LT1247 - 1MHz Off-Line Current Mode PWM and DC/DC Converter


  • Current Mode Operation to 1MHz
  • 30ns Current Sense Delay
  • <250mA Low Start-Up Current
  • Current Sense Leading Edge Blanking
  • Pin Compatible with UC1842
  • Undervoltage Lockout with Hysteresis
  • No Cross-Conduction Current
  • Trimmed Bandgap Reference
  • 1A Totem Pole Output

Typical Application

LT1247 Typical Application


The LT®1246/LT1247 are 8-pin, fixed frequency, current mode, pulse width modulators. These devices are designed to be improved plug compatible versions of the industry standard UC1842 PWM circuit. The LT1246/ LT1247 are optimized for off-line and DC/DC converter applications. They contain a temperature compensated reference, high gain error amplifier, current sensing comparator, and a high current totem pole output stage ideally suited to driving power MOSFETs. Start-up current has been reduced to less than 250µA. Cross-conduction current spikes in the totem pole output stage have been eliminated, making 1MHz operation practical. Several new features have been incorporated. Leading edge blanking has been added to the current sense comparator. This minimizes or eliminates the filter that is normally required. Eliminating this filter allows the current sense loop to operate with minimum delays. Trims have been added to the oscillator circuit for both frequency and sink current, and both of these parameters are tightly specified. The output stage is clamped to a maximum VOUT of 18V in the on state. The output and the reference output are actively pulled low during under-voltage lockout.


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
LT1247CN8#PBF N-8 N C 05-08-1510 (N8) Yes
LT1247CS8#PBF SO-8 S8 C 05-08-1610 (S8) Yes
LT1247CS8#TRPBF SO-8 S8 C 05-08-1610 (S8) Yes

LT1247 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
LT1247CN8#PBF N-8 C $2.60 $2.10 Yes
LT1247CS8#PBF SO-8 C $2.85 $2.30 Yes
LT1247CS8#TRPBF SO-8 C $2.36 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
DC227A-A LT1247CS8 LT1431CS8 | 35W, Isolated Forward Converter, Half Brick, 36 to 72Vin, 5V or 3.3Vout @ 7A, 500V DC Isolation Contact Factory
DC227A-B LT1247CS8 LT1431CS8 | 35W, Isolated Forward Converter, Half Brick, 36 to 72Vin, 5V or 3.3Vout @ 7A, 1500V DC Isolation Contact Factory
DC227A-C LT1247CS8 LT1431CS8 | 35W, Isolated Forward Converter, Half Brick, 36 to 72Vin, 5V or 3.3Vout @ 7A, 500V DC Isolation, High Efficiency Contact Factory
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Click here to view our complete list of demo boards


  • Off-Line Converters
  • DC/DC Converters

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