JPH10150721A - Protective circuit for secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stop charging or discharging and thereby increase the safety by inserting a switching device in series with a charging and discharging circuit of a secondary battery and switch-controlling the terminal voltage of the secondary battery through an output terminal of an over-charging and -discharging preventive circuit. SOLUTION: FETs 3 and 4 which are switching devices are serially connected to a charging and discharging circuit of batteries 1 and 2. While the terminal voltages of both batteries 1 and 2 are between a charging forbidden region and a discharging forbidden region, output terminals (d) and (e) of an over-charging and -discharging preventive circuit 5 become a high level and thereby the FETs 3 and 4 turn on and the charging and discharging are conducted normally. When the terminal voltages of the batteries 1 and 2 exceed the charging forbidden voltage, the output terminal (e) of the over-charging and -discharging preventive circuit 5 becomes a low level and the FET 4 turns off and thereby the charging is stopped and the overcharging of the batteries can be prevented. When the terminal voltages of the batteries 1, 2 become lower than the discharging forbidden voltage during discharging, the output terminal (d) of the over-charging and -discharging preventive circuit 5 becomes a low level and the FET 3 turns off and then the discharging is stopped and the overdischarging of the batteries can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a protection circuit for protecting a rechargeable battery from overcharge or overdischarge, and more particularly to overcharge or overdischarge of a rechargeable battery against disconnection of the rechargeable battery. The present invention relates to a protection circuit that can protect the protection circuit. Related.

[0002]

2. Description of the Related Art In general, in a non-aqueous solvent secondary battery such as a lithium secondary battery or a lead storage battery, if the battery voltage becomes too high during charging, the battery performance deteriorates and safety is impaired. A voltage higher than a predetermined value is not generated on the device side. However, when the charger is broken, the voltage of the secondary battery is monitored in consideration of the fact that a voltage higher than a predetermined value is applied to the terminal of the secondary battery during charging, and the battery is charged so that the battery voltage is within a predetermined range. Had to control. Especially,
In the case of a lithium secondary battery, for example, a battery voltage of 4.5
When the voltage exceeds V, gas is generated due to decomposition of the electrolytic solution, and as a result, the pressure inside the battery rises, the safety valve is operated, and the liquid may leak. Therefore, when a lithium secondary battery is used, it is general that the battery is charged via a protection circuit having a function of interrupting charging when the battery voltage rises and reaches a charging prohibition voltage. The charge prohibition voltage is set to a voltage (for example, 4.35 V) slightly lower than the voltage at which the decomposition of the electrolytic solution starts.

[0003] In addition, non-aqueous solvent secondary batteries such as lithium secondary batteries and lead-acid batteries deteriorate battery performance and impair safety even if the battery voltage becomes too low during discharging. A voltage lower than a predetermined value is prevented from being generated on the used device side as a load. However, if the equipment used is broken, the discharge of the secondary battery is controlled so that the battery voltage is within a predetermined range by monitoring the voltage of the secondary battery in consideration of the fact that the voltage of the secondary battery will be lower than a predetermined value at the time of discharging. I needed to. In particular, in the case of a lithium secondary battery, if the battery voltage is discharged to a non-recovery voltage (for example, 1 V), it may not be used at all even if subsequently charged. For this reason, when a lithium secondary battery is used, it is general that the battery is discharged through a protection circuit having a function of interrupting the discharge when the battery voltage decreases and reaches a discharge prohibition voltage. The discharge inhibition voltage is a voltage of 2 V at which the negative electrode copper begins to melt.
A slightly higher voltage (for example, 2.3 V) is set.

A conventional protection circuit having such a function includes, for example, a voltage detection circuit for detecting a battery voltage and a FET for cutting off a charging current or a discharging current based on an output of the voltage detection circuit. When the battery voltage reaches the charging prohibition voltage, the first and second switch elements
The switching current of the switch element is turned off to interrupt the charging current,
When the battery voltage reaches the discharge prohibition voltage, the second switch element is turned off to interrupt the discharge current.

[0005]

In the above-described conventional protection circuit for a secondary battery, when the battery voltage reaches a charging prohibition voltage, the first switch element is cut off to stop charging.
If the connection between the intermediate connection point of the secondary battery and the protection circuit is disconnected for some reason, the voltage detection circuit cannot detect the battery voltage. In this case, the first switch element cannot be shut off, and the battery is overcharged while maintaining the charged state.

In the conventional protection circuit for a secondary battery, when the battery voltage reaches the discharge prohibition voltage, the second switch element is cut off to stop the discharge. When the point is disconnected from the protection circuit, the voltage detection circuit cannot detect the battery voltage. Therefore, even if the battery voltage reaches the discharge prohibition voltage, the second detection is performed without generating the discharge prohibition signal.
In this case, the switch element cannot be cut off and the discharge state is maintained, resulting in overdischarge.

[0007] The present invention provides a protection circuit for a secondary battery that can detect the occurrence of an abnormality and reliably protect against overcharging and overdischarging when the intermediate connection point of the secondary battery is disconnected. The purpose is to:

[0008]

In order to solve the above problems, a protection circuit for a secondary battery according to the present invention includes a switch element inserted in series in a charge / discharge circuit of the secondary battery, Control means for detecting a terminal voltage via a battery voltage detection terminal connected to the secondary battery, and turning off the switch element when the terminal voltage is out of a predetermined voltage range;
Abnormality detection that detects that the connection between the secondary battery and the battery voltage detection terminal is disconnected, and sets the battery voltage detection terminal to the same potential state as when the terminal voltage of the secondary battery is out of the predetermined voltage range. Means.

Here, the abnormality occurrence detecting means is, specifically, a pull-up resistor connected between the battery voltage detection terminal and a potential point higher than the potential of the battery voltage detection terminal, or a battery voltage detection terminal connected to the battery voltage detection terminal. It is constituted by a pull-down resistor connected between a potential point lower than the potential of the detection terminal.

When a pull-up resistor is used,
It is desirable to have a pull-up resistance cut-off means for separating the battery voltage detection terminal from the pull-up resistor when the terminal voltage of the secondary battery drops to the discharge prohibition voltage.

Further, even in the case of using a pull-down resistor, it is desirable to have a pull-down resistor cut-off means for disconnecting the battery voltage detection terminal from the pull-down resistor when the terminal voltage of the secondary battery drops to the discharge prohibition voltage.

As described above, when the connection between the secondary battery and the battery voltage detecting terminal is disconnected, the battery voltage detecting terminal is set to the same potential state as when the terminal voltage of the secondary battery is out of the predetermined voltage range. Accordingly, the switch element inserted in series in the charge / discharge circuit of the secondary battery is shut off by the function of the protection circuit, and charging / discharging is stopped, so that the secondary battery is reliably protected from overcharge or overdischarge.

Further, when the connection between the secondary battery and the battery voltage detection terminal is disconnected by using a pull-up resistor or a pull-down resistor, the battery voltage detection terminal is switched to a terminal when the terminal voltage of the secondary battery is out of a predetermined voltage range. When the terminal voltage of the secondary battery drops to the discharge prohibition voltage, disconnect the pull-up resistor or pull-down resistor from the battery voltage detection terminal to prevent overdischarge due to current consumption at these resistors. This can be prevented.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. (First Embodiment) FIG. 1 is a diagram showing a protection circuit for a secondary battery according to an embodiment of the present invention. Secondary batteries (hereinafter simply referred to as batteries) 1 and 2 to be protected are non-aqueous solvent secondary batteries such as lithium batteries and batteries that are charged at a constant voltage such as a lead storage battery. Is a lithium secondary battery as an example.

The batteries 1 and 2 are connected in series, and their charge / discharge circuits include first and second NPN field-effect transistors (hereinafter referred to as F-type transistors) constituting switch elements in series.
3 and 4 are connected. Specifically, the source terminal of the first FET 3 is connected to the negative terminal of the battery 2 and the drain terminal of the first FET 3 is connected to the second FET.
4 is connected to the drain terminal.

The first FET 3 has a parasitic diode D3
Are connected in parallel so as to be in a forward direction during charging as shown in FIG.
4 are connected in parallel so as to be in a forward direction at the time of discharge as shown in FIG.

The plus terminal of the battery 1 is connected to a plus terminal (+) as an external connection terminal, and the source terminal of the second FET 4 is connected to a minus terminal (1) as an external connection terminal. A charger is connected between the external connection terminals (+) and (-) during charging, and a load is connected during discharging.

The overcharge / discharge prevention circuit 5 monitors the terminal voltage of the battery 1 via the battery voltage detecting terminals a and b and the terminal voltage of the battery 2 via the battery voltage detecting terminals b and c, respectively. It comprises an overcharge prevention circuit that generates a charge inhibition output when the terminal voltage falls below a predetermined charge inhibition voltage during charging, and an overdischarge prevention circuit that generates a discharge inhibition output when the terminal voltage exceeds a predetermined discharge inhibition voltage during discharging.

That is, the battery voltage detection terminal a of the overcharge / discharge prevention circuit 5 is a plus terminal of the battery 1, the battery voltage detection terminal b is a minus terminal of the battery 1 and a plus terminal of the battery 2, and the battery voltage detection terminal c is a When the terminal voltage of any of the batteries 1 and 2 reaches a predetermined charge prohibition voltage, the overcharge / discharge prevention circuit 5 generates a charge prohibition output, and the overcharge / discharge prevention circuit 5 From the high level to the low level. When the terminal voltage of any of the batteries 1 and 2 reaches a predetermined discharge prohibition voltage, the overcharge / discharge prevention circuit 5 generates a discharge prohibition output, and the overcharge / discharge prevention circuit 5
From the high level to the low level.

Between the plus terminal of the battery 1 and a battery voltage detection terminal b, which is a battery voltage detection terminal, a pull-up resistor 6 as abnormality detection means is connected. Therefore, if the connection between the intermediate connection point of the batteries 1 and 2 and the battery voltage detection terminal b is disconnected for some reason, the battery voltage detection terminal b has substantially the same potential as the plus terminal of the battery 1 due to the pull-up resistor 6.

Next, the operation of the battery protection circuit of FIG. 1 will be described. First, when the terminal voltages of the batteries 1 and 2 are both between the charge prohibition voltage and the discharge prohibition voltage, the output terminals d and e of the overcharge / discharge prevention circuit 5 are both at a high level. , The second FETs 3 and 4 are all turned on, and charging and discharging are performed normally.

The charger connected to the external connection terminals (+) and (-) has a charging voltage per one battery lower than a predetermined charging prohibition voltage set in the overcharge / discharge prevention circuit 5. Normally, the terminal voltages of the batteries 1 and 2 are both lower than a predetermined charge prohibition voltage, and the output terminal e of the overcharge / discharge prevention circuit 5 is at a high level.
Maintain a conductive state.

On the other hand, when the charging voltage increases due to a failure of the charger and one or both of the batteries 1 and 2 exceed a predetermined charging prohibition voltage, the output terminal of the overcharge / discharge prevention circuit 5 Since e becomes low level and the second FET 4 is turned off, charging is stopped and overcharging of the battery is prevented.

On the other hand, at the time of discharging, when the terminal voltage of one or both of the batteries 1 and 2 decreases and becomes lower than the discharge inhibition voltage, the output terminal d of the overcharge / discharge prevention circuit 5 becomes low level, and the first FET 3 Is turned off, the discharge is stopped, and overdischarge of the battery is prevented.

Here, for some reason, the batteries 1, 2
When the connection between the intermediate connection point and the battery voltage detection terminal b of the overcharge / discharge prevention circuit 5 is disconnected, the battery voltage detection terminal b has substantially the same potential as the plus terminal of the battery 1 due to the pull-up resistor 6. 2 is the battery voltage detection terminal b
And the battery voltage detection terminal c. Battery 1, 2
Normally exceeds the charge inhibition voltage, the output terminal e of the overcharge / discharge prevention circuit 5 goes low,
Since the FET 4 is in a non-conductive state, charging is stopped, and overcharging of the battery is prevented.

(Second Embodiment) FIG. 2 shows a second embodiment of the present invention.
1 shows a protection circuit for a secondary battery according to the embodiment. This embodiment has a configuration in which a transistor 7 serving as a pull-up resistor cutoff switch is connected in series to the pull-up resistor 6 in the protection circuit of FIG. That is, the pull-up resistor 6 is connected between the plus terminal of the battery 1 and the collector of the transistor 7 serving as a switching element, the emitter of the transistor 7 is connected to the battery voltage detection terminal b, and the base of the transistor 7 is connected to the output terminal d. Have been.

When the terminal voltages of the batteries 1 and 2 are both between the charge prohibition voltage and the discharge prohibition voltage, the output terminals d and e of the overcharge / discharge prevention circuit 5 are both at a high level, Since both FETs 3 and 4 are conductive, charging and discharging are performed normally. At this time, since the output terminal d of the overcharge / discharge prevention circuit 5 is at a high level, the transistor 7
Is conducting.

Here, for some reason, the batteries 1, 2
When the connection between the intermediate connection point and the battery voltage detection terminal b of the overcharge / discharge prevention circuit 5 is disconnected, the battery voltage detection terminal b has substantially the same potential as the plus terminal of the battery 1 due to the pull-up resistor 6. 2 is the battery voltage detection terminal b
And the battery voltage detection terminal c. Battery 1, 2
Normally exceeds the charge inhibition voltage, the output terminal e of the overcharge / discharge prevention circuit 5 goes low,
Since the FET 4 is in a non-conductive state, charging is stopped, and overcharging of the battery is prevented.

When one or both terminal voltages of the batteries 1 and 2 become lower than the discharge prohibition voltage, the output terminal d of the overcharge / discharge prevention circuit 5 becomes low level, and the transistor 7 becomes non-conductive. Then, no current flows through the pull-up resistor 6.

As described above, according to the present embodiment, in addition to the above-described embodiment, when one or both terminal voltages of the batteries 1 and 2 are equal to or lower than the discharge inhibition voltage, the battery with the pull-up resistor 6 1 can be prevented from being consumed, and overdischarge of the battery can be prevented.

(Third Embodiment) FIG. 3 is a diagram showing a protection circuit for a secondary battery according to another embodiment of the present invention. As a pull-up cut-off switch, a transistor instead of the transistor 7 in the previous embodiment is used. The switch circuit 11 is used.
This switch circuit 11 has a first transistor 7 connected in series to a pull-up resistor 6, a collector connected to the base of the transistor 7 via a resistor 9, an emitter connected to a voltage detection terminal c, and a base The second transistor 8 is connected to the output terminal d via the resistor 10.

According to the present embodiment, even when the potential at the high level of the output terminal d is relatively low, the transistor 9 is turned on without fail, and the transistor 7 is also turned on without fail. Can be.

Although the embodiment of the present invention has been described above, the present invention is not limited to the above embodiment, and can be implemented with various modifications as follows. (1) In the above embodiment, the pull-up resistor 6 connected between the voltage detection terminal b and a potential point higher than the potential of the voltage detection terminal b (the plus terminal of the battery 1 in the above embodiment) is used as the abnormality detection means. Although the example of using is described, for example, a pull-down resistor connected between the voltage detection terminal b and a potential point lower than the potential of the voltage detection terminal b may be used. In this case, for example, when the connection between the intermediate connection point of the batteries 1 and 2 and the voltage detection terminal b is disconnected, the voltage between the battery voltage detection terminals b and c becomes equal to or lower than the discharge inhibition voltage, and the output terminal d becomes low. Level, and the first FET 3 is turned off so that discharging is prohibited, thereby preventing overdischarging of the battery.

(2) Also in the case where the pull-down resistor is used, the terminal voltage of the battery drops to the discharge prohibition voltage as in the case of using the pull-up resistor cutoff switch in the second and third embodiments. A pull-down resistor cutoff switch for separating the battery voltage detection terminal b from the pull-down resistor is provided to prevent overdischarge of the battery due to current consumption in the pull-down resistor when the battery terminal voltage is equal to or lower than the discharge inhibition voltage. be able to.

(3) In the above embodiment, a non-aqueous solvent battery was described as an example of a battery charged at a constant voltage. However, a lead storage battery or another battery may be used. (4) In the above embodiment, the case where two batteries are connected in series has been described. However, the present invention can be applied to a case where a large number of batteries are connected in series. Can also be applied.

(5) In the above embodiment, the example in which the FETs 3 and 4 as the first and second switch elements are connected to the minus terminal side of the battery 2 has been described. Is also good. (6) In addition to the protection described in the above embodiment, a protection element such as a PTC, a thermostat, or a thermal fuse may be inserted into the charge / discharge circuit.

[0037]

As described above, according to the secondary battery protection circuit of the present invention, even if the battery is disconnected from the battery voltage detecting terminal for some reason, the charging or discharging operation is performed by the abnormality occurrence detecting means. Discharge can be interrupted,
It is possible to further improve safety compared to the conventional protection circuit.

[0038]

[Brief description of the drawings]

[0039]

FIG. 1 is a block diagram showing a configuration of a protection circuit for a secondary battery according to a first embodiment of the present invention.

[0040]

FIG. 2 is a block diagram showing a configuration of a protection circuit for a secondary battery according to a second embodiment of the present invention.

[0041]

FIG. 3 is a block diagram showing a configuration of a protection circuit for a secondary battery according to a third embodiment of the present invention.

[0042]

[Explanation of symbols]

 1, 2, secondary battery 3, 4, first and second FET (switch element) 5, overcharge / discharge prevention circuit 6, pull-up resistor 7, first transistor 8, second transistor 9, 10, Resistance 11 ... Switch circuit

Claims (5)

[Claims] 1. A switch element inserted in series in a charge / discharge circuit of a secondary battery, and a terminal voltage of the secondary battery is detected via a battery voltage detection terminal connected to the secondary battery. Control means for turning off the switch element when the voltage is out of a predetermined voltage range; and detecting that the connection between the secondary battery and the battery voltage detection terminal has been disconnected. And an abnormality detecting means for setting the same potential state as when the terminal voltage is out of the predetermined voltage range. 2. The apparatus according to claim 1, wherein said abnormality occurrence detecting means comprises a pull-up resistor connected between said battery voltage detecting terminal and a potential point higher than the potential of said battery voltage detecting terminal. A protection circuit for the secondary battery according to the above. 3. The apparatus according to claim 1, wherein said abnormality occurrence detecting means comprises a pull-down resistor connected between said battery voltage detecting terminal and a potential point lower than a potential of said battery voltage detecting terminal. Secondary battery protection circuit. 4. A switch element inserted in series in a charge / discharge circuit of a secondary battery, and a terminal voltage of the secondary battery is detected via a battery voltage detection terminal connected to the secondary battery. Control means for turning off the switch element when the voltage rises to a predetermined charging prohibition voltage; and a control means connected between the battery voltage detection terminal and a potential point higher than the potential of the battery voltage detection terminal; When the connection between the next battery and the battery voltage detection terminal is disconnected, a pull-up resistor for setting the battery voltage detection terminal to the same potential state as when the terminal voltage rises to the charging prohibition voltage; and A protection circuit for a secondary battery, comprising: a pull-up resistor cutoff unit that disconnects the battery voltage detection terminal and the pull-up resistor when the voltage drops to the discharge prohibition voltage. 5. A switch element inserted in series in a charge / discharge circuit of a secondary battery, and a terminal voltage of the secondary battery is detected via a battery voltage detection terminal connected to the secondary battery. Control means for turning off the switch element when the voltage drops to a predetermined discharge prohibition voltage; and a control means connected between the battery voltage detection terminal and a potential point lower than the potential of the battery voltage detection terminal; A pull-down resistor for setting the battery voltage detection terminal to the same potential state as when the terminal voltage drops to the discharge inhibition voltage when the connection between the next battery and the battery voltage detection terminal is disconnected; and A protection circuit for a secondary battery, comprising: a pull-down resistor cutoff unit that disconnects the battery voltage detection terminal and the pull-down resistor when the voltage drops to a forbidden voltage.