DEMO MANUAL DC1803A
LT3512: Monolithic
High Voltage Isolated
Flyback Converter
DESCRIPTION
The flyback converter requires a minimum loading to
maintain good regulation. A Zener diode is placed between
VOUT+ and VOUT– to clamp output voltage to ~7.5V if minimum load requirement is not met. Depending on the input
voltage and the output regulation requirement, a 20mA to
30mA minimum load is usually sufficient.
The demo circuit uses a diode-Zener clamp to limit the
peak spike voltage due to transformer leakage inductance.
A diode-Zener clamp is more efficient than a RCD clamp.
The LT3512 operates in boundary mode and also provides
output voltage temperature compensation.
PERFORMANCE SUMMARY
PARAMETER
The LT3512 data sheet gives a complete description of
the part, operation and application information. The data
sheet must be read in conjunction with this quick start
guide for demo circuit 1803A.
Design files for this circuit board are available at
http://www.linear.com/demo
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.
90
80
70
EFFICIENCY (%)
Demonstration circuit 1803A is a monolithic high voltage
isolated flyback converter featuring the LT®3512. The demo
circuit is designed for a 5V isolated output from an input
voltage range of 36V to 75V. The maximum output current
is 500mA. VIN can be lower if output current is less than
500mA. The circuit doesn’t require an opto-isolator due to
the output voltage being sensed directly from the primary
side transformer winding. A third winding is used to bias
the LT3512 for highest efficiency.
60
50
40
30
VOUT = 5V
TA = 25°C
VIN = 36V
VIN = 75V
20
10
0
50 100 150 200 250 300 350 400 450 500
LOAD CURRENT (mA)
DC1803A F01
Figure 1. DC1803A Efficiency
(TA = 25°C)
CONDITIONS
Minimum Input Supply Voltage
Maximum Input Supply Voltage
VALUE
UNITS
36
V
75
V
Output Voltage
IOUT = 500mA
5
V
Output Voltage Tolerance
IOUT = 500mA
±5
%
Switching Frequency
VIN = 36V, IOUT = 500mA
160
kHz
VIN = 75V, IOUT = 500mA
240
kHz
500
mA
84
%
Maximum Output Current
Efficiency
VIN = 36V, IOUT = 500mA
dc1803af
1
DEMO MANUAL DC1803A
QUICK START PROCEDURE
Demonstration circuit 1803A is easy to set up to evaluate the performance of the LT3512. Refer to Figure 2 for
proper measurement equipment setup and to follow the
procedure below:
Note: When measuring the input or output voltage ripple, care must be
taken to avoid a long ground lead on the oscilloscope probe. Measure the
input or output voltage ripple by touching the probe tip directly across the
VIN and GND or VOUT+ and VOUT– terminals.
Note: Make sure GND and VOUT– are not connected together accidently,
such as by two oscilloscope probes.
1. With power off, connect the input power supply to VIN
and GND.
2. Connect a load of 500mA or less to VOUT+ and VOUT–
terminals (not GND).
3. Turn on the power at the input.
4. Check for the proper output voltage (5V).
Note: If there is no output, temporarily disconnect the load to make
sure that the load is not set too high.
5. Once the proper output voltage is established, adjust the
load and input within the operating ranges and observe
the output voltage regulation, ripple voltage, efficiency
and other parameters.
Figure 2. Proper Measurement Equipment Setup
PARTS LIST
ITEM
QTY REFERENCE
Required Circuit Components
1
1
C2
2
1
C3
3
1
C5
4
1
C9
5
1
C10
6
1
D1
7
1
D2
8
1
D4
9
1
D5
10
1
R3
11
1
R4
PART DESCRIPTION
MANUFACTURER/PART NUMBER
CAP., X7R, 1μF 100V, 10%, 1206
CAP., X5R, 47μF 10V, 10%, 1210
CAP., ELECT., 10μF 100V
CAP., X7R, 4.7μF 16V, 10%, 0805
CAP., X7R, 3300pF, 50V, 0402
DIODE, SCHOTTKY, SOD-123
DIODE, SOD-123
ZENER DIODE, SOD-123
ZENER DIODE, SOD-123
RES., CHIP, 806k, 1%, 0805
RES., CHIP, 169k, 1%, 0603
MURATA, GRM31CR72A105KA01L
MURATA, GRM32ER61A476KE20L
SUN ELEC., 100CE10BS
TAIYO YUDEN, EMK212B7475KG
AVX, 04025C332KAT2A
DIODES INC SBR1A40S3
DIODES INC. BAV21W-7-F
ON SEMI., MMSZ5266BT1G
CENTRAL SEMI., CMHZ5236B TR
VISHAY, CRCW0805806KFKEA
VISHAY, CRCW0603169KFKEA
dc1803af
2
DEMO MANUAL DC1803A
PARTS LIST
ITEM
QTY REFERENCE
12
1
R5
13
1
R6
14
1
R7
15
1
R8
16
1
T1
17
1
U1
Additional Demo Board Circuit Components
1
1
C6
2
0
C7 (OPT)
3
1
D3
4
1
R9
Hardware-For Demo Board Only
1
6
E1-E6
PART DESCRIPTION
RES., CHIP, 31.6k, 5%, 0402
RES., CHIP, 75k, 1%, 0402
RES., CHIP, 16.9k, 1%, 0402
RES., CHIP, 10k, 1%, 0402
TRANSFORMER, 175μH
I.C., LT3512EMS, 16-PIN MSOP
MANUFACTURER/PART NUMBER
VISHAY, CRCW040231K6JNED
VISHAY, CRCW040275K0FKED
VISHAY, CRCW040216K9FKED
VISHAY, CRCW040210K0FKED
WÜRTH ELEC., 750311559
LINEAR TECH., LT3512EMS
CAP., X7R, 1000pF 2000V, 10%,1206
CAP., 0402
DIODE, SCHOTTKY, SOD-323
RES., CHIP, 20, 1%, 0402
AVX 1206GC102KAT1A
TESTPOINT, TURRET, 0.095"
MILL-MAX, 2501-2-00-80-00-00-07-0
CENTRAL SEMI., CMDSH-3 TR
VISHAY, CRCW040220R0FKED
SCHEMATIC DIAGRAM
5
4
3
2
1
5(9,6,21+,6725<
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5(9
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D
D
EN / UVLO
E5
EN/UVLO
NC
LT3512EMS
SW
D5
CMHZ5236B
7
C3
47uF
10V
1210 VOUTE3
8
VOUT+
+5V@500mA
VOUT-
C6
1000pF
2000V
1206
U1
7
6
VOUT+
E1
Lp = 175uH
D2
BAV21W
14 R4 169K
0603
5
1
MMSZ5266BTIG
1
RFB
R5
31.6K
2
D1 SBR1A40S3
2
1
2
2
1
3
1
3
D4
1
E4
C2
1uF
100V
1206
+ C5
10uF
100V
R3
(OPT) 806K
0805
2
GND
T1
750311559
E2
VIN
VIN
36V - 75V
4
16
C
C
11
TC
R6
75K
RREF
GND
GND
GND
6
D3
1
2
R9 20
CMDSH-3
12
9
8
5
10
VC
BIAS
BIAS
E6
BIAS
R7
16.9K
C7
(OPT)
R8
10K
C10
3300pF
C9
4.7uF
16V
0805
B
B
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LT3512EMS
DEMO CIRCUIT 1803A
6+((7 2) 1
dc1803af
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation
that the interconnection of its circuits as described herein will not infringe on existing patent rights.
3
DEMO MANUAL DC1803A
DEMONSTRATION BOARD IMPORTANT NOTICE
Linear Technology Corporation (LTC) provides the enclosed product(s) under the following AS IS conditions:
This demonstration board (DEMO BOARD) kit being sold or provided by Linear Technology is intended for use for ENGINEERING DEVELOPMENT
OR EVALUATION PURPOSES ONLY and is not provided by LTC for commercial use. As such, the DEMO BOARD herein may not be complete
in terms of required design-, marketing-, and/or manufacturing-related protective considerations, including but not limited to product safety
measures typically found in finished commercial goods. As a prototype, this product does not fall within the scope of the European Union directive on electromagnetic compatibility and therefore may or may not meet the technical requirements of the directive, or other regulations.
If this evaluation kit does not meet the specifications recited in the DEMO BOARD manual the kit may be returned within 30 days from the date
of delivery for a full refund. THE FOREGOING WARRANTY IS THE EXCLUSIVE WARRANTY MADE BY THE SELLER TO BUYER AND IS IN LIEU
OF ALL OTHER WARRANTIES, EXPRESSED, IMPLIED, OR STATUTORY, INCLUDING ANY WARRANTY OF MERCHANTABILITY OR FITNESS
FOR ANY PARTICULAR PURPOSE. EXCEPT TO THE EXTENT OF THIS INDEMNITY, NEITHER PARTY SHALL BE LIABLE TO THE OTHER FOR
ANY INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES.
The user assumes all responsibility and liability for proper and safe handling of the goods. Further, the user releases LTC from all claims
arising from the handling or use of the goods. Due to the open construction of the product, it is the user’s responsibility to take any and all
appropriate precautions with regard to electrostatic discharge. Also be aware that the products herein may not be regulatory compliant or
agency certified (FCC, UL, CE, etc.).
No License is granted under any patent right or other intellectual property whatsoever. LTC assumes no liability for applications assistance,
customer product design, software performance, or infringement of patents or any other intellectual property rights of any kind.
LTC currently services a variety of customers for products around the world, and therefore this transaction is not exclusive.
Please read the DEMO BOARD manual prior to handling the product. Persons handling this product must have electronics training and
observe good laboratory practice standards. Common sense is encouraged.
This notice contains important safety information about temperatures and voltages. For further safety concerns, please contact a LTC application engineer.
Mailing Address:
Linear Technology
1630 McCarthy Blvd.
Milpitas, CA 95035
Copyright © 2004, Linear Technology Corporation
dc1803af
4
Linear Technology Corporation
LT 0411 • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
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●
www.linear.com
© LINEAR TECHNOLOGY CORPORATION 2011