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DEEP DISCHARGE PREVENTION CIRCUIT FOR BATTERY

IP.com Disclosure Number: IPCOM000006481D
Original Publication Date: 1992-Aug-01
Included in the Prior Art Database: 2002-Jan-08
Document File: 1 page(s) / 54K

Publishing Venue

Motorola

Related People

Robert B. Ford: AUTHOR

Abstract

The described circuit within a battery housing is used to disconnect the internal cells from the battery terminals when discharge has progressed to a low limit condition. A battery so designed will protect itself from deep discharge damage. This feature is essential in the design of present Lithium-Ion technology batteries for safe operation (must not progress z4vlcell) and is a benefit in preventing cell reversal for other battery technologies as well.

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MOTOROLA INC. Technical Developments Volume 16 August 1992

DEEP DISCHARGE PREVENTION CIRCUIT FOR BATTERY

by Robert B. Ford

  The described circuit within a battery housing is used to disconnect the internal cells from the battery terminals when discharge has progressed to a low limit condition. A battery so designed will protect itself from deep discharge damage. This feature is essential in the design of present Lithium-Ion technology batteries for safe operation (must not progress z4vlcell) and is a benefit in preventing cell reversal for other battery technologies as well.

  The circuit uses a switch coupled to a control cir- cuit to provide this discharge protection. The switch must have exceptional conduction properties so that its volt- age drop is minimal during use at highest operating cur- rent. Use of a T-mos field effect Transistor meets this requirement without drive circuit complexity, The con- trol circuit must latch to the battery "off' condition when tripped and remain in this state until reset occurs by connection to a charger. The control circuit below corn- prised of stages Ql, 2 & 3 performs this function. Bat- tery terminal voltage is sensed by Ql and its collector path drives both the latch path Q2 and the inverter Q3. The diode CR1 is used in most batteries to prevent dis- charge when the battery is in an inactive charger. The R3 path provides the reset current for Ql to cause Q2 to unlatch for battery "on" operation.

  Batteries comprised of...