Buck Converter Calculator

Step-down (buck) converter math: duty cycle, inductor ripple, output ripple estimates, and peak currents. Includes Show Work + share link.

How to Use

  1. Enter input voltage (Vin) and target output voltage (Vout).
  2. Enter load current (Iout), switching frequency (fSW), and your inductor/capacitor values (optional).
  3. Pick a ripple target (% of Iout) to estimate a recommended inductor range.
  4. Open “Show Work” to see the formulas and steps in base units.
Converter Lab View
Visual feedback: duty cycle + ripple/peak current indicators.
D
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ΔIL
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Ipk
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ΔVout
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Risk: —
Vin SW L Vout C Load Iout Diagram is conceptual (idealized). Use datasheet values for final design.
Inputs & Settings
Enter your values. Results update instantly. Sharing is manual (button only).
Common: 5V, 12V, 14.4V, 24V
Must be less than Vin for a buck converter
Used for peak/valley current estimates
Typical: 150 kHz – 2 MHz (depends on controller)
Leave blank to calculate recommended L from ripple target
Used for ripple estimate (capacitive component)
Used for ripple estimate (ESR component)
Common design target: 20%–40%
Model affects duty/efficiency assumptions (JS will apply)
Show Work (step-by-step)
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Work is shown in base units (V, A, Hz, H, F, Ω) for clarity and consistency.

Buck Converter Formulas

Quick answer: Ideal buck output is Vout ≈ D × Vin, where D is duty cycle.

Use these as design starting points; real designs require datasheet limits and component selection.

  • Duty cycle (ideal): D = Vout / Vin
  • Inductor ripple current: ΔIL ≈ (Vout × (1 − D)) / (L × fSW)
  • Peak/valley: Ipk = Iout + ΔIL/2, Ivalley = Iout − ΔIL/2
  • Output ripple (estimate): ΔVout ≈ ΔIL/(8 × fSW × C) + (ΔIL × ESR)
Notes: Ripple formulas are simplified (continuous conduction assumption). JS will label assumptions used.

FAQ

What’s the difference between buck and boost?

A buck converter steps voltage down. A boost converter steps voltage up. (Some topologies can do both.)

Why does frequency matter?

Higher switching frequency can reduce inductor/cap size, but increases switching losses and EMI complexity.

What ripple target is “normal”?

A common starting point is 20%–40% inductor ripple current relative to load current.

Is this enough to pick parts?

It’s a strong starting point. Final selection needs controller limits, inductor saturation current, diode/MOSFET ratings, thermal, and layout/EMI considerations.

Tool Info

Last updated:

Updates may include unit support, edge-case handling, and improved ripple/efficiency modeling.