Natural convection cooled low-profile power supplies are getting popular due to better form factor and fanless operation such as in entertainment power supplies. In response to increasing power requirements within the same factor, this study explores the design of an ultra-compact totem pole (TP) power factor correction (PFC) converter constrained to a height of 12 mm, delivering 3.7 kW of power. The requirement to incorporate a low-profile EMI filter and employ planar inductors with a restricted number of turns mandates an elevation of the input current ripple frequency into the MHz range. Achieving this involves elevating the input ripple frequency through a multi-level and multi-phase approach, while still maintaining a reasonable switching frequency for the FETs. Various multi-level and multi-leg topologies, including 2-phase 7-level, 3-phase 5-level, and 4-phase 4-level configurations, undergo optimization with a focus on power loss, volume, and cost considerations. After a comprehensive evaluation, the 2-phase 7-level topology is identified as the optimal solution. This configuration leverages 100V GaN FETs and integrates two planar inductors with dimensions of 22/16/10 mm.
