Buck Converter Calculator (Duty Cycle and Inductor)
Duty cycle, inductor value, ripple and peak current, and input current of a step-down (buck) converter from the voltages, load current, switching frequency and efficiency.
Results
The dashed line marks the value you entered.
What this tool does
A buck converter chops the input and averages it with an inductor, so the ideal duty cycle is simply Vout ÷ Vin; losses make the real one a little larger, which the efficiency term here lumps together. The inductor is chosen for the ripple current you will accept: a common rule of thumb is 20–40 % of the output current, and the peak current, output plus half the ripple, is what the inductor must carry without saturating. A higher switching frequency allows a proportionally smaller inductor, at the price of more switching loss.
Formula
D = Vout ÷ (Vin × η) (ideal: Vout ÷ Vin) · L = (Vin − Vout) × D ÷ (f × ΔI) · Iin = Vout × Iout ÷ (Vin × η)
Variables
| Symbol | Meaning | Unit |
|---|---|---|
vi | Input voltage | V |
vo | Output voltage | V |
io | Output current | A |
f | Switching frequency | kHz |
rp | Inductor current ripple (share of the output current) | % |
et | Efficiency | % |
L | Inductance needed | µH |
D | Duty cycle, allowing for losses | % |
DI | Duty cycle, lossless | % |
DL | Ripple current, peak to peak | A |
IP | Peak inductor current | A |
II | Average input current | A |
ST | Can this converter do it? | — |
Worked example
- Input voltage12 V
- Output voltage5 V
- Output current2 A
- Switching frequency100 kHz
- Inductor current ripple (share of the output current)30 %
- Efficiency90 %
- Inductance needed54.0 µH
- Duty cycle, allowing for losses46.3 %
- Duty cycle, lossless41.7 %
- Ripple current, peak to peak0.60 A
- Peak inductor current2.30 A
- Average input current0.93 A
- Can this converter do it?Yes
Limitations
- Electrical installations are governed by national wiring rules. Cable sizing also depends on installation method, grouping, ambient temperature and protection devices, which this calculator does not evaluate.
- Coverage and consumption figures vary between products. Take the values from the manufacturer's datasheet for the product you are actually using.