JP2004164982A - Protective circuit for cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a protective circuit for a cell capable of breaking charge and discharge currents at overcharge without using a semiconductor device for conducting the control of the charge and discharge currents. <P>SOLUTION: A cell module 9 has a built-in short-circuit permitting circuit 20 permitting the short circuit of charge and discharge currents between a positive charge and discharge terminal and a negative charge and discharge terminal. The short-circuit permitting circuit 20 is structured of transistors 3, 4, and resistors 7, 8. An output terminal of an overcharge detecting circuit 2 is connected to a base of the transistor 3, and a collector is connected to a positive terminal of the topmost unit cell. An emitter is connected to the end of a resistor 8 with the other end connected to the negative charge and discharge terminal, and separated from a point connected to the base of the transistor 4. A collector of the transistor 4 is connected to the end of the resistor 7 with the other end connected to the positive charge and discharge terminal, and the emitter is connected to the negative charge and discharge terminal. A fuse 5 is melted by short circuiting the short-circuit permitting circuit 20 at the overcharge. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a protection circuit for a battery, and more particularly, to an overcurrent protection circuit between a + terminal and a + charge / discharge terminal of a battery having one or more cells or between a − terminal and a −charge / discharge terminal of the battery. The present invention relates to a battery protection circuit in which a fuse is inserted.
[0002]
[Prior art]
Conventionally, as a battery protection circuit, a circuit that detects an overcharge voltage at the time of overcharge and cuts off a charging current has been used. In particular, lithium ion batteries that have recently been put to practical use have a problem in safety during overcharge due to their high energy density characteristics, and the internal pressure of the battery may become extremely high during overcharge. For this reason, in an assembled battery in which a plurality of lithium-ion batteries (unit cells) are connected in series or in parallel, in order to ensure safety during overcharge, the voltage of all the units is detected and the overcharge voltage is detected. In such a case, a protection circuit that cuts off the charging current to the battery pack has been used. In other words, in such a protection circuit, a semiconductor element is inserted into the charge / discharge line, and in a normal state (other than at the time of a battery abnormality such as overcharging), the semiconductor element is turned on to allow a charge / discharge current to flow. At the time of overcharging (battery abnormality), each cell is protected by turning off the charge / discharge current by turning off the semiconductor element (for example, see Patent Document 1).
[0003]
FIG. 2 shows an example of such a protection circuit. The voltage of each cell constituting the assembled battery 1 is determined by the corresponding overcharge detection circuit 2, and the overcharge detection circuit 2 outputs a high-level signal (Hi) when normal. When all the cells are normal, Hi is output as the overcharge output signal. When the overcharge output signal is output at Hi, the switch 10 including the semiconductor element such as the FET is turned on, and the supply of the charge / discharge current is allowed. On the other hand, at the time of overcharging, an overcharge output signal is output as a low level signal (Lo). As a result, the switch 10 is turned off, and the charge / discharge current is cut off.
[0004]
[Patent Document 1]
JP-A-2002-186173
[Problems to be solved by the invention]
However, in the conventional protection circuit, charging and discharging cannot be performed unless the semiconductor element is turned on in a normal state. Therefore, a semiconductor element capable of continuously supplying an assumed charging and discharging current is required. Therefore, when the battery pack is charged and discharged with a large current, there is a problem that the heat generation and the volume of the semiconductor element increase and the cost increases. In particular, in a lithium-ion secondary battery for an electric vehicle that has recently been put into practical use, a charge / discharge current of the order of 100 A is applied. Therefore, it is necessary to provide a semiconductor element that allows a large current on the battery module 9 side, thereby generating heat. In many cases, the battery module 9 has only an overcharge signal terminal and the charging / discharging power supply 6 interrupts the charging current (see FIG. 2). However, in this configuration, since the element for interrupting the charging / discharging current is not built in the battery module side, for example, when the charging / discharging power supply side fails and the battery module is overcharged, the charging current cannot be interrupted. Has the possibility of impairing the safety of each unit cell constituting.
[0006]
The present invention has been made in view of the above circumstances, and has as its object to provide a battery protection circuit that can cut off a charge / discharge current at the time of overcharge without using a semiconductor element that controls the conduction of the charge / discharge current.
[0007]
[Means for Solving the Problems]
In order to solve the above problems, the present invention provides an overcurrent interruption between a + terminal and a + charge / discharge terminal of a battery having one or more single cells or between a − terminal and a −charge / discharge terminal of the battery. In the battery protection circuit with a fuse inserted therein, the battery protection circuit has a short-circuit permitting circuit for allowing a short circuit between the + charge / discharge terminal and the − charge / discharge terminal. A short-circuit current is supplied to the battery by operating the short-circuit permitting circuit, and the fuse for applying an excessive current is cut off.
[0008]
According to the present invention, the battery is charged and discharged by the charge / discharge current flowing through the overcurrent cutoff fuse during normal operation, and the short circuit provided between the + charge / discharge terminal and the −charge / discharge terminal during overcharge. The allowable circuit operates, a short-circuit current flows through the fuse, and the charging current is cut off by blowing the fuse. According to the present invention, a short-circuit permitting circuit for permitting a short circuit between the + charge / discharge terminal and the − charge / discharge terminal is provided. And a semiconductor device for controlling a normal charge / discharge current is not required, so that a battery protection circuit with reduced heat generation, volume and cost of the semiconductor device can be obtained.
[0009]
In this case, the short-circuit allowable circuit may include a semiconductor element or a relay. Also, when the voltage is high in an assembled battery composed of a plurality of cells, the short-circuit current may be too large and the contacts of a semiconductor element or a relay may be blown instantaneously and the overcurrent cutoff fuse may not be blown. Since the short-circuit permitting circuit includes a current limiting element, the fuse can be surely blown to cut off the overcharge current. Furthermore, if the time during which the short-circuit allowable circuit operates is limited to a time during which the short-circuit allowable circuit is not damaged, the charge and discharge of the battery can be restored by replacing the fuse after overcharging, and at the same time, a semiconductor element or a relay, etc. , The heat generation, volume and cost can be suppressed.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment in which a battery protection circuit according to the present invention is applied to a battery module will be described with reference to the drawings.
[0011]
As shown in FIG. 1, the battery module 9 of the present embodiment includes an assembled battery 1 configured by connecting a plurality of unit cells in series. The cell 1 includes, for example, a nonaqueous electrolyte obtained by dissolving a positive electrode using lithium manganate as a positive electrode active material and a negative electrode using amorphous carbon as a negative electrode active material, in which lithium hexafluorophosphate is dissolved in an organic solvent. A lithium-ion secondary battery coupled via the like can be used.
[0012]
The + terminal of the uppermost unit cell of the assembled battery 1 is connected to one end of a fuse 5 for interrupting excessive current, and the other end of the fuse 5 is connected to a charging / discharging power supply 6 via a + charging / discharging terminal of the battery module 9. Have been. On the other hand, the negative terminal of the lowest unit cell of the assembled battery is connected to the charging / discharging power supply 6 via the negative charging / discharging terminal. The charge / discharge power supply 6 functions as a charger when the battery module 9 is charged, and functions as a load when the battery module 9 discharges.
[0013]
The + terminal and the-terminal of each cell constituting the assembled battery 1 are connected to an overcharge detection circuit 2 which determines whether or not the voltage of the cell is equal to or higher than a predetermined voltage (overcharge voltage). . The overcharge detection circuit 2 can be composed of, for example, an OP amplifier and a resistor.
[0014]
In addition, the battery module 9 has a built-in short-circuit permitting circuit 20 that allows a short-circuit of the charge / discharge current between the + charge / discharge terminal and the −charge / discharge terminal. The short-circuit permitting circuit 20 includes NPN transistors 3 and 4 and resistors 7 and 8 for limiting a short-circuit current to the transistors 3 and 4. More specifically, the output terminal of each overcharge detection circuit 2 is connected to the base of the transistor 3, and the collector of the transistor 3 is connected to the + terminal of the highest cell. The other end of the emitter of the transistor 3 is connected to one end of a resistor 8 whose other end is connected to a negative charge / discharge terminal. The collector of the transistor 4 is connected to one end of the resistor 7 whose other end is connected to the + charge / discharge terminal, and the emitter is connected to the −charge / discharge terminal.
[0015]
Next, the operation of the battery module 9 of the present embodiment will be described.
[0016]
The voltage of each cell constituting the assembled battery 1 is determined by each overcharge detection circuit 2, and the overcharge detection circuit 2 outputs Lo when normal. As a result, the transistor 3 is turned off and the transistor 4 is also turned off, so that no short-circuit current flows through the fuse 5. At the time of overcharge, the overcharge detection circuit 2 outputs a Hi signal, the transistor 3 is turned on, and the transistor 4 is also turned on. As a result, a closed circuit is formed between the + terminal of the uppermost unit cell of the assembled battery 1, the fuse 5, the resistor 7, the transistor 4, and the-terminal of the lowermost unit cell of the assembled battery 1. 5, the fuse 5 is blown, and the charging current is cut off. When the fuse 5 is blown, the closed circuit becomes an open circuit, and no short-circuit current flows through the transistor 4. Therefore, the short-circuit current flows through the transistor 4 for a very short time from when the short-circuit current starts flowing through the fuse 5 to when it is blown.
[0017]
Next, the operation and the like of the battery module 9 of the present embodiment will be described.
[0018]
Since the battery module 9 of the present embodiment has a built-in short-circuit allowable circuit 20 for allowing a short circuit of the charging / discharging current between the + charging / discharging terminal and the − charging / discharging terminal, there is a problem in terms of heat generation, volume, and cost. The charge / discharge current is cut off by operating the short-circuit permitting circuit 20 and blowing the fuse 5 at the time of overcharge, without using the semiconductor element (the switch 10 in FIG. 2) for controlling the conduction of the charge / discharge current. Although a large current is required to blow the fuse 5, the battery module 9 draws its power from the battery pack 1, does not require a special power supply, and requires a short blow time for the fuse 5. Therefore, the short-circuit allowable circuit 20 can be configured by using a relatively small-capacity semiconductor element (transistors 3 and 4) having small heat generation, volume, and cost. Therefore, according to the battery module 9 of the present embodiment, unlike the conventional battery protection circuit, a semiconductor element that allows the charging and discharging current to flow is not required, and a semiconductor that allows the fusing current of the fuse 6 to flow for a short time during overcharge. Since it can be constituted by elements, heat generation, volume and cost can be suppressed.
[0019]
Further, in the battery module 9 of the present embodiment, when the fuse 5 is blown, the fuse 5 can be reused simply by replacing the fuse 5, and the short-circuit allowable circuit 20 is provided not on the charge / discharge power supply 6 side but on the battery module 9 side. Since the battery module 9 can be incorporated in the battery module 9 alone, overcharge protection of a single cell can be achieved, which is an extremely large industrial value.
[0020]
Furthermore, in the battery module 9 of the present embodiment, since the short-circuit allowable circuit 20 is configured to include the resistors 7 and 8 for limiting the short-circuit current, the semiconductor elements (transistors 3 and 4) are instantaneously blown and the fuse 5 is blown. It eliminates the possibility that it cannot be blown. Therefore, in the battery module 9, the overcharge current from the charging / discharging power supply 6 can be reliably shut off.
[0021]
In the present embodiment, a bipolar transistor is exemplified as the semiconductor element constituting the short-circuit allowable circuit 20, but the present invention is not limited to this, and a field effect transistor (FET) or the like may be used. . Further, in the present embodiment, an example in which the short-circuit permitting circuit 20 is configured to include a semiconductor element has been described. However, the present invention is not limited to this, and includes, for example, a relay such as replacing the transistor 4 with a relay. It may be configured. Even in such a configuration, the resistor 7 has a function of preventing the contact of the relay from being blown instantaneously and ensuring that the fuse 5 is blown.
[0022]
Further, in the present embodiment, the example in which the fuse 5 is inserted between the + terminal of the uppermost unit cell and the + charge / discharge terminal of the battery module 9 is shown. It may be inserted between the negative and charge / discharge terminals of the module 9.
[0023]
【The invention's effect】
As described above, according to the present invention, a short-circuit permitting circuit for permitting a short circuit between the + charge / discharge terminal and the −charge / discharge terminal is provided, so that the charge / discharge current can be cut off during overcharge. At the same time, it is possible to charge and discharge with a large current in a normal state, and it is not necessary to use a semiconductor element for normal charge / discharge current control, so that a battery protection circuit that suppresses heat generation, volume, and cost of the semiconductor element is obtained. Can be obtained.
[Brief description of the drawings]
FIG. 1 is a block circuit diagram of a battery module according to an embodiment to which the present invention can be applied.
FIG. 2 is a block circuit diagram showing a conventional battery protection circuit.
[Explanation of symbols]
1 assembled battery (battery)
3, 4 transistor (semiconductor element)
5 Fuse 7, 8 resistance (element for current limiting)
9 Battery module (battery protection circuit)
20 Short circuit allowable circuit

Claims (4)

In a battery protection circuit, an overcurrent cutoff fuse is inserted between a positive terminal and a positive charging / discharging terminal of a battery having one or more single cells or between a negative terminal and a negative charging / discharging terminal of the battery. A short-circuit permitting circuit for permitting a short circuit between the + charge / discharge terminal and the -charge / discharge terminal, and when the single cell becomes overcharged, the short-circuit permitting circuit is operated to short-circuit the battery A protection circuit for a battery, wherein a current flows and a fuse for applying an excessive current is cut off. The protection circuit for a battery according to claim 1, wherein the short-circuit allowable circuit includes a semiconductor element or a relay. The battery protection circuit according to claim 1, wherein the short-circuit allowable circuit includes a current limiting element. 4. The battery protection circuit according to claim 1, wherein a time during which the short-circuit allowable circuit operates is limited to a time during which the short-circuit allowable circuit is not damaged. 5.

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