The boost converter steps up a lower input voltage to a higher output voltage. The boost inductor is the energy storage element that makes this possible. Designing the boost inductor correctly—with the right inductance, saturation margin and low loss—is critical for efficiency and stability.
This guide walks through boost converter inductor design from first principles.
Shaanxi SiRui Technology Co., Ltd. manufactures boost inductors for PFC, LED drivers, battery-powered and industrial applications. Contact: sales@sirui-tech.com | Web: www.sirui-tech.com
1. Define Requirements
- Input voltage range (V_in)
- Output voltage (V_out) and power (P_out)
- Switching frequency (f_sw)
- Target ripple current (ΔI_L): 20–40% of average input current
2. Calculate Inductance
L = V_in × (V_out – V_in) / (V_out × f_sw × ΔI_L)
Example: 12V to 24V, 48W output, 200kHz, 1A ripple: L = 30 μH → choose 33 μH.
3. Peak and RMS Current
- I_peak = I_in_avg + ΔI_L / 2 (size Isat 20–30% above this)
- I_rms determines copper loss and DCR heating
4. Core Selection
| Power Level | Core Type |
|---|---|
| Low power (<50W) | Ferrite EE/EI, toroidal |
| Medium power (50–500W) | Powder core toroidal, EE gapped |
| High power (>500W) | Large powder core toroid, cut core |
Powder cores (Sendust, Kool Mµ, High Flux) are preferred for soft saturation with DC bias.
5. Boost vs Buck Inductor
| Parameter | Buck | Boost |
|---|---|---|
| Current | Output current | Input current |
| Worst case | Max load current | Min input voltage (highest I_in) |
| Core saturation | I_out + ripple/2 | I_in_avg + ripple/2 |
6. Common Mistakes
- Inductance too low: high ripple, high peak current
- Inductance too high: large size, slow transient response
- Saturation margin too tight at low line (minimum V_in)
- Forgetting diode forward voltage in V_out calculation
- Not checking at minimum V_in: input current is highest
7. PFC Boost Inductor Special Considerations
PFC uses a boost converter with rectified sine wave input (85–265 VAC). The PFC inductor must handle widely varying input voltage, high peak current at low line, and continuous or critical conduction mode. PFC inductors are typically large powder core toroids.
8. Sirui-Tech Boost Inductors
- PFC boost inductors: powder core toroidal, 100 μH–10 mH
- LED driver boost inductors: compact, low profile
- Battery-powered boost inductors: low DCR for efficiency
Conclusion
Boost inductor design starts with the input voltage range and output power. Calculate inductance, size the core for peak current (highest at minimum input voltage), and choose powder core for soft saturation. Pay special attention to low-line operation.
Need a custom boost inductor? Contact Sirui-Tech at sales@sirui-tech.com with your voltage, power and frequency.