Design of a Wide-Input-Voltage PCB-Embedded Transformer Based Active-Clamp Flyback Converter Considering Permeability Degradation

Today, high power density, high efficiency, and wide-input-voltage operation are becoming increasingly important in power electronics for automotive applications. Active-clamp flyback (ACF) converters, showing a good tradeoff between simplicity and efficiency, are widely used in this industry. With benefits of small profile, low cost, and high reliability in mass production, the printed-circuit-board (PCB) embedding technique of magnetic components has attracted strong interest; however, magnetic cores can lose significant permeability due to the mechanical stress during this fabrication process; as a result, transformer properties, such as leakage inductance, coupling coefficient, and effective turns ratio change, affecting the input-voltage operating range as well as the working temperature. In this article, a detailed analysis of the design constraints of automotive ACF converters with a wide-input-voltage requirement is presented, focusing on the impact that the embedding process has on the transformer properties and the converter operation. Specifically, experiments are performed to investigate the permeability degradation effect, based on which correction factors are derived and added to the proposed design optimization process. A 10-W dual-output high power density (53.2 W/in
³
) integrated ACF converter prototype based on GaN devices operating at 1 MHz is built and demonstrated for this purpose.