Buck / Boost Converter Calculator

This buck / boost converter calculator computes duty cycle, minimum inductance, capacitor sizing, and MOSFET/diode stress for buck (step-down), boost (step-up), and inverting buck-boost topologies. Interactive SVG circuit diagrams show the exact topology, and a PWM waveform visualizes on/off timing — features an AI text response cannot replicate. Free, no sign-up.

Converter Mode

Step-down: Output voltage is lower than input

Presets

Input Parameters

Input Voltage (V)

Output Voltage (V)

Output Current (A)

Switching Frequency (kHz)

Circuit Topology

Calculated Results

Duty Cycle

44.7%

D = 0.4472

Min. Inductance

10.14 µH

Inductor Ripple Current

600.00 mA

Inductor Peak Current

2.300 A

Min. Output Capacitor

3.00 µF

Output Ripple Voltage

50.00 mV

Min. Input Capacitor

4.94 µF

Switch Voltage Stress

12.000 V

Switch Peak Current

2.300 A

Switch RMS Current

1.342 A

Diode Voltage Stress

12.000 V

Diode Avg. Current

1.106 A

Input Avg. Current

980.39 mA

Recommended Standard Values (E12)

Recommended Inductor

12.00 µH (E12)

Recommended Output Cap

3.30 µF (E12)

Recommended Input Cap

5.60 µF (E12)

Input Power

11.765 W

Output Power

10.000 W

Power Loss

1.765 W

η = 85%

PWM Duty Cycle Waveform

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What is a Buck / Boost Converter Calculator?

A buck / boost converter calculator determines the key design parameters for switch-mode DC-DC power supplies. It computes the duty cycle from input and output voltages, sizes the inductor to limit ripple current, selects output and input capacitors for a target ripple voltage, and calculates voltage and current stress on the switching MOSFET and freewheeling diode. Buck converters step voltage down (e.g., 12 V to 5 V), boost converters step voltage up (e.g., 5 V to 12 V), and inverting buck-boost converters can produce an output either above or below the input. Practical designs must account for diode forward voltage drop, MOSFET on-resistance, and overall converter efficiency — all of which this calculator includes.

How to Use This Calculator

Select the converter mode: buck (step-down), boost (step-up), or buck-boost (inverting)
Enter input voltage, desired output voltage, output current, and switching frequency
Optionally adjust advanced settings such as inductor ripple percentage, output ripple percentage, efficiency, diode Vd, and switch Vds
View the interactive SVG circuit diagram showing the selected topology
Read the calculated results: duty cycle, minimum inductance, capacitor values, and component stress levels
Use the PWM waveform to visualize the on and off switching periods

Frequently Asked Questions

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

For an ideal buck converter, D = Vout / Vin. When accounting for the diode forward voltage (Vd) and switch on-drop (Vds), D = (Vout + Vd) / (Vin − Vds + Vd). For example, with Vin = 12 V, Vout = 5 V, Vd = 0.5 V, and Vds = 0.2 V, D ≈ 0.447 or 44.7 %.

What is the minimum inductance needed for a buck converter?

L_min = (Vin − Vout − Vds) × D / (ΔI_L × f_sw), where ΔI_L is the desired inductor ripple current (typically 20–40 % of the average inductor current). A higher switching frequency or smaller ripple target requires a larger inductance.

Why does a boost converter need a larger output capacitor than a buck converter?

In a boost converter the output capacitor alone supplies load current during the switch on-time, so C_out = I_out × D / (f_sw × ΔV_out). In a buck converter the inductor delivers current to the output continuously, so C_out = ΔI_L / (8 × f_sw × ΔV_out), which is typically much smaller.

What switching frequency should I use for a DC-DC converter?

Common switching frequencies range from 100 kHz to 2 MHz. Higher frequencies allow smaller inductors and capacitors but increase switching losses. For most general-purpose converters, 200–500 kHz offers a good balance between component size and efficiency.