LT3573 - Isolated Flyback Converter without an Opto-Coupler


  • 3V to 40V Input Voltage Range
  • 1.25A, 60V Integrated NPN Power Switch
  • Boundary Mode Operation
  • No Transformer Third Winding or Opto-Isolator Required for Regulation
  • Improved Primary-Side Winding Feedback Load Regulation
  • VOUT Set with Two External Resistors
  • BIAS Pin for Internal Bias Supply and Power NPN Driver
  • Programmable Soft-Start
  • Programmable Power Switch Current Limit
  • Thermally Enhanced 16-Lead MSOP

Typical Application

LT3573 Typical Application
LT3573 Typical Application


The LT®3573 is a monolithic switching regulator specifically designed for the isolated flyback topology. No third winding or opto-isolator is required for regulation. The part senses the isolated output voltage directly from the primary-side flyback waveform. A 1.25A, 60V NPN power switch is integrated along with all control logic into a 16‑lead MSOP package.

The LT3573 operates with input supply voltages from 3V to 40V, and can deliver output power up to 7W with no external power devices.The LT3573 utilizes boundary mode operation to provide a small magnetic solution with improved load regulation.


For complete and up to date package information and drawings, please refer to our packaging page

Part Number Package Code Temp Package
LT3573EMSE#PBF MS-16E MSE E 05-08-1667 RoHS
LT3573EMSE#TRPBF MS-16E MSE E 05-08-1667 RoHS
LT3573IMSE#PBF MS-16E MSE I 05-08-1667 RoHS
LT3573IMSE#TRPBF MS-16E MSE I 05-08-1667 RoHS

LT3573 Package Drawing

Order Info

  • Part numbers ending in PBF are lead free. Solder plated terminal finish (SnPb) versions are non-standard and special terms and conditions and pricing applies if available. Please contact LTC marketing for information.
  • Part numbers containing TR or TRM are shipped in tape and reel or 500 unit mini tape and reel, respectively
  • Please refer to our general ordering information or the product datasheet for more details

Package Variations and Pricing

Part Number Package Temp Price
LT3573EMSE#PBF MS-16E E $3.95 $2.76 Yes
LT3573EMSE#TRPBF MS-16E E $2.82 Yes
LT3573IMSE#PBF MS-16E I $4.46 $3.12 Yes
LT3573IMSE#TRPBF MS-16E I $3.18 Yes
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* The USA list pricing shown is for BUDGETARY USE ONLY, shown in United States dollars (FOB USA per unit for the stated volume), and is subject to change. International prices may differ due to local duties, taxes, fees and exchange rates. For volume-specific price or delivery quotes, please contact your local Linear Technology sales office or authorized distributor.

Demo Boards

Linear Technology offers many demo boards free of charge to qualified customers. Contact your local sales office or distributor to inquire about a demo board. Certain demo boards are also available for sale via credit card on this website. Demo boards are for evaluation purposes only. It remains the customer’s responsibility to verify proper and reliable operation in the actual end application.

Part Number Description Price Documentation
DC1228A LT3573EMSE | 10V to 30VIN, 5Vout at 1A Isolated Monolithic Flyback Converter $100.00
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  • Industrial, Automotive and Medical Isolated Power Supplies

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Design Tools


LTspice® IV is a powerful, fast and free simulation tool, schematic capture and waveform viewer with enhancements and models for improving the simulation of switching regulators. Click here to download LTspice IV

To launch a ready to run LTspice demonstration circuit for this part:

  • Step 1: If you have not installed LTspice on this computer, download and install LTspice IV
  • Step 2: Once LTspice is installed, click on the link(s) below to launch the simulation
  • Step 3: If LTspice IV does not automatically open after clicking the link above, you can instead run the simulation by right clicking on the link and selecting "Save Target As." After saving the file to your computer, start LTspice and open the demonstration circuit by selecting 'Open' from the 'File' menu

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