LT3825 - Isolated No-Opto Synchronous Flyback Controller with Wide Input Supply Range


  • Senses Output Voltage Directly from Primary Side Winding—No Opto-Isolator Required
  • Synchronous Driver for High Efficiency
  • Input Voltage Limited Only by External Power Components
  • Accurate Output Regulation without User Trims
  • Switching Frequency from 50kHz to 250kHz
  • Synchronizable
  • Load Compensation
  • Programmable Undervoltage Lockout
  • Available in a Thermally Enhanced 16-Lead TSSOP Package

Typical Application

LT3825 Typical Application
LT3825 Typical Application
LT3825 Typical Application


The LT3825 is an isolated switching regulator controller designed for medium power flyback topologies. A typical application is 10W to 60W with input voltage limited onlyby external power path components. A third transformer winding provides output voltage feedback.

The LT3825 is a current mode controller that regulates output voltage based on sensing secondary voltage via a transformer winding during flyback. This allows for tight output regulation without the use of an opto-isolator,improving dynamic response and reliability. Synchronous rectification increases converter efficiency and improves output cross regulation in multiple output converters.

The LT3825 operates in forced continuous conduction mode which improves cross regulation in multiple winding applications.Switching frequency is user programmable and can be externally synchronized. The part also has load compensation, undervoltage lockout and soft-start circuity.


CAD Symbols and Footprints: The downloadable Zip file below contains the schematic symbol and PCB footprints.

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

Part Number Package Code Temp Package
LT3825EFE#PBF TSSOP-16 FE E 05-08-1663 (BC) Yes
LT3825EFE#TRPBF TSSOP-16 FE E 05-08-1663 (BC) Yes

LT3825 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
LT3825EFE#PBF TSSOP-16 E $4.43 $3.10 Yes
LT3825EFE#TRPBF TSSOP-16 E $3.16 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
DC1143A LT3825EFE Demo Board | Synchronous Isolated Flyback, 36V ≤ Vin ≤ 72V, Vout: 3.3V @ 6A Contact Factory
DC894A-A LT3825EFE Demo Board I Synchronous Flyback Converter, Vin=36V-72V, Vout=3.3V@12A $150.00
DC894B-C LT3825EFE Demo Board | Isolated, 36V ≤ VIN ≤ 72V, VOUT = 12V @ 5A $150.00
DC894C-B LT3825EFE Isolated Demo Board | Sync Flyback Controller, 36V ≤ VIN ≤ 72V; VOUT = 5V @ 8A $150.00
DC894C-C LT3825EFE Isolated Demo Board | Sync No Opto Flyback Controller, 36V ≤ VIN ≤ 72V; VOUT = 12V @ 5A $150.00
DC950A-A LT3825EFE Demo Board | Isolated Synchronous Flyback, 36V ≤ Vin ≤ 72V, Vout: 5V/2A, 3.3V/3A, 2.5V/3A $150.00
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Click here to view our complete list of demo boards


  • Isolated Medium Power (10W to 60W) Supplies
  • Isolated Telecom, Medical Converters
  • Instrumentation Power Supplies
  • Isolated Power over Ethernet Supplies

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Design Tools


LTspice® software 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

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
  • Step 2: Once LTspice is installed, click on the link(s) below to launch the simulation
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