NCP1217 ONSEMI [ON Semiconductor], NCP1217 Datasheet - Page 11

• Manufacturer Part Number: NCP1217
• Description: Enhanced PWM Current−Mode Controller for High−Power Universal Off−Line Supplies
• Manufacturer: ONSEMI [ON Semiconductor]

Ramp Compensation
subharmonic oscillations. These oscillations take place at
half the switching frequency and occur only during
Sufficient margin shall be kept between normal Pin1 level and the latchoff point in order to avoid false triggering.
Ramp compensation is a known mean to cure
Figure 21. The Skip Cycle Takes Place at Low Peak Currents which Guarantees Noise−Free Operation
Figure 20. Output Pulses at Various Power Levels (X = 5.0 ms/div) P1 t P2 t P3
300 M
200 M
100 M
0
315.40 U
882.70 U
MAX PEAK
CURRENT
NCP1217, NCP1217A
http://onsemi.com
1.450 M
11
Continuous Conduction Mode (CCM) with a duty−cycle
greater than 50%. To lower the current loop gain, one usually
injects between 50 and 100% of the inductor down−slope.
Figure 22 depicts how internally the ramp is generated.
2.017 M
CURRENT LIMIT
SKIP CYCLE
2.585 M
Power P1
Power P2
Power P3