80 mA fast-blow SMD fuse — NANO² 451 series
The 0451.080NR is a Littelfuse NANO²® 451 series board-mount fuse rated 80 mA at 125 VAC and 125 VDC, with a fast-blow response time. Its 50 A breaking capacity at rated voltage means it safely interrupts a short-circuit fault up to that level without rupturing the package — a critical parameter for secondary-side protection in power supplies where the prospective fault current can hit tens of amps. The 0.00033 melting I²t figure tells you the energy needed to open the element; at 80 mA nominal load, this fuse clears fast on a hard overcurrent, but the low I²t also means it may nuisance-open on inrush pulses from a capacitive input filter if the pulse energy exceeds that threshold.
Surface-mount footprint and temperature envelope
Housed in a 2-SMD square end block package measuring 6.10 mm x 2.69 mm x 2.69 mm, the 0451.080NR mounts directly on the PCB — no through-hole leads, so the solder joint is the only mechanical anchor.
Obsolete — sourcing through independent channels
Littelfuse has marked the 0451.080NR as obsolete. No pin-compatible drop-in replacement from Littelfuse has been published, so a board spin or a parametric substitute search is the path for new designs.