The possible failure situations of a PPTC (resettable fuse) include the following:
- Long-term overcurrent: When the PPTC encounters a long-term small overcurrent, although it will not act immediately, it may gradually age over time, increase resistance, and eventually fail to recover to its original state.
- Environmental factors: PPTCs are very sensitive to temperature. Excessively high ambient temperature may cause its trigger temperature to drop, resulting in premature action under normal working current. In addition, extreme temperature cycles may cause material aging or damage.
- Current shock: Although the PPTC can withstand a certain amount of overcurrent shock, if the overcurrent is too large or lasts too long, it may cause permanent damage to the material which cannot be recovered.
- Frequent action: Multiple actions of a PPTC will cause its internal structure to gradually age, and the resistance value may continue to increase, eventually causing the component to fail to recover normally.
- Physical damage: External shock, mechanical stress, or improper operation during installation may cause structural damage to the PPTC, leading to failure.
- Aging problem: After long-term use, the material of the PPTC may age and the electrical performance may deteriorate, resulting in failure to recover normally or excessive resistance value.
These failure modes are mainly caused by the material properties and usage environment of the PPTC, so it is necessary to carefully select the appropriate model in the application and ensure that its working environment is within the design range.