Datasheet

UCC28050, UCC28051
UCC38050, UCC38051
SLUS515F−SEPTEMBER 2002 − REVISED MARCH 2009
11
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APPLICATION INFORMATION
UDG−02124
+
C
D
Load
+
R
IAC
X
X
MULT
L
SQ
R
Q
Gate Driver
Logic
V
AC
I
AC
÷
Z
CD
I
MO
V
EA
V
REF
Figure 1. Basic Block Diagram of CRM Boost PFC
The power stage equations and the transfer functions of the CRM are the same as the CCM. However,
implementations of the control functions are different. Transition mode forces the inductor current to operate
just at the border of CCM and DCM. The current profile is also different and affects the component power loss
and filtering requirements. The peak current in the CRM boost is twice the amplitude of CCM leading to higher
conduction losses. The peak-to-peak ripple is twice the average current which affects MOSFET switching
losses and magnetics ac losses.
UDG−02123
I
AVERAGE
(C) CRM
(b) DCM
(a) CCM
I
PEAK
I
AVERAGE
I
PEAK
I
AVERAGE
Note: Operating Frequency >> 120 Hz
Figure 2. PFC Inductor Current Profiles