Buck & boost DC-DC converter calculator

Quick design numbers for a buck or boost converter: enter input/output voltage, current and switching frequency, and read duty cycle and the inductor you need.

Converter configuration

Input voltage (V_in)VOutput voltage (V_out)VOutput current (I_out)A — full-load output currentSwitching frequencykHz — the controller's switching rateInductor ripple fractionPeak-to-peak ΔI as a fraction of I_out — typical 0.2–0.4Diode forward dropV — ~0.5 for a Schottky diode

Buck design numbers

Duty cycle

(V_out + V_d) ÷ (V_in + V_d − V_sw)

44.35%

Inductor value

Minimum for the chosen ripple

10.35 µH

Inductor ripple (ΔI)

I_out × ripple fraction, peak-to-peak

0.6 A

Average inductor current

= I_out

2 A

Switch peak current

Average + ΔI ÷ 2 — size the switch and sense resistor for this

2.3 A

Average input current

V_out × I_out ÷ (V_in × 90%)

0.9259 A

Verify the inductor's saturation current is well above the 2.3 A peak current shown above.

About the model

Continuous-conduction mode (CCM) is assumed: the inductor current never falls to zero. The duty cycle comes from volt-second balance across the inductor, and the inductance is sized so the peak-to-peak ripple stays at the fraction of load you entered. Real designs close the loop with an error amplifier, add input/output capacitance and a compensation network — the inductor here is the minimum for the chosen ripple, not a complete design.

For the parts themselves: DC-DC converters, power inductors and Schottky diodes carry the ratings the datasheet math above needs.

Browse related parts:

DC-DC converters power inductors Schottky diodes

Frequently asked questions

How do I calculate the duty cycle of a buck converter?

The tool uses D = (V_out + V_d) / (V_in + V_d − V_sw) for a buck, from volt-second balance across the inductor in continuous-conduction mode. With the defaults of 12 V in, 5 V out, a 0.5 V diode drop and 0.1 V switch drop, D ≈ 44%, and the boost formula is D = (V_out + V_d − V_in) / (V_out + V_d − V_sw).

How do I size the inductor for a buck or boost converter?

L = (V_in − V_out) × D / (f × ΔI) for a buck and L = V_in × D / (f × ΔI) for a boost, where ΔI = I_out × ripple fraction and f is the switching frequency in Hz. With a 0.3 ripple fraction the tool sizes the minimum inductance that keeps the peak-to-peak ripple at that fraction.

What inductor current rating do I need?

Check that the inductor saturation current is well above the switch peak current, which is the average inductor current plus half the ripple. In a buck the average inductor current equals I_out; in a boost it is I_out / (1 − D), so the inductor sees more current than the output.

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ICBOMS provides this tool for reference only.