Design and Implementation of a Stepped Air-Gap Inductor for Buck Converters

This paper proposes the design and implementation of an inductor with a stepped air-gap for a buck converter with improved feedback control. Typically, a power converter needs to maintain stable operation during any load transient. When designing the compensator for a converter according to the traditional method for continuous conduction mode (CCM), the same compensator is employed from light load to full load, which leads to poor response at some operating points, especially at light load. To achieve a better system response, a stepped air-gap inductor is proposed to increase the inductance at light load, which is analyzed and compared with a traditional inductor. The proposed stepped air-gap inductor reduces the influence of the magnetic flux leakage on the winding. The effect of having two different inductance values on the controller design is discussed, and the conditions for discontinuous conduction mode (DCM) at light load with the stepped air-gap inductor are outlined. A 48-V to 12-V buck converter rated for 60 W is built and tested to verify the proposed stepped air-gap inductor. With the proposed stepped air-gap inductor, experimental results show that undershoot and overshoot were improved 50% and settling time was decreased to 20% and 30% during light-to-full load transients, compared to the traditional inductor. Hence, the proposed stepped air-gap inductor can effectively improve system response.