Appliance Design - March 2008 - (Page 30)

POWER Taming the Li-ion New batterymanagement ICs aid design of high-voltage, Li-ion battery packs. by michael l. coletta Michael L. Coletta is principal engineer, Intersil Corp., Milpitas, Calif. 30 applianceDESIGN March 2008 n the past, high-voltage, battery-operated products depended upon large, heavy lead-acid type batteries to deliver the necessary power. The size and weight of lead-acid battery packs often limited the range of battery-operated products that could be developed. Thanks to advances in battery technology, high-voltage battery packs can now be found in cordless power tools, cordless home appliances, mobile medical equipment, electric bicycles and more. These products present a unique set of challenges to today’s product designers. The three characteristics most important to endusers of battery-operated products tend to be portability (light weight), high performance, and low cost. By contrast, the most important concerns for product designers are usually safety, reliability, and usable product life. Each of these requirements, which are often in conflict, must be satisfied and balanced against each another. To meet both user requirements and environmental regulations, for instance, designers are adopting the latest generations of lithium-ion battery technology. New generation Li-ion cells can meet the needs of systems with high-power requirements, as well as systems with high-energy requirements. These Li-ion battery packs all share the need for in-pack battery monitoring and protection circuitry that was not necessary for battery packs using nickel-cadmium or nickel-metal- I hydride cells. Li-ion battery packs generally require safety features such as: Pack over-current monitoring and short-circuit monitoring. Cell over-voltage and under-voltage monitoring. Pack/cell temperature monitoring. Additionally, cell balancing and packcapacity monitoring may also be desired to further enhance the user experience. While low-voltage battery powered products such as notebook computers and camcorders present a fairly constant demand for power from the battery, high-voltage battery products such as power tools and various mobility products have a higher demand for instantaneous power that must be supplied from the battery. Because of the extreme demands that can come from these devices, the battery pack monitoring and protection electronics are more complicated and provide additional levels of protection not found in the typical constant-demand battery packs. Well-designed multi-cell monitoring and protection integrated circuits offer multiple levels of detection for error conditions, as well as timing windows for these error conditions to clear. At the same time, these ICs also provide hard limits beyond which a hard fault condition is deemed to have occurred. Fig. 1 illustrates a simple example of a Li-ion battery pack that might be seen in a cordless power tool or small home appliance applicawww.applianceDESIGN.com http://www.appliancedesign.com

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Appliance Design - March 2008 Contents Editorial Shipments/Forecasts News Watch A New Appliance is Set to Break into Homes Soon - the Micro CHP Unit, which Generate both Heat and Power. Thermally Enhanced Varistors Help Protect Low-Power Systems Against Damage Caused by Over-Current, Over-Temperature and Over-Voltage Faults. Hybrid Controller Reduces Standby Power Consumption and Improves Active-Mode Efficiency. Battery-Management ICs Solve Design Challenges for Cordless Appliances Using High-Voltage, Lithium-Ion Battery Technology. A Semiconductor Solution Protects the Relay in a Temperature Controller for a Cooking Appliance. New Polyurethane Foam Insulation System Optimizes both Insulation Performance and Productivity. Innovations in Decorative, Pre-Finished Metals Expand Range of Design Options for Appliance Designers. Design Marts Association Report: AHAM Advertiser's Index

Appliance Design - March 2008

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