SERIES PROTECTIONS

Series protections protect circuits from over currents, when the nominal max allowed current is exceeded.
Fuses, power resistors, Circuit Breaker and PTC thermistors(Positive Temperature Coefficient) are used as series protections.

Usually consumer devices protections do not use fuse being irreparable. leaving to upstream devices such as thermal switches this duty. On the other hand applications for avionics, expressly demand a non restorable
fuse. In these cases the fuse is replaced by a power resistor, to limit current.

PTC: These devices vary their resistance according to the temperature, the greater it is the current that flows, the greater will be the temperature and therefor greater will be the resistance, protecting the downstream device. They are frequently used in protections, both for power and phone lines, because they are restorable (even if slowly).

EPCOS e VISHAY are without a doubt the most important producers of PTC

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