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.