At present, the mainstream mobile phone chargers on the market have changed from 500mA~700mA charging current to 1A~2A charging current. The increase in charging current also puts forward higher requirements for the charging data line, not only the diameter of the power line and the grounding line in the data line has become thicker, but also the reliability of the small microUSB port contact. high. If the microUSB port has poor contact during use, or foreign objects (similar to sweat) etc. happen, then during the 2A current charging process, there will be a lot of power consumption at the microUSB port (I2R If the power consumption greatly exceeds the range that the microUSB port of the mobile phone can withstand, the port will heat up, and then burn to black. In severe cases, the mobile phone will be burned and a fire may occur. In the actual use of smartphones, cases of mobile phones burned or even exploded are also heard from time to time. This poses a major danger to the personal safety of consumers. The safety protection of smartphone microUSB ports has become an urgent need for many manufacturers to improve. Subject.

In view of the above risks in the microUSB port of the smart phone data line, it is proposed to use a positive temperature coefficient thermistor, a resettable fuse, PPTC, to install the protection element inside the microUSB data line for effective overcurrent and overtemperature protection.

Polymer self-recovery fuses are composed of semi-crystalline polymer and conductive particles. At normal temperature, conductive particles form a low-resistance grid in the polymer. However, whether due to an increase in current through the device or due to an increase in ambient temperature, when the temperature reaches the switching temperature (TSw) of the device, the lens in the polymer will melt and become amorphous. During the melting of the lens, its volume will increase and the conductive particles will be separated, resulting in an increase in the non-linear resistance of the device. As long as the externally applied power supply voltage remains at this level, the device will always be locked in the operating state (that is, the device will always remain latched in the protection state). Once the voltage drops or the power supply is disconnected and restarted, the PPTC self-recovery fuse will return to its normal working state.

Place the PPTC resettable fuse in the microUSB port. When the port temperature exceeds a certain value, the resettable fuse will act, and the resistance will increase to cut off the charging current up to 2A, cooling down the temperature of the microUSB port without damaging the port. The use of Shuoke Electronics' PPTC resettable fuse device as a protection scheme has the characteristics of high reliability, low cost, and simple use. It is not only widely used on smart phones, but also very common on other mobile smart devices such as tablet computers.