1 A fast-blow SMD fuse for secondary-side protection
The Littelfuse 0451001.NR is a 1 A fast-blow surface-mount fuse from the NANO²® 451 series, rated for 125 V AC and 125 V DC with a 50 A breaking capacity at rated voltage. Packaged in a 2-SMD square end block format on tape and reel, it is designed for automated pick-and-place assembly in high-volume production.
Breaking capacity and I²t — what they mean for your circuit
The 50 A breaking capacity at 125 V AC/DC means this fuse can safely interrupt a fault current up to 50 A without rupturing or sustaining arc — critical for protecting downstream components in a secondary-side power rail. A melting I²t of 0.459 A²s defines the energy needed to open the fuse element. This value governs inrush-withstand capability: a capacitor bank or DC-DC input with a surge exceeding this I²t will nuisance-blow the fuse on startup. The DC cold resistance of 0.153 Ohms sets the voltage drop at rated current — 153 mV at 1 A — which matters for low-voltage rails where every millivolt of headroom counts.
Obsolete — sourcing through independent distribution
No official successor order code is recorded for this part. The part carries CSA, PSE, and UL approvals, so any sourced inventory should be verified for authentic marking and traceability to these agencies.
Board-fit and environmental envelope
The fast-blow response time means it opens within milliseconds of a sustained overcurrent — appropriate for protecting semiconductor rectifiers and DC-DC converters that cannot tolerate prolonged fault energy.