25
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.fair
childsemi.com/fps
FPS
™
Design Guide
Vfb
4
Vcc
3
GND
2
Drain
1
L&S
5
3
2
2
1
4
5
1
2
1
2
1
2
6
10
R104
5K1
0.25W
CONN1
B2P-VH
R101
200k
C203
10nF
50V
R201
1K
R202
1K
R204
15K
R205
3.9K
IC101
FS6X1220RT
C201
220uF
25V
C202
220uF
25V
+
R105
18R
R102
18R
D201
MBRF10100
D102
1N4148
IC201
KA431
CONN2
B2P-VH
C103
12nF
50V
+
R203
33k
R103
300K
0.5W
C105
47nF
50V
C104
47nF
50V
C102
1nF
50V
C101
47uF
100V
+
+
CONN3
B2P-VH
D101
UF4004
PC
H11A817A
36V - 72V
DC input
12V/2A output
Sleep Mode
On/Off Control
Primary 40 turns
Vcc 18 turns
12V 12 turns
Lp = 22uH EPC19
T1: EPC19
The Fairchild Power Switch family is also useful in DC input applications. Here the FS6X1220 has a 200V MOSFET with R
DS(on)
of
less than 0.3W. The topology is very similar to the AC input flyback topology. One important difference is the additional L&S pin-
which serves two functions. First, if the voltage drops below 2.55V, the device stops switching. If the voltage drops below 1.8V, the
device goes into a shutdown mode which consumes only 300µA in the Vcc line.
• Flyback solution for this power level has good efficiency at a reasonable cost architecture can easily be expanded
to support multiple outputs
• Dual function shut down pin
– Undervoltage lockout below 2.55V
– 300µA shutdown below 1.8V
• Full protection features of FPS family integrated on chip
– Shor
t cir
cuit, overvoltage, temporary overload are no problem fully avalanche rated part
Fairchild Devices Description
FS6X1220RT Fairchild Power Switch (3.2A/300kHz)
UF4004 Fast Recovery Diode (1A/400V)
1N/FDLL4148
General Purpose Diode (10mA/100V)
H11A817A Optocoupler (CTR = 80% – 160%)
KA431 Shunt Regulator
24W Single Output 48V DC/DC Flyback Converter
Typical Application – 48V DC Input Industrial Equipment, Central Office, Basestations, Routers
Examples of Typical Application Circuits
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General