JPH08190936A - Charge/discharge protecting device of secondary battery - Google Patents

Abstract

PURPOSE: To prevent deterioration of a switch by preventing current carrying to a parasitic diode which is not in a using purpose, when charging current and discharging current are shut off with a switching element containing the parasitic diode to prevent overcharge and overdischarge of a secondary battery. CONSTITUTION: In a charged state, a control circuit 210 detects each voltage of secondary batteries 10, 12, and when either one voltage reaches a first set voltage or higher in the vicinity of the upper limit of operation-capable voltage, a charge shut off switching element 220 is controlled so as to make off. Thereby, charging current is shut off to prevent overcharge of the batteries 10, 12. At the same time, a discharge shut off switching element 230 is shut off to shut off discharge current. As a result, discharge current to a parasitic diode 222 of the charge shut off switching element 220 is shut off to prevent current carrying. Similarly, during discharge, when battery voltage reaches a second set voltage or lower, the discharge shut off switching element 230 is made off to shut off discharge current, and at the same time, the charge shut off switching element 220 is made off to prevent current carrying to a parasitic diode 232 of the discharge shut off switching element 230.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a secondary battery charge / discharge protection device for preventing overcharge and overdischarge of a secondary battery,
In particular, the present invention relates to a secondary battery charge / discharge protection device used in, for example, a power supply device detachably mounted in a portable electronic device.

[0002]

2. Description of the Related Art With the miniaturization of various electronic devices such as video camera integrated VTRs (video tape recorders), personal computers, and telephones, many portable electronic devices have been developed. A primary battery or a secondary battery is widely used as a power source for these portable electronic devices. In particular, secondary batteries are widely used in portable electronic devices because they can be used repeatedly.

When such a secondary battery is used as a power supply device, it is necessary to prevent overcharge and overdischarge of the secondary battery. For example, when the secondary battery is in an overcharged state or an overdischarged state, the substance inside the battery is decomposed, resulting in a problem that the battery capacity is reduced. If this overcharging and overdischarging are repeated, the capacity of the battery will decrease at an accelerating rate and the battery life will be exhausted.

As a preventive measure against these problems, the battery voltage is monitored so that the charging path is shut off when the battery voltage exceeds a predetermined set voltage during charging, and the battery voltage drops below another set voltage during discharging. In this case, a method of cutting off the discharge path is adopted. For example, in Japanese Utility Model Laid-Open No. 02-136445, the battery voltage of each of a plurality of rechargeable batteries connected in series is detected, and the voltage of any one of the rechargeable batteries is above or below a set voltage. In this case, a protection circuit for a rechargeable battery has been proposed, which cuts off the charging path or the discharging path, respectively.

In this case, as means for shutting off the charging path and the discharging path, considering cost and external size,
Switching off by means of semiconductor switches is generally applied to advantage. For example, JP-A-04-33271 and JP-A-04-75430
Japanese Patent Laid-Open Publication No. 04-75431 and the like propose a power supply device for a secondary battery using a field effect transistor including a parasitic diode inside as a switch element.
Particularly, in the device described in Japanese Patent Laid-Open No. 04-75430, a first field effect transistor for blocking a charging path and a second field effect transistor for blocking a discharging path are serially connected to one terminal side of a secondary battery. When the voltage across the battery drops to a first voltage near the chargeable voltage, the first field effect transistor is turned on to open the charging path, and the voltage rises to a second voltage higher than the first voltage. At this time, the first field effect transistor is turned off to cut off the charging path, and when the battery voltage rises to the third voltage near the dischargeable voltage, the second field effect transistor is turned on to open the discharge path, When the voltage dropped to the fourth voltage lower than the voltage of 3, the second field effect transistor was turned off to interrupt the discharge path. In this case, at the time of overcharge protection that cuts off the charging path, the first field effect transistor in the off state secures the discharging path by the internal parasitic diode that conducts in the direction opposite to the charging direction. At the time of over-discharge protection in which the discharge path is blocked, in the second field effect transistor in the off state, the charge path is secured by the internal parasitic diode that conducts in the direction opposite to the discharge direction. That is, since the field effect transistor includes a parasitic diode that causes a current to flow in a direction opposite to the blocking direction due to its structure, only a blocking effect in one direction can be expected. In the above publication, by positively utilizing this phenomenon, two field effect transistors are connected in series in opposite directions and overcharge and overdischarge while securing a charge path and a discharge path by a parasitic diode when they are off. Was to prevent.

[0006]

However, in the above-mentioned prior art, since the parasitic diodes inside the switch element, which are not originally intended to be used due to their original structure, are utilized to secure the respective charge / discharge paths, There is a drawback that the element itself is likely to be deteriorated, the function as a switch is deteriorated, and the element is easily broken. Therefore, if the switch function is deteriorated, the charging / discharging path cannot be cut off at a desired time, and if it is used without knowing it, there is a problem that the above-mentioned problem due to overcharge or overdischarge of the secondary battery occurs. It was

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above problems and provide a more reliable charge / discharge protection device for a secondary battery by preventing deterioration and destruction of elements while maintaining protection operations against overcharge and overdischarge. To aim.

[0008]

SUMMARY OF THE INVENTION In order to solve the above problems, a secondary battery charge / discharge protection device according to the present invention includes a secondary battery charging / discharging device which prevents overcharge and overdischarge of a rechargeable secondary battery. In the discharge protection device, a first switch means that is connected in series to a charging / discharging path of the secondary battery, is normally turned on to conduct a current in a charging direction, and shuts off the path in the charging direction when turned off, A first switch means including therein a parasitic diode that conducts with a current in a discharge direction when turned off;
The second switch means is connected in series to the charging / discharging path of the secondary battery and is normally turned on to conduct current in the discharging direction and to cut off the path in the discharging direction when turned off. Second switch means which internally includes a parasitic diode that conducts with current, and when the battery voltage of the secondary battery is detected and the battery voltage becomes equal to or higher than a first set voltage near the upper limit of operable voltage. Control means for turning off the first switch means and for turning off the second switch means when the battery voltage becomes equal to or lower than a second set voltage in the vicinity of the lower limit of the operable voltage. When the first switch means or the second switch means is turned off, the other switch means is turned off at the same time.

Further, a plurality of secondary batteries are connected in series, and the control means monitors the battery voltage of each secondary battery, and one of the voltage values becomes equal to or higher than the first set voltage. When the first switch means and the second switch means are turned off, and the second switch means and the first switch means are turned off when one of the voltage values becomes equal to or lower than the second set voltage. Good. Further, the secondary battery has a plurality of batteries connected in series, and the control means monitors the voltage between both ends of the batteries connected in series, and when the voltage value becomes equal to or higher than the first set voltage. The first switch means and the second switch means may be turned off, and the second switch means and the first switch means may be turned off when either one of the voltage values becomes equal to or lower than the second set voltage.

On the other hand, the secondary battery is used alone, and the control circuit detects the voltage across the single secondary battery and controls the first switch means and the second switch means to be off. Good. Also, the first switch means and the second
Both switch means may be connected in series to either the positive or negative charging / discharging path for the secondary battery.

[0011]

According to the secondary battery charge / discharge protection device of the present invention, the first switch means and the second switch which are normally turned on are provided.
Both the charging and discharging paths of the secondary battery are secured with the switch means of, and the charging current from the charger is received via these.
Or supply the discharge current to the load. When the control unit detects that the battery voltage of the secondary battery has become equal to or higher than the first set voltage during charging in this state, the first
The switch means is turned off to cut off the charging path to prevent overcharge in the secondary battery. At this time, the control means simultaneously turns off the second switch means to cut off the current in the discharging direction from the secondary battery. This prevents energization of the parasitic diode, which attempts to conduct due to the current in the direction opposite to the interruption direction when the first switch means is off. Also,
During discharging, when the control means detects that the battery voltage of the secondary battery has become equal to or lower than the second set voltage, the second switch means is turned off to interrupt the discharge path to prevent over-discharging in the secondary battery. To prevent. At this time, the control means simultaneously turns off the first switch means to cut off the current in the charging direction to the secondary battery. As a result, the conduction of the parasitic diode in the second switch means is prevented.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a secondary battery charge / discharge protection device according to the present invention will now be described in detail with reference to the accompanying drawings. FIG. 1 shows an embodiment in which the charge / discharge protection device according to the present invention is applied to a secondary battery power supply device 30. The secondary battery power supply device 30 in the present embodiment includes two secondary batteries 10,1.
A power source formed as a so-called battery pack 30 in which the positive terminal 32 and the negative terminal 34 are provided to the outside by connecting the two in series and via the charge / discharge protection device 20 that prevents overcharging and overdischarging. The device is, for example, a power supply device that is detachably mounted in a portable video camera integrated VTR.

Specifically, the secondary battery 10, 1 in this embodiment is
2 is, for example, a nickel-cadmium (Ni-Cd) battery,
Nickel-metal hydride (Ni-H) batteries, preferably lithium-ion (L
i ⁺ ) A secondary battery or the like is used. For example, a lithium-ion secondary battery has an operating voltage range of 2.5 to 4.2V per cell, and when the terminal voltage exceeds about 4.3V due to charging, it causes a larger deterioration in performance than normal cycle deterioration. Further, when the terminal voltage of the battery becomes about 2.4 V or less due to discharge, it causes a larger deterioration in performance than normal cycle deterioration. In particular, when the characteristics of the batteries vary, the battery that has been fully charged or emptied first tends to be overcharged or overdischarged before the other battery. Therefore, the charging / discharging protection device 20 of the present embodiment includes the secondary batteries 10 and 12.
For example, in the case of a lithium-ion battery, the terminal voltage of each battery 10 and 12 is detected and
The charging path and the discharging path are cut off so that the voltage of 0 and 12 does not exceed 4.3 V and below 2.4 V, respectively, to prevent overcharging and overdischarging of the respective batteries 10 and 12.

Specifically, the charge / discharge protection device 20 of this embodiment
Is a control circuit 210 and a switching device 220 for blocking the charging path.
And a switch element 230 for disconnecting the discharge path.
The control circuit 210 detects the terminal voltage of each of the secondary batteries 10 and 12, and based on the detection result, the switching elements 220 and 23.
This is a switch control circuit for controlling 0 respectively, and particularly in this embodiment, the switch elements 220 and 230 are simultaneously turned on / off by a control signal from a common control line 240. For example, as shown in FIG. 2, the control circuit 14 includes a first battery voltage detection circuit 300, a second battery voltage detection circuit 302, and a first battery voltage detection circuit 302.
Comparison circuit 304, second comparison circuit 306, first OR circuit 308, second OR circuit 310, and switch drive circuit 312
And have.

The first battery voltage detection circuit 300 is connected to the positive terminal and the negative terminal of the first secondary battery 10, respectively, and detects the detected voltage according to the potential difference between them.
A detection circuit for supplying to 304. Similarly, the second battery voltage detection circuit 302 is connected to the positive terminal and the negative terminal of the second secondary battery 12, and supplies the detected voltage corresponding to the potential difference to the second comparison circuit 306. Advantageously, as shown in FIG. 1, the potential from the negative terminal of the first secondary battery 10 and the potential from the positive terminal of the second secondary battery 12 are common to the first.
Are supplied to the voltage detecting circuit 300 and the second voltage detecting circuit 302, and each of the detecting circuits 300 and 302 detects the potential difference from the other terminal voltage with reference to this.

The first comparison circuit 304 is a one-input / two-output comparator which detects whether or not the voltage value from the first voltage detection circuit 300 is equal to or higher than the first set voltage or lower than the second set voltage. It is a comparison circuit formed by. First
The set voltage is set to a voltage value in the vicinity of the upper limit value of the operable voltage of each of the secondary batteries 10 and 12, for example, a voltage value of 4.2 to 4.3 V, which is lower than 4.3 V in the case of a lithium ion battery. In the case of a lithium ion battery, for example, the second set voltage is set to a voltage of 2.4 to 2.5 V that exceeds 2.4 V near the lower limit of the operable voltage. Similarly, the second
The comparison circuit 306 is formed of a one-input / two-output comparator that detects whether the voltage value from the second voltage detection circuit 302 is equal to or higher than the first set voltage or equal to or lower than the second set voltage. It is a comparison circuit. Each comparison circuit 30
The output of 4,306 is supplied to the first OR circuit 308 as a result of detection as to whether it is the first set voltage or higher, and is supplied to the second OR circuit 310 as it is detected as to whether it is the second set voltage or lower. It

The first OR circuit 308 is a first comparison circuit 304.
And a detection result of the second comparison circuit 306, which is a logical sum, and supplies an effective output to the switch drive circuit 312 when any output detects a voltage value equal to or higher than the first set voltage. To do. Similarly, the second OR circuit 310 is
Of the output of the result of detection of the voltage value equal to or lower than the second set voltage by the comparison circuit 304 and the second comparison circuit 306 of the switch drive circuit 312. Is a logic circuit that supplies an effective output to the.

The switch drive circuit 312 includes a switching device 220 for shutting off the charging path and a switching device 23 for shutting off the discharging path.
It is a voltage generation circuit that generates a signal to control 0 off,
It is a control circuit which responds to the logic output from the first OR circuit 308 and the second OR circuit 310 and supplies a predetermined output to the switch elements 220 and 230. Particularly, in this embodiment, the first and second switch elements 220 and 230 are simultaneously turned off by the effective output from the first OR circuit 308, and the first and second effective elements are output by the effective output from the second OR circuit 310. Switch element 220,230
Are turned off at the same time, and the effective output of either OR circuit 308, 310
If it is not output from both switch elements 220, 23
Turn 0 on.

Returning to FIG. 1, the charge path cutoff switch element 220 is a semiconductor switch formed by a field effect transistor (FET) that operates at a low voltage such as C-MOS, and is normally turned on. It is a first switch element that conducts a current in the charging direction (direction of arrow X in the figure) and turns off by a control voltage from the control circuit 210 to cut off the current in the charging direction. Advantageously, for example, a normally-off type P-channel enhancement type field effect transistor which is turned on at a negative voltage is used, and its drain D has a positive terminal side of the secondary battery 10 as shown in FIG. The source S is connected to the input / output terminal 32 side through the discharge path blocking switch element 230, and the gate G is connected to the control circuit.
The control voltage from 210 is applied. Due to its structure, the field-effect transistor 220 internally has a parasitic diode 222 which is turned on between the source S and the drain D in the direction opposite to the blocking direction, that is, a current in the discharging direction.

The discharge path cutoff switch element 230 is a semiconductor switch formed of, for example, a normally-off type P-channel enhancement type field effect transistor like the charge path cutoff switch element 220.
Is connected in series between the switch element 220 and the input / output terminal 32, and is normally turned on to allow a current in the discharge direction (direction of arrow Y in the figure) to pass through, and when it is turned off, the current in the discharge direction is cut off. This is the second switch that does. That is, the source S is connected to the source side of the first switch element 220 in the opposite direction to the first field effect transistor 220, and the drain D
Is connected to the input / output terminal 32 side, and the control circuit 21 is connected to the gate G.
A control signal from 0 is supplied. Due to its structure, the second field-effect transistor 230 internally includes a parasitic diode 232 that conducts with a current in the drain D-source S direction, that is, the discharge direction in the off state.

The operation of the secondary battery charge / discharge protection device of the present embodiment having the above-mentioned structure will be described. First, the battery pack 30 formed as a secondary power supply device is attached to, for example, a portable electronic device, and connected to the internal circuit of the device at terminals 32 and 34. Next, when charging the secondary batteries 10 and 12, when the power cord of the device is connected to an AC power source, the charging circuit inside the device supplies the charging current to the power supply device 30 via the terminals 32 and 34. . At this time, if the control circuit 210 detects the voltages of the secondary batteries 10 and 12 and the respective voltage values are within the predetermined values, the control voltage from the control circuit 210 to the switch elements 220 and 230 is a negative voltage. , The switch elements 220 and 230 are in the ON state.
As a result, the charging current flows from the terminal 32 to the switching elements 220 and 23.
Is supplied to the secondary batteries 10 and 12 via 0, and further current flows in the charging direction to the device side via the terminal 34, and the secondary batteries 10 and 12 are supplied.
Each is charged.

In this state, if charging progresses and one of the secondary batteries 10 and 12 becomes fully charged, and if the charged state continues, the battery that is fully charged first becomes the upper limit of the operable state. Reach For example, as shown in FIG. 7, the first secondary battery
When 10 reaches the upper limit of the operable state, the detected voltage from the first battery voltage detection circuit 300 of the control circuit 210 is, for example, 4.2V.
Then, this is detected by the first comparison circuit 304 and the first
The valid output is supplied to the OR circuit 308 of. At this time, the second voltage detection circuit 302 detects that the voltage of the second secondary battery 12 has not reached 4.2 V, and the second comparison circuit
It is assumed that the output from 306 to the first OR circuit 308 is an invalid output. However, in the first OR circuit 308, the effective output from the first comparison circuit 304 causes the switch drive circuit 312
Supply a valid output to. This enables the switch drive circuit
312 supplies a positive control voltage to the respective gates G of the first field effect transistor 220 and the second field effect transistor 230.

The first receiving the control voltage from the control circuit 210
In the field effect transistor 220, the drain-source current is cut off, and the current in the charging direction X from the terminal 32 is cut off. As a result, overcharge of the first secondary battery 10 is prevented. At this time, if the secondary batteries 10 and 12 are discharged,
In the first field effect transistor 220, the parasitic diode 222 becomes conductive in the direction opposite to the blocking direction X. However, in this embodiment, since the control circuit 210 also supplies the control signal for turning off to the second field effect transistor 230 at the same time, the discharge from the secondary batteries 10 and 12 to be discharged due to the interruption of the charging current. The current is cut off by the second switch element 230. Therefore, the current to the parasitic diode 222 of the first switch element 220, which is about to be energized by the discharge current, is blocked by the second switch element 230, and
Conduction of the parasitic diode 222 in the switching element is prevented.

Next, as shown in FIG. 7, after the charging current is cut off, the voltage of the secondary battery 10 is lowered for a while due to the influence of the internal impedance of the battery and the averaging of the ion concentration inside the battery, and this is controlled. The control signal to the first and second switch elements 220 and 230 detected by the circuit 210 is set to a negative voltage. Thereby, the first and second switch elements 220, 230
Is turned on again, the charging current is switched to 220,
It is supplied to the secondary batteries 10 and 12 via 230 and charging is restarted. In this state, when one of the secondary batteries 10, 12 reaches the upper limit of the operable voltage, the control circuit 210 detects the voltage and turns off the switch elements 220, 230 to turn the secondary battery 10 12 on. Prevents 12,12 overcharge. In this way, while preventing overcharge of the secondary batteries 10 and 12,
Set 10,12 to full charge voltage.

On the other hand, when the electronic device is in use, when the power switch of the device is turned on, the secondary batteries 10 and 12 are discharged to supply power to the device. At this time, if the control circuit 210 detects the voltages of the secondary batteries 10 and 12 and the respective voltage values are within a predetermined value, the control voltage from the control circuit 210 to the switch elements 220 and 230 is set to a negative voltage state. The switch elements 220 and 230 are turned on. As a result, the discharge current flows from the positive terminal of the battery 10 to the switching elements 220 and 230.
Then, the current flows into the device through the terminal 32 and the terminal 32, and a current flows from the device through the terminal 34 to the battery 12 in the discharge direction Y, so that the secondary batteries 10 and 12 are discharged.

In this state, for example, the secondary batteries 10 and 12
If the battery is a lithium-ion secondary battery, the voltage value of each of the secondary batteries 10 and 12 will drop below 3.0V when continuous shooting for 1 hour or longer is performed with a camera-integrated VTR device. Further, when the operation of the device is continued and the discharge of the secondary batteries 10 and 12 progresses, as shown in FIG.
0,12 approaches the lower limit of operable voltage. For example, the first secondary battery 10 approaches the lower limit value, and the detected voltage from the first battery voltage detection circuit 300 is, for example, 2.4V to 2.
When it reaches 5V, this is detected by the first comparison circuit 304 and the effective output is supplied to the second OR circuit 310. At this time, the second voltage detection circuit 302 detects that the voltage of the second secondary battery 12 has not reached 2.4 V, and the second comparison circuit 306 outputs the second OR circuit. The output to 310 is invalid. However, in the second OR circuit 310, the effective output from the first comparison circuit 304 supplies the effective output to the switch drive circuit 312. As a result, the switch drive circuit 312 supplies a positive control voltage to the gates G of the first field effect transistor 220 and the second field effect transistor 230.

In the second field effect transistor 230 which receives the control voltage from the control circuit 210, the current between the drain and the source is cut off, and the current in the discharge direction Y from the batteries 10 and 12 is cut off. As a result, over-discharge of the batteries 10 and 12 is prevented. At this time, a current in the direction opposite to the cut off discharge direction Y is about to flow in the circuit and the second field effect transistor
The parasitic diode 232 of 230 tries to conduct. However, in this embodiment, since the control circuit 210 also supplies the control signal for turning off to the first field effect transistor 220 at the same time, the current in the charging direction, which is about to flow in the circuit due to the interruption of the discharge current, is not supplied to the first field effect transistor 220. It is cut off by the switch element 220 of. Therefore, the current to the parasitic diode 232 of the second switch element 230 is blocked by the first switch element 220, and the parasitic diode 232 of the second switch element 230 is blocked.
Is prevented from being conducted.

Next, in order to clarify the characteristic point of the present invention, the effect is clarified by comparing the comparative example shown in FIG. 8 with this embodiment, and the comparative example of FIG. 8 differs from that of FIG. The point is that control signals are individually supplied from the control circuit 210 to the switch elements 220 and 230. According to this, when the control circuit 210 detects that the batteries 10, 12 are fully charged during charging, the charge cutoff switch element 220 is turned off. As a result, the current in the charging direction is cut off, and the current in the discharging direction at that time passes through the parasitic diode 222 of the first switch element 220, which is off from the batteries 10 and 12.
Further, it flows to the terminal 32 through the second switch element 230 which is turned on. When discharged, either battery 10,12
When the discharge limit approaches the discharge limit, the discharge cutoff switch element 230 is turned off. As a result, the discharge current is cut off, and the current in the charging direction at that time is turned off from the terminal 32.
Through the parasitic diode 232 of the switching element 230 of the above, and further flows into the batteries 10 and 12 through the first switching element 220 which is turned on. Therefore, when the respective switching elements 220 and 230 are off, the parasitic diodes 222 and 232
An electric current flows through the element, and a current different from the original structure causes deterioration of the element, resulting in deterioration of the switch characteristics, and eventually destruction of the element itself.

In the present embodiment, the respective switch elements 220 and 230 are simultaneously controlled to be turned off, and a current in a direction different from the breaking direction of the respective switches 220 and 230 generated when the switches are turned off is blocked by the other switch element 220, 230. Switch element 220,230 parasitic diode
It prevents the 222,232 from being energized to prevent the deterioration of switch characteristics and the destruction of elements.

In the above embodiment, the case where the battery pack 30 is mainly mounted in the camera-integrated VTR has been described as an example, but the present invention can of course be mounted in other electronic equipment. Further, in the above-mentioned embodiment, the case where the lithium ion battery is used has been mainly described, but other secondary batteries may be used in the present invention, and the first and second set voltages at that time are different from those of the respective batteries. Of course, you may change it depending on the characteristics.
Furthermore, in the above embodiment, the case where the field effect transistor is used as the switch element has been described as an example, but other electronic switches may be used in the present invention.

In the above embodiment, two secondary batteries 10,1 are used.
Although the case of using 2 has been described as an example, the present invention can of course be applied to the case where one battery is used alone as shown in FIG. Further, in the above embodiment, the control circuit 210 is configured to detect the terminal voltage of each of the batteries 10 and 12. However, in the present invention, the voltage across the plurality of batteries connected in series as shown in FIG. May be detected. Further, although the above embodiment has been described by taking the case of using two batteries as an example, the present invention also includes the case of using three or more N batteries as shown in FIG. Further, in the above embodiment, the switch elements 220 and 230 are arranged on the plus terminal 32 side, but in the present invention, they may be arranged on the minus terminal 34 side, for example, as shown in FIG.

As described above, the present invention is not limited to the above-described embodiments at all, and includes all the improvements or applications made without departing from the matters recited in each claim of the claims.

[0033]

As described in detail above, according to the charge / discharge protection device for a secondary battery according to the present invention, the switch elements are connected in series in the opposite direction to the charge / discharge path of the secondary battery. Since it is configured to control ON / OFF at the same time, when one of the switching elements is turned off, the parasitic diode is blocked by the other switching element before the parasitic diode becomes conductive. It is possible to prevent energization of the parasitic diode. As a result,
It is possible to prevent the deterioration of the device, prevent the device from being damaged due to the deterioration of the device performance and the device, and to obtain the secondary battery charge / discharge protection device with safer operation.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram showing an embodiment of a secondary battery power supply device to which a secondary battery charge / discharge protection device according to the present invention is applied.

FIG. 2 is a functional block diagram showing an example of an internal configuration of a control circuit applied to the embodiment of FIG.

FIG. 3 is a circuit configuration diagram showing another embodiment of a secondary battery power supply device to which a secondary battery charge / discharge protection device according to the present invention is applied.

FIG. 4 is a circuit configuration diagram showing another embodiment of a secondary battery power supply device to which a secondary battery charge / discharge protection device according to the present invention is applied.

FIG. 5 is a circuit configuration diagram showing another embodiment of a secondary battery power supply device to which a secondary battery charge / discharge protection device according to the present invention is applied.

FIG. 6 is a circuit configuration diagram showing another embodiment of the secondary battery power supply device to which the secondary battery charge / discharge protection device according to the present invention is applied.

FIG. 7 is a diagram for explaining a charge / discharge protection operation of the secondary battery according to the embodiment of FIG.

FIG. 8 is a circuit configuration diagram showing a comparative example for clarifying the effect of the secondary battery charge / discharge protection device according to the present invention.

[Explanation of symbols]

 10,12 Secondary battery 210 Control circuit 220 Charge cutoff switch element 230 Discharge cutoff switch element 222,232 Parasitic diode 240 Common control line

Claims (5)

[Claims] 1. A charge / discharge protection device for a secondary battery, which prevents overcharge and overdischarge of a rechargeable secondary battery, wherein the device is connected in series to a charge / discharge path of the secondary battery and is normally turned on. Is a first switch means that conducts a current in the charging direction and cuts off the path in the charging direction when the switch is off, and includes a parasitic diode inside that conducts with a current in the discharging direction when the switch is off. Means and second switch means connected in series to the charging / discharging path of the secondary battery, normally turned on to conduct current in the discharging direction, and to cut off the path in the discharging direction when turned off. Second switch means including a parasitic diode inside which is sometimes conducted by a current in the charging direction, and a battery voltage of the secondary battery is detected so that the battery voltage is higher than or equal to a first set voltage in the vicinity of an operable voltage upper limit. If it becomes And a control means for turning off the second switch means when the battery voltage becomes equal to or lower than a second set voltage in the vicinity of the lower limit of operable voltage. A charge / discharge protection device for a secondary battery, wherein when the first switch means or the second switch means is off-controlled, the other switch means is simultaneously off-controlled. 2. The charging / discharging protection device for a secondary battery according to claim 1, wherein a plurality of batteries are connected in series to the secondary battery, and the control means controls the battery voltage of each secondary battery. The first switch means and the second switch are monitored when any one of the battery voltages exceeds a first set voltage.
The switch means is turned off, and the second switch means and the first switch means are turned off when any one of the battery voltages becomes equal to or lower than the first set voltage. Charge / discharge protection device. 3. The charging / discharging protection device for a secondary battery according to claim 1, wherein a plurality of batteries are connected in series to the secondary battery, and the control means is provided between both ends of the batteries connected in series. When the voltage is monitored and the voltage value becomes equal to or higher than the first set voltage, the first switch means and the second switch means are turned off, and the voltage value becomes equal to or lower than the second set voltage. A charging / discharging protection device for a secondary battery, characterized in that the second switch means and the first switch means are turned off. 4. The charging / discharging protection device for a secondary battery according to claim 1, wherein the secondary battery is used alone, and the control circuit detects the voltage across both ends of the secondary battery. When the value becomes equal to or higher than the first set voltage, the first switch means and the second switch means are turned off, and when the value becomes equal to or lower than the second set voltage, the second switch means and A charge / discharge protection device for a secondary battery, wherein the first switch means is turned off. 5. The secondary battery charge / discharge protection device according to claim 1, wherein the first switch means and the second switch means are both positive or negative charge / discharge paths with respect to the secondary battery. A charging / discharging protection device for a secondary battery, wherein the charging / discharging protection device is arranged in series with one of the two.