Isolated power factor corrected offline regulator needs no opto

October 11, 2011 // By Christoph Hammerschmidt
Linear Technology announces the LT3798, an isolated flyback controller with single stage active power factor correction (PFC). A power factor of greater than 0.97% is accomplished by actively modulating the input current eliminating the need for an extra switching power stage and associated components. In addition, no opto-isolator or signal transformer is required for feedback since the output voltage is sensed from the primary-side flyback signal.

A LT3798-based design easily complies with the IEC6100-3-2 Harmonic Current Emissions specification. Efficiencies greater than 86% can be achieved with output power levels up to 100W. The device's input voltage range is dependent on the choice of external components and it can operate over a 90VAC to 277VAC range, and can easily be scaled higher or lower. Furthermore, the LT3798 can be designed into high input voltage DC applications, making it well suited for industrial, EV/EHV automotive, mining and medical applications. The LT3798 utilizes mode operation enabling the use of a smaller transformer compared to continuous conduction mode designs, further reducing the solution size.

The LT3798 is available in a thermally enhanced 16-pin MSOP package. The LT3798E version operates from -40°C to 125°C, with 1000-piece price starting at $X.XX each. The LT3798I industrial grade version operates from -40°C to 125°C, with 1,000-piece pricing starting at $X.XX each. The LT3798H industrial grade version operates from -40°C to 150°C, with 1,000-piece pricing starting at $X.XX each. All are available from stock. For more information, visit