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Buck Converter Duty Cycle Calculator

Work out buck converter duty cycle instantly with clear inputs, formula shown and shareable results.

About Buck Converter Duty Cycle Calculator

In continuous conduction a buck converter's duty cycle is simply Vout/Vin, independent of load. Inductor value follows from the allowed ripple: L = (Vin - Vout) x D / (dI x f), so higher switching frequency permits a smaller inductor for the same ripple.

Formula

Buck converter

D = Vout / Vin; L = (Vin - Vout) x D / (delta_I x fsw)

Worked example

With the default values below, Buck Converter Duty Cycle Calculator returns Duty cycle of 20.833%. Change any input above and every figure here is recalculated in your browser.

Inputs used

Input voltage
24 V
Output voltage
5 V
Switching frequency
300 kHz
Inductor ripple current
30 %

Results

Duty cycle
20.833% %
Switch on time
0.69 µs
Suggested inductance for 1 A output
43.98 µH
Ideal duty ratio
0.20833

Step by step

  1. 1Values used
  2. 2Buck converter
  3. 3Duty cycle= 20.833 %
  4. 4Switch on time= 0.69 µs
  5. 5Suggested inductance for 1 A output= 43.98 µH
  6. 6Ideal duty ratio= 0.20833

Assumptions and limits

  • The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax or fees or charges into account.
  • Figures are rounded for display to 5 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
  • Electrical results are planning estimates only. Verify against the applicable wiring rules (IEC 60364, BS 7671, NEC or local code) and have all installation work designed and checked by a qualified electrician.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Electrical results are planning estimates only. Verify against the applicable wiring rules (IEC 60364, BS 7671, NEC or local code) and have all installation work designed and checked by a qualified electrician.

Frequently Asked Questions

Does duty cycle change with load?

Not in continuous conduction mode. In discontinuous mode at light load it does, which is why light-load regulation behaves differently.

What ripple should I design for?

20-40% of maximum output current is the usual compromise between inductor size and output capacitor ripple.

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