The trend toward high power density, high operating frequency, and low profile in power converters has exposed a number of limitations in the use of conventional wirewound magnetic component structures. Transformers made of the planar principle eliminate virtually some shortcomings of old‐fashioned wire wound types, and thus planar magnetics, has in recent years, become increasingly popular in high frequency power converters. First, an overview of basic planar magnetics technology used in general dc‐dc converters is presented. PCB or flexible PCB windings as a main construction together with planar cores yield a number of advantages over the conventional magnetics. Meanwhile, some limitations of planar magnetics are also introduced. Secondly, fundamental characteristics of planar magnetics are investigated through winding conduction loss, core loss, leakage inductance and interwinding capacitance. Accordingly, a clear cognition for the intrinsic properties of planar magnetics has been given. Trade‐offs is unavoidable in the magnetics design, and thus an analysis of tradeoffs is necessary for an optimum design in a high quality dc‐dc converter. In addition, an improved interwinding arrangement is proposed to further reduce winding conduction loss, leakage inductance, and even interwinding capacitance. With the development of multilayer PCB, the integrated magnetics with planar structure can be easily implemented. Hence, planar integrated magnetics technique as a major part of this thesis is investigated. The history and the evolution of integrated magnetics in power converters have been described. It is recalled, that integrated magnetics allows less number of parts, lower volume and cost of the converter, and higher efficiency. Many innovative ideas are proposed and experimentally verified. • E‐I‐E core structure with integrated transformers and inductors is applied into the two recent developed dc‐dc topologies. • A new method to integrate the current balancing transformer with common input inductor for the primary‐parallel dc‐dc converter is proposed. • A low profile and low cost integrated inductors with stacked I‐cores for multiplephase interleaved dc‐dc converters is proposed. • Ultra‐thin coupled inductors design for flexible PV module is introduced. A 1.5‐ mm thickness integrated coupled inductor with sandwich core structure is under investigation. • A “four quadrants integrated transformer” utilizing orthogonal flux to decouple the two primary windings has been applied to a dual‐input isolated boost dc‐dc converter.