Buck Converter Inductor Calculator
Estimate the inductor value for a buck converter from input voltage, output voltage, output current, switching frequency, and target ripple current. Also calculate duty cycle, peak inductor current, RMS current estimate, and stored energy.
Buck converter inductor formula
A buck converter steps a higher DC voltage down to a lower DC voltage. The inductor stores energy during the switch on-time and releases energy during the off-time. A common first-pass design method is to choose a ripple current target, then calculate the inductance required to produce that ripple at the selected switching frequency.
Higher inductance lowers ripple current but may increase size, cost, and transient-response limitations. Lower inductance increases ripple and peak current, which can stress the inductor, switch, diode or synchronous FET, and output capacitor.
Worked example
A practical design would choose a nearby standard value, then verify saturation current, RMS current, DC resistance, core loss, transient behavior, and the regulator manufacturer's recommended operating range.
Typical ripple current starting points
| Ripple target | Use case | Comment |
|---|---|---|
| 20% | Lower ripple designs | Larger inductor, lower peak current |
| 30% | Common starting point | Balanced size and ripple |
| 40% | Compact designs | Smaller inductor, higher peak current |
Trusted references
For deeper converter design background, use non-competitor technical references such as Texas Instruments AN-1197 Selecting Inductors for Buck Converters and Texas Instruments – Select inductors for buck converters.
Common questions
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Use L = Vout × (Vin − Vout) ÷ (Vin × ΔIL × fs), where ΔIL is the desired inductor ripple current and fs is the switching frequency in hertz.
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A common starting range is about 20% to 40% of output current. Lower ripple usually means a larger inductor; higher ripple usually means a smaller inductor but higher peak current.
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Peak inductor current is approximately Iout + ΔIL ÷ 2 in continuous conduction mode. The inductor saturation-current rating should be above this value with suitable margin.
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Efficiency is used only for the input-current estimate. The ideal buck duty-cycle and basic inductance formula do not directly use efficiency.
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No. Boost, buck-boost, flyback, and other converter topologies use different inductor or magnetics equations.
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Higher switching frequency gives less time for current to rise and fall each cycle, so a smaller inductor can produce the same ripple current.
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No. A production design should also verify regulator stability, saturation current, RMS current, DCR, core loss, output capacitor ripple, thermal rise, and layout.
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Ripple and peak current increase. This can cause higher losses, more output ripple, noise problems, and possible saturation.