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
Circuit Topology
Calculated Results
Recommended Standard Values (E12)
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.