DEMO CIRCUIT 950A
LT3825 AND
GUIDE
QUICK START
LT3837
LT3825 and LT3837
Non-opto Synchronous Fly-
back Controller
DESCRIPTION
Demonstration circuit 950A is a 30W multi-output syn-
chronous flyback converter in 1/8 brick format featuring
the LT3825 and LT3837. Output voltage sensing is im-
plemented without the use of opto-coupler, by sensing
the voltage across a primary side auxiliary winding. A
load compensation circuit is used to compensate for
voltage drops caused by load currents.
DC950A-A has input voltage range 36V-72V and features
the LT3825.
DC950A-B has input voltage range 9V-36V and features
the LT3837.
Demonstration circuit 950A uses a transformer design
with tapped secondary winding, to achieve higher effi-
ciency and better cross regulation than is possible with a
transformer that uses a separate winding for each out-
put.
Design files for this circuit board are available. Call
the LTC factory.
L
, LTC, LTM, LT, Burst Mode, OPTI-LOOP, Over-The-Top and PolyPhase are registered
trademarks of Linear Technology Corporation. Adaptive Power, C-Load, DirectSense, Easy
Drive, FilterCAD, Hot Swap, LinearView, µModule, Micropower SwitcherCAD, Multimode
Dimming, No Latency
∆Σ,
No Latency Delta-Sigma, No R
SENSE
, Operational Filter, PanelProtect,
PowerPath, PowerSOT, SmartStart, SoftSpan, Stage Shedding, SwitcherCAD, ThinSOT,
UltraFast and VLDO are trademarks of Linear Technology Corporation. Other product names
may be trademarks of the companies that manufacture the products.
PERFORMANCE SUMMARY
Specifications are at TA = 25°C
SYMBOL
V
IN
V
OUT
PARAMETER
Input Supply Range
Output Voltage
CONDITIONS
DC950A-A
DC950A-B
V
OUT1
V
OUT2
V
OUT3
I
OUT1
(5V output)
I
OUT2
(3.3V output)
I
OUT3
(2.5V output)
DC950A-A,V
IN
=48V,I
OUT1
=2A,I
OUT1
=3A,I
OUT3
=3A
DC950A-B,V
IN
=24V,I
OUT1
=2A,I
OUT1
=3A,I
OUT3
=3A
MIN
36
9
4.85
3.20
2.42
0
0
0
TYP
MAX
72
36
5.15
3.40
2.58
4
4
4
UNITS
V
V
V
V
V
A
A
A
%
%
I
OUT
Output Current (Note: Total output power not to
exceed 30W)
Efficiency Efficiency
5V
3.3V
2.5V
2
3
3
90
89
EQUIPMENT
8 DMMs
1 DC Supply 0-72V 1A for DC950A-A test
1 DC Supply 0-36V 5A for DC950A-B test
3 Adjustable loads 0-3A
1
LT3825 AND LT3837
GETTING STARTED
Demonstration circuit 950A is easy to set up to evaluate
the performance of the LT3825 and LT3837. Refer to
Figure 1 for proper measurement equipment setup and
follow the procedure below:
1.
With power off, connect the input power supply to Vin
and GND.
2.
With no loads, adjust input voltage to be within the
input voltage range (36V-72V for DC950A-A, 9V-36V
for DC950A-B) and turn on the power at the input.
3.
Check for the proper output voltages. Vout1 = 5V,
Vout2 = 3.3V, Vout3 = 2.5V.
4.
Adjust the loads and study the performance of the
circuit. Note that the load current should not exceed
4A, and the total load on the three outputs should not
exceed 30W continuous power.
Figure 1. Proper Measurement Equipment Setup
2
LT3825 AND LT3837
DC950A-A BILL OF MATERIAL
Item
Qty
Reference
Part Description
Manufacture / Part #
REQUIRED CIRCUIT COMPONENTS
1
1
1
C38
Capacitor, NP0, 33pF, 50V, 0603
2
1
C41
Capacitor, NPO, 330PF, 50V, 0603
3
1
C1
Capacitor, NPO 330PF 100V 1206
4
2
C34,C30
Capacitor, X7R, 2200pF, 50V, 0603
5
3
C19,C31,C32
Capacitor, X5R, 0.1uF, 25V, 0603
6
1
C40
Capacitor, X7R, 1000pF, 50V, 0603
7
1
C36
Capacitor, X5R, 0.47uF, 16V, 0603
8
6
C3,C4,C13,C14,C26,C27 Capacitor, X5R, 47uF, 6.3V, 1210
9
0
C33,C39
Capacitor, 0603
10
1
C35
Capacitor, X7R, 3300PF, 50V, 0603
11
1
C37
Capacitor, NPO, 680PF, 50V, 0603
12
1
C9
Capacitor, NPO, 150pF, 200V, 1206
13
1
C18
Capacitor, X7R, 22uF, 16V, 1210
14
2
C20,C21
Capacitor, X7R, 2.2uF, 100V, 1812
15
1
D2
BAS21
16
2
D8,D6
BAT54
17
1
D5
BAT54A
18
1
D10
BAT54S
19
1
D9
B0530W
20
0
D4
Zenerdiode, 12V, 5%, SOT23
21
1
L5
Inductor, 330uH
22
1
L6
Inductor, 120uH
23
1
Q1
MOSFET, n-ch, SO8
24
1
Q3
MOSFET, n-ch, SO8
25
2
Q7,Q9
Transistor, npn, SOT23
26
3
Q8,Q10,Q12
Transistor, pnp, SOT23
27
0
Q4
Transistor, npn, SOT23
28
1
Q5
MOSFET, n-ch, SO8
29
1
Q6
MOSFET, n-ch, SO8
30
1
R11
Resistor, 0 OHMS 0603
31
1
R2
Resistor, 18 OHMS 1206
32
2
R21,R16
Resistor, 15 OHMS 0603
33
1
R15
Resistor, 330 OHMS 0603
34
2
R9,R29
Resistor, 1.00k, 0603
35
1
R14
Resistor, 1.00k, 0805
36
1
R22
Resistor, 3.01K, 0603
37
1
R30
Resistor, 4.64K, 0603
38
3
R19,R23,R28
Resistor, 10.0K, 0603
39
1
R12
Resistor, 28.7K, 0805
40
1
R25
Resistor, 100K, 0603
41
1
R27
Resistor, 150K, 0603
42
1
R5
Resistor, 22 OHM, 1206
43
1
R17
Resistor, 0.025 OHM 1% 1206
44
1
R26
Resistor, 1.00K, 0603
45
1
R6
Resistor, 47K, 1206
46
1
R13
Resistor, 402K, 0805
47
0
R4,R18
Resistor, 1206
48
1
R8
Resistor, 91 OHMS 0805
49
1
R20
Resistor, 14.7K, 0603
50
1
R24
Resistor, 12.4K, 0603
AVX, 06035A330KAT2
AVX, 06035A331KAT
AVX, 12061A331KAT
AVX, 06035C222JAT
AVX, 06033D104KAT2A
AVX, 06035C102KAT2A
AVX, 0603YD474M
TDK, 3225X5R0J476M
OPT
KEMET, C0603C332J5RAC
AVX, 06035A681JAT
AVX, 12062A151KAT2A
TDK, C3225RX7R1C226M
TDK, C4532X7R2A225M
Diodes, Inc.,BAS21-7-F
Diodes, Inc.,BAT54-7-F
Diodes, Inc.,BAT54A-7
Diodes, Inc.,BAT54S-7-F
Diodes, Inc.,B0530W-7-F
OPT
Coilcraft, DO1608C-334MLB
Wurth Elektronik, 744 032 121
Vishay, Si4850EY-T1-E3
Vishay, Si4840DY-T1-E3
Zetex, FMMT619TA
Zetex, FMMT718TA
OPT
Vishay, Si4840DY-T1-E3
Vishay, Si4488DY-T1-E3
VISHAY, CRCW06030000Z0EA
VISHAY, CRCW120618R0JNEA
VISHAY, CRCW060315R0FKEA
VISHAY, CRCW0603330RFKEA
VISHAY, CRCW06031K0FKED
VISHAY, CRCW08051K0FKED
VISHAY, CRCW06033011FRT6
VISHAY, CRCW06034K64FKED
VISHAY, CRCW060310K0FKED
VISHAY, CRCW080528K7FKED
VISHAY, CRCW0603100KJNEA
VISHAY, CRCW0603150KJNEA
VISHAY, CRCW120622ROJNEA
IRC, LRF1206LF-01-R025-F
VISHAY, CRCW06031K00FKEA
VISHAY, CRCW120647K0JNEA
VISHAY, CRCW0805402KFKEA
OPT
VISHAY, CRCW080591R0FKEA
VISHAY, CRCW060314K7FKEA
VISHAY, CRCW060312K4FKEA
4
LT3825 AND LT3837
51
52
53
1
1
1
T2
T1
U1
Gatedrive transformer
EFD20 Flyback transformer
LT3825EFE#PBF
Pulse Engineering, PA0173
Pulse Engineering, PA2046NL
Linear Technology,
LT3825EFE#PBF
Sanyo, 100ME12AX+TS
Kemet, T520B107M006ASE070
MURATA,
GA343DR7GD472KW01L
Cooper, FP2-S200
Cooper, HCP0703-4R7-R
KEYSTONE, 8833(SNAP ON)
Mill-Max, 2501-200-80-00-00-07-0
ADDITIONAL DEMO BOARD CIRCUIT COMPONENTS
2
1
1
C8
Capacitor, electrolytic, 12UF, 100V
2
3
C7,C17,C23
Capacitor, TANT, 100uF, 6.3V, 3528
3
1
C43
Capacitor, X7R, 4700pF 250V, 1812
4
3
L1,L3,L4
Inductor, 0.2uH
5
1
L2
Inductor, 4.7uH
HARDWARE-FOR DEMO BOARD ONLY:
1
4
(STAND-OFF),
STAND-OFF, NYLON 0.50"
2
6
E1-E6
Turret, 0.094"
Notes:
1. Required Circuit Components are those parts that are required to implement the circuit function
2. Additional Demo Board Circuit Components are those parts that provide added functionality for the demo
board but
are not required in the actual circuit.
DC950A-B BILL OF MATERIAL
Item
Qty
Reference
Part Description
Manufacture / Part #
REQUIRED CIRCUIT COMPONENTS
1
1
1
C38
Capacitor, NP0, 33pF, 50V, 0603
2
1
C41
Capacitor, NPO, 330PF, 50V, 0603
3
1
C1
Capacitor, NPO 330PF 100V 1206
4
2
C34,C30
Capacitor, X7R, 2200pF, 50V, 0603
5
3
C19,C31,C32
Capacitor, X5R, 0.1uF, 25V, 0603
6
1
C40
Capacitor, X7R, 1000pF, 50V, 0603
7
1
C36
Capacitor, X5R, 0.47uF, 16V, 0603
8
6
C3,C4,C13,C14,C26,C27 Capacitor, X5R, 47uF, 6.3V, 1210
9
0
C33,C39
Capacitor, 0603
10
1
C35
Capacitor, X7R, 3300PF, 50V, 0603
11
1
C37
Capacitor, NPO, 680PF, 50V, 0603
12
1
C9
Capacitor, NPO, 560pF, 100V, 1206
13
0
C18
Capacitor, 1210
14
2
C20,C21
Capacitor, X7R, 4.7uF, 50V, 1812
15
1
D2
BAS21
16
2
D8,D6
BAT54
17
1
D5
BAT54A
18
1
D10
BAT54S
19
1
D9
B0530W
20
1
D4
Zenerdiode, 11V, 5%, SOT23
21
1
L5
Inductor, 330uH
22
1
L6
Inductor, 120uH
23
1
Q1
MOSFET, n-ch, SO8
24
1
Q3
MOSFET, n-ch, SO8
25
2
Q7,Q9
Transistor, npn, SOT23
26
3
Q8,Q10,Q12
Transistor, pnp, SOT23
AVX, 06035A330KAT2
AVX, 06035A331KAT
AVX, 12061A331KAT
AVX, 06035C222JAT
AVX, 06033D104KAT2A
AVX, 06035C102KAT2A
AVX, 0603YD474M
TDK, 3225X5R0J476M
OPT
KEMET, C0603C332J5RAC
AVX, 06035A681JAT
AVX, 12061A561KAT2A
OPT
TDK,C4532X7R1H475MT
Diodes, Inc.,BAS21-7-F
Diodes, Inc.,BAT54-7-F
Diodes, Inc.,BAT54A-7
Diodes, Inc.,BAT54S-7-F
Diodes, Inc.,B0530W-7-F
Vishay, BZX84C11-V
Coilcraft, DO1608C-334MLB
Wurth Elektronik, 744 032 121
Vishay, Si4850EY-T1-E3
Vishay, Si4840DY-T1-E3
Zetex, FMMT619TA
Zetex, FMMT718TA
5
Talking
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