What is duty cycle in a buck converter?

Duty cycle D = Vout / Vin (for ideal converters) is the fraction of each switching period that the high-side switch is ON. A 12 V → 5 V design runs at roughly 41.7% duty cycle.

What happens if the inductor is smaller than the calculated value?

A smaller inductor increases ripple current (ΔIL) and peak switch current beyond your design target, raising output voltage ripple and component stress. It does not drop into discontinuous conduction mode (DCM) at full load; DCM occurs only when the load current falls below half the ripple current (Iout < ΔIL / 2).

How do I choose the switching frequency?

Higher frequency allows smaller inductors and capacitors but increases switching losses and may require faster (more expensive) FETs. Common ranges: 100–500 kHz for general-purpose designs, 1–3 MHz for tiny form factors.

What ripple ratio should I use?

A ripple ratio (ΔIL / Iout) of 20–40% is typical. Lower ripple means a larger inductor; higher ripple risks DCM under light load. 30% is a common starting point.

Does this account for diode or switch voltage drops?

No — this is an ideal (lossless) first-order approximation. Real designs should add the forward voltage of the diode (or synchronous FET) to Vin for a more accurate duty cycle.

Buck Converter Calculator

Enter input voltage, output voltage, switching frequency, and load current to get duty cycle, inductor, and capacitor values for your buck converter design.

Converter Parameters

Input Voltage V_in (V)

Output Voltage V_out (V)

Load Current I_out (A)

Switching Frequency f_sw (kHz)

Inductor Ripple Ratio ΔI_L / I_out (%) (typical: 20–40%)

Max Output Voltage Ripple ΔV_out (mV)

Duty Cycle

—

D = V_out / V_in

Min Inductance

—

L_min for CCM at full load

Inductor Current

—

I_L,peak = I_out + ΔI_L/2

Min Capacitance

—

C_min for ΔV_out spec

Design Breakdown

Parameter	Value	Formula
Enter parameters and click Calculate

Inductor Current Waveform

Triangular ripple in continuous conduction mode (CCM). Peak = I_out + ΔI_L/2, valley = I_out − ΔI_L/2.

Summary

Enter input voltage, output voltage, switching frequency, and load current to get duty cycle, inductor, and capacitor values for your buck converter design.

How it works

Enter the input voltage (Vin) and desired output voltage (Vout).
Set the switching frequency (typically 50 kHz – 2 MHz).
Enter the maximum load current (Iout) and acceptable ripple ratio (ΔIL/Iout, typically 20–40%).
The calculator computes duty cycle D = Vout / Vin.
Minimum inductance L = (Vin − Vout) × D / (f × ΔIL) is derived to keep the converter in continuous conduction mode.
Output capacitor C = ΔIL / (8 × f × ΔVout) limits output voltage ripple to your spec.

Use cases

Designing a power supply for microcontrollers or FPGAs from a battery or bus rail.
Selecting inductors and capacitors for switch-mode power supply (SMPS) prototypes.
Verifying datasheet reference designs for buck regulator ICs.
Estimating efficiency trade-offs when choosing switching frequency.
Teaching power electronics — visualizing how frequency and ripple interact.
Quick sanity-check before running full SPICE simulation.

Frequently Asked Questions

Last updated: 2026-09-22 · Reviewed by Nham Vu