LTC3765 - Active Clamp Forward Controller and Gate

By Analog Devices Inc 179

LTC3765 - Active Clamp Forward Controller and Gate

Linear Technology's LTC3765 is a start-up controller and gate driver for use in a self-starting, secondary-side control forward converter. When combined with the LTC3766 secondary-side synchronous forward controller, a complete isolated power supply is created using a minimum of discrete parts. A proprietary scheme is used to multiplex gate drive signals and bias power across the isolation barrier through a small pulse transformer. The LTC3765 contains an on-chip bridge rectifier that extracts gate drive bias power from this pulse transformer, eliminating the need for a separate bias supply. A precision undervoltage lockout circuit and linear regulator controller ensure a quick, well-controlled start-up.

The LTC3765 includes an active clamp output for driving an external PMOS, as well as an adjustable delay to optimize efficiency. The active clamp architecture reduces voltage stress on the main power switch, and provides the highest possible efficiency. Overcurrent protection and the Direct Flux Limit guarantee zero transformer saturation without compromising transient response.

  • Supports self-starting secondary-side control
  • Direct Flux Limit™ guarantees no saturation
  • Active clamp drive with delay adjustment
  • On-Chip bridge rectifier eliminates need for separate gate drive bias supply
  • Wide input supply range: 8 V and up (limited only by external components)
  • Linear regulator controller for fast start-up
  • High speed gate drivers
  • Precision UVLO with adjustable hysteresis
  • Overcurrent protection
  • Overtemperature protection
  • Adjustable start-up frequency and soft-start
  • Tiny 16-lead MSOP package


  • Isolated battery chargers
  • Isolated 48 V telecommunication systems
  • Servers and embedded computing
  • Automotive and heavy equipment