A high efficient integrated planar transformer for primary-parallel isolated boost converters

A simple, easy to manufacture and high efficient integrated planar transformer design approach for primary parallel isolated boost converters is presented. Utilizing the same phase flux flow, transformers are integrated, reducing the total ferrite volume and core loss for the same peak flux density. Number of turns is minimized for easy manufacturing by cascade placement of planar cores increasing the effective cross-sectional area. AC losses in the windings as well as the leakage inductance of the transformer are kept low by extensive interleaving of the primary and secondary turns. The idea of transformer integration is further extended to multiple primary power stages using modular geometry of the planar core, further reducing the core loss and allowing a higher power density. To verify the validity of the design approach, a 4-kW prototype converter with two primary power stages is implemented for a fuel cell fed battery charger application with 50-110 V input and 65-105 V output. Input inductors are coupled for current sharing, eliminating the use of current sharing transformers. An efficiency of 94% is achieved during nominal operating condition where the input is 70-V and the output is 84-V.