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dc1825af
DEMO MANUAL DC1825A
Description
LT8300
100VIN 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,
withanominal48V.Theoutputcurrentcapabilityincreases
with the input voltage.
TheDC1825Aneedsaverysmallminimumload(~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
circuitcanbeeasilymodifiedfordifferentapplicationswith
some pre-designed transformers.
performance summary
TheLT8300isasimple-to-usehighvoltagemonolithiciso-
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-
tionmaintainshighefficiencyatlightloadswhileminimizing
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
VIN Quiescent Current IOUT = 0mA, VIN = 75V 400 µA
Output Voltage VIN = 22V – 75V
IOUT = 1mA – 250mA 4.75 5 5.25 V
Maximum Output Current VIN = 22V 250 mA
Output Voltage Ripple (Peak to Peak) VIN = 22V – 75V, IOUT = 250mA 50 mV
Typical Switching Frequency VIN = 48V, IOUT = 250mA 330 kHz
Minimum Switching Frequency IOUT = 0mA 8 kHz
Efficiency VIN = 48V, IOUT = 250mA 80 %
Specifications are at TA= 25°C
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