The LT3573 is a monolithic switching regulator specifically designed for the isolated flyback topology. No third winding or opto-isolator is required for regulation. The part senses the isolated output voltage directly from the primary-side flyback waveform. A 1.25A, 60V NPN power switch is integrated along with all control logic into a 16 lead MSOP package. The LT3573 operates with input supply voltages from 3V to 40V, and can deliver output power up to 7W with no external power devices. The LT3573 utilizes boundary mode operation to provide a small magnetic solution with improved load regulation.