Ferrite Cores for DC-DC Converters

Buck, boost, flyback and LLC converters all depend on magnetic components, but the demands on the core differ by topology and by how much DC current the inductor must carry. This guide maps ferrite cores to DC-DC converter roles and shows where the material boundary lies.

1. Where ferrite cores appear in a DC-DC converter

• Inductor in buck / boost / buck-boost stages — energy storage and filtering
• Transformer in flyback, forward, push-pull and LLC topologies — isolation and voltage scaling
• EMI chokes on the input and output — noise suppression

2. Inductor core selection

The inductor stores ½·L·I² and must not saturate at the peak current. At low-to-medium current and frequencies up to ~1 MHz, MnZn ferrite with a controlled air gap is the standard, low-cost choice. As current grows, the gap and core grow, and the design crosses over to a distributed-gap powder core — FeNi (Bs ≥1.5 T), Sendust or MPP — which keeps inductance stable under bias with less core material.

3. Transformer core selection

Transformers are loss- and turns-ratio-limited rather than energy-limited. MnZn ferrite in E, ETD, PQ or planar shapes covers flyback and LLC transformers from tens of watts to kilowatts. LLC resonant tanks favor PQ cores for the round window and low stray flux; planar cores suit low-profile, high-frequency designs.

4. Frequency boundary

Below ~1 MHz, MnZn ferrite minimizes loss. From 1 MHz to 100 MHz+, NiZn ferrite or metal-powder cores are needed as eddy-current loss in MnZn climbs. Modern POL converters at MHz frequencies therefore use molded metal inductors rather than ferrite.

5. Practical selection checklist

• Fix topology, frequency, input/output voltage and peak current
• For inductors: compute L, stored energy and peak flux; size for the worst case
• For transformers: size by core loss at the switching frequency and required turns ratio
• Check the bias curve and temperature rise on the first sample

For high-current output stages in EV OBC/DC-DC and solar converters, compare gapped ferrite against FeNi powder cores before finalizing — the High Flux Cores Guide and the Saturation Flux Density note explain the trade-off with data.

YUTE Magnetics supplies custom ferrite cores and FeNi powder-core inductors for DC-DC converters. Send your topology, frequency and current targets for a free engineering evaluation.