Soft Ferrite Material by Powder Injection Molding Process for Power Electronics

The current trend toward the rise in the operating frequency in power electronics allows a dramatic miniaturization of power converters but requires reliable passive components. Spinel ferrites could be appropriate magnetic materials for transformers and inductors, within the range 0.5-5 MHz, providing that power core loss, enhanced by the frequency rise, remains low. This work investigates the opportunity to shape magnetic cores by powder injection molding (PIM), while keeping a low power dissipation in components. It paves the way for designing new core geometries incorporating additional functions such as thermal management. A commercial Mn-Zn granulated ferrite powder was used in this study. The densification state of the ferrite feedstock (wax binder system) was investigated after injection and debinding in samples (ring-shaped cores) sintered with different temperatures: 1140 °C/4 h, 1145 °C/4 h, 1150 °C/4 h, 1155 °C/4 h, and 1160 °C/4 h. A Low carbon content (<; 100 ppm) was confirmed by Instrumental Gas Analysis (IGA) and X-ray diffraction (XRD) analysis revealed that the spinel phase formation was fully achieved after sintering. Core losses data (from 100 to 900 kHz at 50 mT) at different temperature (from room to 110 °C) were analyzed by separating the contributions of the hysteresis (P
_h
~ A.f), eddy current (P
_e
~ B.f
²
), and residual (P
_r
~ C.
^fn,
with n > 2) losses. The evolution of the total power losses (P
_t
) for toroids made by PIM was compared to the ones of samples fabricated by uniaxial compression (UC). It appears that the losses by hysteresis were always lower for PIM than for UC, whereas it was the opposite for eddy current and residual losses. Microstructural analyses showed that open porosity plays an important role in this behavior.