a2) United States Patent
`US 6,172,482 B1
`(10) Patent No.:
`
`Eguchi Jan. 9, 2001
`(45) Date of Patent:
`
`US006172482B1
`
`(54) BATTERY PROTECTION CIRCUIT AND
`ELECTRONIC DEVICE
`
`(56)
`
`References Cited
`U.S. PATENT DOCUMENTS
`
`(75)
`
`Inventor: Yasuhito Eguchi, Kanagawa (JP)
`
`5,703,463 * 12/1997 Smith .
`
`(73) Assignee: Sony Corporation, Tokyo (JP)
`
`(*) Notice:
`
`Under 35 U.S.C. 154(b), the term of this
`patent shall be extended for 0 days.
`
`(21) Appl. No.: 09/379,499
`
`(22) Tiled:
`
`Aug. 23, 1999
`
`(30)
`
`Foreign Application Priority Data
`
`AUg. 26, 1998
`
`(TP)
`
`cesssssssssssessseesseessssssssseeseeeeen P10-240477
`
`Lambe C07 ieeeeeecsesceeccecennnneneeeecececeennte HO01M 10/76
`(SV)
`(52) U.S. Cl. ..........
`320/134; 320/136
`
`(58) Field of Search 0...eee 320/127, 128,
`320/134, 136
`
`* cited by examiner
`Primary Examiner—Edward H. Tso
`(74) Attorney, Agent, or Firm—Frommer Lawrence &
`Haug, LLP.; William S. Frommer
`(57)
`ABSTRACT
`
`Asecondary battery needs to be protected by an inexpensive
`structure having a small number of components. To this end,
`the structure includes a fuse 41 with a heater, connected to
`a positive electrode side of a battery cell 2, as a secondary
`battery, a driving FET 42 for driving the heater of the fuse
`41 and a detection control IC 3 which, on detecting at least
`the over-charging state of the battery cell 2, drives the
`driving FET 42 to fuse the heater of the fuse 41.
`
`6 Claims, 10 Drawing Sheets
`
`
`
`RV1
`ex;RV1=4.4V
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`39
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`C1: OVERCHARGING DETECTION UNIT
`
`APPLE-1028
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`APPLE-1028
`
`1
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`

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`U.S. Patent
`
`Jan. 9, 2001
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`Sheet 1 of 10
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`US 6,172,482 B1
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`200
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`202
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`235
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`FIG.1
`(PRIOR ART)
`
`2
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`

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`US 6,172,482 B1
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`O
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`4, DETECTION
`CONTROL
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`390
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`U.S. Patent
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`Jan. 9, 2001
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`Sheet 2 of 10
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`RV1
`ex;RV1=4.4V
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`C1: OVERCHARGING DETECTION UNIT
`FIG.3
`
`3
`
`

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`U.S. Patent
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`Jan. 9, 2001
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`Sheet 3 of 10
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`US 6,172,482 B1
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`5
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`4
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`CONTROL
`
`DETECTION
`
`FIG.4
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`4
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`

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`U.S. Patent
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`Jan. 9, 2001
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`Sheet 4 of 10
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`US 6,172,482 B1
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`
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`FIG.5
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`5
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`

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`U.S. Patent
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`US 6,172,482 B1
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`Jan. 9, 2001
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`Sheet 5 of 10
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`FIG.6
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`U.S. Patent
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`Jan. 9, 2001
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`Sheet 6 of 10
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`US 6,172,482 B1
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`BYPASS
`CURRENT
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`U/
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`+imV DETECTION
`ERROR
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`0
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`OmV
`|
`DETECTION
`VALUE FULL
`CHARGING
`VOLTAGE
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`FIG.7
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`7
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`U.S. Patent
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`Jan. 9, 2001
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`US 6,172,482 B1
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`Sheet 7 of 10
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`FIG.8
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`8
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`U.S. Patent
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`Jan. 9, 2001
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`Sheet 8 of 10
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`US 6,172,482 BI
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`U.S. Patent
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`Jan. 9, 2001
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`Sheet 9 of 10
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`US 6,172,482 BI
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`U.S. Patent
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`Jan. 9, 2001
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`Sheet 10 of 10
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`US 6,172,482 BI
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`FIG.11
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`11
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`11
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`US 6,172,482 B1
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`1
`BATTERY PROTECTION CIRCUIT AND
`ELECTRONIC DEVICE
`
`BACKGROUND OF THE INVENTION
`1. Field of the Invention
`
`This invention relates to a battery protection circuit for
`preventing at least overcharging of a secondary battery and
`an electronic device having the battery protection circuit.
`2. Description of the Related Art
`Amongelectronic devices loaded with battery packs for
`power supply, also referred to as a battery package, and
`adapted for being fed from the battery pack with the power
`for driving the devices, there are, for example, a portable
`so-called note-book type personal computer, occasionally
`abbreviated to note-book personal computer, an information
`terminal, a video tape recorder, a sound recorder, and a
`portable telephone. Among non-portable type electronic
`devices of this type, there is, for example, an electric car
`having, for example, a motorfor assisting the motive power.
`The battery packs used in these electronic devices are
`frequently provided with secondary battery cclls that can be
`charged/discharged repeatedly. As such secondary battery
`cells, so-called lithium ion secondary batteries, having a
`high volumetric energy density, are frequently used.
`However, the lithium ion secondarybatteries are narrow
`in tolerance values for over-charging or over-discharging.
`Thus, the battery packs are usually provided with a battery
`protection circuit
`for preventing over-charging or over-
`discharging of the lithium ion secondary batteries.
`FIG. 1 showsanillustrative structure of a conventional
`battery protection circuit provided in a battery pack 200
`having a lithium ion secondary battery cell 202.
`Referring to FIG. 1,
`terminals 211, 212 are charging/
`discharging terminals of the battery pack, with the terminal
`211 being a battery plus terminal and with the terminal 212
`being a ballery minus terminal (GND side terminal). The
`battery pack 200 furnishesthe current via these plus terminal
`211 and minus terminal 212 from the battery cell 202 to a
`main body portion of the electronic device, by way of
`charging. On the other hand, the battery pack 202 is charged
`by the charging current furnished from an external charger,
`not shown,via these plus terminal 211 and minus terminal
`212.
`
`2
`FETs 205, 206 are provided for charging/discharging
`control,
`these FE'Is 205, 206 being connected in series
`between the plus terminal 211 and the positive terminal side
`of the battery cell 202, thus undesirably raising the internal
`resistance. Although there is such a battery protection circuit
`having FETs connected in parallel to realize a low internal
`resistance, the number of component parts is increased in
`this case to raise the cost.
`
`There are occasions wherein it is necessary to provide a
`spare protection circuil in addition to the inherent protection
`circuit, that is two protection circuits, thus further increasing
`the number of components and increased cost.
`If, with the use of a dual FET with the outer shape TSSOP
`and an N channel, with a drain-to-source withstand voltage
`of 20 V, a gate withstand voltage of 12 V and with an
`on-resistance of 35 mQ, with gate voltage being 2.5 V, two
`such parallel-connected FETs are used for charging/
`discharging,
`the element resistance is 70 mQ, that is the
`resistance per FET is 35 mf&2. On the other hand,if these
`FETs are connected in series with each other, the element
`resistance is 35 mQ, that is the resistance per FET is 17.5
`m2. FIG. 1 shows an example of a P-channel FET, which
`has a higher internal resistance than the N-channel FET, so
`that it is more undesirable.
`
`SUMMARYOF THE INVENTION
`
`It is therefore an object of the present invention to provide
`an inexpensive battery protection circuit made up of a
`smaller number of components and an electronic device
`provided with a battery pack having the battery protection
`circuit.
`
`In one aspect, the present invention provides a battery
`protection circuit including over-charging detection means
`for detecting at least the over-charging state of a secondary
`battery, fuse means fitted with the heater and which is
`connected to a current path of the secondary battery, and
`heater driving means for driving the heater of the fuse
`means. The heater driving means drives the heater of the
`fuse means to blow off the fuse when the over-charging
`detection is established.
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`invention provides an
`the present
`In another aspect,
`electronic device operated by the current supplied from a
`secondary battery and adapted to charge the secondary
`45
`battery, including a battery pack having over-charging detec-
`Afield effect transistor (FET) 206 and anotherfield effect
`tion meansfor detecting at least the over-charging state of a
`transistor (FET) 205 are connected in series between a plus
`secondary battery, fuse meansfitted with a heater, and which
`terminal 211 of the battery pack 200 and the positive
`is connected to a current path of the secondary battery; and
`terminal of the battery cell 202. The FETs 206, 205 are
`heater driving means for driving the heater of the fuse
`provided as a charging on/off controlling switching device
`means. The heater driving means drives the heater of the
`and as a discharging on/off controlling switching device,
`fuse means to blow off the fuse when the over-charging
`respectively. These FETs 205, 206 are provided with para-
`detection is established.
`sitic diodes.
`A control IC circuit 203 has its terminal 235 fed with a
`voltage value of the plus terminal 211, while having its
`terminals 231 and 232 fed with the positive terminal side
`voltage value and with the negative terminal side voltage
`value of the battery cell 202, respectively. The control IC
`circuit 203 outputs a driving signal for the switching opera-
`tion (on/off operation) of the FET 206 and a driving signal
`for the switching operation (on/off operation) of the FET 205
`from its terminals 233, 234, respectively. That is, the control
`IC circuit 203 monitors a voltage value of the plus terminal
`211 and the voltage values of the positive and negative
`terminal sides of the battery ccll 202 to control the switching
`operation (on/off operation) of the FETs 205, 206.
`Meanwhile, in the battery pack employing the FET for
`charging/discharging control, as shown in FIG. 1, the two
`
`According to the battery protection circuit and the elec-
`tronic device, according to the present invention, the fuse of
`the heater connected to the current path of the secondary
`battery is blown off on detection of at least the over-charging
`state of the secondary battery. Thus, the secondarybattery is
`protected by an incxpensivestructure with a smaller number
`of componentparts.
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 is a schematic circuit diagram showing a battery
`pack haprovided with a conventional battery protection
`circuit.
`
`FIG. 2 is a circuit diagram for illustrating a specified
`internal structure of a detection control IC of a battery pack
`of a first embodiment of the present invention.
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`US 6,172,482 B1
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`3
`FIG. 3 is a schematic circuit diagram for illustrating a
`specified internal structure of a detection control IC of the
`first embodimentof the battery pack
`FIG. 4 is a schematic circuit diagram for illustrating the
`structure of a second embodiment of the battery pack.
`FIG. 5 is a circuit diagram for illustrating the specified
`internal structure of a detection control IC of the second
`
`embodimentof the battery pack.
`FIG. 6 is a schematic circuit diagram for illustrating the
`structure of a third embodiment of the battery pack.
`FIG. 7 is a graph for illustrating the relation between the
`bypass current and a detection error in the third embodiment.
`FIG. 8 is a circuit diagram for illustrating the specified
`internal structure of a detection control IC of the third
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`embodiment of the battery pack.
`FIG. 9 is a diagrammatic view for conceptually illustrat-
`ing the relation between a first over-charging voltage, a
`second over-charging voltage (full charging voltage) and an
`over-discharging voltage.
`FIG. 10 is a block circuit diagram showing anillsutrative
`structure of a system employing a battery pack having a
`battery protection circuit according to each embodiment of
`the present invention.
`FIG. 11 is a perspective view showing howa battery pack ,
`equipped with the battery protection circuit of each embodi-
`mentof the present invention is loaded on a note-book type
`personal computer.
`DESCRIPTION OF THE PREFERRED
`EMBODIMENTS
`
`30
`
`Referring to the drawings, preferred embodiments of the
`present invention will be explained in detail.
`The battery protection circuit of the present invention can
`be provided within a battery pack used on, for example, a
`notebook type personal computer, an information terminal,
`a video tape recorder or a sound recorder, as a portable
`electronic apparatus, and on an electric bicycle having a
`driving powerassisting motor, as a non-portable type elec-
`tronmic device.
`It
`is noted that
`the embodiments given
`below are merely illustrative and are not
`intended for
`limiting the scope of the invention.
`TIG. 2 shows a schematic structure of a battery protection
`circuit according to a first embodiment of the present
`invention.
`
`Referring to FIG. 2, a battery cell 2 is one of, for example,
`a lithium ion secondary cell, a lead secondary accumulator,
`a Ni—Cd secondary battery (nickel-cadmium secondary
`battery), a Ni hydrogen secondary battery (nickel-hydrogen
`secondary battery),
`a N—Zn battery (nickel-zinc
`accumulator), a polymer secondary battery, and an air Zn
`secondary battery (zinc-air battery).
`In the preferred
`embodiment,
`it
`is assumed that a lithium ion secondary
`battery is used as the battery cell 2.
`to charging/
`The terminals 11, 12 are equivalent
`discharging terminals of the battery pack 1 and operate as a
`battery plus terminal, referred to below as a plus terminal 11,
`and as a battery minus terminal GND, referred to below as
`the minus terminal 12. ‘The battery pack 1 furnishes the
`powerfrom the battery cell 2 to the main bodyportion ofthe
`electronic device via these terminals 11, 12, by way of
`discharging. On the other hand,the battery cell 2 is charged
`by the charging current from the charging current furnished
`from the external charger, not shown,via these terminals 11,
`12.
`
`An over-charging protection unit 4 is made up of a fuse
`fitted with a heater 41 and a driving FET 42 for driving the
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`heater of the fuse fitted with the heater 41 . The fuse portion
`of the fuse fitted with the heater 41 is inserted and connected
`
`between the plus terminal 11 of the battery pack 1 and the
`positve terminal of the battery cell 2, while the gate of the
`drive FET 42 is connected to an over-charging control
`terminal 33 of a detection control IC 3. If,
`in the over-
`charging protection unit 4, the driving FET 42 isfired, curent
`flows in the fuse fitted with the heater 41 to heat up the
`heater to raise its temperature. If, as a result of temperature
`increase in the heater, caused by the current flowing therein,
`such that the melting point of the fuse is reached by the
`continued temperature increase in the heater,
`the fuse is
`blown off, thus interruptiung the connection between the
`plus terminal 11 and the positive terminalof the battery cell
`2. It is noted that the internal resistance of the fuse fitted with
`the heater 41 is 10 m@ or less, such that
`the internal
`resistance of the battery protection circuit of FIG. 2 is
`extremely low.
`The detection control IC 3 has its cell plus terminal
`detection termina] 31 and a cell minus terminal 32 fed with
`
`a positive electrode side vlotage value of the battery cell 2
`and with the negative electrode side voltage value of the
`battery cell 2, respectively, while outputting a driving signal
`for switching operation (on/off operation) for the driving
`FET 42 of the over-charging protection unit 4 from the
`over-charging control terminal 33. This driving signal for
`switching operation is referred to below as an over-charging
`control signal. Thatis, the detection control IC 103 monitors
`voltage values on the positive and negative electrode sides
`of the battery cell 2 to output a driving control signal
`(over-charging control signal) based on these voltage values
`to control the switching (on/off operation) of the driving
`FET 4 of the over-charging protection unit 4, in order to
`control the switching operation (on/off operation) of the
`driving FET 42 of the over-charging protection unit 4. The
`specified internal structure of the detection control IC 103
`will be explained subsequently.
`the charging
`During charging of the battery pack 1,
`current is furnished from an external charger, not shown, via
`the plus terminal 11 and the minus terminal 12. This
`charging current chargesthe battery cell 2 to increase the cell
`voltage. If the voltge of the external chargeris limited to the
`full charging voltage of the battcry cell 2, the battery cell 2
`is charged to this full charging voltage without being raised
`to a higher voltage.
`However, if the external charger is in disorder or is a
`charger for an incorrect voltage, such that a high charging
`voltage is applied across the battery cell 2, the cell voltage
`of the battery cell 2 is raised to higher than the fill charging
`voltage.
`The above-described detection control IC 3 is detecting
`the cell voltage of the battery cell 2 by the positive electrode
`side voltage value from the cell plus voltage detection
`terminal 31 and the negative voltage side voltage value from
`the minus terminal 12, such that, if the cell voltage reaches
`an over-charging protection voltage, as a pre-set voltage, the
`detection control
`IC 3 outputs, from the over-charging
`control terminal 33, a driving signal for firing the driving
`FET 42 (over-charging control signal).
`If the driving FET 42 is fired in this manner, the fuse fitted
`with the heater 41 of the over-charging protection unit 4 is
`heated and blownoff to interrupt the charging current to the
`battery cell 2. This enables prohibition of over-charging to
`the battery cell 2.
`The fuse fitted with the heater 41 may be of the non-
`restorable type, that is of the type in which it cannot be
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`US 6,172,482 B1
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`5
`is blownoff.
`restored to the conducting state once it
`‘Therefore, if the battery protection action once occurs,that
`is if once it is blown, it cannot be re-used. However, the
`above-described operation is thought to be sufficient as the
`operation of the battery protection circuit because there is no
`risk of occurrence of the over-charging protection operation
`as long as charging is cxccuted using a chargerof the correct
`nominal charging voltage.
`The battery protection circuit of the above-described first
`embodimentis felt to be most suited to a system in which the
`following precautions are used. Thatis, the battery protec-
`tion circuit of the preferred embodimentpreferably is such
`a system in which the battery protection circuit is loaded on
`a battery pack having charging/discharging terminals diffi-
`cult to short and in which the electronic device employing
`the current pack is provided with a mechanism [or turning
`off the discharging current on over-discharging, with the
`leakage current following the turning off of the discharging
`current being extremely small. The shape of the chareging/
`discharging terminal in the battery pack needs to be con-
`trived to prevent the fuse from being blown off due to
`shorting caused by some mistake or other such as duing
`transport of the battery pack or when the battery pack is
`being handled by itself. The function of turning off of the
`discharging current on the side of the clectronic device is
`required for protecting the battery cell
`from over-
`discharging. The allowable leakage current after turning off
`the discharging current, determined on the basis of the
`residual capacity until the battery cell is drastically deterio-
`rated by the over-discharging as from the ends of discharg-
`ing and the allowable time during which the battery pack
`may be left mounted on the electronic device in use, is
`preferably 1 WA orless.
`The specified internal structure of the detection control IC
`3 of the first embodiment of the battery protection circuit
`shownin FIG. 2 is explained with reference to FIG. 3.
`Referring to FIG. 3, the detection control IC 3 is made up
`of an overcharging detection unit Cl having the function as
`a comparator with hysteresis and which is adapted for
`detecting the overcharging of the battery cell 2, and an
`over-charging reference voltage source 70 for generating an
`over-charging detecting reference voltage RV1 correspond-
`ing to the overcharging protection voltage. In the preferred
`embodiment, the over-charging detecting reference voltage
`RVI is set to, for example, 44 V.
`The overcharging detection unit Cl compares the cell
`voltage of the battery cell 2 inputted from the cell plus
`voltage detection terminal 31 (positive electrode side
`voltage) to the over-charging detecting reference voltage
`RVI1from the over-charging reference voltage source 70. If
`the cell voltage is higher than the over-charging detecting
`reference voltage RV1 (4.4 V), the overcharging detection
`unit Cl outputs a high-level signal (H-signal) as an over-
`charging control signal from the over-charging controlter-
`minal 33.
`
`The over-charging control signal, outputted by this over-
`charging control terminal 33,
`is a driving signal for the
`driving FET 42, such that, when the over-charging control
`signal is at the H-level, the driving FET 42 isfired to heat
`up the heater of the fuse fitted with the heater 41 to blowoff
`the fuse. This assures protection against over-charging of the
`battery cell 2.
`The purpose of providing the hysteresis in the comparator
`of the overcharging detection unit Cl is to maintain the
`over-charging detection state even if the voltage of the
`battery cell 2 is lowered by the current flowing when the
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`driving FET 42 is turned on. The comparator of the over-
`charging detection unit Cl is preferably provided with dead
`time of tens of msec to several sec for the comparator of the
`overcharging detection unit Cl.
`A second embodiment o the battery protection circuit of
`the present invention is hereinafter explained.
`FIG. 4 shows the schematic structure of a battery protec-
`tion circuit according to a second embodimentof the present
`invention. The battery protection circuit of the present
`second embodiment, shown in FIG. 2, corresponds to the
`structure of FIG. 2 also having an FETfor protection against
`over-charging and over-current,
`referred to below as a
`discharging control FET 5.
`In the second embodiment,
`limiting conditions for the equipments in use are less strict,
`and only one discharging controlling FET 5 is added, so that
`the internal resistance is smaller. It is noted that, in FIG. 4,
`parts or components similar to those of FIG. 2 are depicted
`by the same reference numerals and are not explained
`specifically.
`The discharging controlling FET 5 is inserted and cpon-
`nected between the plus terminal 11 and, for example, the
`fuse portion of the fuse fitted with the heater 41 of the
`over-charging protection unit 4, and has its gate connected
`to a discharging controlling FET control terminal 34 of the
`detection control IC 3.
`
`the detection control IC 3 of the present second
`Also,
`embodiment has a terminal voltage detection terminal 35
`connected to the plus terminal 11 and detects the over-
`charging and over-current based on the voltage and current
`values supplied via this terminal voltage detection terminal
`35. On detection of the over-charging or the over-current,
`the detection control IC 3 outputs a driving signal for
`switching (on/off operation) of the discharging controlling
`FETS, referred to below as the discharge FET control signal,
`from the discharging controlling FET control terminal 34.
`Meanwhile, the detection control IC 3 detects the current by
`voltage drop caused by the on-resistance of the discharging
`controlling FET 5 and the voltage drop across the fuse
`resistor of the fuse fitted with the heater 41.
`
`If the battery cell 2 is in the over-discharging state, the
`detection control IC 3 detects the over-discharging and turns
`off the discharging controlling FET 5 by the discharging
`FET control signal from the discharging controlling FET
`control terminal 34 (over-discharging protection operation).
`This turns off the current from the battery pack 1 to the load,
`that is the equipmentin use, as a result of which the battery
`cell 2 can be prevented from becoming over-discharged.
`Also, if the battery cell 2 is in the over-currentslate due to,
`for example, terminal shorting, the detection control IC 3
`detects the over-current to turn off the discharging control-
`ling FET 5 by the discharging FET control signal from the
`discharging controlling FET control
`terminal 34 (over-
`current protection operation). This prevents destruction of
`the battery cell 2, that is the battery pack 1.
`The detection control IC 3 of the present second embodi-
`ment also has the function of detecting the full charging
`voltage of the battery cell 2, based on the positive electrode
`side voltage value from the cell plus voltage detection
`terminal 31 and the negative electrode side voltage value
`from the cell minus voltage detection terminal 32 to turn off
`the discharging controlling FET 5 by the discharging FET
`control signal from the discharging controlling FET control
`terminal 34 if the full charging voltate is detected ultimately.
`That is, if the battery cell 2 is in the full charging voltage,
`the detection control IC 3 turns off the discharging control-
`ling FET 5 by the discharging FET control signal from the
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`discharging controlling FET control terminal 34. The speci-
`fied internal structure of the detection control IC 3 for the
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`that no practical problemits raised if the above value VM is
`set to several hundreds of mV. However, there are occasions
`wherein a smaller value of the voltage drop by the parasitic
`diode is desirable. Therefore, the value VM is set to several
`mV to hundreds of mV, if so disired.
`In controlling the discharging controlling FET 5 by detet-
`ing the above value VM,
`there may be contemplated a
`method of digitally turning the gate voltage of the FET 5
`on/off and a method of analogically controlling the gate
`voltage. Although these methods are not explained in detail,
`it is possible to make designing so that approximately the
`same results will be obtained by these methods.
`Referring to FIG. 5, the specified internal structure of the
`detection control IC 3 of the second embodiment shown in
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`second embodiment will be explained subsequently.
`In the discharging controlling FET 5,
`there exists the
`parasitic diode, as shown in FIG. 4. Therefore,
`if the
`discharging controlling FET 5 is turnedoff, the currentin the
`discharging direction may be turned off, however, the cur-
`rent in the charging direction cannot be turned off, however,
`the current in the charging direction cannot be turnedoff.
`However, the current in the charging direction can also be
`turned off for the potential difference within the forward
`voltage drop Vf. That is, the charging current can also be
`turned off if the maximum voltage VCmaof the charger is
`within a certain range. Thus, in the present second embodi-
`FIG. 4 is explained. It is noted that components similar to
`mentofthe battery protection circuit, it is possible to control
`those shown in FIG. 3 are depicted by the same reference
`the battery cell 2 to its fully charged stale in the interior of
`numerals and are not explained specifically.
`the battery pack 1 by turning off the discharging controlling
`Referring to FIG. 5, the detection control IC 3 includes a
`FET5responsiveto the detection of the fill charging voltage
`first over-charging detection unit Cl, having the function
`of the battery cell 2 to control the charging current.
`similar to that of the overcharging detection unit Cl shown
`Also, if the present second embodiment is provided with
`in FIG. 3, and a second over-charging detection unit C2,
`full charging control meansfor controlling the battery ccll 2
`whichis provided with a first overcharging reference voltage
`to the fully charged state in the inside of the battery pack 1,
`source 70 for generating a reference voltage RV1 similar to
`the following merit
`is accrued. That
`is,
`if there is not
`that produced by the reference voltage source 70 of FIG. 3,
`provided in the battry pack the overcharging control means
`and which has the function as a comparatorfor detecting the
`such as that provided in the second embodiment, the full
`over-charging of the battery cell 2. The detection control IC
`charging voltage of the battery cell 2 needs to be controlled
`3 also includes a second over-charging reference voltage
`on the charger side, so that the voltage generating portion
`source 71 for generating a second detection reference volt-
`needs to be designed to high precision. If conversely the
`age RV2 corresponding to the full charging voltage of the
`overcharging control means such as that provided in the
`battery cell 2, an overcharging detection unit C3, having the
`second embodimentis provided in the battery pack 1 as in
`function of a comparator for detecting the over-discharing,
`the second embodiment, the voltge generating portion of the
`and an over-charging reference voltage source 72 for gen-
`charger can be lowered,that is the voltage allowance range
`erating an over-discharging detection reference voltage RV3
`in the charger can be broader, so thatit is possible to use a
`as a reference for detecting the over-charging in the over-
`less costly charger. As a more specified example,if, with the
`charging detection unit C3. The detection control IC 3 also
`full charging voltage in the battery cell 2 of 4.2 to 4.25 V,
`includes an excess current detection unit C5 having the
`there is not provided the full voltage control means in the
`function as a comparator for detecting the excess current,
`battery pack, the voltage on the charger side needs to be of
`and an excess current reference voltage source 76 for
`a precision of 4.225+0.025 V, whereas, if there is provided
`generating an excess current detecting reference voltage
`no full charging control means on the charger side,
`the
`RV5 as a reference for detecting the excess current in the
`chargerside voltage is 4.2 V to 4.7 V for the forward voltage
`excess current detection unit C5. The detection control IC 3
`drop of the parasitic diode Vf=0.5 V.
`Thus, in the present second embodiment, the discharging
`controlling FET 5 can also be used for charging control,
`though to a limited extent.
`On the other hand,if the cell voltage of the battery cell 2
`is higher than the full charing voltage,
`the discharging
`controlling FET 5 is turned off. The battery cell 2 can be
`discharged fromthis state as follows:
`First, if a load is connected to the plus terminal 11 and the
`minus terminal 12 when the discharging controlling FET 5
`is off, the voltage at the plus terminal 11 is lowered toeards
`the potential of the minus terminal 12. The potential of the
`plus terminal 11 is monitored by the detection control IC 3
`via terminal voltage detection terminal 35, such that,if the
`potential at the plus terminal 11 is lower by a certain value
`(VM)than the potential of the positive electrode side of the
`battery cell 2 (potential of the cell plus voltage detection
`terminal 31), the detection control IC 3 controls the dis-
`charging controlling FET 5 in the on-direction, by the
`discharge FET control signal from the discharging control-
`ling FET control terminal 34, to allow the flowing of the
`discharging current. This is tantamount to the discharging
`with the charging FET (FET 206 of FIG. 1) inthe prior-art
`example being turned off. Since the FET 206 of FIG. 1 has
`been discharged in an amount corresponding to the forward
`voltage drop of Vfof the parasitic diode, it may be presumed
`
`also includes a discharging state detection unit C4, having
`the function of a comparator for detecting the discharging
`state, a discharging state reference voltage source 75 for
`generating a discharging state detection reference voltage
`RV4 as a reference for detecting the discharging state in the
`discharging state detection unit C4, an AND (logical
`product) gate 74 and an OR(logical sum) gate 77. In the
`preferred embodiment, the first over-discharging detection
`reference voltage RVI is set to, for example, 4.4 V, the
`second over-discharging detection reference voltage RV2 is
`set to a smaller value of say tens of mV and the excess
`current detecting reference voltage RV5 is set to a value
`corresponding to the current value of the order of one
`hundred and several tens of mV to several hundreds of mV
`desired to be detected.
`
`As in the case of FIG. 3, the first over-charging detection
`unit C1 comparesthe cell voltage (voltager of the positive
`electrode side) of the battery cell 2 to the first excess current
`detecting reference voltage RV1 from the first overcharging
`reference voltage source 70 and outputs an H-lvel signal as
`an over-charging control signal from the excess current
`control terminal 33 when the cell voltage becomes higher
`than the first over-discharging, detection reference voltage
`RVI1 (4.4 V). This fires the driving FET 42 ti heat up the
`heaterof the fuse fitted with the heater 41 to blow of the fuse
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`to protect he battery cell 2 against excess charging.
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`H level. Since the output of the discharging state detection
`unit C4 is at the H level, the output of the two-input AND
`gate 74 is at
`the H level. Thus,
`if the output of the
`overcharging