JP2002204534A - Protective device for secondary cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a protective device for a secondary cell capable of preventing a switching device from having thermal destruction due to the passage of a heavy current by conducting an overcurrent protection at the time of not only discharging but also charging. SOLUTION: This secondary cell, constructed by serially connecting a plurality of battery cell blocks 1A, 1B, and serially providing a charging FET 4 and a charging FET 4 and a discharging FET 5 composed of FETs with parasitic diodes as a switching device capable of an on/off control with a control circuit 6 in a charging/discharging path, is formed with charging and discharging current detecting means 7, 8. The control circuit 6 is provided with a means of controlling the FETs 4, 5 to prevent the generation of charging and discharging of detecting an overcurrent, where a charging current or discharging current exceeds a prescribed level.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

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

[0003] In view of the above, various types of protection devices for secondary batteries 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. There is disclosed a circuit in which a voltage of a secondary battery is detected by a circuit, and 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 charge FET) 4 with a parasitic diode for overcharge protection and an overdischarge protection connected in series between terminals 2 and 3 and connected in series to these 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, the space between the discharge FET 5 and the battery cell block 1B on the charge / discharge path is grounded,
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 interrupt 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, 1
B are detected as voltages V _BA and V _BB of FIG.
As shown in FIG. 2, in the illustrated example, the voltage V _BA of the battery cell block 1A is the 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.
(For example, 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 at the time of 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 as shown in FIG. When a current of 5.0 A) or more flows continuously 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.

Conventionally, overcurrent protection has been performed only for discharge current. In particular, in a lithium ion secondary battery, it is important to protect the charge FET 4 and the discharge FET 5 from thermal destruction due to large current overheating. It is desired that overcurrent protection be performed on the power supply. Conventionally, if the current is a certain value or more, the current is cut off for a certain period of time irrespective of the magnitude of the current. It is desirable that the delay time from the detection of the overcurrent to the confirmation be varied accordingly.

In view of the above, the present invention provides overcurrent protection during both charging and discharging to reliably prevent the destruction of the switching element, and to reduce the detection delay time in overcurrent protection according to the magnitude of the current value. It is an object of the present invention to provide a protection device for a secondary battery, which is variable to appropriately prevent the destruction of a switching element.

[0011]

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, and a charging / discharging switch that can be turned on / off by a control circuit in a charging / discharging path. A charge / discharge current detecting means is provided in a secondary battery in which an element is interposed, and a means for controlling a switching element to prohibit charging / discharging when detecting an overcurrent in which a charging current or a discharging current exceeds a predetermined value is controlled. It is characterized by being provided in a circuit.

Preferably, the detection element is started when the charging / discharging current exceeds a predetermined value, and the switching element is controlled so as to confirm the overcurrent after a predetermined delay time and prohibit the charging / discharging. The delay time is set in inverse proportion to the detected current value. The delay time may be set in inverse proportion to the square of the detected current value, or may be set to be exponentially shorter than the detected current value.

[0013]

According to the protection device for a secondary battery of the present invention, when an overcurrent whose charging current or discharging current exceeds a predetermined value is detected,
By controlling the switching element to inhibit charging or discharging, respectively, and performing overcurrent protection not only at the time of discharging but also at the time of charging, it is possible to prevent thermal destruction of the switching element due to passage of a large current, In particular, in the lithium ion battery, the destruction of these switching elements is important for ensuring safety, so that the effect is large.

In addition, charging and discharging are prohibited after a predetermined delay time after the charging and discharging current exceeds a predetermined value.
If the delay time is set in inverse proportion to the detected current value, the power loss due to the switching element differs depending on the magnitude of the current value, so that the switching element is compared with a case where a fixed delay time is set with a fixed detected current value. Thermal destruction can be reliably prevented.

Further, if the delay time is set in inverse proportion to the square of the detected current value, the current is cut off when the amount of heat generated by the current of the switching element becomes constant, and a reasonable delay time can be set. Thus, the destruction of the switching element can be reliably prevented while widening the allowable range of the large current.

Further, even if the delay time is set to be exponentially shorter with respect to the detected current value, the current can be cut off on the safer side with respect to the switching element, and the switching element has higher reliability. Destruction can be prevented.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a protection device for a secondary battery according to the present invention will be described below with reference to FIGS.

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 overdischarge 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. 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 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 by 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,
If the voltage is smaller than 0.3 V in the example 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 is changed to a second voltage value (for example, 4.00
V) When it becomes below, the charging FET 4 is turned on to release the overcharge protection function.

As for the release operation of the overcharge protection function, when the charging FET 4 is turned off and the charging current I _CHG is cut off, the discharging current I _DCHG having a specified current value (for example, 0.2 A) or more is applied. 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 the power is lost due to the 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 and V _BB of both ends becomes 0.3 V or more, as shown in FIG. 2B, even if both ends of the battery cell blocks 1A and 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 charge and discharge are permanently prohibited, that is, use is prohibited, without performing a release operation.

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 or the like. In addition, it is possible to detect that the cell balance has been lost, and to prevent the overcharge by preventing the use of the secondary battery based on the detection.

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 the 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, 2.60V) in the illustrated example, the discharge FET 5
_Is turned off to shut off the discharge current I _DCHG, and the voltage V _BB of the battery cell block 1B is set to a 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 shown 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 the power loss in the parasitic diode 5a of the discharge FET 5 due to the charge current.
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 charging FET 4 and the discharging FET 5 are turned off, and thereafter the charging and discharging 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 ends 1A and 1B_BA, V_BBRelative voltage value | V_BA
-V _BBWas used, but both battery cell blocks 1A and 1B
Terminal voltage V_BA, V_BBRelative voltage | V_BA-V_BB| Time derivative
Value, ie, d | V_BA-V_BB│ / dt and its fine
Minute value, for example, change in relative voltage per 10 minutes
If it exceeds, both charging FET4 and discharging 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, the deterioration progresses at an accelerated rate.
Using the differential value of the relative voltage degrades the magnitude of the relative voltage
While 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 inhibited so that charging or discharging is prohibited. 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 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. This 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 is therefore highly effective. 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, when the FET is on, it can be regarded as a resistor (R), 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 surely 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.

[0031]

According to the secondary battery protection device of the present invention,
As is apparent from the above description, when an overcurrent is detected in which the charging current or the discharging current exceeds a predetermined value, the switching element is controlled so as to prohibit the charging or the discharging, respectively. By performing the protection, the thermal destruction of the switching elements due to the passage of a large current can be prevented. In particular, in the case of a lithium ion battery, the destruction of these switching elements is important for safety assurance, so that the effect is large.

Further, charging and discharging are prohibited after a predetermined delay time after the charging and discharging current exceeds a predetermined value.
If the delay time is set in inverse proportion to the detected current value, the power loss due to the switching element will differ depending on the current value.Therefore, the thermal destruction of the switching element will be less than when a fixed delay time is set with a fixed detected current value. It can be reliably prevented.

Further, if the delay time is set in inverse proportion to the square of the detected current value, the current is cut off when the amount of heat generated by the current of the switching element becomes constant, and a reasonable delay time can be set. Thus, the destruction of the switching element can be reliably prevented while widening the allowable range of the large current.

Even if the delay time is set to be exponentially shorter than the detected current value, the current can be cut off on the safer side with respect to the switching element, and the switching element with higher reliability can be obtained. Destruction can be prevented.

[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 Charge / discharge current detecting means

Continued on the front page (72) Inventor Tetsuhide Konno 1006 Kazuma Kadoma, Kadoma City, Osaka Prefecture F-term (reference) in Matsushita Electric Industrial Co., Ltd. HJ17 5H030 AA03 AA04 AA06 AS18 AS20 BB26 DD05 FF42

Claims (4)

[Claims] In a secondary battery in which a plurality of battery cell blocks are connected in series and a charging and discharging switching element that can be turned on and off by a control circuit is interposed in a charging and discharging path, a charging and discharging current is controlled. A protection device for a secondary battery, comprising: a detection circuit; and a control circuit, comprising: a control circuit for controlling a switching element so as to prohibit charging / discharging when an overcurrent in which a charging current or a discharging current exceeds a predetermined value is detected. . 2. A switching device that starts a detection operation when a charging / discharging current exceeds a predetermined value, controls a switching element so as to confirm an overcurrent after a predetermined delay time and prohibit charging / discharging, and the delay time 2. The protection device for a secondary battery according to claim 1, wherein is set in inverse proportion to the detected current value. 3. A detection operation is started when the charging / discharging current exceeds a predetermined value, and after a predetermined delay time, an overcurrent is confirmed and the switching element is controlled so as to prohibit charging / discharging. 2. The protection device for a secondary battery according to claim 1, wherein is set in inverse proportion to the square of the detected current value. 4. A switching operation is started when a charging / discharging current exceeds a predetermined value, and after a predetermined delay time, an overcurrent is confirmed and a switching element is controlled so as to prohibit charging / discharging. 2. The protection device for a secondary battery according to claim 1, wherein is set to be exponentially shorter than the detected current value.