First,what is a resettable fuse

Resettable fuse is named for the traditional disposable fuse. A resettable fuse is an overcurrent electronic protection element that is commonly used to protect circuits from electrical faults such as overloads and short circuits, increasing the reliability and life of equipment. Unlike conventional fuses, resettable fuses can be reset automatically without the need for replacement. According to different materials, resettable fuses can be categorized into polymer resettable fuses and ceramic resettable fuses. According to different package forms are divided into plug-in resettable fuses and patch resettable fuses.

Second,the principle of resettable fuse

Resettable fuse is composed of specially treated Polymer and conductive particles (Carbon Black) distributed inside.

Under normal operation, the polymerization resin closely to the conductive particles, bound in the crystalline structure outside, constituting a chain of conductive electrical pathway, at this time, the resettable fuse for the low-resistance state (a), the line flowing through the resettable fuse of the current generated by the heat of the small, will not change the crystal structure.

When a short circuit or overload occurs in the line, the large current flowing through the resettable fuse, the heat generated by the polymerized resin melts, the volume grows rapidly, forming a high-resistance state (b), the operating current decreases rapidly, thus restricting and protecting the circuit.

When the fault is removed, the resettable fuse is re-cooled and crystallized, the volume shrinks, the conductive particles re-form the conductive path, and the resettable fuse is restored to a low-resistance state, thus completing the protection of the circuit without manual replacement.

Third, the resettable fuse action principle

The action principle of the resettable fuse is a dynamic balance of energy, the current flowing through the resettable fuse, due to the relationship between the thermal effect of the current, producing a certain degree of heat (resettable fuse resistance), the heat generated by all or part of the distribution to the environment, and did not distribute out of the heat will increase the temperature of the resettable fuse components.

During normal operation, the temperature is low and the heat generated is balanced by the heat dissipated.

The resettable fuse element is in a low resistance state, the resettable fuse does not operate. When the current flowing through the resettable fuse element increases or the ambient temperature rises, the resettable fuse still does not operate if the balance between the heat generated and the heat emitted is reached.

When the current or ambient temperature increases again, the resettable fuse will reach a higher temperature.

If the current or ambient temperature continues to increase, the heat generated will be greater than the heat emitted, so that the resettable fuse element temperature increases suddenly, at this stage, a very small change in temperature will cause a significant increase in the resistance value, then the resettable fuse element is in a high-resistance protection state, the impedance increases to limit the current, the current in a very short period of time dropped sharply, thus protecting the circuit equipment from damage as long as As long as the heat generated by the applied voltage is sufficient to dissipate the heat from the resettable fuse element, the resettable fuse element in the changed state can remain in the action state (high resistance).

When the applied voltage disappears, the resettable fuse is automatically restored.