Overcurrent Protection Device Self-recovery Fuse PPTC

- Feb 02, 2018 -

Self-recovery fuse (PPTC: Polymer self-recovery fuse) is a positive temperature coefficient polymer thermistor, used for overcurrent protection, can replace current fuses. When the circuit is working properly, its resistance is very small (pressure drop is very small), when the circuit appears over the current to increase its temperature, the value of a sharp increase in several orders of magnitude, so that the current in the circuit reduced to the safety of the following, so that the circuit behind the protection, after the flow disappeared automatically restored to low resistance. The effect is similar to the switch element, but the response speed is slow. It has three kinds of package forms: lead type, slice type (belt type) and mount type.

The polymer self-recovery fuse consists of a polymer matrix and a carbon black particle that makes it conductive. Since the polymer fuses as a conductor, the current is passed through. When there is a current through the polymer self-recovery fuse, the resulting heat will make it swell. Thus the carbon black particles will be separated and the resistance of the polymer self recovery fuse will rise. This will make the polymer self-recovery fuse faster to produce heat, expand more, and further increase the resistance. When the temperature reaches 125°c, the resistance changes significantly, so that the current decreases significantly. At this point the small current flowing through the polymer self-recovery fuse is sufficient to keep it at this temperature and in a high resistance state. When the fault is cleared, the polymer fuses to the original shape to reconnect the carbon black particles, thereby reducing the resistance to a specified level of maintaining current. The above procedure can be cycled several times.


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