LT3825 AND LT3837
1
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 PARAMETER CONDITIONS MIN TYP MAX UNITS
V
IN
Input Supply Range DC950A-A
DC950A-B
36
9
72
36
V
V
V
OUT
Output Voltage V
OUT1
V
OUT2
V
OUT3
4.85
3.20
2.42
5V
3.3V
2.5V
5.15
3.40
2.58
V
V
V
I
OUT
Output Current (Note: Total output power not to
exceed 30W)
I
OUT1
(5V output)
I
OUT2
(3.3V output)
I
OUT3
(2.5V output)
0
0
0
2
3
3
4
4
4
A
A
A
Efficiency
Efficiency 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
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
DEMO CIRCUI
950
QUICK START GUID
LT3825 and LT3837
Non-opto Synchronous Fly
back Controlle
