Printed circuit board integrated toroidal radio frequency inductors

Modern power semiconductors allow for switching frequencies of power converters in the very high frequency (VHF) band (30 MHz to 300 MHz). The major advantage of this frequency increase is a remarkable reduction of the size of power converters due to smaller passive components. However crucial attention needs to be payed to switching losses, so that the size reduction in electrical components does not get consumed by a major increase in heatsink size. This paper is investigating the major size limiting component in power converters: the inductor. In the VHF range, inductors are typically implemented as solenoids, either in spiral or cylindrical form. Those have the disadvantage of excessive stray fields, which can cause losses and disturbances in adjacent circuitry. Therefore this paper presents the analysis, design and realization of a printed circuit board (PCB) integrated inductor under significant consideration of the losses in the inductor. The analysis results in a general design tool which is verified by a prototype inductor. Its inductance is 50 nH and has a quality of 149 at 100 MHz.