Choosing the right powder core is one of the most important decisions in power inductor and transformer design. Among the widely used alloy powder cores, three materials dominate: Sendust (iron-silicon-aluminium), iron powder, and MPP (molybdenum permalloy). Each offers a different trade-off between permeability, core loss, DC bias stability, and cost. This guide compares the three materials side by side and explains how to select the best core for your application.
Sendust Core (Kool Mµ / Iron-Silicon-Aluminium)
Sendust cores are made from an iron, silicon, and aluminium alloy, typically with 85% Fe, 9.6% Si, and 5.4% Al. They offer a stable permeability across temperature (the material has a near-zero temperature coefficient around 60-100 °C) and relatively low core loss at medium frequencies. Distributed air gaps give Sendust excellent DC bias stability, making it a preferred choice for PFC inductors, buck-boost inductors, and EMI filter chokes.
Compared with iron powder, Sendust achieves higher permeability (typically 26-125 µ) with lower core loss and tighter tolerance, at a moderate cost increase. Its main limitation is saturation flux density (around 1.0 T) and higher loss at very high frequencies than MPP.
Iron Powder Core
Iron powder cores are made from pure iron particles coated with an insulating binder and pressed into shape. They offer the highest saturation flux density among powder cores (around 1.4-1.5 T), excellent DC bias stability, and the lowest cost per unit of stored energy. These attributes make iron powder cores the default choice for boost PFC inductors, inverter input chokes, and applications where large DC currents must be handled.
The trade-offs are higher core loss (especially above 100 kHz), wider permeability tolerance (typically ±15%), and a significant permeability drop under DC bias. For low-frequency, high-current applications such as 50/60 Hz line chokes and power factor correction, iron powder remains extremely cost-effective.
MPP Core (Molybdenum Permalloy Powder)
MPP cores are made from a nickel-iron-molybdenum alloy (about 81% Ni, 17% Fe, 2% Mo). They provide the lowest core loss of the three powder cores, the most stable permeability with minimal change under DC bias and temperature, and the tightest tolerance (±5% typical). MPP is therefore the material of choice for high-frequency, precision applications such as flyback output inductors, telecom DC-DC converters, and filter chokes where efficiency matters most.
The main drawbacks of MPP are its high cost (roughly 3-5 times iron powder) and lower saturation flux density (around 0.7-0.8 T). For designs where core loss and stability dominate and budget allows, MPP wins.
Sendust vs Iron Powder vs MPP: Comparison Table
| Parameter | Iron Powder | Sendust (Kool Mµ) | MPP |
|---|---|---|---|
| Initial permeability | 10-100 (typically 14-75) | 26-125 | 14-550 (typically 14-125) |
| Saturation flux density | ~1.4-1.5 T (highest) | ~1.0-1.05 T | ~0.7-0.8 T |
| Core loss | Highest | Medium | Lowest |
| DC bias stability | Good (but permeability drops fastest) | Excellent | Excellent (best stability) |
| Permeability tolerance | ±15% | ±10% | ±5% |
| Temperature stability | Good | Near-zero TC (best) | Very good |
| Relative cost | Lowest | Medium | Highest (3-5x iron powder) |
| Typical applications | PFC inductors, line chokes, high-current filters | PFC, buck/boost, EMI chokes, solar inverters | Flyback outputs, DC-DC converters, precision filters |
How to Select the Right Powder Core Material
1. Frequency and switching topology. Below ~50 kHz and for very high currents, iron powder offers the best cost-performance. For 50-200 kHz designs where core loss matters, Sendust is usually the sweet spot. Above 200 kHz or for efficiency-critical designs, MPP provides the lowest loss.
2. DC bias requirement. If the inductor carries large DC current with a small ripple, choose a material with high saturation flux and distributed gap: iron powder or Sendust. If the permeability must stay stable under bias, MPP is superior.
3. Tolerance and temperature stability. For precision circuits with tight inductance tolerance, MPP (±5%) beats iron powder (±15%). Sendust offers the best temperature coefficient near the operating window.
4. Cost target. When unit cost dominates, iron powder wins. When efficiency and size drive the design, the higher cost of Sendust or MPP is usually recovered by smaller cores and lower cooling requirements.
Sirui Alloy Powder Core Solutions
Shaanxi SiRui Technology Co., Ltd supplies Sendust cores, iron powder cores, MPP cores, and high-flux cores, available as bare cores, wound inductors, or complete custom magnetic assemblies. Our engineering team helps you select the right material, turns count, and core size for your PFC, inverter, DC-DC, and EMI applications. All products are ISO 9001:2015 certified and RoHS / REACH compliant.
For a deeper comparison, read our Alloy Powder Core: Sendust, MPP, High Flux & Kool Mu Guide, Transformer Core Materials: Ferrite, Iron Powder, Sendust, MPP & Nanocrystalline, and Nanocrystalline Core: Properties, Benefits & Selection Guide. For samples or a design review, contact sales@sirui-tech.com.
FAQ
Is Sendust better than iron powder?
It depends on the application. Sendust offers lower core loss and tighter tolerance with better DC bias stability, while iron powder offers higher saturation flux density at lower cost. For PFC and medium-frequency designs, Sendust is usually the better engineering choice; for very high currents at low cost, iron powder wins.
Why is MPP so much more expensive than iron powder?
MPP uses a high-nickel alloy with more complex processing and tighter material control, which delivers the lowest core loss and the most stable permeability. The cost premium is justified when efficiency, precision, or thermal performance is critical.
Can Sendust cores replace MPP cores in a design?
Sometimes, but not always. Sendust has higher core loss and looser tolerance than MPP, so efficiency-critical or precision designs may need more turns, a larger core, or a redesign. Evaluate core loss at your operating flux and frequency before substituting.