Printed Circuit Board Embedded Inductors for Very High Frequency Switch-Mode Power Supplies

The paper describes the design of three different structures for printed circuit board embedded inductors. Direct comparison of spirals, solenoids and toroids are made with regard to inductance, dc and ac resistance, electromagnetic field and design flexibility. First the equations for the impedances are given and an example of the achievable impedances are given. Prototypes are then made and measured. The differences between the three structures and the accuracy of the formulas are evaluated. Finite element simulations are used to investigate the magnetic field around the structure, in order to take possible electromagnetic interference problems into account, when the structures are compared. The simulated fields are verified through near field measurements performed on the prototypes. Finally design flexibility are considered, both regarding scalability and design of the individual inductors and implementation in a complete design. At the end of the paper a summary of pros and cons of the three structures are listed.