PTC thermistors have been used in a wide variety of applications over the years.  PTC thermistor applications make use of the characteristics inherent in their composition.  Generally, PTC thermistor applications are broken up into two distinct categories that utilize different characteristics of the PTC.  The first characteristic is those applications that utilize the voltage-current of current-time characteristics of the PTC thermistor.  These are sometimes known as self-heated applications.  The other general category is zero power or sensing applications.  Unlike the NTC thermistor, the resistance versus temperature characteristic of a PTC thermistor is not well defined and applications that utilize the resistance versus temperature characteristic tend to utilize only a small portion of the RvT curve and utilize broader tolerances than that of NTC thermistors.