Overcurrent Circuit Protection
The circuit designer has a choice of technologies when faced with the task of providing overcurrent protection. The traditional fuse and the Polymer based PTC (positive temperature coefficient) device represent the most common solutions employed. Understanding the differences between these two components simplifies choosing the best protection device for the application.

Fuses have been referred to as “one time” devices, in that the fuse will provide protection from the overload by opening only once and then it needs to be replaced. The heart of a typical fuse is a length of wire which is heated to its melting point by the excessive current. The circuit current flow decreases to zero as the wire melts open.

The PTCalso reacts to the excessive current but is known as a “resettable” device. The polymer based unit can provide overcurrent circuit protection a number of times when reset by removing the overload. The conductive polymer increases in resistance when heated by the overload and limits the circuit current.