How to choose and design inductors for step-down DC/DC converters—from low-power POL to high-current point-of-load regulators
Introduction
The buck (step-down) converter is the most widely used DC/DC topology in the world. The inductor is the heart of every buck converter—its value directly determines output ripple, transient response, efficiency, and size.
Shaanxi SiRui Technology Co., Ltd. supplies magnetic cores and custom inductors for buck converter applications worldwide. Contact: sales@sirui-tech.com | Web: www.sirui-tech.com
1. Core Material Comparison
| Material | Bsat | DC Bias | Best Application |
|---|---|---|---|
| Ferrite (gapped) | 0.4–0.5 T | Hard saturation | Low current, high freq |
| Sendust | ~1.0 T | Soft, gradual | General purpose |
| High Flux | ~1.5 T | Excellent DC bias | High current, POL |
| MPP | ~0.75 T | Excellent, low loss | Premium efficiency |
2. Inductor Value Calculation
L = (Vin – Vout) × Vout / (Vin × fsw × ΔIL). Higher switching frequency = smaller inductor. Modern POL regulators run at 1–2 MHz for this reason.
3. Key Design Parameters
- Saturation current (Isat): Add 20–30% margin for temperature and transients
- RMS current (Irms): Determines temperature rise
- DCR: Lower = higher efficiency, but larger size
- Core loss: Significant at high frequency and high ripple
4. Common Design Mistakes
- Only looking at inductance value (ignore DC bias curve!)
- Underestimating core loss at high frequency
- Forgetting temperature effects on Bsat
- Using ferrite where powder cores would be better
5. Custom Cores from SiRui-Tech
At Shaanxi SiRui Technology Co., Ltd., we supply Sendust cores for general-purpose buck inductors, High Flux cores for high-current POL regulators, MPP cores for premium efficiency, and gappable ferrite cores for low-current high-frequency designs.
Web: www.sirui-tech.com | Email: sales@sirui-tech.com
Conclusion
As POL regulators push toward higher current (40A+ per phase) and higher frequency (1–2 MHz), powder cores are increasingly replacing gapped ferrite for buck inductors.