DEMO MANUAL DC1825A
LT8300
100V
IN
Micropower Isolated Flyback
Converter with 150V/260mA Switch
Description
Demonstration circuit 1825A is an isolated flyback con-
verter featuring the
LT
®
8300.
This demo circuit outputs
5.0V, and maintains tight regulation with a load current
from ~1mA to 250mA and over an input from 22V to 75V,
with a nominal 48V. The output current capability increases
with the input voltage.
The DC1825A needs a very small minimum load (~1mA) to
regulate the output voltage, thanks to the accurate current
limit capability and ultra low switching frequency of the
LT8300 at very light load. The standby input current of
the demo circuit is less than 400µA (typical) because of
the low quiescent current design of the IC and very small
minimum load requirement.
The Performance Summary table summarizes the perfor-
mance of the demo board at room temperature. The demo
circuit can be easily modified for different applications with
some pre-designed transformers.
The LT8300 is a simple-to-use high voltage monolithic iso-
lated flyback converter. No third winding or opto-isolator
is required for regulation. The part sets the isolated out-
put voltage with a single external resistor and integrates
compensation and soft start circuitry inside. Boundary
mode operation provides a small magnetic solution with
improved load regulation. Low ripple Burst Mode
®
opera-
tion maintains high efficiency at light loads while minimizing
the output voltage ripple. A 260mA, 150V DMOS power
switch is integrated along with all high voltage circuitry
and control logic into a 5-lead ThinSOT™ package.
The LT8300 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 DC1825A.
Design files for this circuit board are available at
http://www.linear.com/demo
L,
LT, LTC, LTM, Linear Technology, the Linear logo and Burst Mode are registered trademarks
and ThinSOT is a trademark of Linear Technology Corporation. All other trademarks are the
property of their respective owners.
performance summary
PARAMETER
Input Voltage
V
IN
Quiescent Current
Output Voltage
Maximum Output Current
Output Voltage Ripple (Peak to Peak)
Typical Switching Frequency
Minimum Switching Frequency
Efficiency
Specifications are at T
A
= 25°C
MIN
22
TYP
48
400
4.75
250
50
330
8
80
5
5.25
MAX
75
UNITS
V
µA
V
mA
mV
kHz
kHz
%
CONDITIONS
I
OUT
= 0mA, V
IN
= 75V
V
IN
= 22V – 75V
I
OUT
= 1mA – 250mA
V
IN
= 22V
V
IN
= 22V – 75V, I
OUT
= 250mA
V
IN
= 48V, I
OUT
= 250mA
I
OUT
= 0mA
V
IN
= 48V, I
OUT
= 250mA
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DEMO MANUAL DC1825A
Quick start proceDure
The DC1825A is easy to set up to evaluate the performance
of the LT8300. Refer to Figure 1 for proper equipment
setup and follow the procedure below.
1. With power off, connect the input power supply to the
board through VIN (E1) and GND (E3) terminals. Connect
the load to the terminals VOUT+ (E4) and VOUT– (E2)
on the board.
2. Turn on the power at the input. Increase VIN slowly to
22V.
NOTE: Make sure that the input voltage is always within
spec. To operate the board with higher input/output
voltage, input capacitor, output capacitor and output
diode with higher voltage ratings are needed.
NOTE: To run overload tests on the demo board with
V
IN
higher than 40V, a RC snubber (200Ω, 150pF) or
Schottky plus Zener clamp circuit is recommended to
make sure the voltage spike at the switching node is
always less than 150V.
3. Check for the proper output voltages. The output should
be regulated at 5.0V (±5%).
NOTE: The LT8300 requires very small minimum load
to maintain good output voltage regulation. A Zener
diode is placed on the output to clamp the voltage to
~5.0V. This Zener is optional, and can be replaced with
a 5.1k resistor.
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 VIN (E1) and GND (E3), or VOUT+ (E4) and
VOUT– (E2) terminals. See Figure 2 for proper scope
probe technique.
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DEMO MANUAL DC1825A
Quick start proceDure
Figure 1. Proper Measurement Equipment Setup
INPUT OR OUTPUT CAPACITOR
Figure 2. Proper Scope Probe Placement for Measuring Input or Output Ripple
85
80
75
EFFICIENCY (%)
V
OUT
(V)
70
65
60
55
50
0
50
150
100
200
LOAD CURRENT (mA)
250
DC1825A F03a
5.00
4.95
V
IN
= 22V
V
IN
= 48V
4.90
4.85
4.80
4.75
4.70
4.65
4.60
4.55
4.50
0
50
150
100
200
LOAD CURRENT (mA)
250
DC1825A F03b
V
IN
= 48V
V
IN
= 22V
Figure 3. Typical Efficiency and Regulation Curves
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DEMO MANUAL DC1825A
parts List
ITEM
1
2
3
4
5
6
7
8
9
10
1
2
QTY
1
1
1
1
1
1
1
1
1
1
0
0
REFERENCE
C2
C3
C4
D1
D2
R1
R2
R3
T1
U1
C1
R4
PART DESCRIPTION
CAP., X7R, 2.2µF 100V, 10% 1210
CAP., X5R, 100µF 6.3V, 20% 1210
CAP., X7R, 4700pF 1000V, 10% 1210
DIODE, SCHOTTKY, 30V 1A PWRDI123
SMT ZENER DIODE, 5.6V SOD-523
RES., CHIP, 806k, 1%, 0805
RES., CHIP, 53.6k, 1%, 0603
RES., CHIP, 365k, 1%, 0603
TRANSFORMER 7:1
I.C., LT8300ES5, TSOT-23
CAP., 0805
RES., 0805
MANUFACTURER/PART NUMBER
MURATA, GRM32ER72A225KA35L
AVX, 12106D107MAT2A
VISHAY/VITRAMON, VJ1210Y472KXGAT5Z
DIODES INC., DFLS130-7
DIODES INC., BZT52C5V6T-7
VISHAY, CRCW0805806KFKEA
VISHAY, CRCW060353K6FKEA
VISHAY, CRCW0603365KFKEA
WÜRTH ELECTONIK, 750312366
LINEAR TECH., LT8300ES5#PBF
OPT
OPT
Required Circuit Components
Additional Demo Board Circuit Components
dc1825af
4
5
4
3
2
1
REVISION HISTORY
ECO
__
2
PRODUCTION
ZHONGMING Y. 1-9-12
REV
DESCRIPTION
APPROVED
DATE
D
D
E1
VIN
T1
3
4
6
750312366
D1
DFLS130L
2
1
2
2
R4
OPT
1
SW
4
SW
D2
5.6V
BZT52C5V6T-7
C3
100uF
6.3V
1210
1
+5V
SEE QSG
E4
VOUT+
+5V / 0.25A
R1
806K
1%
1
EN/UV
GND
RFB
VIN
R2
53.6K
1%
3
2
5
U1
LT8300ES5
C1
OPT
0805
E2
VOUT-
schematic Diagram
VIN
22V - 75V
C2
2.2uF
100V
1210
E3
C
*
C
GND
R3 365K
C4
3.3nF
250
1210
B
B
NOTE: UNLESS OTHERWISE SPECIFIED
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 representa-
tion that the interconnection of its circuits as described herein will not infringe on existing patent rights.
1. ALL RESISTORS AND CAPACITORS ARE 0603.
CUSTOMER NOTICE
APPROVALS
1630 McCarthy Blvd.
Milpitas, CA 95035
Phone: (408)432-1900
www.linear.com
Fax: (408)434-0507
LTC Confidential-For Customer Use Only
A
A
LINEAR TECHNOLOGY HAS MADE A BEST EFFORT TO DESIGN A
CIRCUIT THAT MEETS CUSTOMER-SUPPLIED SPECIFICATIONS;
TECHNOLOGY
HOWEVER, IT REMAINS THE CUSTOMER'S RESPONSIBILITY TO PCB DES.
HZ
VERIFY PROPER AND RELIABLE OPERATION IN THE ACTUAL
APP ENG. ZHONGMING Y.
TITLE: SCHEMATIC
APPLICATION. COMPONENT SUBSTITUTION AND PRINTED
CIRCUIT BOARD LAYOUT MAY SIGNIFICANTLY AFFECT CIRCUIT
PERFORMANCE OR RELIABILITY. CONTACT LINEAR
TECHNOLOGY APPLICATIONS ENGINEERING FOR ASSISTANCE.
100V MICROPOWER ISOLATED FLYBACK CONVERTER
SIZE
IC NO.
N/A
SCALE = NONE
3
THIS CIRCUIT IS PROPRIETARY TO LINEAR TECHNOLOGY AND
SUPPLIED FOR USE WITH LINEAR TECHNOLOGY PARTS.
4
DEMO CIRCUIT 1825A
DATE:
LT8300ES5
2
REV.
2
Monday, July 02, 2012
SHEET 1
1
OF 1
5
DEMO MANUAL DC1825A
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