Ferrite Cores for DC-DC Converters
DC-DC converters use ferrite for transformers and for low-to-medium current inductors, sized by frequency and stored energy. Below ~1 MHz, MnZn ferrite gives the lowest loss; above it, NiZn or metal-powder cores take over. When the inductor carries tens of amps, a FeNi powder core (Bs ≥1.5 T) keeps the design smaller and more stable than gapped ferrite.
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.
Frequently Asked Questions
Where are ferrite cores used in DC-DC converters?
They appear in the transformer of isolated topologies and in low-to-medium current inductors. Below roughly 1 MHz manganese-zinc ferrite usually gives the lowest loss, while above it NiZn ferrite or metal powder cores take over.
How do I choose a core for a DC-DC inductor?
Size the core by the energy it must store and the current it must carry, then check loss at the switching frequency. If the inductor carries tens of amps continuously, a powder core is often the more practical choice than ferrite.
Why do high-current DC-DC stages use powder cores instead of ferrite?
Ferrite saturates around 0.3–0.5 T, so a high-current inductor would need a large ungapped core or a gapped one that radiates fringing flux. Powder cores have a distributed air gap and higher saturation, allowing stable inductance in a smaller part.
Is ferrite suitable for the transformer in a DC-DC converter?
Yes. Isolated topologies use ferrite transformers because the function is energy transfer with symmetrical flux, where high permeability and low core loss matter more than stored energy. Whether the core is gapped depends on the topology.
What is the frequency boundary between ferrite and other materials?
As a working boundary, MnZn ferrite below about 1 MHz, with NiZn ferrite or metal-based cores above it. Confirm against your specific grade, flux swing and thermal conditions rather than treating the boundary as fixed.
Pages associées
Besoin d’aide pour choisir ?
Envoyez le point de fonctionnement et l’enveloppe mécanique — nous proposons noyau et bobinage.