Buck Converter Calculator

A buck converter steps down a higher input voltage to a lower output voltage using a high-speed switching element and an energy-storage inductor. The fundamental relationship is dictated by the duty cycle (D), defined as the ratio of output voltage (V_out) to input voltage (V_in): D = V_out / V_in. Based on this duty cycle, the required inductance (L) to maintain a specific inductor ripple current (I_ripple) at a given switching frequency (f_sw) is calculated using the formula: L = (V_in - V_out) × D / (f_sw × I_ripple).

Let us walk through a practical engineering scenario. Suppose you want to design a step-down converter with an input voltage (V_in) of 24 V and a desired output voltage (V_out) of 5 V. Your switching frequency (f_sw) is set to 250 kHz, and you want to limit the inductor ripple current (I_ripple) to 0.4 A. First, calculate the duty cycle: D = 5 / 24 = 0.2083 (or 20.83%). Next, apply the inductance formula: L = (24 - 5) × 0.2083 / (250,000 × 0.4). This yields L = 3.96 × 10^-6 Henries, meaning you would select a standard 3.9 µH inductor for your circuit.

When implementing your calculations into physical hardware, always select an inductor with a saturation current rating significantly higher than your peak switch current to prevent core saturation. Additionally, choose your switching frequency as a trade-off: higher frequencies allow for smaller physical inductors and capacitors, but increase switching losses and thermal dissipation in your power transistors.