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Double Protection Circuit for Li-Ion Battery Pack

IP.com Disclosure Number: IPCOM000122799D
Original Publication Date: 1998-Jan-01
Included in the Prior Art Database: 2005-Apr-04
Document File: 2 page(s) / 103K

Publishing Venue

IBM

Related People

Mito, T: AUTHOR [+2]

Abstract

Disclosed is a circuit for Li-Ion battery pack used in notebook (Personal Computer (PC).

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 85% of the total text.

Double Protection Circuit for Li-Ion Battery Pack

      Disclosed is a circuit for Li-Ion battery pack used in notebook
(Personal Computer (PC).

      An Li-Ion battery pack contains over/under voltage protection
circuit in a battery pack.  When a cell voltage exceeds over around
4.35V, the charge FET (Field Effect Transistor) will turn off and
stop further over-charge to the battery.  Also under-voltage of less
than 2.5V, discharge FET will turn off in order to avoid deep
discharge of the  cell.  Fig. 1 shows a basic Li-Ion battery pack in
industry.  BMU (Battery Management Unit) contains a Fuel Gauge
Function and an over/under voltage protection circuit.  Charge and
discharge FETs are turned off at over- charge or under-voltage mode
as following circuits.

      Once one of the charge FETs is shorted, there is no device
which turns the charge current off from the over-charge voltage from
the charger.  The Battery vent mechanism and CID (Current
Interruption Device) are final safety protections of the battery
pack.  Single cell protection is confirmed, but sometimes multi-cell
over- charge behavior is different from single cell.  It is easy to
start thermal runaway.  This circuit adds one more individual
over-voltage protection  circuit (Over Voltage Self Kill Circuit)
which does not rely on charge  control FETs (Fig. 2).  Sense voltage
is set around 4.35V of higher voltage than first over- voltage level.
This voltage is sensed, heat up fusing res...