ePoly (Polymer PTC Resettable Fuse)
Self-resetting over-current protection using positive-temperature-coefficient polymers.
What is it?
ePoly devices (also called PTC / PolySwitch / Multifuse) are resettable fuses based on a polymer matrix with conductive carbon-black filler. At normal current the polymer is low-resistance. Under fault current it heats up, the polymer expands, the carbon-black network breaks, and resistance rises by 4-6 orders of magnitude — effectively interrupting the current. When the fault clears and the device cools, it returns to low resistance — no replacement needed.
When do you need it?
- USB host port over-current protection (computers, hubs).
- Battery-pack over-current protection.
- Motor protection where occasional stalls shouldn't blow a fuse.
- Speaker line protection.
- Any rail where automatic recovery after fault is desired (instead of a one-shot fuse).
How to pick the right one
- Ihold (Hold Current)
- Maximum current the device will pass indefinitely without tripping. Should exceed your normal operating current with margin.
- Itrip (Trip Current)
- Minimum current that will reliably trip the device. Should be below the load's failure threshold.
- Vmax (Maximum Voltage)
- Maximum rail voltage the device can interrupt safely.
- Time-to-trip
- How fast the device opens at a given over-current. Faster = better load protection but more nuisance trips during inrush.
- R(typ) and R(max)
- Series resistance in normal state. Affects voltage drop and self-heating.
What Magnias offers
Magnias ePoly portfolio covers SMD packages from 0805 to 2920 with hold currents from 50 mA to 12 A, voltage ratings 6 V to 60 V. Includes specific variants for DDR5 RDIMM (MGF06F-6000A 6 A for rev 0/1, MGF06F-7000A 7 A for rev 2).