Tyco Electronics’ Resettable Overcurrent Protection Device For Li-ion Batteries Offers Size And Cost Benefits

MHP technology uses a new hybrid circuit protection approach that combines a bimetal protector in parallel with a polymeric positive temperature coefficient (PPTC) device. This integrated solution provides resettable overcurrent protection and utilizes the low resistance of the PPTC device to help prevent arcing in the bimetal protector at higher currents, while also heating the bimetal to keep it open and in a latched position.

Due to advances in lithium ion (Li-ion) technology, smaller, lighter weight, and higher power Li-ion batteries can now replace nickel cadmium or lead acid batteries previously used in high-rate-discharge battery applications. This trend has resulted in a rapidly expanding market for high-rate-discharge Li-ion battery applications, which, in turn, has created the need for cost-effective, robust circuit protection devices that help ensure battery safety in end-products.

However, few protection solutions address high-rate-discharge battery applications and traditional circuit protection techniques tend to be large, complex and/or expensive. In response, MHP technology provides a cost-effective, space-saving device that conventional circuit protection approaches are unable to deliver.

The initial product in a planned family of MHP devices, the MHP30-36 device, has a 36VDC/100A maximum rating and a time-to-trip of under five seconds at 100A (at 25 degrees C). The device’s hold current is 30A and the initial resistance is under two mOhms.

The MHP30-36 device offers excellent arc suppression characteristics compared to standard breaker devices that must limit the number of switching cycles since arcing between contacts may damage them. The MHP30-36 device can also help reduce the number of discharge FETs and accompanying heat sinks in applications that typically use IC-plus-FET battery protection designs.

“Available in a convenient small form factor, the MHP30-36 device provides a rugged, resettable circuit protection solution that offers battery pack designers and manufacturers a method to optimize space, reduce cost, enhance safety and help meet future battery safety requirements,” said Ty Bowman, Global Battery Market Manager.

The MHP device technology can be configured for various applications, and higher voltage (up to 400VDC) and hold current (60A) devices are currently in development. Future design considerations include battery protection in Li-ion battery packs used in e-scooters and light electric vehicles (LEVs), as well as standby-power applications and non-battery applications such as electric motor protection.