12 A fast-blow SMD fuse for secondary-side protection
The Littelfuse 0451012.MRSN is a 12 A, 125 VAC fast-blow surface-mount fuse in 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. Its 35 A breaking capacity at rated voltage means it safely interrupts fault currents up to that level without rupturing the package — a key parameter for secondary-side protection in power supplies and DC-DC converter output stages where the available fault current is bounded by the downstream rail.
Melting I²t and cold resistance for inrush sizing
With a melting I²t of 47.97 and a DC cold resistance of 0.0049 ohms, this fuse tolerates moderate inrush pulses from capacitive loads or motor starts without nuisance opening. The low cold resistance keeps voltage drop across the fuse under 60 mV at full rated current, which matters for low-voltage rails where every millivolt of headroom counts.