A Buck-Boost Converter Calculator is an interactive tool that computes the ideal duty cycle, approximate inductor value, and expected inductor current ripple for a non-isolated buck-boost DC-DC converter, helping designers quickly estimate component values and examine how switching frequency affects ripple.

How to use the Buck-Boost Converter Calculator

This tool is designed to help engineers, hobbyists, and students quickly estimate the key operating values of a buck-boost converter and visualize how inductor ripple varies with switching frequency. It is sized (max-width 760px) and styled to fit neatly between two sidebars on a standard WordPress layout and uses Plotly.js to present an interactive ripple vs frequency chart.

Inputs you must provide

1. Vin (Input Voltage) — the DC input to the converter.
2. Vout (Output Voltage) — target output. Use a negative value if you want the typical inverting buck-boost output.
3. Iout (Load Current) — expected steady output current in amperes.
4. Switching Frequency (fs) — the converter switching frequency in kHz. Higher frequencies typically reduce passive size but increase switching losses.
5. Target Inductor Ripple (ΔI) — the preferred peak-to-peak ripple current in the inductor; designers often choose 20–40% of load current.
6. Estimated Efficiency (%) — a conservative guess for converter efficiency (used to estimate input current).
7. Topology — choose “Inverting Buck-Boost” (typical single-switch inverting topology) or “Non-inverting” (magnitude used for estimation).

What the calculator computes

• Duty cycle (D): the fraction of switching period during which the switch is ON. For the inverting buck-boost topology used here the ideal relationship is Vout=−D1−DVinVout​=−1−DD​Vin​, which the calculator uses to compute D.
• Inductor value (L): computed from the target ripple ΔI and the chosen switching frequency using L=Vin⋅DΔI⋅fsL=ΔI⋅fs​Vin​⋅D​ (ideal continuous conduction assumption).
• Estimated inductor ripple (ΔI): recomputed from the chosen L and fs to show the expected ripple.
• Estimated input current: based on Pout and estimated efficiency (Pin = Pout/eff).

These estimates assume ideal components and continuous conduction. They are meant for preliminary selection and quick trade-offs.

Design guidance and interpretation

• Duty cycle insights: A higher magnitude of output (relative to input) increases the duty cycle. As D approaches 0.5–0.9 extreme, converter stress increases and practical switching losses and component limits must be checked.
• Inductor selection: The calculator returns a nominal inductor value for your target ripple. In practice you should select a standard value slightly larger than the calculated L to reduce ripple and account for saturation. Check the inductor’s saturation current — it must exceed the peak inductor current (Ipeak ≈ Iavg + ΔI/2).
• Switching frequency trade-offs: Increasing fs reduces L for the same ripple but raises switching losses and may require more expensive MOSFETs, drivers, or layout attention. Use the Plotly graph to balance component size and ripple.
• Efficiency and losses: The tool uses a simple efficiency factor to estimate input current. Real systems experience switching, conduction, diode, and core losses that vary with current, temperature, and layout; bench measurement or SPICE simulation is necessary for final validation.

Plotly.js use and visualization

Plotly.js is used to generate an interactive ripple-vs-frequency graph. Interactivity helps you quickly answer “If I double the switching frequency, how much smaller can my inductor be—and what ripple will I get?” The plot background is white and blends with the calculator’s white container for clear, professional visuals. Hover, zoom, and pan to inspect values.

Practical checklist before prototyping

• Pick an inductor rated for the peak current plus margin.
• Choose MOSFETs and diodes with appropriate voltage and current ratings and low Rds(on) / forward drop.
• Add proper input and output decoupling capacitors with low ESR.
• Prototype with current-limit testing and thermal monitoring.
• Validate with an oscilloscope and thermal camera if available.

Disclaimer

This calculator uses idealized formulas for continuous conduction and approximate efficiency. It is intended for preliminary design and educational purposes only. It does not replace detailed simulation, manufacturer datasheets, empirical testing, or professional engineering review. The author accepts no responsibility for unintended consequences or damages arising from use of the results.

FAQ

Q: Can I use this for a SEPIC or isolated design?
A: This calculator targets basic inverting and magnitude-based buck-boost approximations. SEPIC and isolated topologies have different steady-state relations and coupling—use a dedicated SEPIC/isolated calculator or detailed simulation for those.

Q: Is the computed inductor value exact?
A: No. It’s an estimate based on the target ripple and assumes ideal behavior. Always select a real inductor with margin for saturation and verify in practice.

Q: Does the plot include losses?
A: No. The plot shows idealized inductor ripple vs switching frequency using the computed L. Losses are represented only by a user-entered efficiency for input current estimation.

Q: What switching frequency should I choose?
A: Choose a frequency balancing size and losses: higher frequency reduces passive size but increases switching and thermal challenges. Typical ranges for power converters are tens to hundreds of kHz depending on power level.

Q: Can this code be placed directly into WordPress?
A: Yes — paste into a Custom HTML block or into a template file where raw HTML/JS is allowed. The calculator container is sized to fit between two standard sidebars; adjust the CSS max-width if your theme uses a different column width.