Power Inductors for Power Supplies: Spec Guide
A power inductor is specified by inductance at rated current, saturation current, DCR, core loss at the switching frequency, temperature rise and footprint. Material choice follows current and frequency: FeNi powder cores (Bs ≥1.5 T) for high-current stages, ferrite for low-power high-frequency stages, Sendust/MPP for filters. Give the manufacturer the full operating profile — not just the nominal inductance — to get a part that survives worst case.
Power inductors look simple — a core and a winding — but the difference between a reliable part and a field failure is in the specification. This guide lists the parameters that matter and the RFQ data a manufacturer needs to quote correctly.
1. The specification parameters
| Parameter | Why it matters |
|---|---|
| Inductance (µH) | Sets ripple and current-mode stability; check at rated current, not at zero |
| Saturation current (Isat) | Inductance must hold at peak current with margin |
| DCR (mΩ) | Sets copper loss and efficiency; drops with size, rises with turns |
| Core loss @ f, ΔB | The frequency-dependent term that decides temperature rise |
| Temperature rise | Hot-spot limit vs ambient and insulation class |
| Size / height | Board density and thermal path constraints |
2. Material by operating point
High-current stages (AI GPU VRM, server POL, EV chargers) need a core with high saturation: FeNi powder with Bs ≥1.5 T keeps the part small and inductance stable under bias. Low-power high-frequency stages favor MnZn ferrite for low loss and cost. Filters and PFC use Sendust or MPP; MHz power delivery uses molded metal inductors at high switching frequencies.
3. Core loss is the frequency-dependent trap
Datasheet loss values are quoted at specific frequencies and flux swings. The real design operates at your PWM frequency with a triangular ripple — ask for loss data at your exact frequency and ripple ratio, and derate for the hottest ambient.
4. RFQ checklist for a power inductor manufacturer
- Inductance tolerance and the current at which it is measured
- Rated DC current and peak transient current
- Switching frequency and ripple current waveform
- Ambient temperature range and allowed temperature rise
- Footprint, height and termination (SMD/through-hole) constraints
- Target efficiency or DCR limit, and any qualification standard (e.g., AEC-Q200)
With a complete profile, a manufacturer can size the core and winding correctly the first time. The High Flux Cores Guide shows the FeNi powder core specifications, and the Core Selection Guide walks through the material decision.
YUTE Magnetics manufactures custom power inductors with IATF 16949 quality management, plus AEC-Q200 stress testing per part number on request. Send the checklist above through the engineering RFQ and get a technical evaluation on the next business day.
Frequently Asked Questions
What parameters define a power inductor?
Inductance at rated current, saturation current, direct-current resistance, core loss at the switching frequency, temperature rise and physical footprint. The inductance at full bias is the value that matters most, not the nominal figure measured at zero current.
Why is inductance specified at current rather than at zero current?
Because the inductor operates under load. A core’s permeability falls as bias increases, so the inductance that controls ripple and loop behaviour at full load can be substantially lower than the catalogue value.
How does switching frequency affect inductor selection?
Higher frequency reduces the inductance needed for a given ripple current, allowing a smaller component, but it raises core loss. The design point is a balance between size, ripple, loss and the output capacitance required.
What is the difference between saturation current and rated current?
Saturation current is the point where inductance falls sharply and the core can no longer store the required energy. Rated current is the level at which the part meets its thermal limits. Both must be checked, because a part can overheat below saturation or saturate below its thermal rating.
What should an RFQ to an inductor manufacturer include?
Switching frequency, inductance at rated current, ripple current, continuous and peak current, acceptable DCR, size and height limits, thermal conditions, and any qualification requirements. That is enough for engineering to propose a design rather than a catalogue number.
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