(12) United States Patent
`Iwaizono
`
`USOO65771 05B1
`US 6,577,105 B1
`Jun. 10, 2003
`
`(10) Patent No.:
`(45) Date of Patent:
`
`(54) CIRCUIT AND DEVICE FOR PROTECTING
`SECONDARY BATTERY
`
`* ) Notice:
`
`(75) Inventor: Yoshinori Iwaizono, Okayama (JP)
`(73) Assignee: Matsushita Electric Industrial Co.,
`Ltd., Osaka (JP)
`Subject to any disclaimer, the term of this
`y
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 0 days.
`(21) Appl. No.:
`09/743,539
`(22) PCT Filed:
`May 17, 2000
`(86) PCT No.:
`PCT/JP00/03160
`S371 (c)(1),
`(2), (4) Date: Jan. 11, 2001
`(87) PCT Pub. No.: WO00/70702
`PCT Pub. Date: Nov. 23, 2000
`Foreign Application Priority Data
`(30)
`May 17, 1999
`(JP) ........................................... 11-1353.25
`Jul. 23, 1999
`(JP) ........................................... 11-209766
`(51) Int. Cl." ............................................... HO1M 10/46
`(52) U.S. Cl. ........................ 320/134; 320/136; 320/150
`(58) Field of Search ................................. 320/127, 128,
`320/134, 136, 150, 153
`
`
`
`(56)
`
`References Cited
`U.S. PATENT DOCUMENTS
`5,146,150 A * 9/1992 Gyenes et al.
`
`5,691,621. A * 11/1997 Phuoc et al.
`5,796,239 A * 8/1998 Van Phuoc et al.
`6,166,516 A * 12/2000 Albright et al.
`FOREIGN PATENT DOCUMENTS
`
`JP
`JP
`JP
`JP
`JP
`JP
`
`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
`
`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 means for shutting off a third FET
`when the anti-Overcharging function of the main control
`means is not operating properly.
`
`30 Claims, 11 Drawing Sheets
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`Samsung Ex. 1007, Page 1 of 23
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`IPR2023-01183
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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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`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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`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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`A fig. 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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`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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`A fig - 7
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`44 a
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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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`U.S. Patent
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`Jun. 10, 2003
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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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`US 6,577,105 B1
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`U.S. Patent
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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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`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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`A f g . 72
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`1
`CIRCUIT AND DEVICE FOR PROTECTING
`SECONDARY BATTERY
`
`US 6,577,105 B1
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`2
`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 ON state. When this MOSFET 35 is 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 power circuit.
`Nevertheless, although an anti-Overcharging circuit that is
`redundantly provided as in the above conventional Structure
`was indeed effective at preventing battery breakdown due to
`a prolonged overcharging State, because the Second control
`means, which was actuated 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 development of 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 power circuit than that in prior art, as well as
`a protective element 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 battery, comprising:
`a first Switching means and a Second Switching means
`connected in Series in a charge/discharge circuit of the
`rechargeable battery;
`
`BACKGROUND OF THE INVENTION
`The present invention relates to a protective circuit 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 leads to the generation of gas or heat due
`to decomposition of electrolyte and may cause breakdown or
`deterioration of the battery. Lithium-based rechargeable
`batteries are particularly Susceptible to deterioration or dam
`15
`age when operated at a Voltage exceeding a predetermined
`range. It is therefore the normal practice to provide a battery
`protection device for protecting the battery from improper
`Sc.
`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 gas is generated within the rechargeable
`battery, it 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 flow of 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.
`The above-mentioned battery protective circuit is
`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
`voltage is detected, a MOSFET 31 serially connected to a
`charging and discharging circuit is put in an OFF State,
`whereby the charging and discharging circuit is shut off, and
`charging current is impeded. When a Voltage below a
`predetermined discharge-permitting Voltage is detected, a
`MOSFET 32 serially connected to the charging and dis
`charging circuit is put in an OFF State, whereby the charging
`and discharging circuit is shut off, and discharging current is
`impeded. This control allows the rechargeable battery 30 to
`be protected against damage or diminished performance due
`to overcharging or overdischarging.
`However, when the battery protective circuit is not oper
`ating 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 of this, as shown in FIG. 13, a battery protective circuit
`configuration has been proposed in which there are provided
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`US 6,577,105 B1
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`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 OFF State 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 Voltage, 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 effectively 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 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 abnormal internal
`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 means through detection of the Second
`charge-prohibiting Voltage, and maintains this OFF State
`until a Second charge-permitting Voltage is detected.
`Specifically, the Second charge-permitting Voltage is Set
`below the first charge-prohibiting Voltage, the result of
`which is 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 OFF state 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.
`Alternatively, the sub-protective circuit may fix the OFF
`State of the Second Switching means after 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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`The first and Second Switching means may be constructed
`of power MOSFETs 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 means are in
`a shutoff State due to the detection of an overcharging State,
`discharge will be possible through the parasitic diodes, and
`the rechargeable battery can be used even in 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 means is turned OFF when the 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 above Said first charge-prohibiting Voltage, and main
`tained in Said charging direction OFF/discharging direction
`ON State 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 below said 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 current of 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 abnormal State, this main protective
`circuit either turns OFF the first Switching means or renders
`it capable of only charging or discharging. If Something
`should go amiss in this main protective circuit, 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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`overcharging is kept from progressing to the point of the
`breakdown of the rechargeable battery. This redundant over
`charging 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, 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 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 first Switching means is an FET
`with no parasitic diode in its interior, and the various
`ON/OFF States 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 Supply to 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 when the detected Volt
`age is above the 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 OFF State 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 power to 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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`6
`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
`down of 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 formed flat, 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 by electrical conduction,
`connected to the Voltage detection means and heat-coupled
`to the PTC device; and
`Switching means for turning on the heating means in
`accordance with the control Signal from the Voltage detec
`tion means.
`Power is Sent to the heating means by the actuation of the
`Switching means through 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 not interfere with
`the input and output circuit, but when an excessively large
`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 by the
`elevated temperature when heated by the heating means, and
`this restricts the current of the input and output circuit of the
`
`Samsung Ex. 1007, Page 15 of 23
`Samsung Electronics Co., Ltd. v. RJ Technology, LLC
`IPR2023-01183
`
`

`

`7
`rechargeable battery. Therefore, when the Voltage detection
`means detects a Voltage indicating an abnormal State 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 power is 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
`when a 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 means for turning on the heating PTC device in
`accordance with the control Signal from the Voltage detec
`tion means.
`Power is sent to the heating PTC device by the actuation
`of the Switching means through a control Signal outputted
`when the 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 damage by Setting 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 by this control
`circuit and overcharging is prevented, but if Something goes
`wrong with 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 means outputs a control Signal through the detection of
`a Voltage higher than the above-mentioned initial value, 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 battery protective 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.
`When power is 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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`US 6,577,105 B1
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`8
`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 element for 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 enhances electrical and mechanical
`performance.
`Leads can also be formed extending from the electrode
`materials, which facilitates circuit conn