PPTCs

PPTCs, short for polymer positive temperature coefficient thermistors, are resettable fuses used to protect electrical circuits from overcurrent. They are typically built from a conductive polymer composite that contains metal particles and are available in radial-lead disc forms as well as surface-mount packages.

In normal operation the PPTC exhibits a relatively low resistance, allowing current to flow with little loss. When excessive current causes self-heating, the polymer matrix undergoes a temperature‑driven change that disrupts conductive pathways and drives the resistance up dramatically. This limits current to protect the circuit. After the fault condition is removed and the device cools, the polymer returns to a state with low resistance, restoring normal operation without the need for replacement.

Ratings are specified by parameters such as hold current (Ih), trip current (It), and maximum operating voltage. PPTCs cover a wide range of current ratings—from milliamps to several amperes—and voltages suitable for many low‑voltage applications. They come in various form factors, including radial discs and surface‑mount chips, to fit different PCB layouts.

Applications include protection for power adapters, battery packs, USB devices, consumer electronics, telecom equipment, and automotive electronics, where a resettable protection device is advantageous.

Advantages of PPTCs include resettable protection after a fault, no need to replace fuses after a trip, and compact, simple integration. Limitations include slower response compared with instantaneous fuses, sensitivity to ambient temperature, performance drift with cycling and heat exposure, and suitability mainly for low‑ to mid‑voltage, moderate‑current applications.