Controlled power fade for battery powered devices

#The present disclosure relates to portable electronic devices powered by batteries and, more particularly, to methods for controlling power fade during operation of such devices.

#Cordless products or devices which use rechargeable batteries are prevalent in the marketplace. Rechargeable batteries may be used in numerous devices ranging from computers to power tools. Since the devices use a plurality of battery cells, the battery cells are commonly packaged in a battery pack. The battery pack may in turn be used to power the devices when coupled thereto. Once depleted, the battery pack may be recharged by a battery charger

#Over the past few years, lithium-ion (Li-ion) batteries have begun replacing nickel-cadmium (NiCd), nickel-metal-hydride (NiMH), and lead-acid batteries in such portable electronic devices. As compared to NiCd and NiMH batteries, Li-ion batteries are lighter but have a larger capacity per unit volume. For this reason, the Li-ion batteries are suitable to devices that are preferably light and which are required to endure continuous use for a long time. Li-ion batteries, however, may deteriorate rapidly when subjected to overcharging, over-discharging, overheating, or other adverse conditions. Therefore, these types of devices employ protective measures to prevent such adverse conditions. Upon detecting an adverse condition, the system can be designed to abruptly terminate discharge of current from the batteries and thereby cease device operation.

#FIG. 1 is a schematic illustrating an exemplary embodiment of a power tool;

#FIG. 2A is a block diagram illustrating inputs and outputs to a discharge control module;

#FIG. 2B is a flow diagram illustrating an exemplary embodiment of a control loop;

#The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure. Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings.

#FIG. 1 depicts an exemplary configuration of a power tool assembly comprised of a power tool 12 and a battery pack 14. The power tool assembly may be comprised of a tool instrument (not shown) which is driven by a motor 22. The motor 22 is controlled by a discharge control module 20. The discharge control module 20 monitors various conditions of the power tool and the battery pack and controls the power output to the motor accordingly. The exemplary configuration is merely provided as a context for describing the concepts presented below. It is understood that the configuration may represent only a portion of the internal circuitry and thus may include additional functionality or components such as protection circuits which are not shown herein for reasons for clarity.

#In the exemplary embodiment, the battery pack 14 is removably coupled via cell tabs or terminals (not shown) to the power tool 12. The battery pack 14 includes three battery cells, 32A, 32B and 32C although more or less cells are contemplated. For purposes of describing the exemplary embodiments, the battery pack 14 employs cells having lithium-ion cell chemistry. It is understood that the battery pack 14 may be composed of cells of another lithium-based chemistry, such as lithium metal or lithium polymer, or another chemistry such as nickel cadmium (NiCd), nickel metal hydride ride (NiMH) and lead-acid, for example. Additionally, other means of coupling the pack 14 to the tool 12 are envisioned or the pack 14 may be integrated into the power tool 12.