DC-DC Converter

Choose a topology — buck, boost, or buck-boost — set the input voltage, duty cycle, inductance, and switching frequency, then watch the output voltage and inductor current ripple update live. The widget flags CCM vs DCM operation so you can see exactly when the inductor current hits zero.

V_in: 24 VD (duty cycle): 0.5 I_out: 2 AL: 100 µHf_sw: 100 kHz

During T_ON (rising)

\small\tfrac{di}{dt} = \tfrac{24-12.0}{100\,\mu\text{H}} = 0.12\;\text{A/µs}

During T_OFF (falling)

\small\tfrac{di}{dt} = \tfrac{-12.0}{100\,\mu\text{H}} = -0.12\;\text{A/µs}

Output voltage

\small V_{out} = D \!\cdot\! V_{in} = 0.5 \!\times\! 24 = 12.0\;\text{V}

Inductor ripple

\small \Delta I_L = \tfrac{(24\!-\!12.0)\!\times\!0.5}{100\text{k}\!\times\!100\mu} = 0.60\;\text{A}

Conduction mode

CCM — Continuous

Minimum inductance for CCM

L_min = 15.0 µH

Quick experiments

Buck 24 V → 12 V. Set V_in = 24 V and D = 0.5 — the output should read 12 V, confirming V_out = D · V_in.
Boost 12 V → 48 V. Switch to boost, set V_in = 12 V and D = 0.75 — the output climbs to 48 V.
Ripple vs inductance. Increase L and watch the inductor current ripple shrink — a larger inductor stores more energy per cycle, smoothing the current.

DC-DC converter topologies

DC-DC converters transfer power from one DC voltage to another with high efficiency (typically 85–95 %) by switching an inductor or transformer at high frequency (tens of kHz to several MHz).

Buck (step-down)

V_out = D × V_in where D is duty cycle (0–1). During the on-time the inductor stores energy; during the off-time it releases energy to the load. Higher switching frequency → smaller L and C values → smaller PCB footprint, but higher switching losses.

Boost (step-up) and flyback

Boost: V_out = V_in / (1−D). Energy stored in inductor during on-time is transferred to output during off-time.
Flyback: isolated topology using a coupled inductor (flyback transformer). Common in offline power supplies for galvanic isolation.

Learn more → DC-DC Converters — Learn

Formula reference

Buck converter output: $V_{out} = D \, V_{in}$
24 V at 20 % duty gives about 4.8 V.
Boost converter output: $V_{out} = \dfrac{V_{in}}{1 - D}$
5 V at 50 % duty gives 10 V.
Inductor ripple current: $\Delta I_L = \dfrac{(V_{in} - V_{out}) D}{L f_{sw}}$
Target 20–40 % of maximum load current.
Output voltage ripple: $\Delta V_{out} \approx \dfrac{\Delta I_L}{8 C f_{sw}}$
Plus the ESR term, which usually dominates in real capacitors.

Symbol	Meaning	Unit
$D$	Duty cycle	—
$f_{sw}$	Switching frequency	Hz
$\Delta I_L$	Peak-to-peak inductor ripple current	A
$L$	Inductance	H

Common mistakes

Choosing an inductor on inductance alone.
Peak current must stay below the saturation rating. A saturated inductor loses inductance, current spikes and the switch fails.
Ignoring discontinuous conduction at light load.
Once inductor current hits zero each cycle, output = duty × input no longer holds and the output rises above the expected value.
Using high-ESR output capacitors.
Output ripple is dominated by ESR times ripple current, not by capacitance. A larger electrolytic with poor ESR can perform worse than a small ceramic.
Routing the high-current loop carelessly.
The switch, inductor and capacitor loop carries fast high current. A large loop area radiates noise and adds inductance that causes ringing on the switch node.
Assuming efficiency is flat across load.
Switching and quiescent losses stay roughly constant, so efficiency collapses at light load unless the part supports burst or pulse-skipping mode.

Frequently asked questions

How does a buck converter step voltage down?

A switch chops the input into pulses and an LC filter averages them. Output equals input times duty cycle, so a 24 V input at 20 percent duty produces about 4.8 V.

What is the difference between buck, boost and buck-boost?

Buck steps voltage down, boost steps it up, and buck-boost can do either but inverts the polarity in its basic form. Which one applies is decided by whether the output must be below or above the input.

What is continuous versus discontinuous conduction mode?

In continuous mode inductor current never reaches zero within a switching cycle. In discontinuous mode it does, which happens at light load and changes the transfer function so output voltage no longer follows duty cycle alone.

How do I choose the inductor for a buck converter?

Pick inductance for an acceptable ripple current, typically 20 to 40 percent of maximum load current, then confirm the saturation rating exceeds peak current. An inductor that saturates causes current to spike and destroys the switch.

Why is my DC-DC converter inefficient at light load?

Switching losses and quiescent current stay roughly constant while output power falls, so they dominate at light load. Many converters add pulse-skipping or burst modes specifically to keep light-load efficiency reasonable.