Spark Plasma Sintering Co-Sintered Monolithic Transformers for Power Electronics

Power integration is a key issue to reduce the volume and weight of electronic devices in power applications. However, transformers produced using classical planar assembly are limited in design. Spark plasma sintering (SPS) is a relatively new technology to produce multi-material compact systems with higher density using lower sintering temperature. The purpose of this paper is to manufacture cubic-centimeter-sized transformers for the high-frequency application using SPS. The prototype presented in this paper is composed of two spiral copper coils separated by an insulated layer and encapsulated in ferrite powder. The assembly is then co-sintered by SPS. The magnetic material used for the transformers is a nickel-zinc-based ferrite, with copper substitution to allow sintering at low temperatures. The low conductivity of this mixed ferrite ensures operation in the frequency range of 1-20 MHz of our final system. Computed tomography scanning has been used to optimize the design of the co-sintered structures. The effects of the composition of the ferrite and the sintering temperature on the transformation ratio are discussed. It is shown that a ferrite with very low conductivity is required to ensure galvanic insulation, as there is a direct contact between the copper spirals and the magnetic parts.