Overmolded metal composite inductor targets automotive power
Kemet has launched a metal composite inductor for automotive power designs.
The MPXV metal composite inductor is AEC-Q200 qualified for use in the automotive sector and is aimed at systems running at higher frequencies and temperatures. Using silicon carbide or gallium nitride switches allows the higher frequency operation with smaller inductors but have to be reliable at higher temperatures and more resistant to electromagnetic interference.
“The unique construction of the metal composite means you have the metal material moulded over the core so the metal composite has a natural EMI shielding effect – these have much better noise characteristics compared to a ferrite inductor,” said Dr Philip Lessner, Senior Vice President and Chief Technology Officer at Kemet. “A composite means we start with an iron alloy of 10 micron particles and coat with a thin insulating layer over the coil – there’s also some binder phenolic materials.”
Unlike a ferrite inductor core which is sintered ceramic, this is an alloy of iron with other doping elements, silicon, aluminium, that give the higher permeability. Some of the dopants are proprietary, but for the most part these aren’t rare earth elements, he says. The particle size and shape is another factor and then the packing density around the winding is another key process.
“There will be some leakage of EMI but we believe in most circuits the basic construction gives you all the protection you need even in the automotive environments at the board level, primarily in the ECU, DC-DC converter and surface mount point of load on control boards under the hood. The maximum temperature is 155°C and we are working for a 180°C rated, that’s on the roadmap,” he added.
“That will require material changes in term of the binder to keep all the parts of the component from degrading, and we are making lab samples of those at the moment at the group in Japan, replace the phenolic binders with something that resists the higher temperatures. We make other components such as tantalum capacitors up to 200 or 230 so we know how to get there,” he said
The next step is to use a material called Nanomet that is in development has a different crystalline, partially amorphous structure. This gives a higher permeability than standard materials to allow less turns of the copper coil and minimise the DC resistance and other parasitics. This could reduce the number of windings in the inductor from 12 to 8.
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