Posted to News on 28th Apr 2011, 00:00
Cost-effective Li-ion overcurrent protection
Tyco Electronics has introduced a Metal Hybrid PPTC (MHP) technology useful for high-rate-discharge battery applications at ratings above 30VDC/30A such as cordless power tools, e-bikes and back-up power supplies. 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 utilises 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°C). The device's hold current is 30A and the initial resistance is under 2mOhms. 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 optimise space, reduce cost, enhance safety and help meet future battery safety requirements," says Ty Bowman, global battery market manager at Tyco Electronics.
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 standby-power applications and non-battery applications such as electric motor protection.
