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Inductor Geometries with Significantly Reduced Height

Fig. 1. A commercial inductor with 2.2 µH inductance and 4 mm packaging height.
The average energy density is low in commercial inductors since the flux density distribution throughout the volume is not constant. The core volume is filled by a large space with little energy, which suggests very low flux density and a magnetic material that is not fully utilized.

The constant-flux inductor introduced herein has the windings configured to distribute the magnetic flux uniformly throughout the magnetic volume to obtain a higher energy density and a smaller package volume. A relatively constant flux distribution is advantageous not only from the density standpoint, but also from the thermal standpoint via the reduction of hot spots, and from the reliability standpoint via the suppression of flux crowding. Therefore, the volume of the inductor can be reduced significantly, whereas the inductance and dc resistance remains the same.

Following the design procedure introduced in the paper, an example inductor was designed and fabricated using the milling method. The measurement results for the designed inductor prototype demonstrate that the constant-flux concept reduced the inductor volume by more than 60%. A com-mercial inductor with slightly less inductance and 25% less dc resistance would be three times as large as the constant-flux inductor. If the constant-flux inductor were designed for dc resistance of 6 m%u2126, it would be 2.5 times smaller than the commercial product.

Fig. 2. Axisymmetric view of the commercial inductor showing unevenly distributed flux density inside the core.
Fig. 3. 3D structure of a constant-flux inductor; total thickness is reduced by half to 2 mm, whereas inductance is kept at the same 2.2 µH.
Fig. 4. Relatively uniform distribution of flux density in the core of the constant-flux inductor.

Fig. 5. Prototype of milled core and milled copper winding.
Fig. 6.
Fig. 7. Dimension comparison between constant-flux inductor and a commercial inductor from Maglayers MMD-12CE-1R5M-V1.

Figure 8. Dimension comparison between constant-flux inductor and a commercial inductor from Maglayers MMD-12CE-1R5M-V1.
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