Improving light load efficiency of high frequency DC/DC converters with planar nonlinear inductors

Light load efficiency of high frequency DC/DC converters used in portable electronic devices is very important for extending lifetime of batteries. This paper proposes to use large-range gradually changed nonlinear inductors with adaptive on time control to improve the light load efficiency not only in DCM, but also in CCM. Loss reduction is demonstrated by calculating loss of a conventional converter and a converter with the proposed method. Multi-permeability magnetic cores based on LTCC technology are advanced to realize the nonlinear inductors. An analytic model is set up to show the design of inductor. A two permeability inductor prototype is fabricated. Its inductance is 91nH at full load, 53nH at no load.