condition, the NCP1230A will
not restart. This feature is provided to prevent catastrophic
failure from accidentally overheating the device.
Internal Sawtooth