Optimum Li-ion Battery Pack Short Circuit and Overcharge Protection with Low Temperature Polymeric PTC Devices while maximizing battery pack run time

摘要

For consumers, the time required to fully charge a pack is important, thus most pack/charger combinations are designed to deliver charge at the fastest possible rate that is safe. Protection devices are usually specified such that they will pass the current required to meet this charge rate at the maximum safe temperature expected during charging. Low temperature PPTC devices are uniquely suited to limiting the charge current dose to the functional pack's operating temperature. The device's resettable function ensures that nuisance tripping, which can be caused by exposure to direct sunlight or other heat sources, does not permanently disable the pack. One-shot secondary overcurrent protectors, such as thermal fuses, are difficult to set at the low temperatures required for charge protection, and may trip in high ambient temperatures, disabling an otherwise functional pack. The new lower resistance PolySwitch VLR device line of PPTC devices is the practical choice for improving Li pack performance without sacrificing either overcurrerrt or overcharge protection. Tyco Electronics' Raychem Circuit Protection division continues to innovate its material offerings in keeping with the demand for lower resistance devices with equivalent or superior overcharge protection. The nickel leads and low profile of PPTC devices allow them to be welded directly to battery cells without encumbering pack design. They meet UL1950/IEC 950 safety requirements and are available in a wide range of sizes and ratings, allowing the designer to select the best device for a specific battery pack protection application. Reference 1: Latest Generation of Low Temperature PPTC Materials For Portable Electronics Li-Ion & NiMH Battery Protection (c) 1998.