Design of multi-permeability distributed air-gap inductors

Distributed air-gap inductors have the advantage of low fringing effect loss. However, the flux density uniformly distributes in the magnetic cores, which results in the magnetic material closer to conductor becoming saturated while the magnetic material far away from the conductor is still not fully utilized. This paper proposes a multi-permeability distributed air-gap inductor structure to increase inductance without the necessity of increasing the inductor volume. The discrete permeability values are investigated. Inductance variations versus number of permeability layers are obtained under the condition that the inductor thickness is constant. To evaluate the proposed method, a three-permeability inductor together with a single permeability inductor is fabricated. The measured results show that the three-permeability inductor has much higher inductance than the single-permeability inductor for the whole load range. Both inductors are tested in a 5V input, 3V output DC/DC converter to compare their performances. The results show the three-permeability inductor could further improve light load efficiency of high frequency DC/DC converters.