FEATURES
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LT3798
Isolated No Opto-Coupler
Flyback Controller
with Active PFC
DESCRIPTION
The LT
®
3798 is a constant-voltage/constant-current iso-
lated flyback controller that combines active power factor
correction (PFC) with no opto-coupler required for output
voltage feedback into a single-stage converter. A LT3798
based design can achieve a power factor of greater than 0.97
by actively modulating the input current, allowing compli-
ance with most Harmonic Current Emission requirements.
The LT3798 is well suited for a wide variety of off-line
applications. The input range can be scaled up or down,
depending mainly on the choice of external components.
Efficiencies higher than 86% can be achieved with output
power levels up to 100W. In addition, the LT3798 can easily
be designed into high DC input applications.
L,
LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear
Technology Corporation. All other trademarks are the property of their respective owners.
Protected by U.S. Patents, including 5438499 and 7471522.
Isolated PFC Flyback with Minimum Number of
External Components
V
IN
and V
OUT
Limited Only by External Components
Active Power Factor Correction
Low Harmonic Distortion
No Opto-Coupler Required
Constant-Current and Constant-Voltage Regulation
Accurate Regulated Voltage and Current (±5% Typical)
Energy Star Compliant (<0.5W No Load Operation)
Thermally Enhanced 16-lead MSOP Package
APPLICATIONS
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Offline 5W to 100W+ Applications
High DC V
IN
Isolated Applications
Offline Bus Converter (12V, 24V or 48V Outputs)
TYPICAL APPLICATION
Universal Input 24W PFC Bus Converter
24.50
V
OUT
vs I
OUT
90V
TO 265V
AC
499k
0.1μF
499k
100k
100k
D3
1M
95.3k
LT3798
V
REF
100k
40.2k
CTRL3
CTRL2
CTRL1
OVP
221k
16.5k
VC
COMP
+
2.2μF
GATE
SENSE
INTV
CC
0.05Ω
24.25
V
OUT
(V)
D2 20Ω
4:1:1
24.00
4.7pF
10μF
2k
DCM
FB
4.99k
22pF
D1
20Ω
90.9k
Z1
560μF
×2
23.75
V
IN
V
IN_SENSE
EN/UVLO
D4
24V
1A
23.50
0
0.2
0.4
0.6
I
OUT
(A)
VAC = 90V
VAC = 120V
VAC = 220V
VAC = 265V
0.8
1
3798 TA01b
Z2
4.7μF
GND
COMP
–
2.2nF
0.1μF
3798 TA01a
3798f
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LINER [ LINEAR TECHNOLOGY ]
