JP3538175B2 - Battery protection device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a secondary battery protection device, and more particularly to a secondary battery protection device effective in a lithium ion secondary battery.

[0002]

2. Description of the Related Art In a secondary battery, when overcharging, overdischarging, or overcurrent flows beyond proper charge / discharge conditions, gas is generated due to decomposition of an electrolytic solution. This causes problems such as a short circuit or overheating inside the battery.

[0003] In view of the above, various protection devices for a secondary battery have been proposed which take measures for preventing overcharge, overdischarge, and overcurrent. For example, in Japanese Patent Application Laid-Open No. 4-75430, switching means for overcharge protection and overdischarge protection comprising a MOS FET with a parasitic diode and the like are arranged in series with a battery in a charge / discharge path of a secondary battery, and control is performed. A circuit is disclosed in which a voltage of a secondary battery is detected by a circuit, and the switching means is turned on / off by the detected voltage.

A specific description will be given with reference to FIGS.
In FIG. 5, a plurality of battery cell blocks 1A and 1B
A MOSFET (hereinafter abbreviated as a charge FET) 4 with a parasitic diode for overcharge protection and an overdischarge protection connected in series between the terminals 2 and 3 and connected in series to the battery cell blocks 1A and 1B. MO with parasitic diode
An S FET (hereinafter abbreviated as a discharge FET) 5 is provided. A control circuit 6 for controlling ON / OFF of the charge FET 4 and the discharge FET 5 is provided.
, The voltage between both ends of each battery cell block 1A, 1B is input. In addition, between the discharge FET 5 and the battery cell block 1B in the charge / discharge path is grounded, and the charge FET 4 and the negative terminal 3 are connected.
Is input to the comparator 9 of the control circuit 6, and the discharge current I _{DCHG is determined by the} voltage across the charge FET 4 and the discharge FET 5.
Is configured to be detected.

At the time of overcharge protection, the control circuit 6
As shown in (a), the charging FET 4 is turned off and the charging current is cut off. However, even in that case, the discharge current I _DCHG
Is the parasitic diode 4a of the charging FET 4 as shown by the arrow.
Flow through. Conversely, at the time of overdischarge protection, FIG.
As shown in FIG. 7, the discharge FET 5 is turned off to cut off the discharge current, and the charging current I _CHG also flows through the parasitic diode 5a of the charging FET 5 as shown by the arrow.

The control circuit 6 controls each of the battery cell blocks 1A, 1A,
B voltage V _BA and V _BB are detected, and during charging, FIG.
As shown in the figure, the voltage V _BA of one of the battery cell blocks 1A in the illustrated example is a first voltage value (for example, 4.30).
V) or more, the charging FET 4 is turned off and the charging current I
_Cut off _CHG . When the voltage V _BA of the battery cell block 1A becomes equal to or lower than the second voltage value (for example, 4.00 V), the charge FET 4 is turned on to release the overcharge protection function.

At the time of discharging, as shown in FIG. 8, the voltage V _BB of one of the battery cell blocks 1B in the example shown in FIG.
(E.g., 2.60 V) or less, the discharge F
ET5 is turned off to cut off the discharge current I _DCHG . Further, the voltage V _BB of the battery cell block 1B is a third voltage value (e.g., 3.20 V) becomes equal to or larger than the discharge FET5 is turned on to release the over-discharge protection function.

In order to prevent an overcurrent from flowing during discharging, a discharging current is detected based on a potential difference generated between both ends of the FETs 4 and 5 connected in series, and a predetermined current value (for example, as shown in FIG. 9). When a current of 5.0 A) or more continuously flows for a specified time (for example, 1.0 ms) or more, discharge FE occurs.
T5 is off. When the detected potential difference becomes equal to or less than a predetermined value, the overcurrent protection function is released.

[0009]

However, it is inevitable that the battery cell blocks 1A and 1B deteriorate due to repeated use, and the deterioration progresses uniformly in the battery cell blocks 1A and 1B. Is rather rare. If deterioration or the like occurs in each of the battery cell blocks 1A and 1B in an unbalanced manner and the capacities of the respective battery cell blocks 1A and 1B become non-uniform, the voltage of the battery cell block having a small capacity at the time of charging is higher than that of the other battery cell blocks. As a result, the voltage of the battery cell block having the smallest capacity during discharge also decreases earlier than the other battery cell blocks.

Therefore, such a battery cell block 1
A protection function against deterioration of A and 1B shall be provided in combination with the above overcharge / discharge prevention function to provide an early protection function for overcharge / discharge due to deterioration, etc., and protection in case of overcharge / discharge due to deterioration etc. It is desired not to cancel the function.

In the above conventional example, the overcharge protection function is not released until the voltage of the battery cell block falls below a predetermined value. Therefore, the current flowing through the parasitic diode (discharge current or overcurrent at the time of overcharge protection) before the release is released. Charge current during overdischarge protection)
There is a possibility that the FET itself may be destroyed by power loss (heat generation) due to this. For example, V _F voltage of the parasitic diode is 0.7
V, the discharge current is 4 A, there is a power loss of 2.8 W during charge protection, and the allowable loss of charge FET 4 (1.4 W)
In this state, if continuous discharge is continued, the charge FET 4 will be thermally destroyed.

In view of the above, the present invention provides a secondary battery having a function of protecting a switching element from being damaged by power loss in a parasitic diode during overcharge and overdischarge protection, and preferably further having a protection function against deterioration of a battery cell block and the like. It is intended to provide a protection device.

[0013]

According to the present invention, there is provided a secondary battery protection device in which a plurality of battery cell blocks are connected in series, an on / off control is possible by a control circuit , and only a discharge current can be supplied.
Switching element for charging with parasitic diode
ON / OFF control by the control circuit and only charging current
Discharge switch with a parasitic diode capable of conducting current
In a secondary battery in which a charging element and a charging / discharging circuit are interposed in series, a means for detecting the voltage of each battery cell block during charging / discharging, and a means for detecting a charging / discharging current are provided. voltage blocks exceed the predetermined voltage range
And the charging switching element is turned off to interrupt charging.
And when it falls below, the discharge switching element is turned off.
On and means for controlling the switching element to shut off the discharge, the charge switching element when the occurrence of interruption of charging consecutive prescribed value or more discharge current GaTadashi constant time or more
To release the interruption of the charge
When the above charging current continues for a specified time or more, the discharge
Means for controlling the switching element so as to release the interruption of the discharge by turning on the switching element for use in the control circuit.

More specifically, the protection device for a secondary battery according to the present invention has a plurality of battery cell blocks connected in series, can be turned on / off by a control circuit , and can only supply a discharge current.
Switching element for charging with parasitic diode
ON / OFF control by the control circuit and only charging current
Discharge switch with a parasitic diode capable of conducting current
In a secondary battery in which a charging element and a charging / discharging circuit are interposed in series, a means for detecting the voltage of each battery cell block during charging / discharging, and a means for detecting a charging / discharging current are provided. voltage blocks exceed the predetermined voltage range
And the charging switching element is turned off to interrupt charging.
And when it falls below, the discharge switching element is turned off.
Interrupting the discharge, and thereafter, when the voltage falls within the predetermined voltage range .
After returning now to narrow another predetermined voltage range, the charge
At the time of cutoff, the charging switching element is turned on to
Release the charge interruption, and when the discharge is interrupted, use the discharge switch.
Means for controlling the switching element so as to release the blocking of the discharge by turning on the switching element, when <br/> the continuous prescribed value or more discharge current GaTadashi constant time or more during interruption of charging
Turning on the charging switching element to cut off the charging
Is released, and a charge current higher than the specified value is
The switching element for discharging when continuous for a predetermined time or more.
The control circuit is provided with means for controlling the switching element so as to turn off the discharge and release the interruption of the discharge .

[0015] Preferably, the control circuit is provided with means for controlling the switching element so that charging and discharging are permanently interrupted when the relative voltage between the battery cell blocks exceeds a certain value.

[0016]

According to the protective device for a secondary battery of the present invention, during the overcharge protection operation, blocking sometimes prescribed value or more discharge current of charging, blocking sometimes prescribed value or more charging current discharge,
Shielding the charge or discharge when each successive predetermined time or more
By controlling so as to cancel the disconnection, the current preferred
It is possible to prevent the switching element Kowasuru the fracture in the power loss due to passing through the raw diodes (exothermic).

[0017] In the present invention, shielding the charge and discharge permanently and relative voltage between the battery cell blocks exceeds a predetermined value
If so as to cross its capacity due to deterioration or the like of each battery cell blocks becomes uneven, when the collapse of the cell balance occurs, Ru <br/> be shut off reliably detect charge and discharge were the same Therefore, overcharging and overdischarging due to deterioration and the like can be prevented, and safety can be improved.

[0018]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a secondary battery protection device according to an embodiment of the present invention; FIG.

In FIG. 1, a plurality of battery cell blocks 1A and 1B composed of lithium ion batteries are connected in series between a positive terminal 2 and a negative terminal 3, and these battery cell blocks 1A and 1B are overcharged in series. MOS FET with parasitic diode for protection (hereinafter abbreviated as charging FET)
4 and MOS FET with parasitic diode for over-discharge protection
(Hereinafter, abbreviated as a discharge FET) 5 is provided. These FETs 4 and 5 have a resistance of about 100 mΩ when turned on. Further, the parasitic diode 4a, V _F of 5a is about 0.7 V. There is provided a control circuit 6 for controlling ON / OFF of the charge FET 4 and the discharge FET 5,
The voltage across the battery cell blocks 1A and 1B is input to the control circuit 6. In order to detect the charge / discharge current, a current detection resistor 7 of about 20 to 50 mΩ is interposed between the discharge FET 5 and the battery cell block 1B in the charge / discharge path. The control circuit 6 is provided with a means 8 for amplifying and detecting a minute potential difference generated in the current detecting resistor 7 by the charging current or the discharging current, and configured to detect the charging current I _CHG and the discharging current I _DCHG. Have been. By interposing the current detection resistor 7 in this manner, the charge F
Highly accurate current detection can be performed irrespective of the operation states of the ET 4 and the discharge FET 5.

Next, the overcharge protection operation according to the above configuration,
The overdischarge protection operation and the overcurrent protection operation will be sequentially described.

First, the overcharge protection operation will be described with reference to FIG. The control circuit 6 detects the voltages V _BA and V _BB across the battery cell blocks 1A and 1B, and determines their relative voltage values | V
_BA −V _BB | is a specified voltage value (for example, 0.3 to 0.5 V,
In the case shown in FIG.
As shown in FIG. 2, when the voltage V _BA of the battery cell block 1A becomes equal to or higher than a first voltage value (for example, 4.30 V) in the illustrated example, the charging FET 4 is turned off and charging is performed. The current I _CHG is cut off, and the voltage V _BA of the battery cell block 1A becomes the second voltage value (for example, 4.00
V) When it becomes less than the above, the charge FET 4 is turned on to release the overcharge protection function.

With respect to the release operation of the overcharge protection function, the discharge current I _DCHG having a specified current value (for example, 0.2 A) or more is generated while the charge FET 4 is turned off and the charge current I _CHG is cut off. When the current flows continuously for a specified time (for example, 10 ms) or more, the voltage of the battery cell block becomes the second voltage value (for example, as shown by a virtual line in FIG. 2A).
Even if the voltage does not fall below 4.00 V), the charging FET 4 is turned on to release the overcharge protection function. As described above, when the discharge current equal to or more than the specified value continuously flows during the overcharge protection operation, the charge FET 4 is turned on, and heat is generated due to power loss in the parasitic diode 4a of the charge FET 4 due to the discharge current, and the charge FET 4 is heated. Prevents destruction.

On the other hand, each of the battery cell blocks 1A, 1B
When the relative voltage value | V _BA −V _BB | of the voltages V _BA , V _BB across both ends becomes 0.3 V or more, as shown in FIG. 2B, even if both ends of the battery cell blocks 1A, 1B Even if the voltages V _BA and V _BB have not reached the first voltage value, the charge F
The ET 4 and the discharge FET 5 are both turned off, and thereafter, without performing the release operation, charging and discharging are permanently prohibited, that is, use is prohibited.

By detecting when the relative voltage value | V _BA -V _BB | exceeds the specified value, the capacity of the battery cell blocks 1A and 1B becomes non-uniform due to deterioration and the like. In addition, it is possible to detect that the cell balance has been lost, and to prevent the use of the secondary battery based on the detection, thereby preventing the overcharge from occurring.

Next, the overdischarge protection operation will be described with reference to FIG. At this time, the control circuit 6 is operated similarly to the overcharge protection operation.
Are voltages V _BA , V _BB across the battery cell blocks 1A, 1B.
Are detected, and when their relative voltage values | V _BA −V _BB | are smaller than a specified voltage value (for example, 0.3 V), FIG.
As shown in (a), when the voltage V _BB of the battery cell block 1B falls below a fourth voltage value (for example, 2.60 V), the discharge FET 5
_Is turned off to cut off the discharge current I _DCHG, and the voltage V _BB of the battery cell block 1B becomes the third voltage value (for example, 3.
When the voltage exceeds 20 V), the discharge FET 5 is turned on to release the overdischarge protection function.

As for the operation of releasing the overdischarge protection function, the specified current value (for example, 0.2 A) in a state where the discharge FET 5 is turned off and the discharge current I _DCHG is cut off as in the overcharge protection operation. When the above charging current I _CHG continuously flows for a specified time (for example, 10 ms), FIG.
As indicated by the imaginary line in FIG.
(For example, 3.20 V), the discharge FET 5 is turned on to release the overdischarge protection function. By turning on the discharge FET 5 when a charge current of a specified value or more continuously flows during the overdischarge protection operation, heat is generated due to power loss in the parasitic diode 5a of the discharge FET 5 due to the charge current and the discharge FET 5 is turned on.
5 is prevented from being destroyed.

On the other hand, each of the battery cell blocks 1A, 1B
When the relative voltage value | V _BA -V _BB | of the voltages V _BA and V _BB of both ends becomes 0.3 V or more, as shown in FIG. Even if the voltages V _BA , V _BB across the battery cell blocks 1A, 1B have not dropped to the fourth voltage value, both the charge FET 4 and the discharge FET 5 are turned off, and thereafter the charging and discharging operations are performed permanently without performing the releasing operation. Discharge is prohibited, that is, use is prohibited.

In the above description, each battery cell block
1A, 1B, etc.
Voltage V across both terminals 1A and 1B_BA, V_BBRelative voltage value | V_BA
-V _BBIs used, but both battery cell blocks 1A and 1B are used.
Terminal voltage V_BA, V_BBRelative voltage | V_BA-V_BB| Time derivative
Value, ie, d | V_BA-V_BB│ / dt
Minute value, for example, change in relative voltage per 10 minutes
If it exceeds, both charge FET4 and discharge FET5 are turned off.
And then prohibit use without performing the release operation.
Good. Generally, deterioration occurs in each of the battery cell blocks 1A and 1B.
When it occurs, deterioration progresses at an accelerated rate,
The magnitude of the relative voltage is degraded when the differential value of the relative voltage is used.
Although it is easy for variations to occur due to factors other than
Precisely due to deterioration of each battery cell block 1A, 1B, etc.
Level can be detected.

Next, the overcurrent protection operation will be described with reference to FIG. With respect to both the charging current and the discharging current, a minute potential difference generated in the current detecting resistor 7 is detected by the amplification detecting means 8 of the control device 6, and when the charging current or the discharging current exceeds a predetermined value, the detection operation is started. As shown by the solid line in FIG. 4 (a), after a predetermined delay time set to be inversely proportional to the detected current value, an overcurrent is confirmed, and the charging FET 4 and the discharging FET 5 are so controlled as to prohibit charging or discharging. Cut off.
In the illustrated example, when the detected current value is 5 A, the delay time is set to 1.
It is set to 0 ms, and to 500 μs at 10 A. In addition,
No matter how large the detected value is, a delay time of 100 μs is set to prevent malfunction due to peak current during charging or use of the device. The overcurrent protection operation is automatically restored after a specified time.

As described above, the overcurrent protection is performed not only at the time of discharging but also at the time of charging.
ET4 and the discharge FET 5 can be prevented from being thermally destroyed.
The destruction of the T4 and the discharge FET 5 is important for ensuring safety, and therefore has a great effect. In order to prevent thermal destruction of the FETs 4 and 5, it is important to vary the delay time according to the current value. That is, the FET can be regarded as a resistor (R) when on, and the power loss when the current I flows is I
² R, and assuming that the power loss is allowed up to a certain delay time (Δt), I ² R · Δt = Const. Holds. Therefore, Δt = Const. / I ² R, and the delay time may be inversely proportional to I ² . Therefore,
By setting the delay time in inverse proportion to the detected current value as described above, the thermal destruction of the FETs 4 and 5 can be prevented more reliably than when a fixed delay time is set with a fixed detected current value. it can.

In the above description, the delay time is set in inverse proportion to the detected current value. However, as shown by the imaginary line in FIG. 4A, the delay time is set in inverse proportion to the square of the detected current value. As is clear from the above description, the current is cut off when the amount of heat generated by the current becomes constant, a reasonable delay time is set, and the breakdown of the FET is reliably performed while widening the allowable range of the large current. Can be prevented. Further, FIG.
As shown in (b), the delay time may be set to be exponentially shorter than the detected current value.

[0032]

According to the secondary battery protection device of the present invention,
As is apparent from the above description, when the charge is cut off , the discharge current of a specified value or more is released, and when the discharge is cut off , the charge current of the specified value or more is released for a specified time or more, and the charge or discharge cutoff is released. Power loss due to the current passing through the parasitic diode
It is possible to prevent the switching element at (heating) is Kowasuru to fracture.

In the present invention, if charging and discharging are interrupted when the relative voltage between the battery cell blocks exceeds a certain value, the capacity of each battery cell block becomes non-uniform due to deterioration or the like, and the cell balance is lowered. When the collapse occurs, the secondary battery is reliably detected and the use of the secondary battery is prohibited, so that overcharge and overdischarge due to deterioration or the like can be prevented, and safety can be improved. .

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a secondary battery protection device according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram of an overcharge protection operation in the embodiment.

FIG. 3 is an explanatory diagram of an overdischarge protection operation in the embodiment.

FIG. 4 is an explanatory diagram of an overcurrent protection operation in the embodiment.

FIG. 5 is a circuit diagram of a conventional secondary battery protection device.

FIG. 6 is a diagram illustrating the operation of the FET with a parasitic diode during charge protection and discharge protection.

FIG. 7 is an explanatory diagram of an overcharge protection operation in the conventional example.

FIG. 8 is an explanatory diagram of an overdischarge protection operation in the conventional example.

FIG. 9 is an explanatory diagram of an overcurrent protection operation in the conventional example.

[Explanation of symbols]

1A Battery cell block 1B Battery cell block 4 Charge FET 5 Discharge FET 6 control circuit 7, 8 Means for detecting charge / discharge current

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-4-331425 (JP, A) JP-A-6-141479 (JP, A) JP-A-6-303728 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) H02J ^7/ 00-7/12 H02J ⁷ /34-7/36 H01M 10/44 H02H 7/18

Claims (4)

(57) [Claims] 1. A plurality of battery cell blocks are connected in series, control on-off controllable discharge current only energized by control circuit
Switching for charging with a possible parasitic diode
On-off control is possible with the element and the control circuit and charging current
Discharge switch with a parasitic diode
In a secondary battery in which a switching element and a charging / discharging circuit are interposed in series, a means for detecting a voltage of each battery cell block during charging / discharging, and a means for detecting a charging / discharging current are provided. upper voltage block a predetermined voltage range or
In other words, the charging switching element is turned off to interrupt charging.
When it falls below, the discharge switching element is turned off.
O means for controlling the switching element to shut off the discharge, the charge switching element when the occurrence of interruption of charging consecutive prescribed value or more discharge current GaTadashi constant time or more Te
To release the charge interruption, and to regulate the discharge interruption.
If the charge current equal to or greater than the specified value continues for
A protection device for a secondary battery, wherein a control circuit is provided with means for controlling the switching element so as to turn on the power switching element and release the interruption of the discharge . Wherein the plurality of battery cell blocks are connected in series, control on-off controllable discharge current only energized by control circuit
Switching for charging with a possible parasitic diode
On-off control is possible with the element and the control circuit and charging current
Discharge switch with a parasitic diode
In a secondary battery in which a switching element and a charging / discharging circuit are interposed in series, a means for detecting a voltage of each battery cell block during charging / discharging, and a means for detecting a charging / discharging current are provided. upper voltage block a predetermined voltage range or
In other words, the charging switching element is turned off to interrupt charging.
When it falls below, the discharge switching element is turned off.
To interrupt discharge, and then the voltage is within the predetermined voltage range .
After returning to another predetermined voltage range , charging
When the charging is switched off, the charging switching element is turned on.
The charge interruption is released, and when the discharge is interrupted, the discharge switch is turned off.
Means for controlling the switching element so that switching element is turned on to release the blocking of the discharge, the charging case during interruption of charging <br/> consecutive prescribed value or more discharge current GaTadashi constant time or more To turn on the switching element for
When the discharge is interrupted, the charging current exceeding the specified value
When the discharge switching element is
A protection device for a secondary battery, characterized in that a control circuit is provided with means for controlling a switching element so as to release a cutoff of the discharge by turning on a cell. 3. The control circuit according to claim 1, wherein the control circuit includes means for controlling the switching element such that charging and discharging are permanently interrupted when the relative voltage between the battery cell blocks exceeds a certain value. 3. The protection device for a secondary battery according to 2. 4. A time-differential value of the relative voltage between the battery cell blocks, characterized in that a means for controlling the switching element to shut off the charging and discharging permanently exceeds a certain value to the control circuit The protection device for a secondary battery according to claim 1.