PolySwitch

PolySwitch refers to a family of polymer-based resettable fuses, also known as polymeric positive temperature coefficient (PPTC) devices. The name originated with Raychem, the inventor of the technology, and is now associated with TE Connectivity’s line of PPTCs. While PolySwitch is a brand name, the devices are widely referred to as polymer resettable fuses and are produced by multiple manufacturers.

Operation in normal use, a PolySwitch device presents a low resistance path in the circuit. When excessive current or a short circuit causes overheating, the polymer matrix undergoes a reversible transition that disrupts the conductive network, causing a rapid rise in resistance and effectively limiting current. Once the fault condition is removed and the device cools, the material returns to its low-resistance state and the circuit is re-energized without replacement.

Construction and ratings vary, but PolySwitch devices are typically small, disk- or chip-shaped polymer elements encapsulated for protection. They are specified by hold current (the maximum current the device can carry without tripping), trip current (the current that initiates the resistance jump), and voltage rating, along with response time and environmental tolerances. The devices are designed for repeated protection cycles rather than one-time faults.

Applications include consumer electronics, power adapters, USB and data devices, battery packs, automotive electronics, and other equipment requiring overcurrent protection that can reset automatically after the fault is cleared. Their main advantages are resettable protection, compact size, and no single-use fuse replacement, while limitations include higher resistance after trip and sensitivity to ambient temperature and long-term aging.

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