Quick AnswerSMPS magnetics run from ~50 kHz to 1 MHz+, where MnZn ferrite offers the best balance of low core loss, high permeability and cost. Choose the material grade by switching frequency, the shape by power and height (E/EI for general transformers, PQ for high-power LLC, RM for compact shielded designs), and check the operating flux stays well below 0.3–0.5 T saturation. For high-current output inductors, a FeNi powder core with Bs ≥1.5 T often beats ferrite.
Almost every switch-mode power supply (SMPS) contains magnetic components: a transformer for isolation and voltage scaling, an inductor for energy storage, and often an EMI choke. This guide covers how to select the ferrite cores for those parts, and when a different material is the better engineering call.
SMPS cores must handle a defined frequency, a power level, a peak current and a thermal budget. The two dominant constraints are core loss at the switching frequency and saturation at the peak current. Ferrite wins the loss battle below ~1 MHz; powder cores win the saturation battle at high current.
MnZn ferrite combines high permeability (1000–15000) with very low core loss in the 100 kHz–1 MHz range, which is exactly the SMPS operating window. NiZn ferrite (µ 10–500) takes over above ~1 MHz for EMI and RF roles, where its high resistivity limits eddy-current loss. Above the ferrite frequency window, metal-powder cores (FeNi, Sendust, MPP) become competitive for inductors.
| Shape | Typical SMPS role |
|---|---|
| E / EI | General-purpose transformers and inductors up to a few hundred watts |
| ETD / EER | Mid-to-high power transformers with a large round window |
| PQ | High-power LLC / DC-DC with low stray flux |
| RM / EP | Compact, shielded designs for telecom and board power |
| EFD | Low-profile transformers for height-constrained boards |
| Toroid | EMI chokes and filter inductors with the lowest stray field |
A transformer is sized mainly by core loss and turns ratio; an inductor is sized by stored energy (½·L·I²) and saturation. Ferrite transformer cores are usually gapped lightly or not at all, while inductor cores need an air gap — discrete for ferrite, distributed for powder cores — to store energy and keep inductance stable under DC bias.
When the output inductor carries high DC current, compare ferrite against a FeNi powder core with Bs ≥1.5 T — the smaller core and stable bias behavior often lower the total cost of the converter. See the High Flux Cores Guide and the Core Selection Guide for the full comparison.
YUTE Magnetics supplies custom ferrite cores and FeNi powder-core inductors for SMPS with IATF 16949 and AEC-Q200 qualification. Share your frequency, power and height targets for a free engineering evaluation.
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