ncp1611 ON Semiconductor, ncp1611 Datasheet - Page 21

• Manufacturer Part Number: ncp1611
• Description: Enhanced, High-efficiency Power Factor Controller
• Manufacturer: ON Semiconductor

load. In particular, the stand−by losses are reduced to a
minimum. Also, this method avoids that the system stalls
between valleys. Instead, the circuit acts so that the PFC
NCP1611 On−time Modulation
boost stage. The initial inductor current at the beginning of
each switching cycle is always zero. The coil current ramps
CCFF maximizes the efficiency at both nominal and light
Let’s analyze the ac line current absorbed by the PFC
Figure 63. Clean Transition Without Hesitation Between Valleys
Figure 62. CCFF Practical Implementation
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stage transitions from the n valley to (n + 1) valley or vice
versa from the n valley to (n − 1) cleanly as illustrated by
Figure 63.
up when the MOSFET is on. The slope is (V
is the coil inductance. At the end of the on−time (t
inductor starts to demagnetize. The inductor current ramps
down until it reaches zero. The duration of this phase is (t
IN
/L) where L
1
), the
2
).