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An N+1 Battery Backup System

IP.com Disclosure Number: IPCOM000014468D
Original Publication Date: 2001-Aug-28
Included in the Prior Art Database: 2003-Jun-19

Publishing Venue

IBM

Abstract

The disclosed circuit requires one additional battery connected in parallel to the required batteries. In Laptop systems, multiple 3.3V cells are connected in series to develop a 12V bulk voltage to power the DC/DC converters inside the computer. Failure of any one of the cells in the series results in failure of the whole battery back even though only one cell in the series is defective. The proposed circuit prevents this from happening by isolating the defective cell while still providing the full power capability. The conventional battery pack uses multiple Lithium or Lithium ion cells in the series to generate +12V DC voltage. As shown in Figure 1 , three cells BT1, BT2 and BT3 are connected in the series. These cells are charged by an AC/DC connector and the charge rate is controlled by a built in charging circuitry in the battery pack. Also, there is a cut out switch inside each cell that opens permanently. As a result, either the cell gets shorted or some other stress is developed inside the cell. The problem arises when any one of the cells in the series becomes defective, the battery pack will become useless. An expensive battery pack has to be replaced by a new battery pack. Sometimes the battery pack is not immediately available and this could be a great problem. BT3 R2 R4 R1