The inductor is the heart of a buck converter. Its value determines ripple current, transient response, and efficiency. Getting the buck inductor right is the difference between a clean, efficient converter and one that buzzes, overheats, or misbehaves under load.
This guide walks through buck converter inductor design from ripple specification to core selection and verification.
Shaanxi SiRui Technology Co., Ltd. manufactures buck converter inductors for DC-DC applications. Contact: sales@sirui-tech.com | Web: www.sirui-tech.com
1. Define Requirements
- Input voltage range (V_in)
- Output voltage (V_out) and current (I_out)
- Switching frequency (f_sw)
- Target ripple current (ΔI_L): typically 20–40% of I_out
2. Calculate Inductance
L = (V_in – V_out) × V_out / (V_in × f_sw × ΔI_L)
Example: 12V to 5V, 5A output, 500kHz, 30% ripple (1.5A): L = 3.9 μH → choose 4.7 μH standard value.
Why 30% ripple? Too much ripple = high RMS loss and capacitor stress. Too little = very large inductor and poor transient response. 20–40% is the sweet spot.
3. Peak Current
I_peak = I_out + ΔI_L / 2
Size saturation current (Isat) at least 20–30% above I_peak. For 5.75A peak, choose Isat > 7A.
4. Core Material Selection
| Application | Core Material |
|---|---|
| Low current (<2A), high freq | Ferrite (Mn-Zn) |
| Medium current (2–10A), DC bias | Powder core (Sendust, Kool Mµ) |
| High current (>10A) | Powder core (High Flux, MPP) |
| Lowest loss, highest freq | Nanocrystalline |
Powder cores are preferred for buck inductors because they saturate softly (inductance decreases gradually rather than abruptly).
5. Loss Breakdown
- Copper loss (I²R): 60–80% of total loss (dominant)
- Core loss: 20–40% (increases with frequency and flux swing)
At high frequency, core loss can exceed copper loss—choose a low-loss core material.
6. Common Mistakes
- Inductance too low: high ripple, high RMS current, hot inductor
- Inductance too high: large size, poor transient response
- Saturation current too close to peak: inductor saturates at full load
- Wrong core material: ferrite saturates hard, powder saturates softly
- No DCR consideration: efficiency lower than expected
7. Sirui-Tech Buck Inductors
- SMD molded inductors: 1–100 μH, up to 30A
- Through-hole power inductors: 1–1000 μH, custom values
- Powder core toroidal inductors: high current, soft saturation
Conclusion
Buck inductor design starts with specifying ripple current (20–40% of output). Calculate inductance, size the core for peak current with saturation margin, and choose powder core for DC bias applications. Verify DCR loss and test thermally at full load.
Need a custom buck inductor? Contact Sirui-Tech at sales@sirui-tech.com with your voltage, current and frequency.