Understanding why inductors saturate, how core material affects DC bias performance, and design strategies to avoid saturation failure
Introduction
Inductor saturation is one of the most common—and most damaging—power supply design mistakes. A saturated inductor doesn’t just lose inductance; it can cause catastrophic failure: output voltage spikes, overcurrent, MOSFET destruction, and even fire.
Shaanxi SiRui Technology Co., Ltd. supplies magnetic cores with optimized DC bias characteristics for power inductor applications.
1. What Is Inductor Saturation?
An inductor stores energy in its magnetic core. As current increases, the core can only absorb so much flux—this is saturation flux density (Bsat). Above Bsat, inductance drops dramatically, and the inductor starts looking like a short circuit.
Hard saturation (ferrite): inductance drops sharply. Soft saturation (powder cores): inductance decreases gradually—more forgiving.
2. Core Material Comparison for DC Bias
| Material | Bsat | DC Bias Behavior | Cost |
|---|---|---|---|
| Ferrite (gapped) | 0.4–0.5 T | Hard saturation | Lowest |
| Sendust | ~1.0 T | Soft, gradual | Low–Medium |
| High Flux | ~1.5 T | Best DC bias | Medium–High |
| MPP | ~0.75 T | Excellent, low loss | Highest |
3. Temperature Effects
Saturation flux density decreases as temperature increases. A core that’s fine at room temperature might saturate at 100°C! Always design for worst-case temperature, not ambient.
4. Practical Design Strategies
- Size for DC bias curve, not just inductance value
- Choose the right core material for your current level
- Add 20–30% margin for temperature and transients
- Verify with bench testing (measure inductance vs DC current)
- Keep inductors away from heat sources
5. Common Mistakes
- Only looking at Isat number (it’s defined differently by every manufacturer!)
- Ignoring temperature effects
- Underestimating transient currents (startup, load steps)
- Using ferrite where powder cores would be better
6. Custom Cores from SiRui-Tech
At Shaanxi SiRui Technology Co., Ltd., we supply Sendust cores, High Flux cores, MPP cores, and gappable ferrite cores optimized for DC bias performance, with detailed DC bias curves for each size.
Conclusion
As power supplies push toward higher current and higher density, powder cores—especially Sendust and High Flux—are increasingly replacing gapped ferrite for power inductors. Their soft saturation behavior and distributed air gap make them more forgiving and reliable.