DC-DC Converter Calculator

A Buck (step-down) converter reduces a higher input voltage to a lower output voltage. It is the most common DC-DC topology, used in everything from smartphone chargers and laptop power rails to automotive electronics. For example, converting a 12 V system rail down to 3.3 V for a microcontroller uses a Buck topology. The duty cycle D = Vout/Vin must be less than 1, meaning Vout must be less than Vin.

A Boost (step-up) converter raises a lower input voltage to a higher output voltage. Common applications include LED drivers (boosting a single-cell battery to the LED forward voltage), power factor correction circuits, and USB charging from low-voltage sources. The duty cycle D = 1 − Vin/Vout means Vout must always be greater than Vin, otherwise the calculator returns no result.

The duty cycle (D) is the fraction of each switching period during which the power switch (MOSFET) is ON. In a Buck converter, D = Vout/Vin. At D = 0.25, the switch is on for 25% of each cycle and off for 75%. The duty cycle directly determines the voltage conversion ratio, and at steady state it is set by the feedback control loop to maintain the target output voltage.

Higher switching frequency (e.g., 500 kHz–2 MHz) allows smaller inductors and capacitors, reducing board area and cost, but increases switching losses in the MOSFET and diode. Lower frequency (e.g., 50–200 kHz) reduces switching losses but requires larger components. Most modern integrated DC-DC controllers operate between 200 kHz and 2 MHz. Enter your target frequency in kHz — the calculator will size the inductor and capacitor accordingly.

Current ripple (ΔIL) is the peak-to-peak variation in inductor current during each switching cycle. Expressed as a percentage of the output current, typical design targets are 20%–40%. A 30% ripple (the default) is a common starting point. Lower ripple requires a larger inductor but reduces output voltage ripple and stress on the capacitor. Higher ripple allows a smaller inductor but may push the converter into discontinuous conduction mode (DCM) at light load.

ESR (Equivalent Series Resistance) is the parasitic resistance of a capacitor. In a DC-DC converter, ESR contributes directly to output voltage ripple: Vripple_ESR = ΔIL × ESR. The calculator outputs the maximum ESR that keeps ripple within your specified voltage ripple percentage. If you select a capacitor with lower ESR (e.g., ceramic MLCC vs. electrolytic), the ripple will be lower than spec; if higher, you will exceed the ripple budget.

Peak current is the maximum instantaneous current through the inductor — important for saturation rating selection. An inductor must never saturate below its peak current. RMS current determines I²R heating losses in the winding resistance — the inductor's current rating should exceed the RMS value. Average current equals the output current (for Buck) or average input current (for Boost/Buck-Boost). All three are shown in the calculator results.

No. This calculator covers non-isolated topologies only: Buck, Boost, and inverting Buck-Boost. Isolated converters such as flyback, forward, push-pull, half-bridge, and full-bridge require transformer design (turns ratio, magnetizing inductance, leakage inductance) and different duty cycle relationships that are outside the scope of this tool. A dedicated flyback calculator or SMPS design software like PSIM or LTspice would be more appropriate for isolated designs.