Buck Converter Calculator

About the Buck Converter Calculator

The **Buck Converter Calculator** designs and analyses a step-down (buck) DC-DC converter — the most widely used switching regulator topology. It steps a higher DC input down to a lower regulated output with high efficiency, found in virtually every modern electronic device from phone chargers to server power supplies. The goal is to show the main electrical stress points before you commit to parts.

Enter the input voltage, desired output voltage, load current, switching frequency, and inductor value, and the calculator returns the duty cycle, average and peak inductor currents, current ripple, CCM/DCM status, critical inductance, power loss, and MOSFET voltage stress. The presets cover common applications: 12 V→5 V USB, 24 V→3.3 V MCU, 48 V→12 V telecom, and 5 V→1.8 V core supply.

Design tables show how output voltage varies with duty cycle, and how ripple changes with frequency, enabling rapid design iteration before you commit to a controller, inductor, or switching-speed target.

When This Page Helps

Buck converters are everywhere, but practical design still means balancing duty cycle, ripple, efficiency, and component rating rather than just hitting the target voltage. This calculator lets you check the main electrical stresses together so you can choose frequency and inductance with a clearer view of current ripple and conduction mode. It is a quick sanity check before deeper component selection or layout work.

How to Use the Inputs

1. Select a preset or enter input and output voltages.
2. Set the output load current.
3. Enter the switching frequency in kHz and inductance in µH.
4. Specify inductor DCR for loss estimation.
5. Read duty cycle, currents, ripple, CCM/DCM, and component stress.
6. Use the tables to optimise frequency and duty cycle.

Example Calculation

Tips & Best Practices

• Target 20–40% inductor current ripple at full load for a good size/efficiency balance.
• Use the critical inductance to ensure CCM at your lightest expected load.
• Higher switching frequency allows smaller inductors but increases switching losses.
• Always rate the MOSFET for at least 1.5× Vin.
• Add input capacitance to handle pulsed input current and reduce EMI.

Duty Cycle Is Only The First Check

A correct duty cycle gets you into the right voltage range, but it does not guarantee a robust design. Once the ratio is fixed, the harder questions are how much ripple current the inductor sees, whether the converter stays in CCM where you need it, and whether the switch and diode losses are acceptable for the thermal budget.

Ripple Sets Magnetic Size And Behavior

Inductor ripple is one of the most useful design signals in a buck stage. Too much ripple pushes peak current up, increases output ripple, and can move the converter into DCM at lighter loads. Too little ripple may mean a larger, slower, or more expensive magnetic than you need. The calculator helps you find a practical middle range before hardware selection.

Leave Margin On Real Components

After the electrical math looks reasonable, compare the predicted stress against actual component ratings with margin for startup, transients, and temperature. MOSFET voltage rating, inductor saturation current, diode reverse voltage, and capacitor ripple current all matter. The calculator narrows the range, but the final design still needs datasheet and layout checks.

Frequently Asked Questions

• What is a buck converter?

  A buck converter is a switching regulator that steps DC voltage down by storing energy in an inductor during the on-time and delivering it to the load during the off-time. It is the standard topology for efficient point-of-load regulation and is used anywhere compact step-down conversion is needed.

• Why not use a linear regulator instead?

  Linear regulators dissipate excess voltage as heat. A buck converter recycles energy with 85-95%+ efficiency, critical for battery-powered and high-power designs where heat would otherwise become the limiting factor.

• What is CCM vs DCM?

  In CCM, inductor current never reaches zero; in DCM it does. CCM is preferred for predictable control and lower ripple at high loads, while DCM tends to appear at light load.

• How do I choose inductance?

  Larger L reduces ripple but increases size and cost. Choose L > Lcrit for CCM at minimum load, targeting 20–40% ripple at full load so the converter stays practical.

• What limits minimum duty cycle?

  The controller minimum on-time usually sets the lower bound. At very low duty cycle, many regulators enter pulse-skipping or burst mode, which changes ripple, noise, and transient behavior and can affect low-load performance.

• What about synchronous buck?

  Replacing the freewheeling diode with a low-side MOSFET reduces conduction loss and can improve efficiency by several percentage points. The tradeoff is more control complexity and the need to manage dead time carefully, especially at high current.