Alloy powder cores – Sendust (Kool Mu), MPP, High Flux, and Iron-Silicon – combine soft saturation, low core loss, and high energy storage, making them the preferred cores for high-current power inductors, DC-DC converters, and PFC circuits. This guide explains what alloy powder cores are, how they compare, and how to select one for your OEM or ODM design.
What Is an Alloy Powder Core?
An alloy powder core is a magnetic core made by pressing finely divided soft magnetic alloy powder – iron-silicon-aluminum, nickel-iron-molybdenum, iron-nickel, or iron-silicon – with a non-magnetic binder into a toroidal or E shape. The distributed air gap created by the insulating binder gives the core a soft saturation curve, low permeability (typically 14 to 125), and low core loss at high frequency. Unlike gapped ferrite, the gap is distributed evenly, which minimizes winding loss from fringing flux and keeps inductance stable under DC bias.
Types of Alloy Powder Cores
Sendust / Kool Mu (Fe-Si-Al): The most popular alloy powder core – low core loss, low cost, and low audible noise. Permeability typically 26-125. Excellent for output inductors and PFC chokes.
MPP (Ni-Fe-Mo): Molybdenum permalloy powder – the lowest core loss of the powder cores and very stable with temperature and DC bias. Permeability 14-550. Used in high-performance filters and audio-grade inductors.
High Flux (Fe-Ni): High saturation flux density (up to 1.5 T) with moderate loss – ideal for high-current, high-temperature applications where saturation margin matters.
Iron-Silicon (Fe-Si): A lower-cost option with high saturation and moderate loss – suited to large current chokes and differential-mode inductors where size and cost dominate.
Alloy Powder Core vs Ferrite vs Iron Powder
Compared with ferrite, alloy powder cores store far more energy (higher saturation flux), handle DC bias with a gradual, soft drop instead of a cliff, and are more stable over temperature – at the cost of lower permeability and slightly higher loss in some grades. Compared with plain iron powder cores, alloy powder cores offer lower core loss and better DC-bias stability, though they are more expensive. For high-frequency, high-current power conversion, alloy powder cores are usually the best balance of size, loss, and cost.
Key Specifications of Alloy Powder Cores
Permeability: 14-550 depending on the material and grade; higher permeability gives more inductance per turn but less DC-bias tolerance.
Saturation flux density: 0.8-1.5 T, versus 0.35-0.5 T for ferrite – the reason powder cores handle high current.
Core loss: Expressed in mW/cm3 at a frequency and flux density; MPP has the lowest loss, iron-silicon the highest of the alloy family.
DC bias (permeability roll-off): The inductance drop under DC current; softer curves in alloy cores mean more usable inductance at full load.
Temperature stability: Low permeability drift over -40 to +125 C, especially in MPP and Sendust.
Shape and size: Toroidal cores dominate; E and PQ shapes for specific winding styles.
How to Select an Alloy Powder Core
Start from the worst-case DC bias and ripple: calculate the required inductance at full load, then choose a material – Sendust for cost-sensitive output inductors, MPP for lowest loss and best stability, High Flux when saturation margin is critical, Iron-Silicon for large current and low cost. Select the core size and permeability that keep the inductance above your minimum at peak current and the core loss within your thermal budget. Verify the temperature rise at your switching frequency and ripple current. Shaanxi SiRui Technology Co., Ltd manufactures alloy powder cores and wound inductors – Sendust, MPP, High Flux, and Iron-Silicon – under ISO 9001:2015 quality management with RoHS and REACH compliant materials.
Applications of Alloy Powder Cores
DC-DC converters and buck/boost inductors, PFC chokes, output filter inductors, inverter inductors, LED drivers, EV chargers and onboard converters, server and telecom power supplies, welding equipment, and renewable energy inverters.
FAQ
What is the difference between Sendust and Kool Mu?
They are the same material – Sendust (iron-silicon-aluminum) sold under the trademark Kool Mu. It is the most widely used alloy powder core for cost and performance balance.
Why use a distributed gap instead of a discrete gap?
The distributed gap reduces fringing flux around a discrete air gap, which cuts winding eddy-current loss and keeps the inductance curve smoother under DC bias.
Which alloy powder core has the lowest loss?
MPP (molybdenum permalloy powder) has the lowest core loss and best temperature/DC stability, but it is the most expensive – choose it for high-performance filters and precision inductors.
Do you supply custom alloy powder cores?
Yes. Shaanxi SiRui Technology Co., Ltd supplies Sendust, MPP, High Flux, and Iron-Silicon cores with custom permeability, shapes, and finished wound inductors, from samples to volume production.
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