Calculator Inputs
Formula Used
This calculator sizes the inductor from ripple current, voltage conversion, and switching frequency. It evaluates min, nominal, and max input points, then selects the worst case.
1) Duty Cycle
Buck: D ≈ Vout / (Vin × η)
Boost: D ≈ 1 − (Vin × η / Vout)
Buck-Boost: D ≈ Vout / (Vout + Vin × η)
2) Average Inductor Current
Buck: IL,avg ≈ Iout
Boost or Buck-Boost: IL,avg ≈ Pout / (Vin × η)
3) Target Ripple Current
ΔIL,target = IL,avg × Ripple%
4) Required Inductance
Buck: L = ((Vin − Vout) × D) / (ΔIL × fsw)
Boost: L = (Vin × D) / (ΔIL × fsw)
Buck-Boost: L = (Vin × D) / (ΔIL × fsw)
5) Peak and RMS Current
Ipeak = IL,avg + ΔIL / 2
Irms ≈ √(IL,avg² + ΔIL² / 12)
6) Stored Energy
E = 0.5 × L × Ipeak²
The recommended inductance equals the worst-case minimum inductance multiplied by the selected safety margin.
How to Use This Calculator
- Select the converter topology that matches your design.
- Enter minimum, nominal, and maximum input voltage values.
- Enter output voltage, output current, and switching frequency.
- Choose the ripple current target as a percentage.
- Enter expected efficiency, inductance margin, and saturation headroom.
- Submit the form to view the result above it.
- Review the controlling point, peak current, and RMS current.
- Use the graph and export buttons for documentation.
Example Data Table
| Example | Topology | Vin Range (V) | Vout (V) | Iout (A) | fsw (kHz) | Ripple (%) | Suggested L Range |
|---|---|---|---|---|---|---|---|
| Industrial 24V to 12V rail | Buck | 18 to 30 | 12 | 5 | 150 | 30 | 22 to 47 µH |
| Battery boost supply | Boost | 9 to 14 | 24 | 2 | 200 | 35 | 22 to 68 µH |
| Wide-input negative rail | Buck-Boost | 10 to 18 | 15 | 1.5 | 250 | 25 | 15 to 47 µH |
| Telecom front-end stage | Buck | 36 to 60 | 12 | 8 | 300 | 25 | 10 to 22 µH |
Frequently Asked Questions
1) What does this calculator size exactly?
It estimates an inductor value for switching converters using voltage, current, ripple target, and frequency. It also reports peak current, RMS current, stored energy, and a recommended saturation current rating.
2) Why are three input voltages used?
Ripple and duty cycle change across the input range. Evaluating minimum, nominal, and maximum input voltage helps identify the worst-case operating point that drives the minimum required inductance.
3) What ripple percentage should I choose?
Many designs start between 20% and 40% of average inductor current. Lower ripple reduces current stress but increases size. Higher ripple shrinks the part but increases peak current and magnetic stress.
4) Why is saturation current important?
An inductor that saturates loses effective inductance and causes excessive ripple or switching stress. Choose a saturation current above the worst calculated peak current, then add practical design headroom.
5) Does this replace detailed magnetic design?
No. This is a fast engineering estimator. Final part selection should still confirm core loss, copper loss, DC resistance, thermal rise, transient response, and vendor derating curves.
6) Why does higher switching frequency reduce inductance?
For the same ripple target, more switching cycles per second mean less volt-second stress per cycle. That reduces the inductance needed to control current ripple.
7) What does CCM mean in the table?
CCM means continuous conduction mode. It indicates the average inductor current stays above half the ripple current, so the current does not fall to zero during the switching period.
8) Should I choose the exact calculated inductance?
Usually no. Designers often choose the next practical standard value and confirm performance. Tolerance, bias effects, temperature, and transient limits can all justify selecting a larger part.