AN-8027 Datasheet, PDF (1/17 Pages) Fairchild Semiconductor – PFC+PWM Combination Controller

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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.
F1
AC
Input
C_IF1
L BOOST
D_BOOST
Drv
R_CS1
C_BOOST
Q1
R RAMP
D1 D2
V_BOUT
R FB1
Drv
Q2
D_R1
Drv
Q3 _DR2
D_R1
L¹
1
D_F1
L¹
2
Vo1
C_O11
C_O12
D_R2
L22
L²
1
D_F2
C_O21
C_O22
Vo2
C_IC2
R_RMS1
R_LF1
R IAC
R_T
C_RMS1
R_RMS2
R_B
C_{RMS2 RRMS3}
C_LF1 C_SS
C_T
R_IC
C_IC1
IEA
IAC
ISENSE
VRMS
SS
VEA
FBPFC
VREF
VD
D
OPFC
FBPWM
OPWM
RT/CT
GND
RAMP
ILIMIT
FAN480X
C_RAMP
C_B
R_LF2
R_CS2
V^D
D
R_VC
C_VC1
C_VC2
C_FB
C_LF2 C_DD C_REF
R_FB2
Figure 1. Typical Application Circuit of FAN480X
R_BIAS
R_D
Vo
1
C_{F RF}
R_OS1
Vo2
R_OS2
R_OS3
© 2009 Fairchild Semiconductor Corporation
Rev. 1.0.0 • 8/26/09
www.fairchildsemi.com