1. Products
  2. Power Management
  3. Switching Regulators
  4. Flyback, Forward, and Isolated Controller
  5. LT3781


Features and Benefits

  • High Voltage Operation up to 72V
  • Synchronizable Operating Frequency and Output Switch Phase for Multiple Controller Systems
  • Synchronous Switch Output
  • Undervoltage Lockout Protection with 6V Hysteresis for Self-Biased Power
  • Fixed Frequency Operation to 350kHz
  • Local ±1% Voltage Reference
  • Input Overvoltage Protection
  • Low Start-Up Current
  • Programmable Start Inhibit for Power Supply Sequencing and Protection
  • Optocoupler Support
  • Soft-Start Control

Product Details

The LT3781 controller simplifies the design of high power synchronous dual transistor forward DC/DC converters. The part employs fixed frequency current mode control and supports both isolated and nonisolated topologies. The IC drives external N-channel power MOSFETs and operates with input voltages up to 72V.

The LT3781 is ideal for output derived power schemes, through the use of a large undervoltage lockout hysteresis range. The part is also equipped with an 18V VCC shunt regulator, which prevents exceeding absolute maximum ratings while in trickle start applications.

The LT3781’s operating frequency is programmable and can be synchronized up to 350kHz. Switch phase is also controlled during synchronized operation to accommodate multiple-converter systems. Internal logic guarantees 50% maximum duty cycle operation to prevent transformer saturation.

The LT3781 is available in a 20-lead SSOP package.


  • Isolated Telecommunication Systems
  • Personal Computers and Peripherals
  • Distributed Power Step-Down Converters
  • Lead Acid Battery Backup Systems
  • Automotive and Heavy Equipment

Product Lifecycle icon-recommended Production

At least one model within this product family is in production and available for purchase. The product is appropriate for new designs but newer alternatives may exist.

Evaluation Kits (5)

Tools & Simulations


LTspice® is a powerful, fast and free simulation software, schematic capture and waveform viewer with enhancements and models for improving the simulation of analog circuits.


Models for the following parts are available in LTspice:


Design Resources

ADI has always placed the highest emphasis on delivering products that meet the maximum levels of quality and reliability. We achieve this by incorporating quality and reliability checks in every scope of product and process design, and in the manufacturing process as well.  "Zero defects" for shipped products is always our goal.View our quality and reliability program and certifications for more information.

Part Number Material Declaration Reliability Data Pin/Package Drawing CAD Symbols, Footprints & 3D Models
LT3781EG#PBF Material Declaration Reliability Data 20-Lead SSOP
LT3781EG#TRPBF Material Declaration Reliability Data 20-Lead SSOP
LT3781IG#PBF Material Declaration Reliability Data 20-Lead SSOP
LT3781IG#TRPBF Material Declaration Reliability Data 20-Lead SSOP
Wafer Fabrication Data R352 Reliability Data

PCN-PDN Information

Select a model from the dropdown below to subscribe to PCN/PDN notifications and view past notifications as well.

Sample & Buy

Ordering FAQs

See our Ordering FAQs for answers to questions about online orders, payment options and more.


Buy Now Pricing

(**) Displayed Buy Now Price and Price Range is based on small quantity orders.


List Pricing

(*)The 1Ku 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 Analog Devices, Inc. authorized distributor. Pricing displayed for Evaluation Boards and Kits is based on 1-piece pricing.


Lead Times

Please see the latest communication from our CCO regarding lead times.



Selecting the Sample button above will redirect to the third-party ADI Sample Site. The part selected will carry over to your cart on this site once logged in. Please create a new account there if you have never used the site before. Contact SampleSupport@analog.com with any questions regarding this Sample Site.

Price Table Help


Evaluation Boards

Pricing displayed is based on 1-piece.

Up to two boards can be purchased through Analog.com. To order more than two, please purchase through one of our listed distributors.

Pricing displayed is based on 1-piece. The USA list pricing shown is for budgetary use only, shown in United States dollars (FOB USA per unit), and is subject to change. International prices may vary due to local duties, taxes, fees and exchange rates.