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dc1825af
DEMO MANUAL DC1825A
Description
LT8300
100V
IN
Micropower Isolated Flyback
Converter with 150V/260mA Switch
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.
performance summary
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.
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
Input Voltage
22
48
75
V
V
IN
Quiescent Current
I
OUT
= 0mA, V
IN
= 75V
400
µA
Output Voltage
V
IN
= 22V – 75V
I
OUT
= 1mA – 250mA
4.75
5
5.25
V
Maximum Output Current
V
IN
= 22V
250
mA
Output Voltage Ripple (Peak to Peak)
V
IN
= 22V – 75V, I
OUT
= 250mA
50
mV
Typical Switching Frequency
V
IN
= 48V, I
OUT
= 250mA
330
kHz
Minimum Switching Frequency
I
OUT
= 0mA
8
kHz
Efficiency
V
IN
= 48V, I
OUT
= 250mA
80
%
Specifications are at T
A
= 25°C
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