LT1725 - General Purpose Isolated Flyback Controller


  • Drives External Power MOSFET with External ISENSE Resistor
  • Application Input Voltage Limited Only by External Power Components
  • Senses Output Voltage Directly from Primary Side Winding—No Optoisolator Required
  • Accurate Regulation Without User Trims
  • Regulation Maintained Well into Discontinuous Mode
  • Switching Frequency from 50kHz to 250kHz with External Capacitor
  • Optional Load Compensation
  • Optional Undervoltage Lockout
  • Available in 16-Pin SO and SSOP Packages

Typical Application

LT1725 Typical Application
LT1725 Typical Application


The LT1725 is a monolithic switching regulator controller specifically designed for the isolated flyback topology. It drives the gate of an external MOSFET and is generally powered from a third transformer winding. These features allow for an application input voltage limited only by external power path components. The third transformer winding also provides output voltage feedback information, such that an optoisolator is not required. Its gate drive capability coupled with a suitable external MOSFET can deliver load power up to tens of watts.

The LT1725 has a number of features not found on most other switching regulator ICs. By utilizing current mode switching techniques, it provides excellent AC and DC line regulation. Its unique control circuitry can maintain regulation well into discontinuous mode in most applications. Optional load compensation circuitry allows for improved load regulation. An optional undervoltage lockout pin halts operation when the application input voltage is too low. An optional external capacitor implements a soft-start function. A 3V output is available at up to several mA for powering primary side application circuitry.


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

Part Number Package Code Temp Package
LT1725CGN SSOP-16 GN C 05-08-1641 (GN16) RoHS
LT1725CGN#PBF SSOP-16 GN C 05-08-1641 (GN16) RoHS
LT1725CGN#TR SSOP-16 GN C 05-08-1641 (GN16) RoHS
LT1725CGN#TRPBF SSOP-16 GN C 05-08-1641 (GN16) RoHS
LT1725CS SO-16 S C 05-08-1610 (S16) RoHS
LT1725CS#PBF SO-16 S C 05-08-1610 (S16) RoHS
LT1725CS#TR SO-16 S C 05-08-1610 (S16) RoHS
LT1725CS#TRPBF SO-16 S C 05-08-1610 (S16) RoHS
LT1725IGN SSOP-16 GN I 05-08-1641 (GN16) RoHS
LT1725IGN#PBF SSOP-16 GN I 05-08-1641 (GN16) RoHS
LT1725IGN#TR SSOP-16 GN I 05-08-1641 (GN16) RoHS
LT1725IGN#TRPBF SSOP-16 GN I 05-08-1641 (GN16) RoHS
LT1725IS SO-16 S I 05-08-1610 (S16) RoHS
LT1725IS#PBF SO-16 S I 05-08-1610 (S16) RoHS
LT1725IS#TR SO-16 S I 05-08-1610 (S16) RoHS
LT1725IS#TRPBF SO-16 S I 05-08-1610 (S16) RoHS

LT1725 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
LT1725CGN SSOP-16 C $7.10 $6.00 No
LT1725CGN#PBF SSOP-16 C $3.55 $3.00 Yes
LT1725CGN#TR SSOP-16 C $6.12 No
LT1725CGN#TRPBF SSOP-16 C $3.06 Yes
LT1725CS SO-16 C $6.86 $5.80 No
LT1725CS#PBF SO-16 C $3.43 $2.90 Yes
LT1725CS#TR SO-16 C $5.92 No
LT1725CS#TRPBF SO-16 C $2.96 Yes
LT1725IGN SSOP-16 I $8.28 $7.00 No
LT1725IGN#PBF SSOP-16 I $4.14 $3.50 Yes
LT1725IGN#TR SSOP-16 I $7.12 No
LT1725IGN#TRPBF SSOP-16 I $3.56 Yes
LT1725IS SO-16 I $8.06 $6.80 No
LT1725IS#PBF SO-16 I $4.03 $3.40 Yes
LT1725IS#TR SO-16 I $6.92 No
LT1725IS#TRPBF SO-16 I $3.46 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
DC373A-A LT1725IGN | 48Vin to 5Vout 2A Module, Isolated Flyback, 1x2 Footprint $150.00
DC373A-B LT1725IGN | 48Vin to 3.3V/3A, 10W Module, Isolated Flyback, 1x2 Footprint $150.00
DC431A LT1725CGN LTC1773EMS | Telecom Input, Isolated 3 Output DC/DC Converter, +36V to +72V Input, Vout = 5V/1A, 3.3V/5A, 2.5V/4A Contact Factory
DC508A LT1725CGN | Low Cost, High Efficiency Synchronous Forward Converter w/o Optoisolator, +Vin = 36V-72V, +Vout = 2.5V/3.3V at 10A Contact Factory
DC562A-A LT1725CGN | Isolated Forward Converter, Vin=36V to 72V, Vout=3.3V@30A Contact Factory
DC562A-B LT1725CGN | Isolated Forward Converter, Vin=36V to 72V, Vout=5V@20A Contact Factory
DC562A-C LT1725CGN | Isolated Forward Converter, Vin=36V to 72V, Vout=12V@12A Contact Factory
DC638A LT1725CGN | Synchronous Flyback Converter, 36V - 72Vin, to 3.3V @ 3.5A, 350mA Input Current Contact Factory
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Click here to view our complete list of demo boards


  • Telecom Isolated Converters
  • Offline Isolated Power Supplies
  • Instrumentation Power Supplies

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