Buck Converter Calculator (Inductor and Capacitor)
By Santaji GadepatilinUpdated October 27, 2026
A buck converter steps a DC voltage down efficiently by switching it on and off and smoothing the result with an inductor and capacitor — far less wasteful than a linear regulator. Learn the buck converter working principle and why capacitor ESR matters for output ripple.
How to use the buck converter calculator
Enter the input and output voltage, output current, switching frequency, the inductor ripple as a percentage of output current, and the allowed output voltage ripple. You get the duty cycle, ripple current, inductance, peak inductor current and minimum output capacitance.
For more background, read Synchronous Rectification in Buck Converters.
The formulas (continuous conduction)
| Quantity | Formula |
|---|---|
| Duty cycle | D = Vo ÷ Vi |
| Inductance | L = Vo(Vi − Vo) ÷ (Vi f ΔI) |
| Peak current | Ipk = Io + ΔI ÷ 2 |
| Output capacitance | C = ΔI ÷ (8 f ΔV) |
Example
24 V to 5 V at 2 A, 500 kHz, 30% ripple (0.6 A):
- D = 20.8%
- L = 5 × 19 ÷ (24 × 500,000 × 0.6) = 13.2 µH → use 15 µH
- Peak current = 2.3 A — choose an inductor rated above this for saturation
- For 20 mV ripple, C ≥ 0.6 ÷ (8 × 500,000 × 0.02) = 7.5 µF → use 22 µF ceramic
Inductance vs frequency (24 V → 5 V, 0.6 A ripple)
| Frequency | Inductance |
|---|---|
| 100 kHz | 66.0 µH |
| 250 kHz | 26.4 µH |
| 500 kHz | 13.2 µH |
| 1 MHz | 6.6 µH |
| 2 MHz | 3.3 µH |
Higher frequency allows smaller inductors and capacitors but increases switching losses.
Design checks
- Inductor saturation current above Ipk with margin; RMS rating above Io.
- Input capacitor sized for RMS ripple current ≈ Io√(D(1 − D)).
- Use the controller datasheet’s compensation and layout guidance — tight loops around the switch, diode and input capacitor matter most.
Frequently asked questions
What is the duty cycle of a buck converter?
Ideally D = V_out ÷ V_in. Converting 24 V to 5 V needs about 21%; losses push it slightly higher.
How do I choose the inductor ripple?
20–40% of the output current is a common compromise between inductor size and ripple. 30% is a good starting point.
How is the inductance calculated?
L = V_out × (V_in − V_out) ÷ (V_in × f × ΔI). For 24 V to 5 V at 2 A, 500 kHz and 30% ripple, L ≈ 13 µH.
What sets the output ripple voltage?
Capacitance and the capacitor's ESR. The formula here covers capacitance; with electrolytics, ripple is usually dominated by ESR × ΔI.