DC1825A: 5V @ 250mA, 22 ~ 75V in, Buck


Demonstration circuit 1825A is an isolated flyback converter 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 performance 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 isolated flyback converter. No third winding or opto-isolator is required for regulation. The part sets the isolated output 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® operation 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.


Manufacturer Analog Devices Inc.
Category AC/DC and DC/DC Conversion
Sub-Category DC/DC SMPS - Single Output
Eval Board Part Number DC1825A-ND
Eval Board Supplier Analog Devices Inc.
Eval Board Normally In Stock
Topology Step Down
Outputs and Type 1 Isolated
Voltage Out: Factory Set 5 V
Current Out 250 mA
Voltage In 22 ~ 75 V
Efficiency @ Conditions >80%, 22V in, 5V @ 95 ~ 250 mA
>75%, 48V in, 5V @ 150 ~ 250 mA
Voltage Out Range 4.75 ~ 5.25 V
Features Current Limit (Adj. or Fixed)
Light Load Mode
Shutdown, Enable, Standby
Soft Start
Under Voltage Protection, Brown-Out
Switching Frequency 330 kHz
Standby Current [Typical] 1.2 µA
Quiescent Current [Typical] 70 µA
Component Count + Extras 10 + 0
Internal Switch Yes
Design Author Linear Technology
Application / Target Market Automotive
Auxiliary Power Supply
Industrial Power
Standby Current [Maximum] 2 µA
Quiescent Current [Maximum] 330 µA
Main I.C. Base Part LT8300
Date Created By Author 2012-07
Date Added To Library 2015-06

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