Linear Technology Corporation (Milpitas, CA) offers 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. 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 complies with the IEC61000-3-2 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 90 VAC to 277 VAC range, and can easily be scaled higher or lower. 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 critical conduction mode operation, enabling the use of a smaller transformer compared to continuous conduction mode designs, further reducing the solution size.