JP2001057740A - Battery protection device - Google Patents

Abstract

(57) [Problem] To provide a battery protection device having high reliability and high cycle life. SOLUTION: A control circuit 8 detects a battery voltage E1 of a secondary battery 5 and a terminal voltage E2 of input / output terminals 11 and 12 connected by a charging / discharging circuit from the secondary battery 5 to detect a battery voltage E1.
A first FET and a second FET connected in series to a charge / discharge circuit when 1 is equal to or lower than a charge inhibition voltage and equal to or higher than a discharge inhibition voltage;
6 and 7 are turned on. When the battery voltage E1 is equal to or higher than the charge prohibition voltage, the first FET 6 is turned off, and when the terminal voltage E2 is E1> E2, the first FET 6 is turned on. When the battery voltage E1 is equal to or lower than the discharge prohibition voltage, the second FET 7 is turned off, and when the terminal voltage E2 is E1> E2, the second FET 7 is turned on. By this control, the first and second FETs
No current flows through the parasitic diodes 6a, 7a of 6, 7
Deterioration due to heat generation can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a battery protection device for protecting a secondary battery such as a lithium ion secondary battery from overcharge or overdischarge.

[0002]

2. Description of the Related Art A secondary battery may be damaged or deteriorated if overcharged or overdischarged beyond proper charge / discharge conditions. In particular, a lithium-based secondary battery is liable to be damaged due to generation of gas due to decomposition of the electrolytic solution due to the progress of overcharging and temperature rise, and therefore, it is necessary to control charging so as not to fall into an overcharged state. Therefore, a battery protection device for preventing overcharge and overdischarge is provided, charging and discharging of the secondary battery is performed through the battery protection device, and when the state of overcharge or overdischarge is detected, the charge / discharge circuit is shut off. Measures are taken to protect the secondary battery.

FIG. 6 shows a configuration of a protection device for a secondary battery disclosed in Japanese Patent No. 2872365, in which a charging / discharging circuit connecting the secondary battery 30 to input / output terminals 34 and 35 includes a first switch. An element 31 and a second switch element 32 are connected in series, and each of the first and second switch elements 31 and 32 is controlled by a control unit 33 into a conductive state and a cutoff state. . Control means 33
Detects the voltage of the secondary battery 30 and controls the first switch element 31 to a conductive state when the battery voltage is equal to or lower than a charge prohibiting voltage at which the battery voltage becomes an overcharged state. When the voltage is higher than the prohibition voltage, the second switch element 3
2 is controlled to a conductive state. That is, when the secondary battery 30 is under appropriate charge / discharge conditions, the first and second switch elements 31 and 32 are in a conductive state, and the charge / discharge circuit of the secondary battery 30 is connected to the input / output terminals 34 and 35. Are electrically connected.

When the battery voltage becomes equal to or higher than the charge prohibiting voltage, the control means 33 controls the first switch element 31 to be in a cut-off state, so that the charge / discharge circuit is cut off, charging is stopped, and the secondary battery 30 is stopped. Is prevented from falling into an overcharged state. When the battery voltage becomes equal to or lower than the discharge inhibition voltage, the control unit 33 controls the second switch element 32 to be in the cutoff state, so that the charge / discharge circuit is cut off, the discharge is stopped, and the secondary battery 30 is turned off. An overdischarge state is prevented.

The first and second switch elements 31, 3
2 has parasitic diodes 31a and 32a between the drain and the source as shown. In the case of the first switch element 31, the parasitic diodes 31a and 32a
In the case of the second switch element 32, the first switch element 3 and the second switch element 3 are arranged such that the forward direction of the parasitic diode 32a is the charge direction of the secondary battery 30.
1, 32 are connected.

As described above, when the control means 33 controls the first switch element 31 to be in the cut-off state in order to prevent overcharging, the discharge circuit is formed through the parasitic diode 31a. Parasitic diode 31a
When the battery voltage becomes equal to or lower than the charge release voltage lower than the charge prohibition voltage due to the discharge, the control unit 33 controls the first switch element 31 to be in a conductive state and passes through the parasitic diode 31a. Return to a discharge state that will not be allowed. Further, when the second switch element 32 is controlled to be in the cut-off state in order to prevent overdischarge, the parasitic diode 32a
Charging circuit is formed through the secondary battery 30
Can be charged through the parasitic diode 32a, and when the battery voltage becomes equal to or higher than the discharge release voltage higher than the discharge prohibition voltage by the charging, the control means 33 controls the second switch element 32 to a conductive state, and The charge state is returned to a state in which the diode 32a does not pass.

[0007] As described above, the parasitic diodes 31a, 3a and 3a of the first and second switch elements 31 and 32 respectively.
2a, it is possible to discharge in a state where charging is prohibited, and it is possible to charge in a state where charging is prohibited.
The use of the secondary battery 30 is possible even in a circuit cut-off state for preventing 0 from overcharge and overdischarge.

[0008]

However, in the above-described conventional configuration, the discharge or charge is performed through the parasitic diode from the state of prohibition of charging or from the state of prohibition of discharging until reaching the release voltage. When a current flows, the first switch element or the second switch element generates heat and has a problem of deterioration. That is, in the power MOSFET used as each of the first and second switch elements, when a current having the same value flows in the forward direction of the parasitic diode as compared with the power loss when the current flows between the drain and the source. Power loss is several times greater than that of the power MOSFET, and even if heat generated by the current flowing between the drain and the source does not cause an abnormality in the power MOSFET, if the same current flows through the parasitic diode, Thermal destruction will occur, leading to deterioration.

It is an object of the present invention to provide a battery protection device that controls discharge current or charge current not to flow through a parasitic diode of a switching element to enable discharge when charging is prohibited and charge when discharging is prohibited. Is to provide.

[0010]

According to a first aspect of the present invention, there is provided a battery protection device, wherein the positive electrode and the negative electrode of the secondary battery and the positive electrode and the negative electrode of the input / output terminal have the same polarity. A first switching means and a second switching means are connected in series to a charging / discharging circuit connected between them, and a battery voltage between a positive electrode and a negative electrode of the secondary battery is controlled by the control means;
Detecting the terminal voltage between the positive electrode and the negative electrode of the input / output terminal, and controlling the first switching means to an on state when the battery voltage is equal to or lower than a charge prohibiting voltage for stopping charging of the secondary battery. When the battery voltage is equal to or higher than the discharge prohibiting voltage for stopping the discharge of the secondary battery, the second switching means is controlled to be in an ON state, and when the battery voltage becomes equal to or higher than the charging prohibiting voltage, the first switching is performed. Controlling the means to an off state and holding the off state; controlling the first switching means to an on state when the terminal voltage is lower than the battery voltage; and controlling the first switching means when the battery voltage becomes equal to or lower than the discharge inhibition voltage. The second switching means is controlled to be in an off state to maintain the off state, and when the terminal voltage becomes higher than the battery voltage, the second switching means is controlled to be in an on state.

According to the configuration of the first invention, when the battery voltage is under the charging prohibition voltage and under the proper charging / discharging condition that is higher than the discharging prohibition voltage, the control means turns on the first and second switching means. Since the state is controlled, the secondary battery is connected to the input / output terminal and can be charged and discharged. When the battery voltage becomes equal to or higher than the charge prohibiting voltage, the control means controls the first switching means to an off state to stop charging the secondary battery, but a discharge state in which the terminal voltage is lower than the battery voltage is detected. In this case, the first switching means is controlled to be in the ON state, thereby enabling the discharge of the secondary battery. When the battery voltage becomes equal to or lower than the discharge prohibiting voltage, the control means controls the second switching means to an off state to stop discharging the secondary battery, but detects a charge state in which the terminal voltage is higher than the battery voltage. When it is done, the second switching means is controlled to the ON state to enable charging of the secondary battery.

When a power MOSFET is used as the first and second switching means, a parasitic diode whose forward direction is opposite to the drain-source direction is built in. In the prior art, charge inhibition is controlled. When the discharge is performed in a state where the discharge is performed, the discharge is performed through a parasitic diode included in the first switching unit. When the discharge is performed in a state where the discharge inhibition control is performed, the discharge is performed through a parasitic diode included in the second switching unit. ing. However, there was a problem that a large charging / discharging current flows through the parasitic diode, thereby causing the switching means to generate heat and resulting deterioration.However, according to the configuration of the present invention, no charging / discharging current flows through the parasitic diode. Such a problem does not occur, and a highly reliable and durable battery protection device can be provided.

According to a second aspect of the present invention, there is provided a battery protection device for connecting a positive electrode and a negative electrode of a secondary battery and a positive electrode and a negative electrode of an input / output terminal between the same electrodes. The first switching means and the second switching means
The switching means is connected in series, and the control means detects the battery voltage between the positive electrode and the negative electrode of the secondary battery and the current direction of the charge / discharge circuit, and the battery voltage controls the charging of the secondary battery. When the voltage is equal to or lower than the charging prohibition voltage to be stopped, the first switching means is controlled to an on state. When the battery voltage is equal to or higher than the discharge prohibition voltage for stopping discharging of the secondary battery, the second switching means is turned on. State, and when the battery voltage becomes equal to or higher than the charge prohibition voltage, the first switching means is turned off to maintain the off state, and when the current direction becomes the discharge direction, the first switching means is turned off. Means is controlled to an on state, and when the battery voltage becomes equal to or less than the discharge inhibition voltage, the second switching means is controlled to an off state to hold the off state, and when the current direction becomes the charging direction, And controlling the second switching means in the ON state.

According to the second aspect of the invention, when the battery voltage is equal to or lower than the charging inhibition voltage and the battery is under appropriate charging / discharging conditions equal to or higher than the discharging inhibition voltage, the control means turns on the first and second switching means. Since the state is controlled, the secondary battery is connected to the input / output terminal and can be charged and discharged. When the battery voltage becomes equal to or higher than the charge prohibition voltage, the control means controls the first switching means to an off state to stop charging the secondary battery. The first switching means is controlled to be in the ON state, and the secondary battery can be discharged. When the battery voltage becomes equal to or lower than the discharge prohibition voltage, the control means controls the second switching means to an off state to stop discharging the secondary battery, but when the current direction is detected as the charging direction, The second switching means is controlled to be in an ON state to enable charging of the secondary battery.

Therefore, when a power MOSFET is used as each of the first and second switching means, no charge / discharge current flows through the parasitic diode incorporated therein,
Since the deterioration caused by the heat generation of the power MOSFET due to the large charge / discharge current flowing through the parasitic diode, which is a problem of the related art, does not occur, a highly reliable and highly durable battery protection device can be provided.

In the configuration of the second invention, the current direction can be detected from the voltage between both ends of the first and / or second switching means. That is, the current direction can be detected from the fact that the voltage gradient direction of the voltage between both ends due to the minute ON resistance of each of the first and / or second switching means differs depending on the charging direction and the discharging direction.

The current direction can be detected from the voltage across the resistor connected in series to the charge / discharge circuit. That is, since the voltage gradient direction of the voltage across the resistor differs depending on the charging direction and the discharging direction, the current direction can be detected.

A battery protection device according to a third aspect of the present invention that achieves the above object is a charge / discharge device that connects the positive electrode and the negative electrode of a secondary battery and the positive electrode and the negative electrode of an input / output terminal between the same electrodes. A first switching means and a second switching means are connected in series to a circuit, and a control means controls a battery voltage between a positive electrode and a negative electrode of the secondary battery and a terminal voltage between a positive electrode and a negative electrode of the input / output terminal. And when the battery voltage is equal to or lower than the charge inhibition voltage for stopping the charging of the secondary battery and the battery voltage is equal to or higher than the discharge inhibition voltage for stopping the discharging of the secondary battery, The switching means is controlled to be in an on state, and when the battery voltage is equal to or higher than the charge inhibition voltage, and when the terminal voltage is higher than the battery voltage, the first and the second are controlled.
Each of the switching means is controlled to be in an off state to maintain the off state. When the terminal voltage becomes lower than the battery voltage, the first
And controlling each of the second switching means to be in an on state, and controlling the first and second switching means to be in an off state when the battery voltage is equal to or lower than the discharge inhibition voltage, and when the terminal voltage is lower than the battery voltage. And maintaining the off state, and controlling the first and second switching means to the on state when the terminal voltage becomes higher than the battery voltage.

According to the configuration of the third invention, the control means controls the first and second switching means to be simultaneously turned on or off by one control signal in accordance with the state of the battery voltage and the terminal voltage. When the battery voltage is equal to or lower than the charge prohibition voltage and equal to or higher than the discharge prohibition voltage, the first and second switching means are turned on to enable charging and discharging regardless of the difference between the terminal voltage and the battery voltage. . When the battery voltage is equal to or higher than the charge prohibition voltage, when the terminal voltage is higher than the battery voltage, the first and second switching means are controlled to be turned off to stop charging. Each of the first and second switching means is controlled to be turned on to enable discharge. When the battery voltage is equal to or lower than the discharge prohibiting voltage, the first and second switching means are turned off to stop discharging when the terminal voltage is lower than the battery voltage, but when the terminal voltage is higher than the battery voltage, the first and second switching means are turned off. And the second switching means is controlled to be ON to enable charging.

Therefore, when a suitable power MOSFET is used as each of the first and second switching means, the discharge current when the parasitic diode incorporated therein is discharged in a state in which the charge inhibition is controlled is performed. In addition, the charging current does not flow when charging is performed in a state where the discharge is inhibited, and a large charge / discharge current flows through the parasitic diode, which is a problem of the related art, and the power MOSFET generates heat. Thus, it is possible to provide a highly reliable and durable battery protection device that does not suffer from the accompanying deterioration.

[0021]

Embodiments of the present invention will be described below with reference to the accompanying drawings to provide an understanding of the present invention.
The embodiment described below is an example embodying the present invention, and does not limit the technical scope of the present invention.

FIG. 1 shows a configuration of a battery protection device 1 according to a first embodiment, which is connected to a secondary battery 5 formed as a lithium ion secondary battery and configured as a battery power supply device. When charging the secondary battery 5 by connecting a charger to the input / output terminals 11 and 12, and discharging the secondary battery 5 by connecting a battery-using device to the input / output terminals 11 and 12, the battery protection device 1 Control is performed so that the secondary battery 5 does not fall into overcharge and overdischarge states.

In FIG. 1, a battery protection device 1 includes a first FET (first switching means) 6 and a second FET
(Second switching means) 7 and a control circuit (control means) 8. A charge / discharge circuit connecting the positive electrode and the negative electrode of the secondary battery 5 to the positive input / output terminal 11 and the negative input / output terminal 12 of the battery power supply includes a positive input / output terminal of the battery power supply. The negative terminal of the secondary battery 5 is connected to the terminal 11 and the first FET 6 and the second
Is connected to the negative electrode input / output terminal 12 through the FET 7 of FIG. The first and second FETs 6 and 7 are configured as power MOSFETs having parasitic diodes 6a and 7a, respectively. The first FET 6 is configured such that the forward direction of the parasitic diode 6a is the discharge direction of the secondary battery 5. Second FET
Numerals 7 are connected so that the forward direction of the parasitic diode 7a becomes the charging direction of the secondary battery 5. The first and second FETs 6 and 7 are controlled so that the source and the drain are turned on (conducted) or turned off (cut off) by a control voltage applied from the control circuit 8 to each gate.

The control circuit 8 detects a battery voltage E1 between the positive and negative electrodes of the secondary battery 5 and a terminal voltage E2 between the positive input / output terminal 11 and the negative input / output terminal 12, and detects these batteries. The first and second FETs 6 and 7 are turned on or off according to the state of the voltage E1 and the terminal voltage E2.

When the battery voltage E1 is equal to or lower than the charge prohibition voltage for prohibiting the charging of the secondary battery 5, the control circuit 8 controls the first FET 6 to turn on. When the battery voltage E1 is equal to or higher than the discharge prohibition voltage for prohibiting the discharge of the secondary battery 5, the control circuit 8 controls the second FET 7 to be on.
That is, when the battery voltage E1 is under appropriate charge / discharge conditions within the range between the charge prohibition voltage and the discharge prohibition voltage, the first
And each of the second FETs 6 and 7 is turned on. With this control, the positive electrode and the negative electrode of the secondary battery 5 are connected to the input / output terminals 11 and 12, respectively, by the first and second FETs.
Since the connection is made via 6, 7, the secondary battery 5 can be charged and discharged.

The control circuit 8 controls the first FET 6 to be turned off when the battery voltage E1 becomes equal to or higher than a charge prohibition voltage for prohibiting charging of the secondary battery 5. The battery voltage E1 of the secondary battery 5 rises with the progress of charging, and overcharging exceeding the full charge leads to deterioration or damage of the secondary battery 5, but by setting the charging prohibition voltage appropriately, Battery 5
Is prevented from falling into an overcharged state.

When the first FET 6 is in the off state by the overcharge prohibition control, the secondary battery 5 can be discharged because the forward direction of the parasitic diode 6a is connected in the discharging direction. Specifically, the input / output terminal 11,
When charging is performed by connecting a charger to the battery 12, the charging is stopped by the battery protection device 1 when the secondary battery 5 reaches a discharge prohibiting voltage that is fully charged due to the charging. Is switched to the connection to the device, a discharge circuit is formed through the parasitic diode 6a of the second FET 7 and the first FET 6, so that the secondary battery 5 can be discharged. However, the discharge through the parasitic diode 6a causes the first F to flow when a large current flows as described above.
ET6 causes deterioration due to the heat generation. Therefore, the control circuit 8 controls the first FET 6 to be on when the terminal voltage E2 is detected to be higher than the battery voltage E1, that is, when the discharge state is detected. With this control, since the discharge current does not flow through the parasitic diode 6a, deterioration of the first FET 6 due to heat generation is prevented.

The control circuit 8 controls the second FET 7 to be turned off when the battery voltage E1 becomes equal to or lower than the discharge prohibition voltage for prohibiting the discharge of the secondary battery 5. In the secondary battery 5, the battery voltage E1 decreases with the progress of the discharge, and the overdischarge in which the battery capacity becomes close to zero causes the deterioration of the secondary battery 5, but the secondary battery can be set by appropriately setting the discharge prohibition voltage. Battery 5
Is prevented from falling into an overdischarged state.

When the second FET 7 is controlled to be in the off state by the overdischarge prohibition control, the parasitic diode 7
Since the forward direction of a is connected to the charging direction, the charging of the secondary battery 5 is possible. Specifically, the battery-equipped device is connected to the input / output terminals 11 and 12, and the discharge proceeds. When the discharge protection voltage is reached, the discharge is stopped by the battery protection device 1 and the use of the device is stopped. When the input / output terminals 11 and 12 are switched to the connection to the charger, a charging circuit is formed through the parasitic diode 7a of the first FET 6 and the second FET 7. Discharge is possible. However, the charging through the parasitic diode 7a causes the second F
ET7 causes deterioration due to heat generation. Therefore,
The control circuit 8 detects the terminal voltage E2 and detects the terminal voltage E2.
Controls the second FET 7 to be on when a charge state lower than the battery voltage E1 is detected. With this control, the charging current does not flow through the parasitic diode 7a, so that the second FE
Deterioration due to heat generation of T7 is prevented.

Next, the electrical protection device 2 according to each of the second and third embodiments will be described. FIG. 2 shows the configuration of the battery protection device 2 according to the second embodiment, and FIG. 3 shows the configuration of the battery protection device 3 according to the third embodiment.
The same reference numerals are given to the same components as those in the configuration of the embodiment, and the description thereof will be omitted.

In FIG. 2, a control circuit 9 detects a battery voltage E1 between the positive electrode and the negative electrode of the secondary battery 5 and a current flowing through first and second FETs 6, 7 connected in series to a charge / discharge circuit. Detect direction. First and second FETs
Each of the first and second FETs 6 and 7 has a very small resistance value in an on state and an off state.
By detecting the direction of the voltage gradient at both ends of 7, it is possible to detect whether the current direction is the charging direction Ic or the discharging direction Id. The direction of the voltage gradient of the charge / discharge circuit is determined by the resistor 13 connected in series to the charge / discharge circuit by the control circuit 10 as in the battery protection device 3 according to the third embodiment shown in FIG.
It is also possible by detecting the voltage between both ends.

The control circuit 9 determines that the battery voltage E1 is
When the battery voltage E1 is equal to or lower than the charge inhibition voltage that inhibits the charging of the secondary battery 5, that is, when the battery voltage E1 is equal to or higher than the discharge inhibition voltage that inhibits the discharge of the secondary battery 5. Under the appropriate charging and discharging conditions, the first and second FETs 6 and 7 are controlled to be in the ON state regardless of the current direction. With this control, the positive electrode and the negative electrode of the secondary battery 5 are connected to the input / output terminals 11 and 12 via the first and second FETs 6 and 7, respectively, so that the secondary battery 5 can be charged and discharged. .

The control circuit 9 controls the first FET 6 to be turned off when the battery voltage E1 becomes equal to or higher than a charge prohibition voltage for prohibiting charging of the secondary battery 5. This first FE
When T6 is controlled to be in the OFF state, the current direction is detected from the voltage between both ends of the first FET 6 and the second FET 7 connected in series to the charging / discharging circuit, and the current direction is changed to the discharging direction Id.
In this case, the control circuit 9 controls the first FET 6 to turn on, and stops discharging through the parasitic diode 6a. By this control, the discharge current is reduced by the parasitic diode 6
Since the first FET 6 does not flow, deterioration of the first FET 6 due to heat generation is prevented.

The control circuit 9 controls the second FET 7 to turn off when the battery voltage E1 becomes equal to or lower than a discharge prohibiting voltage for prohibiting the discharge of the secondary battery 5. This second FE
When T7 is controlled to be in the off state, the current direction is detected from the voltage between both ends of the first FET 6 and the second FET 7 connected in series to the charging / discharging circuit, and the current direction is changed to the charging direction Ic.
In this case, the control circuit 9 controls the second FET 7 to turn on, and stops the discharge through the parasitic diode 6a. By this control, the charging current is reduced by the parasitic diode 6
Since the first FET 6 does not flow, deterioration of the first FET 6 due to heat generation is prevented.

In the case of the battery protection device 3 shown in FIG. 3, the current direction is detected based on the voltage between both ends of the resistor 13, and the control is performed in the same manner as in the case of the battery protection device 2.

Next, a battery protection device 4 according to a fourth embodiment will be described. FIG. 4 shows the configuration of the battery protection device 4. Elements common to the configurations of the above-described embodiments are denoted by the same reference numerals, and description thereof will be omitted.

In FIG. 4, a control circuit (control means) 14
Detects the battery voltage E1 between the positive electrode and the negative electrode of the secondary battery 5 and the terminal voltage E2 between the input / output terminals 11 and 12, and detects the first and second voltages according to the state of the battery voltage E1 and the terminal voltage E2. 2
Are simultaneously turned on or off by one control signal.

FIG. 5 is a flowchart showing the control operation of the control circuit 14. The control operation of the battery protection device 4 will be described below with reference to FIG. S1 shown in FIG.
S2... Are step numbers indicating the control procedure, and correspond to the numbers added to the text.

The control circuit 14 detects the battery voltage E1 (S1), which is equal to or lower than the charge prohibiting voltage for prohibiting the charging of the secondary battery 5 (S2), and prohibits the discharging of the secondary battery 5 for discharging. When the voltage is equal to or higher than the voltage (S3), that is, when the battery voltage E1 is under appropriate charge / discharge conditions within the range between the charge prohibition voltage and the discharge prohibition voltage, an ON control signal is output to output the first and second voltages. FETs 6 and 7 are turned on (S4). With this control, the positive electrode and the negative electrode of the secondary battery 5 are connected to the input / output terminals 11 and 12 via the first and second FETs 6 and 7, respectively, so that the secondary battery 5 can be charged and discharged. Become.

In step S2, the battery voltage E1
Is equal to or higher than the charge inhibition voltage, the terminal voltage E2
Is detected (S5), and the battery voltage E1 is compared with the terminal voltage E2 (S6). When a charge state in which the terminal voltage E2 is higher than the battery voltage E1 is detected, an off control signal is output to output the first control signal. Then, the second FETs 6 and 7 are controlled to be turned off (S7). Since the charge / discharge circuit is shut off by this control, the secondary battery 5 is prevented from being overcharged. The off state of each of the first and second FETs 6 and 7 is held until a discharge state in which the terminal voltage E2 is lower than the battery voltage E1 is detected or the battery voltage E1 becomes a charge release voltage lower than the charge inhibition voltage. You.

When the first and second FETs 6 and 7 are controlled to be in the off state, the control circuit 14 controls the terminal voltage E
2 when a discharge state higher than the battery voltage E1 is detected,
The output signal is switched to the ON control signal to control the first and second FETs 6 to be ON. Terminal voltage E2 is battery voltage E
The first and the second while the state of charge lower than 1 is detected.
FETs 6 and 7 are kept off.

If the battery voltage E1 is lower than the discharge prohibiting voltage in the step S3, the terminal voltage E2 is detected (S8), and the battery voltage E1 is compared with the terminal voltage E2 (S9). Terminal voltage E2 is battery voltage E1
When a lower discharge state is detected, an off control signal is output to control the first and second FETs 6 and 7 to be in an off state (S10). Since the charge / discharge circuit is shut off by this control, the secondary battery 5 is prevented from being over-discharged. The off state of each of the first and second FETs 6 and 7 is determined by detecting whether a charge state in which the terminal voltage E2 is higher than the battery voltage E1 is detected,
The battery voltage E1 is held until the discharge release voltage exceeds the discharge prohibition voltage.

When the first and second FETs 6 and 7 are controlled to be turned off, the control circuit 14 controls the terminal voltage E
2 when a charge state lower than the battery voltage E1 is detected,
The output signal is switched to an ON control signal to control the first and second FETs 6 to be ON to enable charging. While the state of charge in which the terminal voltage E2 is lower than the battery voltage E1 is detected, the first and second FETs 6 and 7 are kept in the off state.

In the configuration of the battery protection device 4, since the first and second FETs 6 and 7 are simultaneously turned on or off by the control circuit 14, current may flow through the respective parasitic diodes 6a and 7a. And the first and second currents caused by a large current flowing through the parasitic diodes 6a and 7a.
Of the FETs 6 and 7 due to heat generation is prevented.

In each of the drawings of the embodiments described above, only one secondary battery 5 is shown. However, even when the secondary batteries 5 are connected in series and in parallel, the same applies depending on the setting of the detection voltage. Can be configured.

[0046]

As described above, according to the present invention, the switching element connected in series to the charge / discharge circuit of the secondary battery is turned on or off to prevent the secondary battery from being overcharged or overdischarged. When the discharge is performed during over-discharge prevention or the over-discharge prevention is performed, control is performed so that the discharge current or the charge current does not flow through the parasitic diode of the switching element. It is possible to solve the conventional problem that the switching elements generate heat and cause deterioration due to heat generation. Therefore, deterioration of the battery protection device integrated as a battery pack together with the secondary battery is prevented from occurring, and a battery protection device with high reliability and a long cycle life can be provided.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a configuration of a battery protection device according to a first embodiment.

FIG. 2 is a circuit diagram showing a configuration of a battery protection device according to a second embodiment.

FIG. 3 is a circuit diagram showing a configuration of a battery protection device according to a third embodiment.

FIG. 4 is a circuit diagram showing a configuration of a battery protection device according to a fourth embodiment.

FIG. 5 is a flowchart illustrating a control operation according to a fourth embodiment.

FIG. 6 is a circuit diagram showing a configuration of a battery protection device according to the related art.

[Explanation of symbols]

 1, 2, 3, 4 Battery protection device 5 Secondary battery 6 First FET (first switching means) 7 Second FET (second switching means) 8, 9, 10, 14 Control circuit (control means) 11) Positive input / output terminal 12 Negative input / output terminal 13 Resistor E1 Battery voltage E2 Terminal voltage Ic Charging direction current Id Discharging direction current

Claims (5)

[Claims] A first switching means and a second switching means are connected in series to a charging / discharging circuit for connecting the positive and negative electrodes of a secondary battery and the positive and negative electrodes of an input / output terminal to the same polarity, respectively. The control means detects a battery voltage between the positive electrode and the negative electrode of the secondary battery and a terminal voltage between the positive electrode and the negative electrode of the input / output terminal, and stops charging the secondary battery. When the voltage is equal to or lower than the charge prohibition voltage to be controlled, the first switching means is controlled to an on state. The first switching means is controlled to be in an off state when the battery voltage becomes equal to or higher than the charge prohibiting voltage, and the off state is maintained, and the first switching is performed when the terminal voltage becomes lower than the battery voltage. means The second switching means is controlled to be in an off state when the battery voltage becomes equal to or lower than the discharge prohibition voltage, the off state is maintained, and when the terminal voltage becomes higher than the battery voltage, the second switching means is turned off. A battery protection device, wherein the switching means is controlled to an on state. 2. A charging / discharging circuit for connecting a positive electrode and a negative electrode of a secondary battery and a positive electrode and a negative electrode of an input / output terminal in the same polarity, respectively, and including a first switching means and a second switching means in series. The control means detects a battery voltage between the positive electrode and the negative electrode of the secondary battery and a current direction of the charging / discharging circuit, and the battery voltage is equal to or less than a charge inhibition voltage for stopping charging of the secondary battery. When the battery voltage is equal to or higher than a discharge prohibition voltage for stopping the discharge of the secondary battery, the second switching means is controlled to an on state. When the voltage becomes equal to or higher than the charge prohibiting voltage, the first switching means is controlled to an off state to maintain the off state, and when the current direction is changed to a discharging direction, the first switching means is controlled to an on state. And When the battery voltage becomes equal to or lower than the discharge prohibition voltage, the second switching means is controlled to an off state to maintain the off state, and when the current direction becomes the charging direction, the second switching means is turned on. A battery protection device characterized by controlling. 3. The battery protection device according to claim 2, wherein the direction of the current is detected from the voltage between both ends of the first and / or second switching means. 4. The battery protection device according to claim 2, wherein a current direction is detected from a voltage across a resistor connected in series to the charge / discharge circuit. 5. A charging / discharging circuit for connecting a positive electrode and a negative electrode of a secondary battery and a positive electrode and a negative electrode of an input / output terminal in the same polarity, respectively, and including a first switching means and a second switching means in series. The control means detects a battery voltage between the positive electrode and the negative electrode of the secondary battery and a terminal voltage between the positive electrode and the negative electrode of the input / output terminal, and stops charging the secondary battery. When the battery voltage is equal to or lower than the charge prohibition voltage to be stopped and the battery voltage is equal to or higher than the discharge prohibition voltage for stopping discharge of the secondary battery, the first and second switching means are controlled to be in an on state, and the battery voltage is equal to or higher than the charge prohibition voltage. , When the terminal voltage is higher than the battery voltage, the first and second switching means are controlled to be in the off state to maintain the off state, and when the terminal voltage is lower than the battery voltage, the first and second switching means are turned off. Second switching Controlling the first and second switching means to an off state when the battery voltage is equal to or lower than the discharge inhibition voltage, and controlling the first and second switching means to an off state when the terminal voltage is lower than the battery voltage. And a first and second switching means that are turned on when the terminal voltage becomes higher than the battery voltage.