Improving Light and Intermediate Load Efficiencies of Buck Converters With Planar Nonlinear Inductors and Variable On Time Control

It has been addressed that light and intermediate load efficiencies of high-frequency buck converters in portable electronic devices are very important for extending lifetime of batteries. This paper proposes to utilize wide range, gradually changeable nonlinear inductors with variable on time control to improve light and intermediate load efficiencies. Integrated multipermeability magnetic cores are advanced to realize the nonlinear inductors. And based on the nonlinear inductors, variable on-time control scheme is proposed to reduce the frequency-dependent loss. The theoretical loss reduction is demonstrated by comparing loss of a converter employing conventional constant on-time control scheme and employing the proposed control scheme. A two-permeability nonlinear inductor prototype is fabricated. Its inductance could vary from 0.13 μH at full load to 0.66 μH at no load. The nonlinear inductor is employed in a 12 V input, 1.6 V output buck converter to evaluate its performance. With the purpose of comparison, other two commercial chip inductors are also tested in the converter. The results show the nonlinear inductor with variable on time control could effectively improve efficiencies of light and intermediate load conditions as theoretical analysis does.