New method of resettable circuit protection for 9V rechargeable battery

　　New MHp devices

　　The rapid growth of the high-rate discharge lithium-ion battery application market has created a need for cost-effective circuit protection devices that can provide a holding current of 30A+ under 30V DC voltage. To meet this need, a hybrid device has been developed that connects a bimetallic protector and a ppTC (Polymer Positive Temperature Coefficient) device in parallel. The resulting MHp (metalhybridppTC, metal hybrid ppTC) device can provide a resettable overcurrent protection function, while also utilizing the low impedance characteristics of the ppTC device to prevent bimetallic protectors from arcing at higher currents.

　　Figure 1 shows the shape and dimensions of a MHp device with a rated holding current of 30A, which is the same size as a typical bimetallic protector with a rated current of only 15A. In addition, the device has a flat-angled design on one side, allowing it to fit compactly between standard 18 mm diameter lithium-ion cells in the battery pack.

　　application

　　MHp circuit protection devices provide battery pack designers and manufacturers with a way to optimize space, reduce cost and enhance safety, and the device technology can be configured for a variety of applications. Devices with higher voltages and holding currents are now in development, and future design considerations include lithium-ion battery packs for cordless power tools, e-bikes, e-motorcycles, light electric vehicles (LEVs), and backup power applications. battery protection in , as well as non-battery applications such as motor protection. design concept

　　Test data shows how a typical bimetallic protector and polymer pTC integrated together, such as the polySwitchRXEF050 device, can provide similar latching benefits to a combination of ceramic pTC and bimetallic protectors while providing additional dissipation at higher currents. arc function.

　　Due to the low contact resistance of the bimetallic contacts, current flows through the bimetallic contacts under normal operation. When an abnormal event occurs, such as a locked rotor in a power tool, a higher current is generated in the circuit, causing the bimetallic contacts to open and their contact resistance to increase. At this point, the current is shunted to the lower impedance ppTC device, which also heats the bimetal, causing it to open and remain in the locked state, thus helping to prevent arcing between the contacts. Please refer to Figure 2.

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