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AN-8027
FAN480X PFC+PWM Combination Controller Application
FAN4800A / FAN4800C / FAN4801 / FAN4802 / FAN4802L
Introduction
This application note describes step-by-step design
considerations for a power supply using the FAN480X
controller. The FAN480X combines a PFC controller and
a PWM controller. The PFC controller employs average
current mode control for Continuous Conduction Mode
(CCM) boost converter in the front end. The PWM
controller can be used in either current mode or voltage
mode for the downstream converter. In voltage mode,
feed-forward from the PFC output bus can be used to
improve the line transient response of PWM stage. In
either mode, the PWM stage uses conventional trailing-
edge duty cycle modulation, while the PFC uses leading-
edge modulation. This proprietary leading/trailing-edge
modulation technique can significantly reduce the ripple
current of the PFC output capacitor.
The synchronization of the PWM with the PFC simplifies
the PWM compensation due to the controlled ripple on the
PFC output capacitor (the PWM input capacitor). In
addition to power factor correction, a number of protection
features have been built in to the FAN480X. These include
programmable soft-start, PFC over-voltage protection,
pulse-by-pulse current limiting, brownout protection, and
under-voltage lockout.
FAN4801/2/2L feature programmable two-level PFC
output to improve efficiency at light-load and low-line
conditions.
FAN480X is pin-to-pin compatible with FAN4800 and
ML4800, only requiring adjustment of some peripheral
components. The FAN480X series comparison is
summarized in the Appendix A.
F
1
AC
Input
L
BOOST
D
BOOST
C
BOOST
Q
1
V
BOUT
R
FB1
Drv
L
1
1
Q
2
D
R1
D
R1
D
F1
L
1
2
C
IF1
Vo1
Drv
R
CS1
R
RAMP
D1
D2
D
R2
Drv
C
O11
C
O12
L
22
L
2
D
F2
1
Vo2
Q
3
D
R2
C
O21
C
O22
C
IC2
R
LF1
R
T
R
RMS2
C
LF1
C
SS
R
B
R
LF2
R
CS2
R
IAC
R
IC
IEA
IAC
ISENSE
VRMS
SS
FBPWM
R
RMS1
C
RMS1
C
IC1
VEA
FBPFC
VREF
VD
D
OPFC
OPWM
GND
ILIMIT
R
D
Vo
1
R
BIAS
V
D
D
R
VC
C
VC2
C
VC1
C
F
R
F
R
OS1
Vo2
C
RMS2
R
RMS3
C
T
RT/CT
RAMP
R
OS2
R
OS3
FAN480X
C
RAMP
C
B
R
FB2
C
FB
C
LF2
C
DD
C
REF
Figure 1. Typical Application Circuit of FAN480X
© 2009 Fairchild Semiconductor Corporation
Rev. 1.0.0 • 8/26/09
www.fairchildsemi.com
FAIRCHILD [ FAIRCHILD SEMICONDUCTOR ]
