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Isolated Power Factor Corrected Offline Regulator Needs No Opto-Isolator


Linear Technology has announced 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 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 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 critical conduction 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 and LT3798I versions operate from -40°C to 125°C. The LT3798H is tested and guaranteed to operate from a -40°C to 150°C operating junction temperature. 1,000-piece pricing starts at $2.25 each. All are available from stock.

Summary of Features of the LT3798:

·                Active PFC Eliminates an Extra Power Stage

·                VIN & VOUT Limited Only by External Components, VIN >400VAC Possible

·                No Opto-Coupler Required

·                Better than ±5% Overall Regulation

·                High Efficiency

·                Low Harmonic Content

·                Low Component Count Results in Small Solution Size

·                Thermally Enhanced 16-Lead MSOP Package      



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