Introduction to Digital Power Conversion
XMC4000/1000 Family
Modulation
Application Guide
74
V1.0, 2015-01
6.7
CRM: PFC using Fixed-On-Time (FOT)
A PFC in CRM mode commutates the MOSFET by fixed length, on-time pulses that are separated by
the time it takes until the inductor current hits the ZCD point again after each pulse. This kind of
control satisfies CRM.
This type of PFC rectifier does not need a feed-forward sensing at the input side to be aligned with
the sinusoidal half-wave curve of input voltage, since the envelope of the inductor (L) current peak
values I
L(PEAK)
will be ‘self-aligning’, due to the fixed On-Time mode pulse stream in the expression:
I
L(PEAK)
= |V
AC
(t)|* t
On
/ L
Figure 59
Mode CRM
– PFC using Fixed-On-Time (FOT) – Example
