3.5 A fast-blow SMD fuse for secondary-side protection
The Littelfuse 045103.5MRSN is a 3.5 A, 125 VAC fast-blow fuse from the NANO²® 451 series, housed in a 2-SMD square end block package. It is designed for board-level overcurrent protection where a quick open time is needed to protect downstream semiconductors or sensitive loads.
Breaking capacity and inrush handling
Rated breaking capacity is 50 A at 125 VAC — sufficient for interrupting low-level fault currents typical of secondary-side DC/DC converter outputs and low-power AC rails without rupturing the package. Melting I²t is 2.469 A²s, which gives a measure of the energy needed to open the fuse. This value helps predict whether the fuse will hold during brief inrush events, such as charging a bulk capacitor bank on a 3.5 A rail.
Operating temperature and approvals
Approved by CSA, METI, and UR (UL Recognized), so it is accepted in North American and Japanese equipment without additional agency review of the fuse itself.