2.5 A fast blow SMD fuse for secondary-side protection
The Littelfuse 045102.5MRSN is a 2.5 A, 125 VAC fast-blow surface-mount fuse from the NANO² 451 series, housed in a 2-SMD square end block package measuring 6.10 mm x 2.69 mm x 2.69 mm. Rated breaking capacity is 50 A at the rated voltage — this fuse safely interrupts fault currents up to that level without rupturing the package, which is the standard clearing capability for this class of secondary-side board-level protection. The fast-blow response clears on sustained overcurrents quickly, making it a fit for protecting DC-DC converter outputs, point-of-load rails, and other circuits where the load does not draw heavy inrush at startup.
Melting I²t and cold resistance — inrush and voltage-drop check
Melting I²t is 1.029 — this is the energy required to open the fuse element. A downstream capacitor bank that charges with a surge exceeding this value will nuisance-blow the fuse unless the pre-charge or soft-start limits the inrush energy below this threshold.
Active lifecycle and sourcing posture
Store the reels in a dry environment per the manufacturer's handling recommendations — the SMD package itself is not moisture-sensitive per JEDEC levels, but the reel packaging should be kept below 30°C / 60% RH to avoid tape deformation during reflow.
Approvals and temperature range
Approved by CSA, METI, and UR — the UR mark indicates UL recognition for North American equipment, CSA covers Canadian acceptance, and METI covers Japanese market compliance. These three approvals cover the major regulatory jurisdictions for power supplies, industrial controls, and consumer electronics.