2.5 A fast-blow SMD fuse for secondary-side protection
The Littelfuse 045102.5MRL is a 2.5 A, 125 V AC/DC fast-blow surface-mount fuse from the NANO²® 451 series, designed to clear quickly on overcurrent events in low-voltage DC rails or secondary AC circuits. With a 50 A interrupting capacity at rated voltage, it handles fault currents typical of secondary-side power supplies and control circuits, though it is not rated for primary distribution-level faults.
Fast-blow response and let-through energy
The fast-blow characteristic with a melting I²t of 1.029 means the fuse opens rapidly on short-circuits, limiting the energy let-through to downstream semiconductors and sensitive loads. A DC cold resistance of 0.0286 Ohms keeps insertion loss low — at 2.5 A the voltage drop is under 72 mV, which matters for low-voltage rails where every millivolt counts.
Housed in a 2-SMD square end block measuring 6.10 mm x 2.69 mm x 2.69 mm, the 045102.5MRL fits dense PCB layouts where space is constrained — common in telecom line cards, battery management systems, and portable equipment.
Temperature grade and approvals
CSA, PSE, and UL approvals mean the part is accepted in North American and Asian regulatory jurisdictions without additional qualification testing.