Inductor saturation is the most common failure mode in power magnetics. When the core saturates, inductance drops sharply, current spikes, and the converter can destroy itself. Understanding saturation—how to calculate it, how to prevent it, and how to test for it—is essential for every power electronics engineer.
This guide explains inductor saturation physics, calculation methods, and practical prevention techniques.
Shaanxi SiRui Technology Co., Ltd. engineers design inductors with verified saturation performance. Contact: sales@sirui-tech.com | Web: www.sirui-tech.com
1. What Is Saturation?
Every magnetic core has a maximum flux density (Bsat). Once flux exceeds Bsat, permeability drops toward air and inductance collapses. Consequences: inductance drops to 10–30% of nominal, current spikes rapidly, MOSFET/diode overstress, audible noise, component failure.
2. Saturation Formula
B = (L × ΔI) / (N × Ae)
| Material | Bsat (at 25°C) |
|---|---|
| Ferrite (Mn-Zn) | 0.35–0.5 T |
| Powder core (Sendust) | 1.0–1.2 T |
| Powder core (MPP) | 0.7–0.8 T |
| Powder core (High Flux) | 1.5 T |
| Nanocrystalline | 1.2 T |
| Silicon steel | 1.8–2.0 T |
Design rule: peak B at max current must be below 70–80% of Bsat (de-rating margin).
3. DC Bias vs AC Flux
- DC bias saturation: static flux from DC current (most common in buck/boost/PFC inductors)
- AC flux saturation: ripple current adds flux on top of DC bias
4. How to Prevent Saturation
- Higher Bsat core: ferrite (0.4T) → powder core (1.0–1.5T)
- Air gap: gapped ferrite stores energy in the gap
- Larger core: more Ae reduces B for same L and current
- Powder core: distributed gap, soft saturation (inductance drops gradually)
5. Soft vs Hard Saturation
Hard saturation (ferrite): inductance drops sharply at Bsat. Unpredictable, dangerous.
Soft saturation (powder core): inductance decreases gradually with DC bias. Predictable, safe. Preferred for power inductors.
6. Testing for Saturation
- DC bias test: apply increasing DC current, measure L with LCR meter
- Waveform observation: if inductor current shows sharp upward bend at peak, it’s saturating
7. Sirui-Tech Saturation Design
- Powder cores (Sendust, MPP, High Flux) for soft saturation
- Gapped ferrite for specific applications
- Verified L vs I_DC curves for every custom design
- De-rate Bsat by 20–30% for safety margin
Conclusion
Inductor saturation is preventable with proper design. Calculate peak flux density, de-rate Bsat by 20–30%, and choose the right core material. Powder cores with soft saturation are the safest choice for high-current DC bias applications.
Need a non-saturating inductor? Contact Sirui-Tech at sales@sirui-tech.com with your inductance and peak current.