Resettable Fuses-PPTC

PPTC Protection principle：
Resettable fuses are desinged and made of polymeric PPTC material in thin  chip form where condrctive particles are dispersed in a polymer that has a crystalline structure .At normal operating conditions there are numerors chains forming conductive paths throughout the PPTC material.Under fault conditions(Tripped State),excessive current flows through the PPTC device and the PPTC material heats up.This makes the polymer matrix's morphollgy change from crystalline to amorphous.Under these conditions the conductive particles move apart from each other,the resistance of the device increases sharply and most of them no longer conduct current to protect the circuit from being damage by the high current.Upon fault current being removed and resettable fuse is cooled off,the resettalbe fuse is restted and allows the current through the circuit again. After connecting in series to a circuit, PPTC resettable fuses remain extremely low resistance and allow the electrical current to flow through it without any restriction.

Resettable Fuses -PPTC
PPTC Selections
For helping you correctly using proper PPTC resettable fuses, please make your choice according to the following methods:

Step 1:
Determine the normal operating current (I) and operating voltage (V) . ( The PEAK volume can be ignored ).

Step 2:
Determine the most suitable PPTC series according to the (I),(V)and the mount type.

Step 3:
If the inner temperature of the device is over 25℃,the current flow through the PPTC element will decrease according to the rise of temperature. In order to providing normal holding current,we can calculate the IH of the PPTC element according to the reduction rate in chart as below.
IH=NORMAL OPERATING CURRENT÷REDUCTION RATE.

Step 4:
According to the PPTC series, which selected in step 2 and  the IH calculated in step3,choose the propet element in the catalogue,the IH of the selected  PPTC must  be equal or greater than the IH that calculated in step 3.

Step 5:
We can locate the operation time of over current protectin according to the TIME TO TRIPCURSE CHART of  the selected  PPTC element.