a2) United States Patent
`US 6,577,105 B1
`(10) Patent No.:
`Jun.10, 2003
`(45) Date of Patent:
`Iwaizono
`
`US006577105B1
`
`(54) CIRCUIT AND DEVICE FOR PROTECTING
`SECONDARY BATTERY
`
`(75)
`
`Inventor: Yoshinori Iwaizono, Okayama (JP)
`
`(73) Assignee: Matsushita Electric Industrial Co.,
`Ltd., Osaka (JP)
`
`(*) Notice:
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 0 days.
`
`JP
`JP
`JP
`JP
`JP
`JP
`
`5,691,621 A * 11/1997 Phuocet al.
`5,796,239 A *
`8/1998 Van Phuocctal.
`6,166,516 A * 12/2000 Albright et al.
`FOREIGN PATENT DOCUMENTS
`
`8-65907
`8-116627
`10-12282
`10-51962
`2872365
`11-113178
`
`3/1996
`5/1996
`1/1998
`2/1998
`1/1999
`4/1999
`
`OTHER PUBLICATIONS
`
`(21) Appl. No.:
`
`09/743,539
`
`(22)
`
`PCTFiled:
`
`May17, 2000
`
`(86) PCT No::
`
`PCT/JP00/03160
`
`§ 371 (<)),
`(2), (4) Date:
`
`Jan. 11, 2001
`
`(87) PCT Pub. No.: WO00/70702
`
`PCT Pub. Date: Nov. 23, 2000
`
`(30)
`
`Foreign Application Priority Data
`
`May 17,1999
`Jul. 23, 1999
`
`(IP)
`(IP)
`
`oocecceccecceccseceseeseesesesesstsseeseees 11-135325
`eceicecceseceeeeeceeeesereceseenerene 11-209766
`
`Tint, C1? eee ccceceeeceseceeeeseeeneenennenes HO1M 10/46
`(SL)
`
`. 320/134; 320/136; 320/150
`(52) US. Ch wo.
`seceessessssuseesessssveveveesen 320/127, 128,
`(58) Field of Search
`320/134, 136, 150, 153
`
`(56)
`
`References Cited
`U.S. PATENT DOCUMENTS
`
`Robert A. Mammano, “Charging the New Batteries—IC
`Controller Track New Technologies”, IEEE AESS Systems
`Magazine, 1995, pp. 20-25.
`
`* cited by examiner
`
`Primary Examiner—Edward H. Tso
`(74) Attorney, Agent, or Firm—Jordan and Hamburg LLP
`
`(57)
`
`ABSTRACT
`
`A protective circuit for protecting a rechargeable battery
`from battery breakdown caused by prolonged overcharging,
`and a protective element incorporated in this circuit are
`provided. A main protective circuit is equipped with main
`control means for shutting off a first FET or a second FET
`when any of overcharging, overdischarging, or excessive
`discharge current
`is detected. A sub-protective circuit is
`equipped with sub-control meansfor shutting off a third FET
`when the anti-overcharging function of the main control
`meansis not operating properly.
`
`5,146,150 A *
`
`9/1992 Gyeneset al.
`
`30 Claims, 11 Drawing Sheets
`
`APPLE-1029
`
`APPLE-1029
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`1
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`U.S. Patent
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`Jun. 10, 2003
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`Sheet 1 of 11
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`US 6,577,105 B1
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`Fig.
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`U.S. Patent
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`Jun. 10, 2003
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`Sheet 2 of 11
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`US 6,577,105 B1
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`Fig.2
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`
`°
`/
`oy
`FOOD)
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`BATTERY
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`TEMPERATURE
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`BATTERYVOLTAGE/BATTERYTEMPERATURE
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`BATTERY
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`VOLTAGE
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`|
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`\
`VOLTAGE 6(V) ( A
`—fto 3
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`TEMPERATURE '
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`——> TIME
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`—
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`3
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`U.S. Patent
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`Jun. 10, 2003
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`Sheet 3 of 11
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`US 6,577,105 B1
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`Fig.4
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`4
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`U.S. Patent
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`Jun. 10, 2003
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`Sheet 4 of 11
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`US 6,577,105 B1
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`Fige.5
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`5
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`Jun. 10, 2003
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`Sheet 5 of 11
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`US 6,577,105 B1
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`U.S. Patent
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`Jun. 10, 2003
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`Sheet 6 of 11
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`US 6,577,105 B1
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`Fig.7
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`7
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`U.S. Patent
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`Jun. 10, 2003
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`Sheet 7 of 11
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`US 6,577,105 B1
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`Fig.8A
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`45
`ata
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`“46a
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`10
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`U.S. Patent
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`Jun. 10, 2003
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`Sheet 8 of 11
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`US 6,577,105 B1
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`Fige.9
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`U.S. Patent
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`Jun. 10, 2003
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`Sheet 9 of 11
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`Jun. 10, 2003
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`Sheet 10 of 11
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`US 6,577,105 B1
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`Fig.117A
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`48a
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`48a
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`U.S. Patent
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`Jun. 10, 2003
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`Sheet 11 of 11
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`US 6,577,105 B1
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`Fig.12
`Prior Art
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`G-—-
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`33
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`Fig.13
`Prior Art
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`30
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`12
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`US 6,577,105 B1
`
`1
`CIRCUIT AND DEVICE FOR PROTECTING
`SECONDARY BATTERY
`
`BACKGROUND OF THE INVENTION
`
`The present invention relates to a protective circuil and a
`protective element
`incorporated therein for protecting a
`rechargeable battery such as a lithium ion rechargeable
`battery against overcharging.
`Charging of rechargeable batteries beyond their suitable
`charge conditions lcads to the gencration of gas or heat duc
`to decomposition of electrolyte and may cause breakdown or
`deterioration of the battery. Tithtum-based rechargeable
`batteries are particularly susceptible to deterioration or dam-
`age when operated at a voltage exceeding a predetermined
`range. It is therefore the normalpractice to provide a battery
`protection device for protecting the battery from improper
`use.
`
`The battery protection devices include those which are
`mounted in the rechargeable battery itself as a PTC (Positive
`Temperature Coefficient) element or a current shutoff valve,
`and those configured as a circuit substrate on which is
`formed a battery protective circuit that shuts off the charging
`and discharging circuit of the rechargeable battery in
`response to an abnormal state, for instance. The above-
`mentioned PTC device is serially connected to the charging
`and discharging circuit of the rechargeable battery, and
`generates heat itself when subjected to an excessively large
`current, thereby preventing the further flow of the exces-
`sively large current through a rapid increase in resistance
`caused by the rise in temperature. With a relatively large
`rechargeable battery, this PTC device is provided inside the
`sealing assembly of the battery. The above-mentioned cur-
`rent shutoff valve is normally installed in the sealing
`assembly, and when gasis generated within the rechargeable
`battery, il is deformed by the rise in internal pressure and
`breaks when the internal pressure exceeds a permissible
`value, thereby releasing the gas and, through its breakage,
`shutting off the flowof current to the charging and discharg-
`ing circuit. PCT elements and current shutoff valves are well
`known as mechanisms provided in relatively large,
`cylindrical, lithium ion rechargeable batteries.
`is
`The above-mentioned battery protective circuit
`disclosed, for example, in Japanese Patent No. 2,872,365,
`and is configured as shown in FIG. 12. The voltage of a
`rechargeable battery 30 is detected by a control means 33,
`and when a voltage over a predetermined charge-permitting
`vollage is detected, a MOSFET 31 serially connected to a
`charging and discharging circuit is put
`in an OFFstate,
`whereby the charging and discharging circuit is shutoff, and
`charging current
`is impeded. When a voltage below a
`predetermined discharge-permitting voltage is detected, a
`MOSFET 32serially connected to the charging and dis-
`charging circuit is put in an OFFstate, whereby the charging
`and discharging circuit is shut off, and discharging currentis
`impeded. This control allows the rechargeable battery 30 to
`be protected against damage or diminished performance duc
`to overcharging or overdischarging.
`However, when the battery protective circuit is not oper-
`aling properly, and particularly when the anti-overcharging
`function is not operating,
`there is the danger that
`the
`electrolyte will decompose as the overcharging state
`progresses and that
`the rechargeable battery 30 will be
`ruptured by the gas generated as the temperature rises. In
`view ofthis, as shownin FIG. 13, a battery protective circuit
`configuration has been proposed in whichthere are provided
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`a control means 34 for preventing overcharging,
`overdischarging, and over-current, and an overcharging con-
`trol means 36 for halting the overcharging state if this
`control means 34 should malfunction.
`
`With this configuration, the control means 34 prevents
`overcharging, overdischarging, and over-current, and when
`an operational aberration occurs, such as a breakdown or
`malfunction in the ability of this control means 34 to prevent
`overcharging, a voltage corresponding to an overcharging
`state is detected by the overcharging control means 36, and
`the overcharging control means 36 puts the MOSFET 35 in
`an ONstate. When this MOSFET35is turned ON,a resistor
`18 generates heat which melts a heat-coupled temperature
`fuse 19, shutting off the charging and discharging circuit of
`the rechargeable battery 30.
`It is thereby possible to avoid a prolonged overcharging
`state, which is the most detrimental state for the recharge-
`able battery 30 to be in. Since the structure for preventing
`overcharging is provided redundantly, and the generation of
`gas due to a prolonged overcharging state is prevented,it is
`also possible to eliminate the above-mentioned current shut-
`off valve that mechanically shuts off the powercircuit.
`Nevertheless, although an anti-overcharging circuit that is
`redundantly provided as in the above conventional structure
`wasindeedeffective at preventing battery breakdown due to
`a prolonged overcharging state, because the second control
`means, which wasactuated when something was amiss with
`the first control means, actuated a non-resettable shutoff
`means, the operation thereof could not be tested, so it was
`impossible to ensure proper operation and obtain high
`reliability by testing individual operating states. The proper
`operation of an overcharging protective circuit is essential
`with rechargeable batteries of high energy density, such as a
`lithium ion rechargeable battery, and it is necessary to be
`able to ensure the reliability of individual batteries or battery
`packs by testing the operation of the protective circuit.
`Meanwhile, a temperature fuse, heating means, and so
`forth are parts that cannot be incorporated into an integrated
`circuit, and therefore require their own installation space,
`and this hinders designing a compact battery pack using
`small rechargeable batteries, or designing a rechargeable
`battery with an attached protective circuit
`in which the
`protective circuit is integrated with the rechargeable battery.
`Making rechargeable batteries smaller is very important
`in terms of making portable devices more compact, and even
`with this smaller size, the energy density per unit of volume
`still needs to be increased. An effective means for achieving
`this is to use an electrical rather than mechanical current
`shutoff valve to shut off the power circuit, and we are
`awaiting the developmentof a protective circuit that effec-
`tively protects a rechargeable battery from a prolonged
`overcharging state, with a smaller structure for the electrical
`shutoff of the powercircuit than that in priorart, as well as
`a protective clement used in this protective circuit.
`It is an object of the present
`invention to provide a
`protective circuit with a compact structure that affords
`reliable protection of a rechargeable battery, and at the same
`time, a protective element
`that
`is compatible with this
`protective circuit.
`DISCLOSURE OF THE INVENTION
`
`To achieve the stated object, the present invention pro-
`vides a battery protective circuit incorporated in a recharge-
`able battcry, comprising:
`a first switching means and a second switching means
`connected in series in a charge/discharge circuit of the
`rechargeable battery;
`
`13
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`13
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`

`

`US 6,577,105 B1
`
`3
`a main protective circuit for
`detecting a battery voltage between positive and nega-
`tive electrodes of the rechargeable battery;
`turning on the first switching means when the battery
`voltage is below a charge-prohibiting voltage, above
`which charging of the rechargeable battery must be
`prohibited; and
`turning off the first switching means when the battery
`voltage is detected to be higher than said charger-
`prohibiting voltage, and maintaining the OFFstate of
`the first switching means until the detected voltage
`becomes below a charge-permitting voltage that is
`lower than said charge-prohibiting voltage; and
`a sub-protective circuit for
`detecting the battery voltage between the positive and
`negative electrodes of the rechargeable battery;
`turning on the second switching means when the bat-
`tery voltage is below a second charge-prohibiting
`voltage which is higher than the first charge-
`prohibiting vollage; and
`turning off the second switching means when the
`battery voltage is detected to be higher than the
`second charge-prohibiting voltage.
`With the above structure, even in the event of a break-
`down or malfunction of the main protective circuit,
`the
`sub-protective circuit detects the overcharging and shuts off
`the charging and discharging circuit of the rechargeable
`battery. This affords a redundant overcharging protective
`circuit, which more cffectively prevents the overcharging of
`the rechargeable battery and keeps the overcharging from
`progressing to the point of the breakdown of the recharge-
`able battery. This redundant overcharging protection allows
`the operation of overcharging protective circuits to be tested
`for each circuit, and makes possible more reliable battery
`protection. Also, since a redundant overcharging protective
`circuit allows overchargingto be effectively prevented, there
`is none of the gas generation that would accompany
`overcharging, making it possible to eliminate mechanisms
`such as a gas escape valve for releasing abnormalinternal
`pressure in a battery caused by gas generation. Therefore, no
`space is needed for providing such gas escape valve or the
`like, making it easier to design a compact rechargeable
`battery. Also, since the circuit can be made up of semicon-
`ductor elements,
`the protective circuit can consist of an
`integrated circuit, making it possible to reduce the size of a
`battery pack and fit the protective circuit inside a recharge-
`able battery.
`In the above structure, the sub-protective circuit turns off
`the second switching meansthrough detection of the second
`charge-prohibiting voltage, and maintains this OFFstate
`until
`a sccond charge-permitting voltage is detected.
`Specifically,
`the second charge-permitting voltage is set
`below the first charge-prohibiting voltage,
`the result of
`whichis that the second switching means is turned OFF by
`the sub-protective circuit, rendering charging impossible.
`Also, the shutoff operation of the second switching means
`prevents the circuit from returning from an OFFstate to an
`ON state, and the state of overcharging protection from
`being ended, due to a decrease in battery voltage when the
`charging circuit is opened.
`Altematively, the sub-protective circuil may fix the OFF
`state of the second switching meansafter the second charge-
`prohibiting voltage has been detected. By fixing the OFF
`state of the second switching means when overcharging is
`detected, the rechargeable battery can be reliably protected
`against loss of battery protection function caused by mal-
`function of the main protective circuit.
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`Thefirst and second switching means may be constructed
`of power MOSFE'Is having parasitic diodes therein, and
`connected such that the forward direction of the parasitic
`diodes is the discharge direction of the rechargeable battery.
`Thereby, even if the first and second switching meansare in
`a shutoff state due to the detection of an overchargingstate,
`discharge will be possible through the parasitic diodes, and
`the rechargeable battery can be used evenin a state in which
`the anti-overcharging function has been actuated.
`To achieve the stated object, the present invention also
`provides a battery protective circuit
`incorporated in a
`rechargeable battery, comprising:
`a first switching means and a second switching means
`connected in series in a charge/discharge circuit of the
`rechargeable battery;
`a main protective circuit for controlling the first switching
`means in accordance with a battery voltage across positive
`and negative electrodes of the rechargeable battery and a
`discharge current of the rechargeable battery; and
`a sub-protective circuit for controlling the second switch-
`ing means in accordance with the battery voltage across
`positive and negative electrodes of the rechargeable battery,
`wherein:
`the first switching means and the second switching means
`are turned on, when the rechargeable battery is in a normal
`condition wherein the voltage across the positive and nega-
`tive electrodes of the rechargeable battery is within a range
`above a discharge-prohibiting voltage and below a
`first
`charge-prohibiting voltage, said discharge-prohibiting volt-
`age being a limit value below which discharging of the
`rechargeable battery must be prohibited, and said charge-
`prohibiting voltage being a limit value above which charg-
`ing of the rechargeable battery must be prohibited;
`the first switching meansis turned OFF whenthe detected
`discharge current is above a predetermined value;
`the first switching means is put in a charging direction
`OFF(discharging direction ON state when the detected volt-
`age is abovesaid first charge-prohibiting voltage, and main-
`tained in said charging direction OFF/discharging direction
`ONstate until a first charge-permitting voltage, that is lower
`than the first charge-prohibiting voltage, is detected;
`the first switching means is put in a discharging direction
`OFF/charging direction ON state when the detected voltage
`is belowsaid discharge-prohibiting voltage, and maintained
`in said discharging direction OFF/charging direction ON
`state until a discharge-permitting voltage, that is higher than
`said discharge-prohibiting voltage is detected;
`the second switching means is turned off when the
`detected voltage is above a second charge-prohibiting
`voltage, which is higher than said first charge-prohibiting
`voltage, and maintained in the OFF state until a second
`charge-permitting voltage, that is lower than said second
`charge-prohibiting voltage, is detected.
`With the above structure,
`the main protective circuit
`detects the voltage and discharge currentof the rechargeable
`battery, and during normal operation puts the rechargeable
`battery in a usable state by turning ON switching elements,
`but in response to an abnormalstate, this main protective
`circuit either turns OFF the first switching meansor renders
`it capable of only charging or discharging. If something
`should go amiss in this main protective circuil, such as a
`breakdown or malfunction, and it should stop preventing
`overcharging,
`then the sub-protective circuit detects the
`overcharging, and shuts off the charging and discharging
`circuit of the rechargeable battery so there is a redundant
`overcharging protective circuit, with which the overcharging
`of the rechargeable battery is effectively prevented, and
`
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`US 6,577,105 B1
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`5
`overcharging is kept from progressing to the point of the
`breakdownofthe rechargeable battery. ‘his redundant over-
`charging protection allows for the individual testing of the
`operationof these circuits, and makes possible more reliable
`battery protection. Also, since a redundant overcharging
`protective circuit allows overcharging to be effectively
`prevented, there is none of the gas generation that would
`accompany overcharging, eliminating the need for space to
`provide a gas escape valve or the like and facilitating the
`design of a compact rechargeable battery. Also, the circuit
`can be made up of semiconductor elements, so the protective
`circuit can consistof an integrated circuit, makingit possible
`to reduce the size of a battery pack and fit the protective
`circuit inside a rechargeable battery.
`In the abovestructure, the first switching means is an FET
`with no parasitic diode in its interior, and the various
`ON/OFFstates are assumed according to the gate voltage
`thereof. Thus a single FET can prevent overcharging,
`overdischarging, and over-current, which allows the battery
`protective circuit to be more compact.
`To achieve the stated object, the present invention also
`provides a battery protective circuit
`incorporated in a
`rechargeable battery, comprising:
`a PTC device connected in series in a charge/discharge
`circuit of the rechargeable battery;
`heating means heat-coupled to the PTC element;
`a first switching means connected to the PTC device for
`controlling power supplyto said heating means;
`a second switching means connected in series in the
`charge/discharge circuit of the rechargeable battery;
`a main protective circuit for
`detecting a battery voltage between positive and nega-
`tive electrodes of the rechargeable battery;
`turning off the first switching means when the detected
`voltage is below a first charge-prohibiting voltage,
`above which charging of the rechargeable battery
`must be prohibited; and
`turning on the first switching means for supplying
`power to the heating means whenthe detected volt-
`age is abovethe first charge-prohibiting voltage, and
`maintaining said ON state of the first switching
`means until a first charge-permitting voltage, that is
`lower than said first charge-prohibiting voltage, is
`detected; and
`a sub-protective circuit for
`detecting the battery voltage between the positive and
`negative electrodes of the rechargeable battery;
`turning on the second switching means when the
`detected voltage is below a second charge-
`prohibiting voltage that
`is higher than the first
`charge-prohibiting voltage; and
`turning off the second switching means when the
`detected voltage is above the second charge-
`prohibiting voltage, and maintaining the OFFstate of
`the second switching means until a second charge-
`permitting voltage, which is lower than said second
`charge-prohibiting voltage, is detected.
`With the above structure, when an overcharging state is
`detected from the voltage of the rechargeable battery, the
`main protective circuit turns on the first switching means
`and sends powerto the heating means, and the PTC device
`serially connected to the charging and discharging circuit of
`the rechargeable battery is heated by this heating means. The
`resistance of the PTC device increases rapidly as the tem-
`perature rises, which restricts charging current
`to the
`rechargeable battery and protects the battery from over-
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`charging. If this main protective circuit should stop prevent-
`ing overcharging due to a problem such as a breakdown or
`malfunction, then the sub-protective circuit detects the over-
`charging and shuts off the charging and discharging circuit
`of the rechargeable battery so there is a redundant over-
`charging protective circuit, with which the overcharging of
`the rechargeable battery is effectively prevented, and over-
`charging is kept from progressing to the point of the break-
`downof the rechargeable battery. This redundant overcharg-
`ing protection allows for the individual
`testing of the
`operation of these circuits, and makes possible more reliable
`battery protection. Also, since a redundant overcharging
`protective circuit allows overcharging to be effectively
`prevented, there is none of the gas generation that would
`accompany overcharging, making it possible to eliminate
`mechanisms such as a gas escape valve for releasing abnor-
`mal internal pressure in a battery caused by gas generation.
`Therefore, no space is needed for providing this gas escape
`valve or the like, making it easier to design a compact
`rechargeable battery. Also, the circuit can be made up of
`semiconductor elements, so the protective circuit can consist
`of an integrated circuit, making it possible to reduce the size
`of a battery pack and fit
`the protective circuit
`inside a
`rechargeable battery.
`In the above structure, the heating means can be con-
`structed of a second PTC device heat-coupled to the first
`PTC device. Both PTC devices may be formedflat, so that
`a good heat-coupling state can be obtained when two PTC
`devices are joined together on their flat sides. Thus the
`charge current-restricting construction can be made
`compact, since it is only necessary to send power to the
`second PTC device, thereby heating the first PTC device and
`increasing its resistance.
`To achieve the stated object, the present invention also
`provides a battery protective circuit for a rechargeable
`battery, comprising:
`voltage detection means connected in series between
`positive and negative electrodes of the rechargeable battery
`for detecting a battery voltage and outputting a control
`signal when a voltage exceeding a predetermined value is
`detected;
`a PTC device serially connected to the voltage detection
`means;
`heating means, which heats up byelectrical conduction,
`connected to the voltage detection means and heat-coupled
`to the PIC device; and
`switching means for turning on the heating means in
`accordance with the control signal from the voltage detec-
`tion means.
`
`Poweris sent to the heating meansbythe actuation of the
`switching meansthrough a control signal outputted when the
`voltage detection means detects a voltage exceeding a
`specific value, such as the voltage resulting from prolonged
`overcharging, and the heating means heats the heat-coupled
`PTC device. A PTC device is characterized by exhibiting a
`positive coefficient
`resistance change with respect
`to
`temperature, and in particular by entering a tripped state in
`which resistance increases rapidly above a specific critical
`temperature. Normally, the resistance is very low and the
`drop in voltage caused by input and output current of the
`rechargeable battery is so small that it does notinterfere with
`the input and output circuit, but when an excessivelylarge
`current flows in, self-generation of heat results in a sharp
`increase in resistance, which prevents excessive current
`flow. The resistance of this PTC device rises sharply bythe
`elevated temperature when heated by the heating means, and
`this restricts the current of the input and output circuit of the
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`US 6,577,105 B1
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`rechargeable battery. Therefore, when the voltage detection
`meansdetects a voltage indicating an abnormalstate such as
`a prolonged overcharging state,
`the tripping of the PTC
`device restricts the input and output current of the recharge-
`able battery so damage to the rechargeable battery due to
`prolonged overcharging is prevented.
`In the above structure, the heating means can consist of a
`second PTC device heat-coupled to the above-mentioned
`PTC device. When poweris sent to the second PTC device
`and the temperature raised, the heat-coupled PTC device is
`heated and the PTC device tripped.
`The present invention also provides a battery protective
`circuit for a rechargeable battery, comprising:
`voltage detection means connected in series between
`positive and negative electrodes of a rechargeable battery for
`detecting a battery voltage and outputting a control signal
`whena voltage exceeding a predetermined value is detected;
`a temperature fuse serially connected to the rechargeable
`battery;
`a heating PTC device heat-coupled to the temperature
`fuse; and
`switching meansfor turning on the heating PTC device in
`accordance with the control signal from the voltage detec-
`tion means.
`
`Poweris sent to the heating PTC device by the actuation
`of the switching means through a control signal outputted
`whenthe voltage detection means detects a voltage exceed-
`ing a specific value, such as the voltage resulting from
`prolonged overcharging, and the heating PTC device raises
`the temperature through current flow, which melts the heat-
`coupled temperature fuse. Therefore, the input and output
`circuit of the rechargeable battery is shut off when the
`voltage detection means detects a voltage indicating an
`abnormal state such as a prolonged overcharging state, so
`damage to the rechargeable battery due to prolonged over-
`charging is prevented.
`In the above structures, the rechargeable battery is redun-
`dantly protected against overcharging damagebysetting the
`voltage exceeding a specific value detected by the voltage
`detection means to be higher than the voltage at which an
`overcharging state is detected. Specifically, when a control
`circuit that detects a state such as overcharging or overdis-
`charging and shuts off the input and output circuit of the
`rechargeable battery is separately configured,
`the initial
`value of the overcharging state is detected bythis control
`circuit and overcharging is prevented, but if something goes
`wrongwith this control circuit, rupture or other such damage
`to the rechargeable battery can be caused by prolonged
`overcharging. If the structure is such that the voltage detec-
`tion meansoutputs a control signal through the detection of
`a voltage higher than the above-mentioned initial valuc, a
`voltage raised by prolonged overcharging will be detected,
`action will be taken to prevent overcharging, and the
`rechargeable battery will be protected even if something
`goes wrong with the control circuit.
`The present invention also provides a protective element
`incorporated in a batteryprotective circuit for a rechargeable
`battery, comprising a plurality of PTC devices formed in a
`flat shape and laminated in a heat-coupled state. One of the
`PTC devices is serially connected to the rechargeable
`battery, and another PTC device is connected to a power
`control circuit controlling the power conduction thereof.
`Whenpoweris sent to the second PTC device heat-coupled
`to the PTC device on the side serially connected to the
`rechargeable battery, the heating caused by current flow
`raises the temperature of the PTC device serially connected
`to the rechargeable battery, which sharply increases the
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`resistance and trips the PTC device, at which point the input
`and output current of the rechargeable battery is restricted.
`Thus the plurality of PTC devices effectively act as a
`protective elementfor the rechargeable battery, by construct-
`ing the power control circuit such that power is sent to the
`PTC device on the heated side upon detection of an abnor-
`mal state in the rechargeable battery such as overcharging.
`In the above structure, the PTC devices can comprise a
`combination of shapes, sizes, and electrical characteristics
`selected as desired, and a suitable combination can be
`selected according to the configuration of the protective
`circuit.
`To be more specific, the PTC device may be constituted
`with two PTC elements formed in a flat shape and joined
`together via an electrode material interposed between the flat
`sides thereof, each of the PTC elements being respectively
`provided with electrode materials joined to their outer sides,
`so that the PTC device will take up less space.
`The electrode materials may be formed from a copper-
`nickel alloy or a clad material made from a copper-nickel
`alloy and nickel, so that the product will lend itself very well
`to soldering and welding, and will also have excellent
`electrical and thermal conductivity. The use of these mate-
`rials facilitates work and enhanceselectrical and mechanical
`
`performance.
`Leads can also be formed extending from the electrode
`materials, which facilitates circuit connections.
`Leads can also be formed extending from the electrode
`materials in two mutually opposite directions, or in various
`different directions,
`the selection of which can be made
`according to the circuit configuration.
`The electrode materials may be formed in smaller outer
`dimensions than the PTC elements to which they are joined,
`so that it will be easier to obtain a good solderjoint between
`the electrode materials and the P'I'C devices.
`The present invention also provides a protective element
`incorporatedin a battery protective circuit for a rechargeable
`battery comprising a temperature fuse and a PTC device
`heat-coupled to the temperature fuse. When the temperature
`fuse is serially connected to the rechargeable battery, and the
`PTC device is connected to the power control circuit that
`controls the power conduction thereof, the heating caused by
`current flow melts the temperature fuse and shuts off the
`input and output currentof the rechargeable battery. Thus the
`temperature fuse and PTC device will effectively act as a
`protective element for the rechargeable battery, by construct-
`ing the power control circuit such that power is sent to the
`PTC device upon detection of an abnormal state in the
`rechargeable battery such as overcharging.
`The plurality of heat-coupled PTC devices may be cov-
`ered with a thermally insulating material, so that the diffu-
`sion of heat will be suppressed and heat coupling will be
`more effective.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 is a block diagram of the structure of the battery
`protective circuit according to a first embodiment of the
`present invention;
`FIG. 2 is a graph of the change in battery temperature and
`battery voltage during prolonged overcharging;
`FIG. 3 is an FET circuit diagram illustrating parasitic
`diodes built into MOSFETS;
`FIG. 4 is a block diagram of the structure of the battery
`protective circuit according to a second embodiment of the
`present invention;
`FIG. 5 is a block diagram of the structure of the battery
`protective circuit according to a third embodiment of the
`present invention;
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`US 6,577,105 B1
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`9
`FIG. 6 is a block diagramof the structure of the battery
`protective circuit according to a fourth embodimentof the
`present invention;
`FIG. 7 is an oblique view illustrating the exploded struc-
`ture of a protective element;
`FIG. 8A is a side view of the protective element, a