An Embedded Inductor Using Sendust Powder Composite Films for Step-Up DC–DC Converter

An embedded inductor constructed with Sendust powder composite films and embedded circuits is proposed. The composite films consist of mixed Sendust flaked powders and EPDM rubber. An embedded circuit is an etched spiral copper trace with 16 turns and two layers. Copper trace is patterned with a dimension of 0.025 mm thickness, 0.1 mm width, and 0.1 mm pitch. Regarding the performances of the proposed inductor, it was obtained that the simulated inductance and copper resistance are 4.7 uH and 770 mΩ, respectively, while the measured results are 5.0 uH and 720 mQ, respectively. Measurements also show that the proposed inductor has relative high permeability and quality factor in a wide range of frequencies. It was confirmed that inductance of this inductor has a good stability to high frequency. To verify the usefulness of this inductor, the embedded inductor with a flexibility and the dimension of 10 mm × 7 mm × 0.3 mm was applied to a step-up dc-dc converter that is fabricated in the flexible printed circuit. The output power of the fabricated dc-dc converter is 1.8 W (4.5 V/400 mA), and the switching frequency is 1.2 MHz. Finally, the fabricated dc-dc converter was tested and the maximum efficiency of 84% was obtained.