A High-Voltage Compatible BCD SoC-ASIC Performing Valley-Switching Control of AC-DC Power Converters Based on PFC and Flyback Cells

This paper presents an ASIC controller suitable for double-stage AC-DC power converters which employ Power Factor Correction (PFC) and Flyback topologies. The PFC cell is used as preregulator to comply with line-current harmonic standards, while the flyback converter operates in quasi-resonant/discontinuous-conduction-mode (QR/DCM) to deliver to the load a maximum output power of 120 W. The control functions of the PFC and of the flyback converters are combined in an unique SoC-ASIC solution to reduce system complexity. The ASIC implements a valley-switching control of both the PFC and the flyback cells to achieve quasi-resonant (QR) operation. The concept of "valley skipping" is also recalled by the proposed ASIC to determine the operating point in the power-frequency characteristic of the power converter. Depending on the output power requirement, the ASIC drives the flyback stage into three different states, resulting from the combination of the QR and valley-skipping modes. The PFC stage is also driven in the QR mode with valley skipping to provide the DC-DC stage with a fixed input voltage of 400 V. To evaluate the performances of the presented ASIC device, a demoboard of a 120 W PFC-flyback system has been realized and tested