DEMO MANUAL DC1961A
LT8309
No-Opto Flyback Converter
with Synchronous Rectifier
Description
Demonstration circuit 1961A features the
LT
®
8309,
a
secondary synchronous driver in an isolated, no opto-
coupler, flyback converter. It regulates a 12V, 5A output
from a 36V to 72V input source.
Output regulation is handled on the primary side by the
LT3748, a boundary conduction mode flyback controller
which senses output voltage directly from the primary, re-
sulting in a simple flyback schematic with no opto-coupler.
The LT8309 synchronous rectifier driver replicates the
behavior of a diode by sensing the synchronous MOSFET
drain-to-source voltage to determine its turn on period.
By replacing the diode with a N-channel MOSFET, applica-
tions are no longer restricted by the heat constraints of
the rectifier diode.
On the DC1961A, the LT8309 is biased from the recti-
fied drain voltage node of secondary side synchronous
MOSFET, not directly connecting to output voltage. This
configuration allows the synchronous MOSFET to remain
conducting at all times, even when output is shorted
to ground, so as to provide a very robust short circuit
performance.
The Performance Summary table summarizes the per-
formance of the demo board at room temperature. For
thermally critical applications, proper amount of air flow
can help to reduce power components’ temperature rise,
therefore greatly improving circuit reliability.
The LT8309 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 1961A.
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.
performance summary
PARAMETER
Input Voltage
Output Voltage
Maximum Output Current
Output Voltage Ripple (Peak to Peak)
Boundary Mode Switching Frequency
Minimum Switching Frequency
Efficiency
Specifications are at T
A
= 25°C
CONDITIONS
V
IN
= 36V to 72V, I
OUT
= 0.15A to 5A
V
IN
= 36V to 72V, I
OUT
= 5A (20MHz BW)
V
IN
= 48V, I
OUT
= 5A
I
OUT
= 0mA
V
IN
= 36V, I
OUT
= 5A
V
IN
= 48V, I
OUT
= 5A
V
IN
= 72V, I
OUT
= 5A
MIN
36
11.4
5
150
133
42
91
91.5
91.5
TYP
48
12
MAX
72
12.6
UNITS
V
V
A
mV
kHz
kHz
%
%
%
dc1961af
1
DEMO MANUAL DC1961A
Quick start proceDure
Demonstration circuit 1961A is easy to set up to evalu-
ate the performance of the LT8309. Refer to Figure 1 for
proper measurement equipment setup and follow the
procedure below:
1. With power off, connect the input power supply to the
board through V
IN
and GND terminals. Connect the
load to the terminals V
OUT+
and V
OUT–
on the board.
2. Turn on the power at the input.
NOTE: Make sure that the input voltage does not exceed
72V. To operate the board with higher input/output volt-
age, input capacitor, output capacitor and MOSFETs with
higher voltage ratings are needed.
3. Check for the proper output voltages. The output should
be regulated at 12V (±5%).
NOTE: The LT3748 requires a minimum load to maintain
good output voltage regulation. On the DC1961A, in order
to avoid pre-loading, a Zener diode is placed between its
V
OUT+
and V
OUT–
to serve as a minimum load.
4. Once the proper output voltage is established, adjust
the input voltage and load current within the operating
range and observe the output voltage regulation, ripple
voltage, efficiency and other parameters.
NOTE: When measuring the input or output voltage ripples,
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 V
IN
and GND, or V
OUT+
and V
OUT–
terminals. See Figure 2 for
proper scope probe technique.
POWER SUPPLY
–
+
–
V
IN
+
+
–
I
IN
+
+
–
I
OUT
–
+
V
OUT
LOAD
–
Figure 1. Proper Measurement Equipment Setup
INPUT OR OUTPUT CAPACITOR
Figure 2. Proper Scope Probe Placement for Measuring Input/Output Ripple
2
dc1961af
DEMO MANUAL DC1961A
parts List
ITEM
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
QTY
1
3
1
1
6
1
1
1
1
1
1
1
1
1
1
1
2
1
1
1
1
1
1
1
1
1
2
1
1
1
1
1
1
1
1
1
1
1
1
REFERENCE
C1
C2, C3, C4
C5
C6
C7-C12
C13
C14
C15
C16
C17
C18
C19
C20
D1
D2
D3
D4, D5
D6
L1
L2
Q1
Q2
R1
R3
R4
R5
R6, R8
R7
R9
R10
R11
R12
R13
R14
R15
T1
U1
U2
PART DESCRIPTION
CAP., ALUM, 47µF, 80V, 20%, SMD
Cap., X7S, 4.7µF, 100V, 20%, 1210
Cap., U2J, 120pF, 250V, 5%, 0805
Cap., X7S, 1µF, 100V, 10%, 0805
Cap., X5R, 47µF, 16V, 10%, 1210
Cap., X5R, 4.7µF, 16V, 20%, 0805
Cap., X7R, 0.22µF, 25V, 10%, 0603
Cap., NPO, 470pF, 25V, 5%, 0603
Cap., X7R, 1µF, 100V, 20%, 1206
Cap., X5R, 4.7µF, 25V, 10%, 0805
Cap., NPO, 47pF, 25V, 5%, 0603
Cap., X7R, 0.033µF, 25V, 10%, 0603
Cap., X7R, 4700pF, 250V, 10%, 1812
Diode, TVS UNI-DIR 85V, 600W, SMB
Diode, 1A/200V, SOD-123
Diode Zener, 13V SMA
DIODE, SWITCHING 150V, 0.2A, SOD123
Zener Diode, 36V, SOD-123
Inductor, 22µH, XAL6060
Inductor, 1µH, XAL6030
MOSFET, N-CH, 80V, 100A, TDSON-8
MOSFET, N-CH, 200V, 36A, TDSON-8
Res., Chip 100, 0.50W, 5%, 1210
Res., Chip 1.2M, 0.1W, 5%, 0603
Res., Chip 51k 0.1W 5% 0603
Res., Chip 68, 1/8W, 5%, 0805
Res/Jumper, Chip 0Ω, 0.25W, 5A, 0603
Res., Chip 160k, 1/8W, 1%, 0805
Res., Chip 3Ω, 1/8W, 5%, 0805
Res., Chip 60.4k, 0.1W, 1%, 0603
Res., Chip 3, 1/10W, 5%, 0603
Res., Chip 7.50k, 0.1W, 1%, 0603
Sense Res., RL Vert. 0.010, 1W, 1%, 0815
Res., Chip 6.04k, 0.1W, 1%, 0603
Res., Chip 2.37k, 0.25W, 1%, 1206
Transformer, ±5%, 20.5µH, EFD20 Platform
I.C., Rectifier Driver, TSOT23-S5
I.C., No-Opto Flyback Converter
FAB, PRINTED CIRCUIT BOARD Rev 2
MANUFACTURER/PART NUMBER
Nippon Chemi-Con, EMZA800ADA470MJA0G
TDK, C3225X7S2A475MT
Murata, GRM21A7U2E121JW31D
TDK, C2012X7S2A105K
Murata, GRM32ER61C476KE15L
TDK, C2012X5R1C475M
TDK, C1608X7R1E224K
AVX, 06033A471JAT2A
TDK, C3216X7R2A105M
TDK, C2012X5R1E475K
AVX, 06033A470JAT2A
AVX, 06033C333KAT2A
Murata, GA343DR7GD472KW01L
Diodes Inc., SMBJ85A-13-F
Central Semi., CMMR1U-02 TR
Central Semi., CMZ5928B TR
Diodes Inc., BAV20W-7-F
Central Semi., CMHZ5258B TR
Coilcraft, XAL6060-223MEC
Coilcraft, XAL6030-102MEB
Infineon, BSC047N08NS3 G
Infineon, BSC320N20NS3 G
Vishay, CRCW1210100RJNEA
Vishay, CRCW06031M20JNEA
Vishay, CRCW060351K0JNEA
Vishay, CRCW080568R0JNEA
Vishay, CRCW06030000Z0EA
Vishay, CRCW0805160KFKEA
Vishay, CRCW08053R00JNEA
Vishay, CRCW060360K4FKEA
Vishay, CRCW06033R00JNEA
Vishay, CRCW06037K50FKEA
SUSUMU, RL3720WT-R010-F
Vishay, CRCW06036K04FKEA
Vishay, CRCW12062K37FKEA
Pulse Engrng., PA1736NLT
Linear Tech. Corp. LT8309ES5#PBF
Linear Tech. Corp. LT3748EMS#PBF
DEMO CIRCUIT #1961A
Required Circuit Components
dc1961af
5
Test/Measurement
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