LT1103 Datasheet, PDF (1/32 Pages) Linear Technology – Offline Switching Regulator

LT1103/LT1105
Offline Switching Regulator
FEATURES
s _{±1% Line and Load Regulation with No Optocoupler}
s _{Switch Frequency Up to 200kHz}
s _{Internal 2A Switch and Current Sense (LT1103)}
s _{Internal 1A Totem-Pole Driver (LT1105)}
s _{Start-Up Mode Draws Only 200µA}
s _{Fully Protected Against Overloads}
s _{Overvoltage Lockout of Main Supply}
s _{Protected Against Underdrive or Overdrive to FET}
s _{Operates in Continuous or Discontinuous Mode}
s _{Ideal for Flyback and Forward Topologies}
s _{Isolated Flyback Mode Has Fully Floating Outputs}
U
APPLICATIONS
s _{Up to 250W Isolated Mains Converter}
s _{Up to 50W Isolated Telecom Converter}
s _{Fully Isolated Multiple Outputs}
s _{Distributed Power Conversion Networks}
DESCRIPTION
The LT^®1103 Offline Switching Regulator is designed for
high input voltage applications using an external FET
switch whose source is driven by the open collector output
of the LT1103. The LT1103 is optimized for 15W to 100W
applications. For higher power applications or additional
switch current flexibility, the LT1105 is available and its
totem pole output drives the gate of an external FET.
Unique design of the LT1103/LT1105 eliminates the need
for an optocoupler while still providing ±1% load and line
regulation in a magnetic flux-sensed converter. This sig-
nificantly simplifies the design of offline power supplies
and reduces the number of components which must cross
the isolation barrier to one, the transformer.
The LT1103/LT1105 current mode switching techniques
are well suited to transformer isolated flyback and forward
topologies while providing ease of frequency compensa-
tion with a minimum of external components. Low exter-
nal part count for a typical application combines with a
, LTC and LT are registered trademarks of Linear Technology Corporation.
TYPICAL APPLICATION
Fully Isolated Flyback 100kHz 50W Converter with Load Regulation Compensation
85V_AC TO 270V_AC
+
+
–
BRIDGE
RECTIFIER
+
LINE
FILTER
220µF
385V
499Ω
1000pF _100Ω
220k
1W
HIGDHANVGOELRT!A!GE!!
1.5KE300A
5W
MUR150
1N4148
BAV21
BAV21
1N4148
V_IN
13k
39µF ⁺
1%
35V
18.7k
FB
GND
4.75k
1%
0.047µF
0.047µF
BUK426-800A
V_SW
LT1103
10Ω
15V
V_C
OSC
+ _1µF
25V
390pF
330Ω
0.1µF
Danger!! Lethal Voltages Present – See Text
OPTIONAL OUTPUT FILTER
MBR2045
+
10µH
+
*50V
3600µF
5V
10A
50V
470µF
*OUTPUT CAPACITOR IS THREE 1200µF,
50V CAPACITORS IN PARALLEL TO
ACHIEVE REQUIRED RIPPLE CURRENT
RATING AND LOW ESR.
WINDINGS FOR
OPTIONAL
±12V_DC OUTPUTS
TRANSFORMER DATA:
COILTRONICS CTX110228-3
L_(PRI) = 1.6mH
N_PRI:N_SEC = 1:0.05
N_BIAS:N_SEC = 1:0.27
LT1103 TA13
5.25
5.20
5.15
5.10
5.05
5.00
4.95
4.90
4.85
4.80
4.75
01
Load Regulation
220V_AC
270V_AC ^110VAC
85V_AC
2 3 4 5 6 7 8 9 10
I_OUT (A)
LT1103 TA02
1