Interactive Buck Converter Calculator
Estimate duty cycle, inductor value, capacitor value, ripple current, and key design checks for a step-down DC-DC converter.
What is a Buck Converter?
A buck converter is a switching power supply that steps a higher DC voltage down to a lower DC voltage efficiently. Instead of wasting extra voltage as heat (like a linear regulator), it rapidly switches a transistor on and off, then smooths energy using an inductor and capacitor. This approach makes buck converters ideal for battery-powered systems, embedded electronics, and high-current applications.
Core Buck Converter Equations
For an ideal buck converter in continuous conduction mode (CCM), these are the most common design equations:
- Duty cycle: D = Vout / Vin
- Inductor ripple current: ΔIL = Iout × (ripple % / 100)
- Inductor value: L = (Vin − Vout) × D / (ΔIL × fsw)
- Output capacitor (approx.): C ≈ ΔIL / (8 × fsw × ΔVout)
These formulas are great for first-pass sizing. Real designs should also include ESR, control loop stability, efficiency losses, and transient response requirements.
How to Use This Calculator
1) Enter electrical requirements
Start with input voltage, desired output voltage, and output current. Then choose switching frequency, ripple percentage, and acceptable output ripple voltage.
2) Click Calculate
The tool returns duty cycle, on/off time, inductor and capacitor estimates, current ripple, and quick design checks.
3) Choose practical parts
Select nearby standard component values, then verify with your controller datasheet and bench measurements.
Example: 24V to 5V at 2A
With 300kHz switching and 30% ripple target, you will typically get an inductor in the tens of microhenries and an output capacitor in the low-to-mid tens of microfarads (minimum ideal estimate). In practical hardware, it is common to increase capacitance and use low-ESR ceramics in parallel with bulk capacitors.
Practical Design Tips
- Ripple target: 20%–40% of load current is a common design range for many converters.
- Inductor saturation current: choose a rating above peak inductor current with margin.
- Voltage ratings: MOSFET, diode, and capacitor voltage ratings should exceed worst-case input and transients.
- Capacitor ESR: real ripple is affected by ESR as well as capacitance.
- PCB layout: keep hot switching loops short to reduce EMI and ringing.
CCM vs DCM
If your inductor current valley goes below zero, the converter may enter discontinuous conduction mode (DCM), especially at light loads. DCM behavior changes gain and ripple characteristics. For precision designs, validate operation over full load and input ranges.
Limitations of Simple Calculators
This calculator assumes idealized equations. It does not directly include inductor DCR, MOSFET RDS(on), diode drop, switching losses, dead time, compensation network effects, or thermal rise. Treat results as a strong starting point, not final verification.
Final Thoughts
A buck converter calculator helps you quickly move from requirements to realistic component targets. Use it to accelerate early design, then refine values using datasheets, simulation, and bench validation for a robust power stage.