Protection
Chip Fuses
One-shot over-current protection for fault containment.
What is it?
A chip fuse is a small SMD device with a metal element that melts and breaks the circuit when current exceeds its rating for long enough. Unlike a resettable PTC, a chip fuse is single-use — once blown, replace it. Chip fuses respond much faster than PTCs at high over-currents, making them the right choice for short-circuit fault containment.
When do you need it?
- Mains-side primary protection in power supplies.
- Battery-pack output where short-circuit current can be very high.
- Critical-fault containment where you specifically WANT the device to be removed from service after a fault (so a technician investigates).
- PCB-level over-current protection for cost-sensitive designs (chip fuses < ePoly).
How to pick the right one
- Rated current (In)
- The maximum continuous current. Pick at least 25% above your worst-case normal current.
- Breaking capacity (IR)
- Maximum short-circuit current the fuse can interrupt safely. Critical for high-voltage rails.
- Rated voltage (UR)
- Maximum DC or AC voltage the fuse can clear after melting.
- Response type (FF / F / T)
- Very-fast (FF) for semiconductor protection, fast (F) general, slow / time-lag (T) for inrush tolerance.
- Package
- 0402, 0603, 1206, 1210, 2410 — bigger = more current rating.
What Magnias offers
Magnias chip fuses are available in 0402 to 2410 SMD packages, rated 0.5 A to 30 A, with both fast-acting and time-lag response. Halogen-free and RoHS compliant.
Common questions
Fuse or ePoly?
Fuse for one-shot fault containment (cost-effective, fast). ePoly for auto-recovery (no service visit needed). Both for layered protection — ePoly for routine overloads, fuse for catastrophic faults.
How fast does a fuse blow?
Depends on the fuse type and the over-current ratio. A fast 1 A fuse at 5 A might blow in <10 ms; at 1.5 A it could take 10+ seconds. Always check the I²t curve in the datasheet.
Can fuses fail intermittently?
Yes — fatigue from repeated near-rating cycles can weaken the element. Don't run fuses at >75% of rating continuously.