JP2004355837A - Packed cell having overcurrent protection circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To simply and inexpensively mount a resistive element onto a substrate and to interrupt a cell current by an accurate current for protecting a cell when an overcurrent flows in the cell. <P>SOLUTION: The packed cell having the overcurrent protection circuit comprises a switching element 3 that is connected to the cell 2 in series and is switched from on to off when the overcurrent flows in the cell 2, the resistive element 4 that is connected to the cell 2 in series and generates a voltage proportional to current flowing in the cell 2, and an overcurrent protection circuit 1 that switches the switching element 3 from on to off for interrupting the cell current when a detection voltage becomes higher than a reference voltage. The overcurrent protection circuit 1 is composed of a chip-on board for mounting the switching element 3, the protection circuit 5, and the resistive element 4 onto the substrate 6; and sets a wire that is wire-bonded onto the chip-on board to be the resistive element 4. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a battery pack having an overcurrent protection circuit that shuts off current when an overcurrent flows through the battery and protects the battery from overcurrent.
[0002]
[Prior art]
The battery pack can be used safely by protecting the battery from overcurrent. To realize this, the battery pack has a built-in overcurrent protection circuit. This overcurrent protection circuit detects the overcurrent of the battery and cuts off the current.
[0003]
The overcurrent of the battery can be detected by the voltage generated at both ends of the resistor connected in series with the battery. This is because the voltage generated at both ends of the resistance element increases in proportion to the product of the resistance and the current. An overcurrent protection circuit that detects the voltage of the resistance element and detects the battery current compares a detection voltage generated across the resistance element with a reference voltage. When the detection voltage becomes higher than the reference voltage, the current is cut off.
[0004]
To achieve this, it is necessary to connect a resistance element in series with the battery. The resistance element is fixed to a substrate on which the overcurrent protection circuit is mounted. In an overcurrent protection circuit for mounting a resistance element, it is necessary to mount the resistance element on a substrate by a method such as soldering. In order to reduce the cost by omitting the resistance element, the battery pack having the circuit configuration shown in FIG. 1 uses the FET 13 connected in series with the battery 12 as a resistance element, and sets the voltage generated in the FET 13 to a reference voltage. To detect overcurrent. The FET 13 is a switching element that cuts off current when an overcurrent flows through the battery 12. Since the overcurrent protection circuit 11 uses the FET 13 connected in series with the battery 12 as a resistance element, there is no need to connect a resistance element for detecting an overcurrent.
[0005]
However, it is difficult for the overcurrent protection circuit shown in FIG. 1 to keep the breaking current constant. This is because the on-resistance of the FET greatly changes. The on-resistance of the FET changes depending on the bias voltage supplied to the gate, and decreases as the bias voltage increases and increases as the bias voltage decreases. The FET has a low on-resistance when the bias voltage applied to the gate is high, and has a high on-resistance when the bias voltage is low. In the FET, a high voltage as close as possible to the battery voltage is applied to the gate in the ON state in order to make the ON resistance as small as possible. For this reason, the gate voltage of the FET becomes almost the battery voltage. Therefore, when the battery voltage decreases, the gate voltage also decreases and the on-resistance increases. If the on-resistance of the FET used as the switching element of the battery pack changes the gate voltage to 3 to 4 V, for example, 25 to 62 mΩ, which is more than twice, the cutoff current also changes more than twice. .
[0006]
Techniques have been developed to overcome this shortcoming. (See Patent Literature 1) The battery pack described in this publication includes a reference voltage control circuit that changes the reference voltage with the battery voltage. The reference voltage control circuit increases the reference voltage when the battery voltage decreases. When the battery voltage decreases, the on-resistance of the FET increases, and the detection voltage generated across the FET when a specified cutoff current flows increases. Therefore, when the battery voltage decreases, the reference voltage is corrected to a high value, and the cutoff current can be controlled to be constant.
[0007]
[Patent Document 1]
JP-A-2001-14042
[Problems to be solved by the invention]
However, realizing this requires a reference voltage control circuit that changes the reference voltage with the battery voltage, which complicates the circuit configuration. Further, the reference voltage control circuit needs to change the reference voltage with the same characteristics as the on-resistance of the FET increases, and if there is a difference between the characteristics of increasing the on-resistance of the FET and the characteristics of increasing the reference voltage. There is also a disadvantage that the breaking current cannot be made constant. Further, since the on-resistance of a semiconductor FET changes not only with the gate voltage but also with the temperature, it is extremely difficult to change the reference voltage so that it exactly matches the change in the on-resistance of the FET. For this reason, it is extremely difficult to cut off the battery current with a fixed breaking current.
[0009]
This disadvantage can be solved by connecting a current detection resistor in series with the battery. The resistance of the current detection resistor does not change with the battery voltage, unlike an FET that is a semiconductor, and changes little with temperature. However, it is necessary to provide a current detection resistor on the circuit board on which the overcurrent protection circuit is mounted, which increases the manufacturing cost.
[0010]
The present invention has been developed to solve this drawback. An important object of the present invention is to provide a battery pack having an overcurrent protection circuit capable of protecting a battery by cutting off the battery current with an accurate current when an overcurrent flows in the battery while mounting the resistor element on the substrate simply and inexpensively. Is to provide.
[0011]
[Means for Solving the Problems]
The battery pack having the overcurrent protection circuit of the present invention includes a switching element 3 connected in series with the battery 2 and switched from on to off when an overcurrent flows through the battery 2, and a battery connected in series with the battery 2 A resistance element 4 for generating a voltage proportional to a current flowing through the element 2 and a detection voltage generated in the resistance element 4 are compared with a reference voltage. When the detection voltage becomes higher than the reference voltage, the switching element 3 is turned off from on. And an overcurrent protection circuit 1 including a protection circuit 5 for interrupting a current flowing through the battery 2. The overcurrent protection circuit 1 is composed of a chip-on-board in which a switching element 3, a protection circuit 5, and a resistance element 4 are mounted on a substrate 6, and a wire formed by wire bonding to the chip-on-board is used as the resistance element 4.
[0012]
The resistance element 4 can be a plurality of wires for wire bonding connected in parallel with each other. The resistance element 4 can change the electric resistance according to the number of wires connected in parallel and set the allowable current to an optimum value. The wire for wire bonding which is the resistance element 4 can be embedded in the sealing resin. The resistance element 4 embedded in the sealing resin can be easily and reliably insulated.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the following examples illustrate a battery pack for embodying the technical idea of the present invention, and the present invention does not specify a battery pack as follows.
[0014]
Further, in this specification, in order to make it easy to understand the claims, the numbers corresponding to the members shown in the embodiments are referred to as “claims” and “means for solving the problems”. Are added to the members indicated by "." However, the members described in the claims are not limited to the members of the embodiments.
[0015]
The battery pack shown in the circuit diagram of FIG. 2 includes an overcurrent protection circuit 1. The overcurrent protection circuit 1 protects the battery 2 by interrupting the current when an overcurrent flows in the battery 2. The overcurrent protection circuit 1 includes a switching element 3 connected in series with the battery 2 and switched from on to off when an overcurrent flows through the battery 2, and a switching element 3 connected in series with the battery 2 and proportional to the current flowing through the battery 2. And a detection voltage generated in the resistance element 4 is compared with a reference voltage, and when the detection voltage becomes higher than the reference voltage, the switching element 3 is switched from on to off to reduce the current. A protection circuit 5 for shutting off is provided.
[0016]
As shown in FIG. 3, the overcurrent protection circuit 1 is configured by a chip-on-board in which the switching element 3, the protection circuit 5, and the resistance element 4 are mounted on a substrate 6. The resistance element 4 is a wire that is wire-bonded to a chip-on-board. The ends of the wires to be wire-bonded by the chip-on-board are connected to the switching elements 3 mounted on the circuit board 6 or the conductive parts of the protection circuit IC, or to the patterns provided on the surface of the circuit board 6. Connected. Since the chip-on-board also performs wire bonding on parts other than the resistance element 4, the resistance element 4 is mounted on the circuit board 6 by wire bonding in the step of wire bonding other parts. In the chip-on-board of FIG. 3, in addition to the resistance element 4, the switching element 3 FET and the resistance element 4 are connected by wire bonding, and the protection circuit 5 and the switching element 3 FET are also connected by wire bonding. Further, the FET of the switching element 3 and the output terminal 7 are also connected by wire bonding. In the chip-on-board, the sealing resin is bonded to the surface of the substrate 6 so that the wires to be wire-bonded are embedded in the sealing resin.
[0017]
The resistance element 4 is configured by wire bonding a plurality of wires. The resistance value of the resistance element 4 can be specified by the thickness, length, and number of wires to be wire-bonded. Also, the allowable current can be set to an optimum value by the number of wires connected in parallel as the resistance element 4. For example, the electric resistance of a wire for wire bonding having a diameter of 30 μm and a length of 1 mm is about 34 mΩ in average of 20 wires. When the electrical resistance of the 20 wires for wire bonding is accurately measured, the minimum value of the electrical resistance is 30.26 mΩ, the maximum value is 39.31 mΩ, the standard deviation is 2.70 mΩ, and the average value is 34.31 mΩ. . When a current of 3 A flows through the resistance element 4 composed of one wire, a voltage of 103 mV is generated at both ends. When these two wires are connected in parallel, a current of 3 A flows and a voltage of 51.5 mV is generated. Therefore, the resistance element 4 composed of the wire for wire bonding can adjust the number of wires connected in parallel, change the electric resistance, and adjust the voltage generated from the electric resistance. Further, the electric resistance can be changed by the length and diameter of the wire. In the overcurrent protection circuit 1 of FIGS. 2 and 3, four wires are arranged in parallel and connected in parallel, so that the electric resistance is 1/4 of one wire.
[0018]
The wire for wire bonding may have, for example, a wire diameter of 20 to 50 μm and a length of 0.5 to 2 mm, or may have three or less wires connected in parallel, or five or more wires.
[0019]
Since the chip-on-board is a circuit board 6 that is electrically connected by wire bonding, the resistance element 4 is configured by wires for wire bonding, and is used for wiring without fixing the dedicated resistance element 4 to the circuit board 6. Configure with wire. Further, since the chip-on-board is electrically connected by wire bonding, even if the number of wires to be wire-bonded increases, the cost increase for that is very small. Therefore, the resistive element 4 composed of wires for wire bonding on the chip-on-board can be extremely economically provided on the circuit board 6, and the electric resistance is optimal for detecting the overcurrent of the battery 2. There is a feature that can be set to a value.
[0020]
The battery 2 incorporated in the battery pack is a lithium ion secondary battery. In a lithium ion secondary battery, the battery voltage decreases as the battery is discharged. The overcurrent protection circuit 1 of the present invention cuts off the current at an accurate current value even when the battery voltage fluctuates, and is therefore most suitable for a circuit in which the battery 2 is a lithium ion secondary battery. However, a secondary battery other than the lithium ion secondary battery, for example, a nickel-cadmium battery or a nickel-hydrogen battery can also be used.
[0021]
The switching element 3 is an FET. The illustrated battery pack includes FETs for charging and discharging. The charging FET and the discharging FET are not turned on / off only when an overcurrent flows, but the charged battery 2 is fully charged, or the discharged battery 2 is completely discharged. Alternatively, the battery 2 is protected by being switched from on to off when the battery temperature becomes abnormally high. If an overcurrent flows during charging, the charging FET is switched from on to off and cuts off the charging current. When an overcurrent flows during discharging, the discharging FET is switched from on to off to cut off the discharging current. The overcurrent protection circuit can detect an overcurrent only when discharging, and when the overcurrent flows in the discharging state, can switch the discharging FET from on to off to cut off the discharging current. Also, the overcurrent protection circuit may detect an overcurrent only during charging, and switch over the charging FET from on to off to shut off the charging current when the overcurrent flows in the charging state. it can. Also, overcurrent can be detected both during discharging and during charging, and when overcurrent flows, the discharging current or charging current can be cut off.
[0022]
The FET includes a diode connected in parallel. The diodes are connected in parallel so that current can flow in the reverse direction when the FET is off. Therefore, discharging can be performed in a state where the charging diode is off, and charging can be performed in a state where the discharging diode is off.
[0023]
The switching element 3, which connects the charging and discharging FETs in series, detects that an overcurrent flows and switches one of the FETs from on to off. For example, if an overcurrent flows during charging, the discharging FET is kept on, the charging FET is switched from on to off, and the charging current is interrupted. When an overcurrent flows, the charging FET is kept on, and the discharging FET is switched from on to off to cut off the discharging current. This battery pack can be discharged even if an overcurrent flows during charging and interrupts the charging current, and can be charged even if an overcurrent flows and interrupts the discharging current when it can be discharged. However, when overcurrent is detected during charging or discharging, both the charging and discharging FETs can be switched from on to off. This battery pack can be used safely because it stops both charging and discharging when an overcurrent flows. In this battery pack, a protection circuit 5 is provided with a reset circuit (not shown). After detecting an overcurrent, it is confirmed that the battery 2 can be used safely. It can be used by switching from off to on.
[0024]
In the overcurrent protection circuit 1 in the figure, the switching element 3 is connected between the battery 2 and the output terminal 7 by wire bonding. The FET which is the switching element 3 is a MOSFET having a built-in parasitic diode. The charging and discharging FETs are connected in series so that the source and the drain are opposite to each other, and are connected to the protection circuit 5 by wire bonding of the gate. The FET that is the switching element 3 is turned on and off by a voltage input from the protection circuit 5.
[0025]
The protection circuit 5 compares a detection voltage generated in the resistance element 4 due to the flow of the load current with a reference voltage, and controls ON / OFF of the FET which is the switching element 3. The protection circuit 5 has a built-in differential amplifier (not shown) for comparing a detection voltage with a reference voltage. The differential amplifier has an input terminal connected to the resistance element 4 and inputs a detection voltage proportional to the load current of the battery 2 to one input terminal. The differential amplifier inputs a reference voltage to the other input terminal.
[0026]
The protection circuit 5 turns on the switching element 3 when the detection voltage is lower than the reference voltage, and turns off the switching element 3 from on when the overcurrent flows through the battery 2 and the detection voltage becomes higher than the reference voltage. Switch.
[0027]
An overcurrent protection circuit that detects overcurrent only when discharging and shuts off the current when overcurrent flows at this time compares the detection voltage with the reference voltage during discharging and makes the detection voltage If the voltage becomes higher than the voltage, it is determined that an overcurrent has occurred, and the discharging FET is switched from on to off. At this time, the charging FET is kept on, so that charging is possible. Also, the charging FET can be switched from on to off so that neither discharging nor charging can be performed.
[0028]
In addition, an overcurrent protection circuit that detects overcurrent only during charging and shuts off the current when an overcurrent flows at this time compares the detection voltage with the reference voltage during charging, and detects the overvoltage. Is higher than the reference potential, an overcurrent is determined, and the charging FET is switched from on to off. Also at this time, the discharging FET can be kept on to make it possible to discharge. Also, the discharging FET can be switched from on to off so that neither discharging nor charging can be performed.
[0029]
The protection circuit 5 does not control the switching element 3 to be turned on / off only when an overcurrent flows, but the charged battery 2 is fully charged, or the discharged battery 2 is completely discharged, or The protection circuit protects the battery 2 by switching the switching element 3 from on to off even when the battery temperature becomes abnormally high. The overcurrent protection circuit 1 uses the switching element of the protection circuit in combination to cut off the current when an overcurrent flows. In this battery pack, it is not necessary to provide a dedicated switching element or a protection circuit to cut off the overcurrent. The protection circuit is a protection circuit IC including a circuit for detecting remaining capacity, full charge, overdischarge, and the like of a battery in addition to a circuit for detecting overcurrent.
[0030]
【The invention's effect】
The battery pack provided with the overcurrent protection circuit of the present invention has a feature that, when an overcurrent flows through the battery, the battery current can be cut off with an accurate current to protect the battery while the resistance element is simply and inexpensively mounted on the substrate. . The battery pack of the present invention includes an overcurrent protection circuit, a switching element that is switched from on to off when an overcurrent flows through the battery, a resistance element that generates a voltage proportional to the current flowing through the battery, and a resistance element. And a protection circuit that switches the switching element from on to off by comparing the detection voltage generated on the chip with a reference voltage, and a chip-on-board mounted on the board, and the wire that is wire-bonded to the chip-on-board is a resistance element. Because. In this overcurrent protection circuit, since the resistance element is configured by wiring wires connected to the substrate, it is not necessary to fix a resistance element dedicated to current detection unlike the related art. In particular, since the chip-on-board is electrically connected by wire bonding, even if the number of wires to be wire-bonded is increased, the cost increase is very small. Therefore, the battery pack of the present invention can realize the feature that the resistance element can be easily and economically mounted on the substrate. Further, since the electrical resistance of a resistance element formed of a wire can be specified by the thickness and length of the wire, the resistance value can be easily and easily set to an optimum resistance value. Therefore, by setting the resistance element to an optimum resistance value, the current flowing through the battery can be accurately detected, the overcurrent can be cut off, and the battery can be reliably protected.
[Brief description of the drawings]
FIG. 1 is a circuit diagram of a conventional overcurrent protection circuit. FIG. 2 is a circuit diagram of a battery pack provided with an overcurrent protection circuit according to one embodiment of the present invention. FIG. 3 is an overcurrent protection circuit formed by a chip-on-board. Schematic diagram showing [Description of symbols]
REFERENCE SIGNS LIST 1 overcurrent protection circuit 2 battery 3 switching element 4 resistance element 5 protection circuit 6 substrate 7 output terminal 11 overcurrent protection circuit 12 battery 13 FET

Claims (3)

A switching element (3) connected in series with the battery (2) and switched from on to off when an overcurrent flows through the battery (2); and a switching element (3) connected in series with the battery (2) and flowing through the battery (2) A resistance element (4) for generating a voltage proportional to the current and a detection voltage generated in the resistance element (4) are compared with a reference voltage, and when the detection voltage is higher than the reference voltage, the switching element (3) is switched. An overcurrent protection circuit (1) including a protection circuit (5) for switching from on to off and interrupting a current flowing through the battery (2);
The overcurrent protection circuit (1) comprises a switching element (3), a protection circuit (5), and a chip-on-board in which a resistance element (4) is mounted on a substrate (6). A battery pack that has an overcurrent protection circuit that is a wire that is wire-bonded to a board. The battery pack having the overcurrent protection circuit according to claim 1, wherein the resistance element (4) is a plurality of wires for wire bonding connected in parallel with each other. A battery pack comprising the overcurrent protection circuit according to claim 1, wherein a wire for wire bonding of the resistance element (4) is embedded in a sealing resin.

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