www.fairchildsemi.com
© 2012 F i hild S
i
d t
C
ti
f i hild
i
AN-6094
Design Guideline for Flyback Charger Using FAN302HL/UL
1. Introduction
More than half of the external power supplies produced
are used for portable electronics such as laptops, cellular
phones, and MP3 players that require constant output
voltage and current regulation for battery charging. For
applications requiring precise Constant Current (CC)
regulation, current sensing in the secondary side is always
necessary, which results in sensing loss. For power
supply designers faced with stringent energy-efficiency
regulations, output current sensing is a design challenge.
The advanced PWM controller FAN302HL/UL can
alleviate the burden of meeting international energy
efficiency regulations in charger designs. The
FAN302HL/UL family uses a proprietary primary-side
regulation (PSR) technique where the output current is
precisely estimated with only the information in the
primary side of the transformer and controlled with an
internal compensation circuit. This removes the output
current sensing loss and eliminates all external current-
control circuitry, facilitating a higher efficiency power
supply design without incurring additional costs. A
Green-Mode function with an extremely low operating
current (200 µA) in Burst Mode maximizes the light-load
efficiency, enabling conformance to worldwide Standby
Mode efficiency guidelines.
This application note presents practical design
considerations for flyback battery chargers employing the
FAN302HL/UL. It includes instructions for designing the
transformer and output filter, selecting the components,
and implementing Constant Current (CC) / Constant
Voltage (CV) control. The design procedure is verified
through an experimental prototype converter using
FAN302UL. Figure 1 shows a typical application circuit
of a flyback converter using the FAN302HL/UL.
N
P
N
S
R
CL
C
CL
+
V
DL
-
AC Line
D
R
C
O1
V
O
C
DL1
R
SNB
C
SNB
I
O
C
VS
R
CS
C
FB
C
O2
R
Bias
TL431
C
FR
R
F1
R
F2
R
FR
Fuse
C
DL2
L
F
C
DD
CS
VDD
VS
HV
FB
GATE
GND
FAN302HL/UL
1
2
3
4
5
6
8
NC 7
R
GATE
R
BF
N
A
R
VS1
R
VS2
D
A
R
VDD
D
CL
Bridge
R
HV
L
O
Figure 1. Typical Application Circuit
