2.5 A fast-blow SMD fuse for secondary-side protection
The Littelfuse 045102.5MR is a 2.5 A fast-blow surface-mount fuse from the NANO²® 451 series, rated for 125 V AC and DC circuits. It sits in a 2-SMD square end block package measuring 6.10 mm x 2.69 mm x 2.69 mm, making it a compact overcurrent protection device for densely populated boards. With a melting I²t of 1.029 and a DC cold resistance of 0.0286 ohms, this fuse coordinates well with downstream semiconductor loads — the low resistance minimizes voltage drop in the 2.5 A path, while the I²t figure helps select the upstream PCB trace width and downstream component surge ratings.
Breaking capacity and approvals for compliance
Rated breaking capacity is 50 A at the rated 125 V — this means the fuse safely interrupts a fault current up to 50 A without rupturing or sustaining an arc. For secondary-side DC rails or AC control circuits at 125 V, this covers most solid-state fault scenarios in telecom, industrial control, and power-supply outputs. Approvals from CSA, PSE, and UL provide acceptance in North American and Japanese regulatory jurisdictions — a signal to compliance engineers that the fuse meets the relevant safety standards for board-level overcurrent protection. The operating temperature range spans -55°C to 125°C, covering industrial and automotive ambient conditions — the fuse element's thermal response shifts at the extremes, but the fast-blow characteristic holds across the band.
Obsolete — sourcing through independent channels
Availability is lot-specific and confirmed at quote time — the 2-SMD square end block footprint and 2.5 A fast-blow characteristic must match the original design's PCB land pattern and coordination study.