A polymeric PTC device comprises a non-conductive crystalline organic polymer matrix that is loaded with carbon black particles to make it conductive. While cool, the polymer is in a crystalline state, with the carbon forced into the regions between crystals, forming many conductive chains. Since it is conductive (the "initial resistance"), it will pass a given current, called the "hold current". If too much current is passed through the device, the "trip current", the device will begin to heat. As the device heats the polymer will expand, changing from a crystalline into an amorphous state. The expansion separates the carbon particles and breaks the conductive pathways, causing the resistance of the device to increase. This will cause the device to heat faster and expand more, further raising the resistance. This increase in resistance substantially reduces the current in the circuit. A small current still flows through the device and is sufficient to maintain the temperature at a level which will keep it in the high resistance state. The device can be said to have latching functionality. The critical material, which is a carbon black and plastic mix, used in the automatically resetting devices described in this article was serendipitously discovered and then described by author and scientist Fred Kohler, and patented as patent #3,243,753 on March 29, 1966.[4]
Since a PPTC device has an inherently higher resistance than a metallic fuse or circuit breaker at ambient temperature, it may be difficult or impossible to use in circuits that cannot tolerate significant reductions in operating voltage, forcing the engineer to choose the latter in a design.
Das spricht die Wikipedia zu den SELBSTRÜCKSETZENDEN Sicherungen. Also quasi ein wahnsinnig beschissener PTC, der imho in dem Gerät (das schon seit der Prototypenphase an genau dem Problem kränkelt) fehl am Platze.
Von ner Schmelzsicherung war hier nie die Rede.
Auch find ichs dämlich, sich in einem FRICKLERFORUM wegen ner überbrückten Sicherung hier an den Pranger stellen zu lassen.
Zuletzt bearbeitet: 02.12.12 20:53 von shpank
