A switching converter moves power by storing it in an inductor and releasing it, switching tens of thousands to millions of times a second. How long the switch stays on each cycle — the duty cycle — sets the output voltage. The inductor is then chosen so the current ripples by only a controlled amount, and the output capacitor so the voltage ripples by only a controlled amount. Get those three right and you have the skeleton of a working buck or boost design; everything else is component selection and layout.
Reviewed: June 19, 2026 · Author: Naveen P N, Founder — AI Calculator · Verified against: TI / onsemi DC-DC design references (CCM).
The converter equations (CCM)
In a boost the inductor sits in the input path and carries the input current, which is larger than the load by 1/(1−D). That is why boost inductors and switches must be rated well above the output current — a 2 A boost output at D = 0.5 draws 4 A through the inductor. The peak inductor current adds half the ripple on top of that average, and your inductor's saturation rating must clear it.
Worked example — 12 V to 5 V buck at 2 A
Scenario: Step 12 V down to 5 V at 2 A, switching at 500 kHz, allowing 30% ripple current and 1% output ripple.
Round the inductor up to a standard 10 µH part rated for at least ~2.5 A saturation, and use a 4.7–10 µF ceramic output capacitor to leave margin for ESR and tolerance. The switch and diode (or synchronous FET) must handle the 12 V input and the 2.3 A peak.
Frequently Asked Questions
D = Vout/Vin for an ideal buck. 12 V → 5 V gives D ≈ 0.42 (switch on 42% of each cycle). Real designs run slightly higher to cover losses.
Allow 20–40% ripple current, then L = Vout(Vin−Vout)/(Vin·ΔIL·fsw) for a buck. More ripple or higher frequency → smaller inductor. Check saturation current.
Buck steps down (Vout<Vin); boost steps up (Vout>Vin). A boost's inductor carries Iout/(1−D), higher than the load current.
Buck: C = ΔIL/(8·fsw·ΔVout). Boost: C = Iout·D/(fsw·ΔVout). Lower ripple or frequency needs more capacitance; ESR often dominates real ripple.
Higher frequency shrinks L and C but adds switching loss and EMI. 100 kHz–2 MHz is typical; 300–500 kHz is a common balance.