Linear Technology DC1745A Demo Manual

Description
Demonstration circuit 1745A is an isolated flyback con-
verter featuring the LT3748 controller for high input voltage
applications. It is designed for a 15V output at up to 3A
from a 100V to 400V DC input. The part senses the iso-
lated output voltage from the third winding of the flyback
transformer during the off time of the power switch. No
opto-coupler or signal transformer is required for regula-
tion. A minimum load of approximately 150mA is required
on the output of the circuit to maintain regulation.
Optionally, the demo circuit can be powered from a uni-
versal offline input (85V~265V, 50/60Hz) using the AC
input terminals. Provisions for an EMI filter and surge
protection are provided in the demo circuit. The EMI filter
is designed to meet the EN55022 Class B standard. The
table below summarizes the performance.
The demo circuit can be easily modified for applications
requiring different output voltages/currents from either
an AC or DC input. Some pre-designed EFD25, EF16,
and EF25 transformers from vendors such as Würth
Electronics, Sumida, Pulse Engineering and Coilcraft can
perForMAnce sUMMArY
PARAMETER
Minimum Input DC Voltage
Maximum Input DC Voltage
Typical Start-Up DC Input Voltage Set by UVLO
Typical Shutdown DC Input Voltage Set by UVLO
Minimum Input AC Voltage
Maximum Input AC Voltage
Output Voltage, V
OUT
Output Current, I
OUT
Minimum Load Current with Regulated Output, I
Typical Efficiency with DC INPUT
Typical Efficiency with AC INPUT
Maximum Ripple Voltage, V
Maximum Switching Frequency at Full Load
Minimum Switching Frequency at Full Load
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CONDITIONS
I
OUT
I
OUT
Line Frequency, 50Hz/60Hz
Line Frequency, 50Hz/60Hz
V
IN
V
IN
MIN
V
IN
V
IN
V
P-P IN
V
IN
V
IN
DEMO MANUAL DC1745A
100V Isolated Flyback Converter
be assembled on the board. Some of these transformers
are listed in Table 1.
The LT3748 is a high input voltage isolated flyback con-
troller that eliminates the need for an optocoupler and
secondary-side reference voltage, all while maintaining
isolation between the primary and secondary-side with
only one part, the transformer, having to cross the isola-
tion barrier. The LT3748 is well suited for a wide variety
of industrial, automotive, medical, telecom, datacom
applications, where regulated isolated output is required.
The LT3748 datasheet gives a complete description of the
part, operation and application information. The datasheet
should be read in conjunction with this quick start guide
for Demonstration Circuit 1745A before powering the
demo circuit.
Design files for this circuit board are available at
http://www.linear.com/demo
L, LT, LTC, LTM, µModule, Linear Technology and the Linear logo are registered trademarks of
Linear Technology Corporation. All other trademarks are the property of their respective owners.
= 25°C)
A
= 3A
= 3A
= 100V ~ 400V (DC), I = 150mA ~ 3A
OUT
= 100V ~ 400V (DC)
= 100V ~ 400V (DC), I = 3A
OUT
= 85V ~ 265V (AC), I = 3A
OUT
= 400V (DC), I = 3A
OUT
= 400V (DC), I = 3A
OUT
= 100V (DC), I = 3A
OUT
LT3748
MIN TYP MAX
100
400
70
60
85 VAC (RMS)
265 VAC (RMS)
15 ±5%
3
150
87
84
750
155
55
dc1745afa
UNITS
V
V
V
V
V
A
mA
%
%
mV
kHz
kHz
1