Electronic Device And Electronic Circuit

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Sunday, July 23, 2006

Resettable fuses

A PolySwitch (also Polyfuse and Multiswitch) is a polymer form of

positive temperature coefficient resistor (PPTC) which acts as a self
repairing fuse.

"PolySwitch" is a registered trademark of Raychem Corporation. While the
generic term for these devices is sometimes called resettable fuses technically
these are not fuses but actually non-linear thermistors.

A PPTC has a current rating. When the current flowing through the PolySwitch
device, (which acts as a resistor) exceeds the current limit of, (for example)
100 mA, the PPTC device warms up above a threshold temperature and the
electrical resistance of the PPTC device suddenly increases from a few ohms
to a few kiloohms.