When a DC-DC converter is initially powered, the input bulk capacitors must be charged. Current flowing into the input terminals of a DC-DC converter is approximately the input I = V/R for typical power supplies with charge times less than 10 milliseconds. Where V is the input voltage change and R is a combination of wiring resistance, the source’s resistance under start-up, and the Equivalent Series Rating (ESR) of the converter’s input bulk capacitors. Larger DC-DC converters often use a large capacitor with very low ESR inside the converter. This inrush current can have a significant effect on the fuse’s life. Size the fuse properly to allow these inrush current pulses to pass without nuisance openings or degrading the fuse element as discussed in melting integral. To calculate current pulse energy, one must first determine the magnitude and duration of the current pulse. The most accurate way to determine parameters of a current pulse is to measure this current in the application under minimum and maximum voltage conditions.