Buck / Boost / Buck-Boost Calculator
Calculate inductor and capacitor requirements for switching regulators.
Switching Regulators transfer energy dynamically using switches and an inductor to step voltage up or down with high efficiency.
Formulas:
- Buck Duty Cycle:
D = Vout / Vin - Boost Duty Cycle:
D = 1 - (Vin / Vout) - Buck L(min):
(Vin - Vout) * D / (f * Ripple_Current)
Usage: Select Buck or Boost mode. Input Vin, Vout, maximum load current, and switching frequency to compute required inductance (L) and output capacitance (C) values.
When you need it: Picking the duty cycle and inductor, and estimating efficiency, for a switching regulator that steps voltage down (buck), up (boost) or either way (buck-boost).
Worked example: A 12 V→5 V buck runs at D = Vout/Vin = 0.42. Inductor ripple is ΔIL = (Vin − Vout) × D / (f × L); at 500 kHz with L = 10 µH, ΔIL = 7 × 0.42 / (500e3 × 10e-6) ≈ 0.59 A.
Tips & gotchas:
- Size the inductor for about 30% ripple current, and make sure its saturation rating exceeds the peak.
- Higher switching frequency shrinks L and C but adds switching loss and EMI.
- A boost can't fully disconnect its output — input feeds through the inductor and diode even when off.
- Keep the switching-node loop small and the input/output caps close to the IC for clean operation.