Isolated Flyback Converter Without an Opto-Coupler

The LT3574 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 0.65A, 60V NPN power switch is integrated along with all control logic into a 16-lead MSOP package.

The LT3574 operates with input supply voltages from 3V to 40V, and can deliver output power up to 3W with no external power switch. The LT3574 utilizes boundary mode operation to provide a small magnetic solution with improved load regulation.

The output voltage is easily set with two external resistors and the transformer turns ratio. Off-the-shelf transformers are available for many applications.

Applications

* Industrial, Automotive and Medical Isolated Power Supplies

* 3V to 40V Input Voltage Range

* 0.65A, 60V Integrated NPN Power Switch

* Boundary Mode Operation

* No Transformer Third Winding or Opto-Isolator Required for Regulation

* Improved Primary-Side Winding Feedback Load Regulation

* VOUT Set with Two External Resistors

* BIAS Pin for Internal Bias Supply and Power NPN Driver

* Programmable Soft-Start

* Programmable Power Switch Current Limit

* 16-Lead MSOP Package