What Is Sendust (Fe-Si-Al) Core? Benefits for Modern Power Inductors

Sendust (Fe-Si-Al) core material, an iron-silicon-aluminium alloy produced as a powder core with distributed air gaps, is a widely used magnetic core for modern power inductors and choke coils. Combining high saturation flux density, low core loss, stable permeability, and excellent DC bias performance, Sendust offers a balanced, cost-effective solution for many medium-frequency power electronics applications. This post explains Sendust’s composition and powder structure, key magnetic properties, performance in the 10 kHz–100 kHz range, advantages versus ferrite and iron-powder cores, and real-world applications.

What Is Sendust (Fe-Si-Al)?

Sendust is a soft magnetic alloy composed primarily of iron (Fe) with controlled additions of silicon (Si) and aluminium (Al). Typical compositions place silicon and aluminium together in a range that optimises resistivity and magnetic behaviour. Unlike solid laminations or sintered ferrites, Sendust is made using powder metallurgy: compacted, annealed powder particles are bonded to form a core. The powder structure inherently creates distributed microscopic air gaps throughout the material rather than a single microscopic gap. This distributed gap reduces losses from localised saturation and improves DC bias tolerance in inductors and chokes.

Explore our Sendust series for standard and custom options: Sendust series

Powder Core Structure & Distributed Air Gaps — Why It Matters

• Powder construction: Tiny insulated metal particles are pressed and heat treated to produce a mechanically robust core with controlled density. 

• Distributed air gaps: microscopic gaps between particles act as many small gaps distributed across the core volume, giving predictable permeability and preventing abrupt saturation. 

• Benefits: reduced audible noise, improved DC bias handling, and uniform flux distribution compared with a single-gap laminated core.

Key Magnetic Properties of Sendust

• High saturation flux density: Sendust sustains higher magnetic flux before saturating than many ferrites, enabling smaller inductors for a given energy storage requirement. 

• Low core loss (at mid frequencies): well-engineered Sendust grades exhibit low hysteresis and eddy current losses across the medium-frequency band. 

• Stable permeability: distributed gaps produce consistent inductance over temperature and operating conditions, simplifying designs.

• Strong DC bias performance: Sendust maintains inductance under substantial DC current, making it ideal for PFC inductors and output chokes where DC bias is present.

Frequency Suitability — Best Use: 10 kHz–100 kHz

Sendust cores excel in medium-frequency switching applications, typically from around 10 kHz up to roughly 100 kHz:

• 10 kHz–50 kHz: excellent performance for many SMPS output chokes, PFC inductors, and DC-DC converter filters. 

• 50 kHz–100 kHz: still effective in many designs, though careful grade and core geometry selection (particle size and compaction density) are required to keep losses low. 

• Above ~100 kHz: ferrite cores usually outperform Sendust due to lower high-frequency loss mechanisms; use Sendust, where DC bias or saturation margin takes priority.

Advantages Compared to Ferrite and Iron Powder Cores

• Versus ferrite: 

  • Better DC bias handling and higher saturation flux density, Sendust maintains inductance under DC current better than ferrite. 

  • Ferrite has much lower loss at high switching frequencies (hundreds of kHz to MHz), so ferrite remains preferable for very high-frequency SMPS.

• Versus generic iron powder cores: 

  • Sendust typically shows lower core loss and improved permeability stability because of its specific Fe-Si-Al chemistry and optimised powder processing. 

  • Iron-powder cores without the Sendust composition may offer similar mechanical robustness but often worse DC bias and higher loss at medium frequencies.

Real-World Applications

Sendust cores are widely used where medium-frequency performance and DC bias tolerance are important:

• SMPS output choke — maintain stable output with ripple filter under load. 

• PFC (Power Factor Correction) Inductors — handle DC bias in the boost PFC stages.

• DC-DC converter inductors — especially in buck converters with significant DC current. 

• EMI filter inductors — where stable permeability improves common-mode and differential-mode attenuation. 

• UPS systems — for both inverter and filtering stages where reliability and thermal stability matter. 

• Solar inverter inductors — smoothing and coupling where long-term thermal performance is required.

Shah Electronics offers sendust cores ideal for PFC inductors and SMPS chokes

Why Sendust Is a Balanced, Cost-Effective Choice

Sendust offers a pragmatic middle ground between ferrite and other iron-based cores. Its high saturation flux density and strong DC bias tolerance mean designers can use smaller, more robust inductors in applications with significant DC currents. Powder metallurgy and distributed gaps deliver thermal stability and predictable permeability while keeping costs competitive. For medium-frequency power electronics (10 kHz–100 kHz) where DC bias and efficiency are both important, Sendust is often the best trade-off between performance, size, and price.

FAQs

1. Is Sendust suitable for high-frequency SMPS? 

   • Sendust works well up to ~100 kHz, but at switching frequencies well above 100 kHz, ferrite cores typically yield lower losses.

2. How does Sendust compare with Ferrite for DC bias? 

   • Sendust outperforms ferrite in DC bias handling and saturation margin, maintaining inductance better under DC current.

3. Can Sendust be used in toroidal inductors? 

   • Yes. Sendust powder cores come in toroidal and pot shapes; toroidal Sendust inductors offer compactness with good DC bias performance.

4. Do Sendust cores need special mounting or cooling? 

   • They are mechanically robust, but like any core, proper PCB layout, thermal path, and occasional forced cooling improve reliability in high-power designs.

5. Where are Sendust cores commonly sourced?

   • Magnetic-materials suppliers and core manufacturers provide standard and custom Sendust powder cores; ask for grade data (loss vs frequency, permeability, and saturation flux) when specifying.

Ready to specify cores for your design? Browse the full Sendust series from Shah Electronics: