US0079691. 19B2
`
`(12) United States Patent
`Odaohhara
`
`(10) Patent No.:
`(45) Date of Patent:
`
`US 7.969,119 B2
`Jun. 28, 2011
`
`(54) OVERVOLTAGE PROTECTION
`(75) Inventor: Shigefumi Odaohhara, Yamato (JP)
`(73) Assignee: Lenovo (Singapore) Pte. Ltd.,
`Singapore (SG)
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 532 days.
`(21) Appl. No.: 12/168,059
`
`(*) Notice:
`
`(22) Filed:
`
`Jul. 3, 2008
`
`(65)
`
`(30)
`
`Prior Publication Data
`US 2009/OOO9143 A1
`Jan. 8, 2009
`
`Foreign Application Priority Data
`
`Jul. 3, 2007 (JP) ................................. 2007-175221
`
`(51) Int. Cl.
`(2006.01)
`H02. 7/00
`(2006.01)
`H02. 7/04
`(52) U.S. Cl. ........................................ 320/134; 320/162
`(58) Field of Classification Search ................... 32Of 134
`See application file for complete search history.
`
`(56)
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`6,222,346 B1 * 4/2001 Mori ............................. 320,134
`6,642,694 B2 * 1 1/2003 Yamanaka et al. ............ 320,134
`7.397.221 B2 * 7/2008 Sakuma et al. ............... 320,134
`2002/0000790 A1
`1/2002 Sano et al. .................... 320,162
`
`FOREIGN PATENT DOCUMENTS
`11-252809
`9, 1999
`JP
`2000-166107
`6, 2000
`JP
`2005-323459
`11, 2005
`JP
`* cited by examiner
`
`Primary Examiner — Edward Tso
`Assistant Examiner — M'Baye Diao
`(74) Attorney, Agent, or Firm — Ference & Associates LLC
`
`ABSTRACT
`(57)
`An overvoltage protection system capable of maintaining a
`high setting Voltage of a battery charger while guaranteeing
`that cell voltage does not exceed a value limited by a threshold
`value. In one preferred embodiment, a battery set is a plurality
`of series-connected battery cells. A protection Voltage mea
`Surement portion measures a cell Voltage of each battery cell.
`A computation portion calculates an open circuit Voltage of
`the battery set outputs a calculated Voltage as a measurement
`Voltage. An overvoltage setting portion stops charging of
`battery set when the value of the cell voltage of any one of the
`battery cells reaches a threshold value. A diagnostic Voltage
`measurement portion measures an open circuit Voltage of
`battery set to output measured Voltage as a diagnostic Voltage.
`A comparing circuit stops charging of the battery set based on
`comparison results of value of the measurement Voltage and
`value of diagnostic Voltage.
`
`21 Claims, 4 Drawing Sheets
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`BATERY
`CHARGER
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`CONVERTER
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`Jun. 28, 2011
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`Sheet 1 of 4
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`U.S. Patent
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`Jun. 28, 2011
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`Sheet 2 of 4
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`US 7.969,119 B2
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`FIG. 2
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`LLI > |----
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`U.S. Patent
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`Jun. 28, 2011
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`Sheet 3 of 4
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`US 7.969,119 B2
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`U.S. Patent
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`Jun. 28, 2011
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`Sheet 4 of 4
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`US 7.969,119 B2
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`FIG. 4
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`FIRST LEVEL
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`Vchg
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`4.25W
`SECOND LEVEL 4.22V
`4.19W
`4.18V
`4.15W
`4.12V
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`FIRST LEVEL
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`Vchg
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`4.25W
`4.22V
`4.19W
`4.18V
`4.15W
`4.12V
`4.11W
`4.08V
`4.05V
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`(A)
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`(B)
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`FIG. 5
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`83 93
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`US 7,969,119 B2
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`1.
`OVERVOLTAGE PROTECTION
`
`CLAIM FOR PRIORITY
`
`This application claims priority from Japanese Application
`No. 2007-175221 filed on Jul. 3, 2007, and which is fully
`incorporated by reference as if fully set forth herein.
`
`5
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`FIELD OF THE INVENTION
`
`The present invention relates generally to an overvoltage
`protection system which is employed in an electric charging
`system for charging a plurality of series-connected battery
`cells.
`
`BACKGROUND OF THE INVENTION
`
`In a notebook personal computer (hereinafter, referred to
`as “note PC for simplicity), which is an example of a por
`table or mobile type electronic device, power consumption
`increases as the operating frequency of a CPU increases; and
`on the other hand, it is requested to provide a longer operation
`time in a mobile environment and to be Smaller in size and
`lighter in weight. Therefore, most rechargeable batteries
`mounted on the note PC take a form of a battery pack which
`includes a plurality of battery cells composed of a lithium ion
`rechargeable battery having high energy density and in which
`the battery cells are combined together by series or parallel
`connection and are accommodated in a housing.
`Upon charging/discharging the lithium ion rechargeable
`battery, it is necessary to precisely control charging/discharg
`ing current and voltage. In particular, it is necessary to strictly
`control the charging Voltage in a constant-voltage control
`period. Therefore, in a battery pack using the lithium ion
`rechargeable battery, an MPU (microprocessor) is provided
`within the battery pack. The battery pack generally employs a
`scheme called a smart battery in which an MPU monitors an
`internal State of the battery pack during charging and dis
`charging to thereby send information to a note PC body or to
`activate a protection circuit. The smart battery is a battery
`device that is compliant with the standards called smart bat
`tery system (SBS), initiated by Duracell Inc. (US) and Intel
`Inc. (US). A battery pack compliant with the above standards
`is also called an intelligent battery.
`In the intelligent battery, an electric circuit portion having,
`mounted on a Substrate, an MPU, a current measurement
`circuit, a Voltage measurement circuit, a remaining capacity
`calculation circuit, a temperature sensor, and the like, and a
`plurality of battery cells are accommodated in a housing. The
`MPU is operable to communicate with an embedded control
`ler of the note PC body via data lines. An overvoltage protec
`tion circuit is also installed in the intelligent battery; there
`fore, when the Voltage of the battery cell experiences
`overvoltage during use, a shutoff element provided in a
`charger circuit can be operated to stop a charging operation.
`According to a technology disclosed in Japanese Laid
`open (Kokai) Patent Publication No. 2000-166107, a first
`protection function portion and a second protection function
`portion are mounted on a lithium ion battery pack, the first
`protection function portion operates an FET to stop charging
`upon detection of a cell voltage of 4.3 V, while the second
`protection function portion blows a temperature fuse with
`resistorto stop charging upon detection of a cell Voltage of 4.5
`V. With such a circuit configuration, even when an abnormal
`ity has occurred in the first protection function portion, the
`second protection functional portion backs up the first pro
`tection function portion, guaranteeing that the Voltage of the
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`battery cell does not exceed an allowable maximum Voltage.
`According to a technology disclosed in Japanese Laid-open
`(Kokai) Patent Publication No. 2005-323459, an overdis
`charge? overcharge detection circuit comprises multiple
`redundant determination circuits with a plurality of different
`thresholds for overvoltage detection in a plurality of battery
`cells.
`In the overvoltage protection circuit, in order to guarantee
`that the cell Voltage during charging of the battery cells does
`not exceed an allowable maximum Voltage, it is necessary to
`forcibly and assuredly stop the charging when the cell Voltage
`exceeds a threshold value. On the other hand, when the bat
`tery charger is operating in a normal manner based on the
`setting Voltage, it is necessary to prevent malfunctioning of
`the overvoltage protection circuit. Since the output Voltage of
`the battery charger has an error with respect to the setting
`Voltage and the cell Voltage varies with a change in ambient
`temperature or drift of the battery charger, it is necessary to
`provide a fixed margin between the setting value of the battery
`charger and the threshold value of the overvoltage protection
`circuit.
`In recent years, lithium ion rechargeable batteries are
`requested to provide a higher safety level. For this reason,
`related business groups are moving to further tighten the
`safety standards of the lithium ion rechargeable batteries.
`Specifically, in the past, the standard allowable maximum
`voltage of the cell voltage was 4.40 V; however, the standard
`allowable maximum voltage is now lowered to 4.25 V so the
`charging system is requested to guarantee that the cell Voltage
`during charging does not exceed the allowable maximum
`Voltage.
`In a case where a plurality (three to four) of lithium ion
`rechargeable batteries are connected in series to form a bat
`tery set, the battery charger is operated Such that the output
`Voltage applied to both ends of the battery set during a con
`stant Voltage control period becomes constant. In order to
`guarantee that during charging of the battery set, the cell
`Voltage does not exceed the allowable maximum Voltage, an
`overvoltage protection circuit is usually provided for stop
`ping the charging when the cell Voltage reaches the threshold
`value. Moreover, as a backup measure, the cell Voltage is
`controlled so as not to exceed the allowable maximum Voltage
`even when the overvoltage protection circuit is not operating
`in a normal manner.
`According to the conventional overvoltage protection cir
`cuit disclosed in Japanese Laid-open (Kokai) Patent Publica
`tion No. 2000-166107, in order to guarantee that the cell
`Voltage does not exceed the allowable maximum Voltage, the
`overvoltage protection circuit is duplicated by the first pro
`tection function portion that monitors the cell Voltage and the
`second protection function portion. The first protection func
`tion portion operates an FET, which is a reversible element,
`and the second protection function portion operates a tem
`perature fuse, which is a non-reversible element, to thereby
`stop the charging. Moreover, the threshold values of the first
`and second protection function portions are set to different
`values so that the reversible element is operated first. That is,
`the second protection circuit has the same construction as the
`first protection circuit so that a prefect backup function can be
`carried out.
`The reason the reversible element is set to operate prior to
`the non-reversible element is as follows. In a state where the
`cell voltage approaches a threshold value at which the revers
`ible element is operated, when the cell voltage temporarily
`exceeds the threshold value due to an abrupt change in ambi
`ent temperature or drift of the overvoltage protection system,
`the charging is preliminarily stopped by the reversible ele
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`US 7,969,119 B2
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`ment. However, once the safety is confirmed, the reversible
`element returns to its original state so that the charging can be
`resumed. The reason the non-reversible element is set to
`operate later is as follows. In order to definitely prevent a
`serious accident which is likely to cause fire hazard, the
`non-reversible element permanently disables the use of the
`battery pack when the charging Voltage exceeds the threshold
`value.
`Such a construction of the duplicated overvoltage protec
`tion circuit composed of the reversible element and the non
`reversible element as disclosed in Japanese Laid-open (Ko
`kai) Patent Publication No. 2000-166107 is generally
`employed in a note PC. In Such an overvoltage protection
`circuit, the charging is not stopped when the charging is
`performed in a normal manner. It is therefore necessary to set
`the setting Voltage of the battery charger to a low value with a
`margin relative to the lower threshold value at which the
`reversible element is operated. However, when the setting
`voltage of the battery charger is lowered, the full charge
`capacity decreases or the time to reach the full charge capac
`ity increases, which is therefore undesirable.
`According to the determination circuit disclosed in Japa
`nese Laid-open (Kokai) Patent Publication No. 2005-323459,
`the determination circuit is duplicated or triplicated so that
`even when one the determination circuits has a fault, the
`determination is continued by the majority rule. The determi
`nation circuits have mutually different overcharge threshold
`values 3.75 V. 4.0 V, and 4.25 V. Therefore, unless the setting
`voltage of the battery charger is set to a value lower than the
`lowest threshold value of the determination circuits, the deter
`mination circuit may detect an abnormality as to the over
`charging.
`In the past, where the allowable maximum voltage of the
`battery cells is 4.40 V, the setting voltage of the battery
`charger can be set to 4.20 V for each battery cell even when
`the overall error of the charging system is considered; there
`fore, there was no problem concerning the full charge capac
`ity. However, when the allowable maximum voltage is low
`ered to 4.25 V and when a duplicated overvoltage protection
`circuit is employed and the setting Voltage of the battery
`charger is lowered by the difference of 0.15 V, it will give rise
`to another problem that the full charge capacity decreases. It
`is therefore necessary to provide an overVoltage protection
`system capable of guaranteeing that the cell Voltage does not
`exceed the allowable maximum Voltage in a manner different
`from the conventional duplicated or triplicated overvoltage
`protection method.
`Accordingly, a compelling need has been recognized in
`connection with addressing Such challenges.
`
`SUMMARY OF THE INVENTION
`
`In accordance with one presently preferred embodiment of
`the present invention, the principle of the present invention as
`broadly contemplated lies in providing overVoltage protec
`tion for charging batteries that is capable of maintaining a
`high setting Voltage of a battery charger while guaranteeing
`that a cell Voltage does not exceed a value, limited by a
`threshold value, using a single overvoltage protection circuit.
`In Summary, one aspect of the invention provides an appa
`ratus, said apparatus comprising: a plurality of series-con
`nected battery cells; a battery charger; a protection Voltage
`measurement portion configured to measure a cell Voltage of
`each of the battery cells; a computation portion configured to
`calculate an open circuit Voltage appearing between opposite
`terminals of the battery set from the cell voltage of each of the
`battery cells to output the calculated Voltage as a measure
`
`4
`ment Voltage; an overvoltage setting portion configured to
`output a first stop signal capable of stopping charging of the
`battery set when the value of the cell voltage of any one of the
`battery cells reaches a threshold value; a diagnostic Voltage
`measurement portion configured to measure the open circuit
`voltage of the battery set to thereby output the measured
`Voltage as a diagnostic Voltage; and a comparing portion
`configured to output a second stop signal capable of stopping
`charging of the battery set based on a comparison result of a
`value of the measurement Voltage and a value of the diagnos
`tic Voltage.
`Another aspect provides an apparatus, said apparatus com
`prising: an electronic device; and a battery pack, wherein the
`battery pack comprises: a battery set having thereina plurality
`of series-connected battery cells; a protection Voltage mea
`Surement portion configured to measure a cell Voltage of each
`of the battery cells; a computation portion configured to cal
`culate an open circuit Voltage appearing between opposite
`terminals of the battery set from the cell voltage of each of the
`battery cells to thereby output a calculated Voltage as a mea
`Surement Voltage; an overvoltage setting portion configured
`to output a first stop signal capable of stopping charging of the
`battery set when a value of the cell voltage of any one of the
`battery cells reaches a threshold value; a diagnostic Voltage
`measurement portion configured to measure an open circuit
`Voltage appearing between opposite terminals of the battery
`set to output a measured Voltage as a diagnostic Voltage; and
`a comparing portion configured to output a second stop signal
`capable of stopping charging of the battery set based on a
`comparison result of a value of the measurement Voltage and
`a value of the diagnostic Voltage.
`Furthermore an additional aspect of the invention provides
`a method, said method comprising the steps of measuring a
`cell voltage of each of the battery cells in a first system to
`thereby generate a measurement Voltage; calculating an open
`circuit Voltage appearing between opposite terminals of the
`battery set from the cell voltage of each of the battery cells to
`thereby generate a measurement Voltage; Stopping the charg
`ing when a value of the cell voltage of any one of the battery
`cells reaches a threshold value; measuring an open circuit
`Voltage appearing between opposite terminals of the battery
`set in a second system to thereby generate a diagnostic Volt
`age; and stopping the charging based on a comparison result
`of a value of the measurement Voltage and a value of the
`diagnostic Voltage.
`For a better understanding of the present invention,
`together with other and further features and advantages
`thereof, reference is made to the following description, taken
`in conjunction with the accompanying drawings, and the
`scope of the invention will be pointed out in the appended
`claims.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 is a block diagram illustrating a charging system
`including a battery pack and a note PC according to an
`embodiment of the present invention;
`FIG. 2 is a diagram for explaining change with time of a
`charging Voltage and a charging current output from a battery
`charger after charging is started;
`FIG. 3 is a block diagram for explaining an overvoltage
`protection system of the battery pack shown in FIG. 1;
`FIGS. 4A and 4B are diagrams for comparison of the
`setting Voltage of a battery charger in a conventional dupli
`cated overvoltage protection circuit and an overvoltage pro
`tection system according to the present embodiment; and
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`FIG. 5 is a plan view for explaining a wiring structure of a
`battery pack.
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`DETAILED DESCRIPTION OF THE PREFERRED
`EMBODIMENTS
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`6
`In the overVoltage protection system according to the
`present invention, even when the protection Voltage measure
`ment portion is not properly operating, the cell Voltage does
`not exceed the value limited by the threshold value. That is,
`the diagnostic Voltage measurement portion measures the
`open circuit Voltage appearing between the opposite termi
`nals of the battery set to output the measured Voltage as a
`diagnostic Voltage, and the comparing portion outputs a sec
`ond stop signal to thereby stop the charging of the battery set
`when there is an abnormality based on the comparison result
`of the value of the measurement voltage and the value of the
`diagnostic Voltage. Moreover, the protection Voltage mea
`Surement portion may measure the cell Voltages of the respec
`tive battery cells to output the measured cell voltages as the
`measurement Voltage, the diagnostic Voltage measurement
`portion may measure the cell Voltages of the respective bat
`tery cells to output the measured cell Voltages as the diagnos
`tic Voltage, and the comparing portion may output the second
`stop signal that stops the charging of the battery set based on
`the comparison result of the values of the measurement volt
`age and the value of the diagnostic Voltage.
`In the overVoltage protection system according to the
`present invention, the diagnostic Voltage measurement por
`tion and the comparing portion can determine whether or not
`the protection Voltage measurement portion is operating in a
`normal manner while the system is in operation; however, the
`diagnostic Voltage measurement portion cannot directly carry
`out the overvoltage protection function. Therefore, in order to
`guarantee that the cell Voltage does not exceed the value
`limited by the threshold value, it is only necessary to equip a
`single overvoltage protection circuit including the overvolt
`age setting portion, and it is not necessary to prepare two
`different overvoltage protection circuits in duplicate. There
`will be a case where due to Some reasons during charging, the
`open circuit Voltage appearing between the opposite termi
`nals of the battery set increases greater than the setting Volt
`age of the battery charger and the measurement Voltage of any
`one of the battery cells exceeds the threshold value.
`In Such a case, the overvoltage setting portion outputs the
`first stop signal to thereby stop the charging, and the value of
`the diagnostic Voltage is not used for stopping the charging;
`therefore, the threshold value of the overvoltage protection
`circuit can be set with one level. In the overvoltage protection
`system according to the present invention, the threshold value
`for overvoltage protection can be set with one level. There
`fore, the setting Voltage of the battery charger can be set to a
`value selected with a margin necessary for a tolerance of the
`overvoltage protection circuit and a tolerance of the output
`Voltage of the battery charger with respect to the setting
`Voltage. Accordingly, it is possible to maintain a high setting
`value compared with the case where the overVoltage protec
`tion circuit is duplicated.
`The diagnostic Voltage measurement portion measures the
`open circuit Voltage of the battery set to output the measured
`Voltage as the diagnostic Voltage. In a case where the over
`Voltage protection circuit is duplicated like the conventional
`method, the diagnostic Voltage measurement portion needs to
`measure the cell voltage as well. However, in the present
`invention, since the diagnostic Voltage measurement portion
`only needs to measure the open circuit Voltage, it is possible
`to simplify the circuit structure compared with the case of
`measuring the cell voltage. Since the threshold value of the
`overvoltage setting portion is set such that the cell Voltage of
`the battery cell does not exceed the allowable maximum
`Voltage, the setting Voltage of the battery charger can be set to
`the maximum value that is allowed in the charging system.
`The maximum value that is allowed in the charging system is
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`For a better understanding of the present invention,
`together with other and further features and advantages
`thereof, reference is made to the following description, taken
`in conjunction with the accompanying drawings, and the
`scope of the invention will be pointed out in the appended
`claims.
`It will be readily understood that the components of the
`present invention, as generally described and illustrated in the
`Figures herein, may be arranged and designed in a wide
`variety of different configurations. Thus, the following more
`detailed description of the embodiments of the apparatus,
`system, and method of the present invention, as represented in
`FIGS. 1 through 5, is not intended to limit the scope of the
`invention, as claimed, but is merely representative of selected
`embodiments of the invention.
`Reference throughout this specification to “one embodi
`ment” or “an embodiment” (or the like) means that a particu
`lar feature, structure, or characteristic described in connec
`tion with the embodiment is included in at least one
`embodiment of the present invention. Thus, appearances of
`the phrases “in one embodiment” or “in an embodiment” in
`various places throughout this specification are not necessar
`ily all referring to the same embodiment.
`Furthermore, the described features, structures, or charac
`teristics may be combined in any Suitable manner in one or
`more embodiments. In the following description, numerous
`specific details are provided, to provide a thorough under
`standing of embodiments of the invention. One skilled in the
`relevant art will recognize, however, that the invention can be
`practiced without one or more of the specific details, or with
`other methods, components, materials, etc. In other instances,
`well-known structures, materials, or operations are not shown
`or described in detail to avoid obscuring aspects of the inven
`tion.
`The illustrated embodiments of the invention will be best
`understood by reference to the drawings, wherein like parts
`are designated by like numerals or other labels throughout.
`The following description is intended only by way of
`example, and simply illustrates certain selected embodiments
`45
`of devices, systems, and processes that are consistent with the
`invention as claimed herein.
`In accordance with one aspect of the present invention,
`there is provided an overvoltage protection system for charg
`ing a battery set having therein a plurality of series-connected
`battery cells with a battery charger. A protection Voltage
`measurement portion measures a cell Voltage of each of the
`battery cells, and a computation portion calculates an open
`circuit Voltage appearing between opposite terminals of the
`battery set from the cell voltage of each of the battery cells
`thereby outputting a calculated Voltage as a measurement
`Voltage. An overVoltage setting portion outputs a first stop
`signal that stops charging of the battery set when the value of
`the cell voltage of any one of the battery cells reaches a
`threshold value. Therefore, as long as an overvoltage protec
`tion circuit including the protection Voltage measurement
`portion and the overVoltage setting portion is operating in a
`normal manner, any of the cell Voltages of the battery cells
`will not exceed the value limited by the threshold value. Here,
`the value limited by the threshold value is determined in
`consideration of a tolerance of the overvoltage protection
`circuit with respect to the actual cell Voltage.
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`determined in consideration of a margin necessary for a tol
`erance of the overvoltage protection circuit with respect to the
`actual cell Voltage and a tolerance of the output Voltage of the
`battery charger with respect to the setting Voltage.
`The first stop signal may operate a reversible shutoff ele
`ment Such as an FET installed in the charging circuit, and the
`second stop signal may operate a non-reversible shutoff ele
`ment. When the second stop signal is output, it is the case
`where either of the protection Voltage measurement portion or
`the diagnostic Voltage measurement portion is abnormal. In
`Such a case, in order to forcibly and assuredly stop the charg
`ing and to guarantee that the cell Voltage does not exceed the
`value limited by the threshold value, it is preferable to operate
`a non-reversible shutoff element different from the reversible
`shutoff element that is operated by the first stop signal. The
`reason the reversible shutoff element is operated by the first
`stop signal is because when the cell Voltage temporarily
`exceeds the threshold value due to a change in ambient tem
`perature or drift of the battery charger, it is preferable to
`resume the charging after confirming the safety.
`The diagnostic Voltage measurement portion may be con
`figured to compare the value of the measurement Voltage with
`the value of the diagnostic Voltage during a period from the
`start to the end of the charging of the battery set to thereby
`output the second stop signal for stopping the charging of the
`battery set based on the comparison results. By doing this, it
`is possible to increase the possibility of detecting an abnor
`mality in the protection Voltage measurement portion or the
`diagnostic Voltage measurement portion in an initial period of
`the charging where the cell voltage is low. Therefore, it is
`possible to increase the safety level as to the allowable maxi
`mum voltage guarantee compared with the case where the
`second stop signal is output in a period where the cell Voltage
`is high to thereby stop the charging. The protection Voltage
`measurement portion and the diagnostic Voltage measure
`ment portion may be implemented as mutually independent
`semiconductor devices. Alternatively or additionally, a wir
`ing system between the diagnostic Voltage measurement por
`tion and the battery cells may be separated from a wiring
`system between the protection voltage measurement portion
`and the battery cells. By doing so, the protection Voltage
`measurement portion and the diagnostic Voltage measure
`ment portion may become highly independent and the system
`reliability will be further improved.
`In accordance with the above-mentioned diverse aspects of
`45
`the present invention, it is possible to provide an overvoltage
`protection system capable of maintaining a high setting Volt
`age of a battery charger while guaranteeing that a cell Voltage
`does not exceed a value limited by a threshold value. Further,
`it is possible to provide an overvoltage protection system
`capable of guaranteeing that a cell Voltage does not exceed a
`value limited by a threshold value while using a single over
`Voltage protection circuit. Furthermore, it is possible to pro
`vide a battery pack and electronic device incorporating the
`overvoltage protection system and to provide an overvoltage
`preventing method that is executed in the overvoltage protec
`tion system.
`The discussion will now turn to the drawings. Referring
`now to FIG. 1, a block diagram illustrating an outlined inter
`nal construction of a battery pack 10 in compliance with the
`SBS standards and a note PC 100 according to one embodi
`ment of the present invention. The battery pack 10 has
`installed in a housing thereof, many electronic components
`including a battery set 14 composed of three, series-con
`nected lithium ion battery cells 11 to 13, a sense resistor 15, a
`discharge FET 17, a charge FET 19, an AFE (analog front
`end) 21, an MPU (micro processing unit) 23, a Voltage regu
`
`55
`
`8
`lator 25, a thermistor 27, and a diagnostic Voltage measure
`ment portion. The battery pack10 is connected to the note PC
`100 via five terminals of a positive (+) terminal 31, a C
`terminal 33, a D terminal 35, a T terminal 37, and a negative
`(-) terminal 39. A discharging current from the battery set 14
`and a charging current to the battery set 14 flow between the
`battery set 14 and the note PC 100 via the positive (+) terminal
`31 and the negative (-) terminal 39. The C terminal 33 and the
`D terminal 35 are connected to a clock terminal and a data
`terminal of the MPU23, respectively, and the T terminal 37 is
`connected to the thermistor 27, which is an element for mea
`suring temperature around the battery cells 11 to 13.
`The AFE 21 and the MPU23 are integrated circuits that are
`operated by a constant Voltage delivered from the Voltage
`regulator 25. Data are exchanged between the AFE 21 and the
`MPU23. The AFE 21 includes analog input terminals V1,V2,
`and V3 for acquiring the respective potential difference in the
`battery cells 11 to 13 and analog input terminals I1 and I2 for
`acquiring potential difference across the sense resistor 15.
`The AFE 21 also includes analog output terminals D-CTL
`and C-CTL for outputting signals that control on/off of the
`discharge FET 17 and the charge FET 19. The AFE 21 mea
`Sures the respective cell Voltages, converts the measurement
`values into digital values, and delivers the converted values to
`the MPU 23.
`The AFE 21 measures the charging current and the dis
`charging current flowing in the battery set 14 from the Voltage
`detected by the sense resistor 15, converts the measurement
`values into digital values, and delivers the converted values to
`the MPU23. The MPU23 is an integrated circuit in which in
`addition to an 8 to 16 bit CPU, a RAM, a ROM, a flash
`memory, and a timer are integrated into one package. The
`MPU 23 monitors the amount of charged or discharged elec
`tricity based on the Voltage or current measurement values
`delivered from the AFE 21 to thereby calculate a remaining
`capacity. Moreover, the MPU 23 has an overcurrent protec
`tion function, an overvoltage protection function (also
`referred to as overcharge protection function), and an under
`Voltage protection (also referred to as overdischarge protec
`tion function). Upon detection of an abnormality in the bat
`tery pack 10 from the voltage or current measurement value
`delivered from the AFE 21, the MPU23 opens