Multipermeability Inductors for Increasing the Inductance and Improving the Efficiency of High-Frequency DC/DC Converters

Distributed air-gap inductors such as iron powder chip inductors and low-temperature cofired ceramic (LTCC) inductors have the advantage of low-fringing effect loss. However, the flux density nonuniformly distributes in the magnetic cores, which results in the magnetic material closer to the conductor becoming saturated while the magnetic material further away from the conductor is still not fully utilized. This paper proposes a multipermeability distributed air-gap inductor structure to increase inductance without the necessity of increasing the inductor volume. The best discrete permeability value is investigated. Based on the best discrete permeability value, inductance as well as the inductance density trends is calculated by varying the number of permeability layers under the condition that thickness for each layer is constant. Also, the inductance variations versus the number of permeability layers are also obtained under the condition that the inductor thickness is constant. A three-permeability inductor and a single-permeability inductor are fabricated to evaluate the proposed method. The measured results show that the three-permeability inductor has a much higher inductance than the single-permeability inductor for the entire load range. Both inductors are tested in a 5-V input, 3-V output dc/dc converter to compare their performances. The results show that the three-permeability inductor can further improve the efficiency of high-frequency dc/dc converters.