Design guide IDP2303(A)
PFC design
Application Note
20
Revision 2.0
2017-05-03
i
S
i
L,ave
i
g
/i
L
T
sw
T
sw
0
0
t
on
t
cyc
i
L,pk
QR2
i
L,pk
i
L,sampled
pk
L
i
,
2
1
QR1
2
on
t
0
t
QR1
4
osc
T
t
of f
t
w
t
t
Figure 13
Current and timing in QR2 operation
3.3.5.2
Frequency law
A frequency law consisting of a maximum switching frequency
𝑓
𝑠𝑤𝑚𝑎𝑥
and the minimum switching
frequency
𝑓
𝑠𝑤𝑚𝑖𝑛
is defined for the valley selection (QRN). In this way, the switching frequency is limited to
the defined range and efficiency at light load can be improved. An illustration of the frequency law is shown
in Figure 14.
