Inductor Current Ripple
Calculate the inductor current ripple of a buck converter, ΔI_L = (V_in × D) ÷ (L × f), from the input voltage V_in, the duty cycle D, the inductance L and the switching frequency f. The result, in amperes, is the peak-to-peak variation of the inductor current each cycle. It is a central design parameter: a typical ripple of 20-40% of the average current is a good compromise. Higher inductance and frequency reduce the ripple (larger inductor, more costly; higher frequency, more switching losses). It also sets the boundary between continuous and discontinuous conduction. Enter the voltage, duty cycle, inductance and frequency.
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Inductor current ripple
In the inductor of a buck converter, current is anything but constant: it rises during the on portion of the cycle (while the source drives the inductor) and falls during the off portion — forming a triangular wave superimposed on the average current. The peak-to-peak amplitude of that swing is the current ripple: ΔI_L = (V_in × D) ÷ (L × f), where V_in is the input voltage, D the duty cycle, L the inductance and f the switching frequency. This ranks among the most important design parameters of a converter, with several trade-offs. A typical ripple of 20 to 40% of the average output current counts as a good balance. Ripple that is too low demands a very large inductor (more volume, weight and cost). Ripple that is too high raises losses (RMS current climbs, and the peaks stress the switch and the capacitor harder) and, at the limit, leads to discontinuous conduction (inductor current reaching zero every cycle) — a different operating mode, with its own conversion ratio and dynamics. The formula shows how to control the ripple: higher inductance or higher frequency both cut it down. Hence the appeal of high switching frequencies (hundreds of kHz up to MHz): they allow smaller inductors and capacitors for the same ripple, shrinking the supply — at the cost of greater switching losses, which grow with frequency, in a balance central to the design. Current ripple also sets the peak inductor current (which must never saturate it) and influences the output voltage ripple. Enter the voltage, the duty cycle, the inductance and the frequency.
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