Boost Inductor Selection Calculator
Size a boost inductor across a battery input range. Estimate input current, worst-case ripple, peak and RMS current, then check ratings and copper loss.
Calculations run locally. Save is device-only; sharing includes the entered values.
Battery examples
Examples are starting points. Enter the loaded input range and check battery droop, undervoltage cutoff, maximum controller duty and current limit. This tool does not predict battery life or efficiency.
Operating conditions
Units are fixed beside each field: V, A, kHz, µH, mΩ and °C.
0 < minimum input ≤ maximum input < output; load, frequency and inductance > 0; 0 < efficiency ≤ 100%; 0 < ripple target < 200%; 0 ≤ tolerance < 100%.
Calculation results
- Required minimum effective L
- 8.8889 µH
- Nominal L allowing for tolerance
- 11.111 µH
- Minimum L from tolerance
- 12 µH
- CCM boundary load
- 0.055556 A
- Peak current
- 1.0259 A
- RMS current
- 0.92772 A
Ripple across input range: 0.112–0.2 A
Duty-cycle range: 16–40%
- Maximum average inductor current
- 0.92593 A
- Ripple / average current
- 22.222 %
Input at maximum absolute ripple: 3 V
Input governing sizing / CCM boundary: 3.3333 V
Input at maximum peak / RMS: 3 V
Worst-case inputs differ: absolute ripple peaks near Vout/2, while ripple ratio and the CCM boundary peak near 2×Vout/3, clamped to the input range. When CCM holds throughout, peak and RMS current are largest at minimum input.
Current at key input voltages
Worst-case inputs differ: absolute ripple peaks near Vout/2, while ripple ratio and the CCM boundary peak near 2×Vout/3, clamped to the input range. When CCM holds throughout, peak and RMS current are largest at minimum input.
| Input voltage | Average inductor current | Inductor ripple (peak-to-peak) | Ripple / average current | Peak current | RMS current |
|---|---|---|---|---|---|
| 3 V | 0.92593 A | 0.2 A | 21.6 % | 1.0259 A | 0.92772 A |
| 3.3333 V | 0.83333 A | 0.18519 A | 22.222 % | 0.92593 A | 0.83505 A |
| 4.2 V | 0.66138 A | 0.112 A | 16.934 % | 0.71738 A | 0.66217 A |
Compare standard inductances
| Nominal L | Minimum L from tolerance | Inductor ripple (peak-to-peak) | Peak current | RMS current | Mode | Ripple target | Use |
|---|---|---|---|---|---|---|---|
| 8.2 µH | 6.56 µH | 0.36585 A | 1.1089 A | 0.93193 A | CCM | Exceeded | |
| 10 µH | 8 µH | 0.3 A | 1.0759 A | 0.92997 A | CCM | Exceeded | |
| 12 µH | 9.6 µH | 0.25 A | 1.0509 A | 0.92873 A | CCM | Met | |
| 15 µH | 12 µH | 0.2 A | 1.0259 A | 0.92772 A | CCM | Met | |
| 18 µH | 14.4 µH | 0.16667 A | 1.0093 A | 0.92718 A | CCM | Met |
Model & formulas
First-pass fixed-frequency CCM approximation: duty and ripple use ideal boost relationships; average inductor current uses input power estimated from your assumed efficiency, not a simulated or measured efficiency. CCM is checked over the entire input range with negative inductance tolerance. DC bias, temperature-dependent inductance, controller limits, startup and transients are excluded. Verify actual duty and current with the controller data sheet and waveforms.
D = 1 − Vin/Vout; Iavg ≈ Vout × Iout / (η × Vin)
ΔI = Vin × D / (f × Lmin)
Lmin = Lnom × (1 − tolerance/100)
Ipeak = Iavg + ΔI/2
Irms = √(Iavg² + ΔI²/12)