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Linear Technology Electronic Components Datasheet

LT1105 Datasheet

Offline Switching Regulator

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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
85VAC TO 270VAC
+
+
BRIDGE
RECTIFIER
+
LINE
FILTER
220µF
385V
499
1000pF 100
220k
1W
HIGDHANVGOELRT!A!GE!!
1.5KE300A
5W
MUR150
1N4148
BAV21
BAV21
1N4148
13k 39µF +
1% 35V
18.7k
4.75k
1%
0.047µF
VIN
FB
GND
0.047µF
BUK426-800A
VSW
LT1103
10
15V
VC OSC
+
330
0.1µF
390pF
1µF
25V
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
±12VDC OUTPUTS
TRANSFORMER DATA:
COILTRONICS CTX110228-3
L(PRI) = 1.6mH
NPRI:NSEC = 1:0.05
NBIAS:NSEC = 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
220VAC
270VAC 110VAC
85VAC
2 3 4 5 6 7 8 9 10
IOUT (A)
LT1103 TA02
1


Linear Technology Electronic Components Datasheet

LT1105 Datasheet

Offline Switching Regulator

No Preview Available !

LT1103/LT1105
DESCRIPTION
200kHz maximum switching frequency to achieve high
power density. Performance at switching frequencies
above 100kHz may be degraded due to internal timing
constraints associated with fully isolated flyback mode.
Included are the oscillator, control, and protection cir-
cuitry such as current limit and overvoltage lockout.
Switch frequency and maximum duty cycle are adjustable.
Bootstrap circuitry draws 200µA for start-up of isolated
topologies. A 5V reference as well as a 15V gate bias are
available to power external primary-side circuitry. No
external current sense resistor is necessary with LT1103
because it is integrated with the high current switch. The
LT1105 brings out the input to the current limit amplifier
and requires the use of an external sense resistor.
The LT1103/LT1105 have unique features not found on
other offline switching regulators. Adaptive antisat switch
drive allows wide ranging load currents while maintaining
high efficiency. The external FET is protected from insuf-
ficient or excessive gate drive voltage with a drive detec-
tion circuit. An externally activated shutdown mode
reduces total supply current to less than 200µA, typical for
standby operation. Fully isolated and regulated outputs
can be generated in the optional isolated flyback mode
without the need for optocouplers or other isolated feed-
back paths.
WAR I G!
DANGEROUS AND LETHAL POTENTIALS ARE
PRESENT IN OFFLINE CIRCUITS!
BEFORE PROCEEDING ANY FURTHER, THE
READER IS WARNED THAT CAUTION MUST
BE USED IN THE CONSTRUCTION, TESTING
AND USE OF OFFLINE CIRCUITS. HIGH
VOLTAGE, AC LINE-CONNECTED POTENTIALS
ARE PRESENT IN THESE CIRCUITS. EXTREME
CAUTION MUST BE USED IN WORKING WITH
AND MAKING CONNECTIONS TO THESE
CIRCUITS. REPEAT: OFFLINE CIRCUITS
CONTAIN DANGEROUS, AC LINE-CONNECTED
HIGH VOLTAGE POTENTIALS. USE CAUTION.
ALL TESTING PERFORMED ON AN OFFLINE
CIRCUIT MUST BE DONE WITH AN ISOLATION
TRANSFORMER CONNECTED BETWEEN THE
OFFLINE CIRCUIT'S INPUT AND THE AC LINE.
USERS AND CONSTRUCTORS OF OFFLINE
CIRCUITS MUST OBSERVE THIS PRECAUTION
WHEN CONNECTING TEST EQUIPMENT TO
THE CIRCUIT TO AVOID ELECTRIC SHOCK.
REPEAT: AN ISOLATION TRANSFORMER
MUST BE CONNECTED BETWEEN THE CIRCUIT
INPUT AND THE AC LINE IF ANY TEST
EQUIPMENT IS TO BE CONNECTED.
ABSOLUTE MAXIMUM RATINGS (Note 1)
VIN .......................................................................... 30V
VSW Output Voltage (LT1103) ................................. 50V
VSW Output Current (200ns)(LT1105) ................. ±1.5A
VC, FB, OSC, SS ........................................................ 6V
ILIM (LT1105) ........................................................... 3V
0VLO Input Current ............................................... 1mA
Lead Temperature (Soldering, 10 sec.)................ 300°C
Maximum Operating Ambient Temperature Range
LT1103C .............................................. 0°C to 70°C
LT1105C .............................................. 0°C to 70°C
Maximum Operating Junction Temperature Range
LT1103C ............................................. 0°C to 100°C
LT1105C ............................................ 0°C to 100°C
LT1105I ......................................... – 40°C to 125°C
Storage Temperature Range ................ –65°C to 150°C
2


Part Number LT1105
Description Offline Switching Regulator
Maker Linear Technology
Total Page 30 Pages
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