Flyback Controller IC Integrates Power Factor Correction

摘要

Linear Technology Corporation's LT3798 is an isolated flyback controller with single stage active power factor correction (PFC). Efficiencies greater than 86% can be achieved with output power levels up to 100W. Depending on the choice of external components, it can operate over a 90VAC to 277VAC input range, and can easily be scaled higher or lower. Furthermore, the LT3798 can be designed into high input voltage DC applications, making it suited for industrial, EV/EHV automotive, mining and medical applications. Fig. 1 shows a typical application for the LT3798. Table 1 lists the key functions of device pins that control LT3798 operation. This IC is a current mode switching controller intended specifically for generating a constant current/constant voltage supply with an isolated flyback topology. To maintain regulation, this topology usually uses output voltage and current feedback from the isolated secondary side of the output transformer to V_(IN). Typically, this requires an opto-isolator. Instead, the LT3798 uses the external MOSFETs peak current derived from a sense resistor to determine the flyback converter's output current, without requiring an opto-coupler.