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

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.

Features
  • 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


Applications
  • Isolated Medium Power (10W to 60W) Supplies
  • Isolated Telecom, Medical Converters
  • Instrumentation Power Supplies
  • Isolated Power over Ethernet Supplies
Packaging
Order Information
Part NumberPackageTempPrice(1-99)Price (1k)*
LT3825EFE#PBFTSSOP-16E$4.43$3.10
LT3825EFE#TRPBFTSSOP-16E$3.16
Demo Boards
Part NumberDescriptionPrice
DC1143ALT3825EFE Demo Board | Synchronous Isolated Flyback, 36V ≤ Vin ≤ 72V, Vout: 3.3V @ 6AContact Factory
DC894A-ALT3825EFE Demo Board I Synchronous Flyback Converter, Vin=36V-72V, Vout=3.3V@12A$150.00
DC894B-CLT3825EFE Demo Board | Isolated, 36V ≤ VIN ≤ 72V, VOUT = 12V @ 5A$150.00
DC894C-BLT3825EFE Isolated Demo Board | 36V ≤ VIN ≤ 72V; VOUT: 5V @ 8A$150.00
DC894C-CLT3825EFE Isolated Demo Board | 36V ≤ VIN ≤ 72V; VOUT: 12V @ 5A$150.00
DC950A-ALT3825EFE Demo Board | Isolated Synchronous Flyback, 36V ≤ Vin ≤ 72V, Vout: 5V/2A, 3.3V/3A, 2.5V/3A$150.00
Datasheet
Design Note
Reliability Data
LT Journal
Press Release
LTspice
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LT3825 Footprints and Symbols
LT3825 - Demo Circuit - Isolated Synchronous Flyback Controller (36-72V to 3.3V @ 12A)