Schurter Polymeric Positive Temperature Coefficient (PPTC) fuse enable convenient protection of low voltage supplies, with the advantage of rest.
At normal temperature there are numerous carbon chains forming conductive paths through the device.
Under fault conditions, I²R heating causes the carbon chains to be pushed apart, with most of them no longer conducting current and the resistance of the device increases sharply.
The PPTC remains latched, providing continuous protection, until the fault is cleared and the power is removed.
Reversing the phase transofrmation allows the carbon chains to reform as the polymer re-crystallises.
The resistance quickly returns to its original value.
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