JPH0883627A - Overdischarging preventing method for secondary battery, charging/discharging control circuit, and battery pack - Google Patents

Abstract

PURPOSE: To provide an overdischarge preventing method for a secondary battery by eliminating the power consumption at the time of nonuse and provide a charging/discharging control circuit and a battery pack using the method. CONSTITUTION: The voltage between the terminals of a secondary battery is detected by a voltage detection control circuit 2; the current from the secondary battery 1 to a load is controlled by a charging/discharging control circuit 7 based on the detected result; a reed switch 6 is provided between the voltage detection control circuit 2 and the secondary battery 1; and the reed switch 6 is turned off when no current is fed to the load from the secondary 1. The reed switch 6 is turned off by the magnetic force of a magnet provided on an upper device compatible with a battery pack 10. The reed switch 6 is turned off at the time of nonuse, the excitation to the voltage detection control circuit 2 is cutoff, no power is consumed, the secondary battery 1 is not overdischarged, and the characteristic deterioration of the secondary battery 1 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 method for preventing overdischarge of a secondary battery, a charge / discharge control circuit and a battery pack capable of preventing overdischarge of the secondary battery.

[0002]

2. Description of the Related Art In recent years, portable electronic devices have rapidly spread, and along with this, rechargeable secondary batteries have come to be used in various portable electronic devices.

Currently, nickel-cadmium batteries are mainly used as secondary batteries, but lithium ion secondary batteries are attracting attention because of their high energy density.

However, some of these high-performance secondary batteries deteriorate their characteristics when they are overcharged or over-discharged. Therefore, the secondary battery is overcharged or overcharged by using a control circuit together. I try not to discharge.

FIG. 2 is a block diagram showing an example of a battery pack using a secondary battery that also uses a control circuit as described above. In the figure, 1 is a secondary battery, 2 is a voltage detection control circuit, 3 is a power control circuit, 4a and 4b are output terminals, and a charge / discharge control circuit 5 is constituted by the voltage detection control circuit 2 and the power control circuit 3. ing.

The positive terminal of the secondary battery 1 is connected to the voltage detection control circuit 2 and the output terminal 4a, and the negative terminal is connected to the voltage detection control circuit 2 and the output terminal 4b via the power control circuit 3. ing. Further, the power control circuit 3 controls the current between the secondary battery 1 and the output terminal 4b based on the control signal from the voltage detection control circuit 2.

According to the above configuration, the voltage between the terminals of the secondary battery 1 is detected by the voltage detection control circuit 2, and the detected voltage becomes equal to or higher than a predetermined upper limit value or lower than a predetermined lower limit value, and the secondary battery is overcharged. Alternatively, when the over-discharge state is about to be reached, a control signal is output from the voltage detection control circuit 2 and the power control circuit 3 cuts off the flow of current between the secondary battery 1 and the output terminal 4b. . This prevents the secondary battery 1 from being overcharged or overdischarged,
This prevents the characteristics of the secondary battery 1 from being deteriorated.

[0008]

However, in the above-mentioned conventional battery pack, since the current always flows from the secondary battery 1 to the voltage detection control circuit 2, power is consumed even when it is not used, and an excessive amount of power is consumed. The secondary battery may reach a discharge state, resulting in deterioration of the characteristics of the secondary battery.

In view of the above problems, an object of the present invention is to provide a method of preventing over-discharge of a secondary battery by eliminating power consumption when not in use, a charge / discharge control circuit using the same, and a battery pack. is there.

[0010]

In order to achieve the above-mentioned object, according to the present invention, in claim 1, the voltage between terminals of a secondary battery is detected by a voltage detection control circuit, and the secondary battery is detected based on the detection result. A method of preventing over-discharge of a secondary battery connected to a charge / discharge control circuit for controlling a current from a battery to a load, wherein a switch is provided between the voltage detection control circuit and the secondary battery,
A method for preventing over-discharging of a secondary battery is proposed in which the switch is turned off when the load is not energized from the secondary battery.

According to a second aspect of the present invention, the voltage detection control circuit detects a voltage between terminals of the secondary battery, which is housed in a case detachably attached to a host device to which power is supplied,
A method for preventing over-discharge of a secondary battery, to which a charging / discharging control circuit for controlling a current from the secondary battery to a load based on the detection result is connected, wherein the method is provided between the voltage detection control circuit and the secondary battery. There is proposed a method for preventing over-discharge of a secondary battery, which is provided with a switch and turns off the switch when the secondary battery is not attached to the host device.

According to a third aspect of the present invention, in the method of preventing over-discharge of a secondary battery according to the second aspect, the switch is a reed switch, and the secondary battery mounting position of the host device corresponds to the reed switch. A method of preventing over-discharge of a secondary battery is proposed, in which a magnet is provided and the reed switch is turned on by the magnetic force of the magnet when the secondary battery is attached to the host device.

According to a fourth aspect of the present invention, in a charge / discharge control circuit connected between a power supply terminal and a secondary battery to prevent over-discharge and over-charge of the secondary battery, a positive terminal of the secondary battery is provided. Between the secondary battery and the power supply terminal, which is connected between the secondary battery and the power supply terminal, and which is connected between the secondary battery and the negative electrode terminal, detects the voltage between the terminals of the secondary battery, and outputs a control signal based on the voltage between the terminals. And a power control circuit that controls the current between the secondary battery and the power supply terminal based on the control signal, and at least provided between the voltage detection control circuit and the secondary battery. A charge / discharge control circuit including one switch is proposed.

Further, according to a fifth aspect of the present invention, there is provided a charge / discharge control circuit which is connected between the power supply terminal provided in the case and the secondary battery and which prevents the secondary battery from being over-discharged and over-charged. In the battery pack, the charge / discharge control circuit is
Connected between the positive electrode terminal and the negative electrode terminal of the secondary battery,
A voltage detection control circuit that detects a voltage between terminals of the secondary battery and outputs a control signal based on the voltage between the terminals, is connected between the secondary battery and a power supply terminal, and is based on the control signal. A battery pack including a power control circuit that controls a current between the secondary battery and the power supply terminal, and at least one switch provided between the voltage detection control circuit and the secondary battery is proposed. To do.

A sixth aspect of the present invention proposes the battery pack according to the fifth aspect, wherein the switch is a reed switch.

[0016]

According to the method of preventing over-discharge of the secondary battery according to claim 1 of the present invention, the voltage between the terminals of the secondary battery is detected by the voltage detection control circuit, and the secondary battery is detected based on the detection result. The current to the load is controlled. Further, when the secondary battery is not energized to the load, the switch between the voltage detection control circuit and the secondary battery is turned off, and the secondary battery is energized to the voltage detection control circuit. Is cut off.

According to the secondary battery over-discharge prevention method of the second aspect, when the secondary battery housed in the case is attached to the host device to which power is to be supplied, the switch is turned on. The secondary battery is energized to the voltage detection control circuit, the voltage between the terminals of the secondary battery is detected by the voltage detection control circuit, and the current from the secondary battery to the host device is detected based on the detection result. Controlled. Also, when the case of the secondary battery is not attached to the host device, the switch between the voltage detection control circuit and the secondary battery is turned off, and the voltage from the secondary battery is The power supply to the detection control circuit is cut off.

According to the secondary battery over-discharge prevention method of the third aspect, when the secondary battery housed in the case is attached to the host device to which power is to be supplied, the host device is installed in the host device. The reed switch provided in the case is turned on by the magnetic force of the provided magnet, the voltage detection control circuit is energized from the secondary battery, and the voltage between the terminals of the secondary battery is detected by the voltage detection control circuit, The current from the secondary battery to the host device is controlled based on the detection result. When the case of the secondary battery is not attached to the host device, the magnetic force of the magnet of the host device does not affect the reed switch, so the voltage detection control circuit and the secondary battery The reed switch between and is turned off, and the power supply from the secondary battery to the voltage detection control circuit is cut off.

According to the charge and discharge control circuit of the fourth aspect, the voltage detection control circuit detects the terminal voltage of the secondary battery and outputs the control signal based on the terminal voltage. A power control circuit controls current between the secondary battery and the power supply terminal based on the control signal.
Further, when the secondary battery is not used, a switch provided between the voltage detection control circuit and the secondary battery is turned off, and the secondary battery is energized to the voltage detection control circuit. Is cut off.

According to the battery pack of the fifth aspect, the voltage detection control circuit detects the terminal voltage of the secondary battery and outputs the control signal based on the terminal voltage. Further, the power control circuit controls the current between the secondary battery and the power supply terminal based on the control signal. Further, when the secondary battery is not used,
A switch provided between the voltage detection control circuit and the secondary battery is turned off, and the power supply from the secondary battery to the voltage detection control circuit is cut off.

According to a sixth aspect of the battery pack, the switch is a reed switch. For example, a magnetic force generating means such as a magnet is provided in a host device to which the battery pack is attached, in correspondence with the reed switch. When the battery pack is attached to the host device, the reed switch is turned on by the magnetic force, the terminal voltage of the secondary battery is detected by the voltage detection control circuit, and the battery pack is not connected to the host device. When in the mounted state, the reed switch is turned off, and the power supply from the secondary battery to the voltage detection control circuit is cut off.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram showing a battery pack using a secondary battery that also uses a charge / discharge control circuit according to the first embodiment of the present invention. In the figure, the same components as those in the conventional example described above are represented by the same reference numerals. That is, 1 is a secondary battery, 2
Is a voltage detection control circuit, 3 is a power control circuit, 4a and 4b are output terminals, 6 is a reed switch, and a charge / discharge control circuit 7 is constituted by the voltage detection control circuit 2, the power control circuit 3, and the reed switch 6. There is.

The positive terminal of the secondary battery 1 is connected to the output terminal 4a and the voltage detection control circuit 2 via the reed switch 6, and the negative terminal is connected to the voltage detection control circuit 2 and the power control circuit. 3 is connected to the output terminal 4b. Further, the power control circuit 3 controls the current between the secondary battery 1 and the output terminal 4b based on the control signal from the voltage detection control circuit 2, and the voltage detection control circuit 2 is energized from the secondary battery 1. If not, the voltage detection control circuit 2 outputs the power control circuit 3 to the secondary battery 1 and the output terminal 4b.
Is electrically disconnected.

As shown in FIG. 3, each of the above-described components is housed in a case 8 to form a battery pack 10, and one side surface of the case 8 is provided with output terminals 4a and 4b. Further, the reed switch 6 is arranged at a position facing the mounting surface of the charger or the host device 20 suitable for the battery pack 10, and the host device 20 has a magnet at a position facing the reed switch 6 when the battery pack is mounted. 21 is provided.

According to the above configuration, the battery pack 1
When 0 is attached to the host device 20, the magnet 21 and the reed switch 6 face each other as shown in FIG. 4, and the reed switch 6 is turned on by the magnetic force generated from the magnet 21.
As a result, the secondary battery 1 is connected to the voltage detection control circuit 2 via the reed switch 6, and the terminal voltage of the secondary battery 1 is detected by the voltage detection control circuit 2. When the detected voltage becomes equal to or higher than the predetermined upper limit value or equal to or lower than the predetermined lower limit value, and the secondary battery is about to reach the overcharged state or the overdischarged state, a control signal is output from the voltage detection control circuit 2 to perform power control. The circuit 3 blocks the flow of current between the secondary battery 1 and the output terminal 4b. As a result, the secondary battery 1 does not enter the overcharged state or the overdischarged state, and the characteristic deterioration of the secondary battery 1 is prevented.

When the battery pack 10 is removed from the host device 20 when it is not used, the magnetic force from the magnet 21 does not affect the reed switch 6, so the reed switch 6 is turned off. This allows
The power supply from the secondary battery 1 to the voltage detection control circuit 2 is cut off, the wasteful power consumption by the voltage detection control circuit 2 is suppressed, and the discharge current of the secondary battery 1 when not in use is self-discharged inside the battery element. Therefore, it takes longer than before to reach the over-discharge state.

Further, since the reed switch 6 is turned on / off by the magnet 21, it can be used only by the host device 20 suitable for the battery pack 10, so that accidents due to misuse can be prevented and safety can be improved. It is possible to improve the sex.

Next, a second embodiment of the present invention will be described.
FIG. 5 is a block diagram showing the second embodiment. The configuration of the battery pack 10 in this embodiment is the same as that of the first embodiment described above, and the difference between the first embodiment and the second embodiment is that the magnet 21 provided in the host device 20 can be moved. There is something I did.

That is, reference numeral 22 in the drawing denotes an operation start switch (power switch) of the host device, which is, for example, a sliding type slide switch. The magnet 21 is attached to one end of the operation start switch 22, and when the switch 22 is turned on, the magnet 21 moves along with the sliding of the switch 22 and faces the reed switch 6. .

According to the above configuration, the battery pack 1
Only when 0 is attached to the host device 20 and the operation start switch 22 is turned on, the secondary battery 1 of the battery pack 10 energizes the host device and the secondary battery 1 through the reed switch 6 The voltage detection control circuit 2 is energized to perform charge / discharge control.

Therefore, even when the battery pack 10 is attached to the host device 20, the operation start switch 22
Is off, the power supply from the secondary battery 1 to the host device 20 is cut off, and the reed switch 6 is turned off, so that the power supply from the secondary battery 1 to the voltage detection control circuit 2 is cut off. Useless power consumption by the voltage detection control circuit 2 is suppressed, and the discharge current of the secondary battery 1 when not in use is only self-discharge inside the battery element, and the time to reach an overdischarge state is longer than before. Become.

In the second embodiment, the operation start switch 22 of the host device 20 is a slide switch, and the magnet 21 is moved together with the slide switch. However, the invention is not limited to this, and the operation start switch 22 is not limited to this. A push button type, a seesaw type, a rotary type, or the like can achieve the same effect by configuring the magnet 21 to move in accordance with the on / off state of the switch.

Next, a third embodiment of the present invention will be described.
FIG. 6 is a configuration diagram showing a battery pack using a secondary battery that also uses the charge / discharge control circuit of the third embodiment. In the figure, the same components as those of the first embodiment described above are represented by the same reference numerals. The difference between the first embodiment and the third embodiment is that the reed switch 6 is replaced by a mechanical switch, for example, a micro switch 9.

That is, 1 is a secondary battery, 2 is a voltage detection control circuit, 3 is a power control circuit, 4a and 4b are output terminals, 9 is a micro switch, and the voltage detection control circuit 2, the power control circuit 3 and the micro switch are provided. The switch 9 constitutes a charge / discharge control circuit 7.

The positive terminal of the secondary battery 1 is connected to the output terminal 4a and is also connected to the voltage detection control circuit 2 via the microswitch 9, and the negative terminal is connected to the voltage detection control circuit 2 and the power control circuit. Output terminal 4b through 3
It is connected to the. Further, the power control circuit 3 controls the current between the secondary battery 1 and the output terminal 4b based on the control signal from the voltage detection control circuit 2, and the voltage detection control circuit 2 is energized from the secondary battery 1. If not, the voltage detection control circuit 2
From the power control circuit 3 to the secondary battery 1 and the output terminal 4
It electrically disconnects from b.

Further, each of the above-mentioned components is housed in a case 31 having an opening at one corner as shown in FIG. 7 to form a battery pack 30, and the opening 3 of the case 31 is formed.
Output terminals 4a and 4b are provided on one side surface adjacent to 1a.

Further, the micro switch 9 is arranged in the vicinity of the opening 31a so that the micro switch 9 is turned on when the charger or the host device 40 having a shape suitable for the battery pack 30 is attached to the opening 31a. ing.

According to the above configuration, the battery pack 3
When 0 is attached to the host device 40, the protrusion 41 of the host device 40 is inserted into the opening 31a of the battery pack 30 as shown in FIG. 7, the protrusion 41 abuts the micro switch 9, and the micro switch 9 is turned on. It becomes a state. As a result, the secondary battery 1 is connected to the voltage detection control circuit 2 via the microswitch 9, and the voltage between the terminals of the secondary battery 1 is detected by the voltage detection control circuit 2.

When the detected voltage becomes equal to or higher than the predetermined upper limit value or equal to or lower than the predetermined lower limit value and the secondary battery is about to reach the overcharged state or the overdischarged state, the voltage detection control circuit 2 outputs a control signal. , The secondary battery 1 by the power control circuit 3
The current flow between the output terminal 4b and the output terminal 4b is cut off. As a result, the secondary battery 1 does not enter the overcharged state or the overdischarged state, and the characteristic deterioration of the secondary battery 1 is prevented.

When the battery pack 30 is removed from the host device 40 when not in use, the host device 40
Since the protruding portion 41 of is removed from the opening 31a, the microswitch 9 is turned off. As a result, the power supply from the secondary battery 1 to the voltage detection control circuit 2 is cut off, wasteful power consumption by the voltage detection control circuit 2 is suppressed, and the discharge current of the secondary battery 1 when not in use is the internal battery element. However, the time required to reach the over-discharged state becomes longer than before.

Further, since the micro switch 9 is turned on / off by the projecting portion 41, it can be used only by the host device 40 suitable for the battery pack 30, and therefore accidents due to misuse can be prevented. It is possible to improve safety.

Next, a fourth embodiment of the present invention will be described.
FIG. 8 is a block diagram showing the fourth embodiment. The configuration of the battery pack 30 in this embodiment is almost the same as that of the third embodiment described above, and the difference between the third embodiment and the fourth embodiment is that a micro switch is provided by a slide switch provided in the host device 40. It is to turn 9 on and off.

That is, reference numeral 42 in the drawing denotes an operation start switch (power switch) of the host device 40, which is, for example, a sliding type slide switch. One end of the operation start switch 42 faces the opening 43 provided corresponding to the opening 31 a of the battery pack 30, and the operation start switch 42
When the switch is turned on, one end 42a of the switch 42 is inserted into the opening 31a as the switch 42 slides, and the micro switch 9 is pressed.

According to the above configuration, the battery pack 3
Only when 0 is attached to the host device 40 and the operation start switch 42 is turned on, the host battery is energized from the secondary battery 1 of the battery pack 30 and the secondary battery 1 via the micro switch 9 is energized. The voltage detection control circuit 2 is energized to perform charge / discharge control.

Therefore, even when the battery pack 30 is attached to the host device 40, the operation start switch 42
Is off, the energization from the secondary battery 1 to the host device 40 is cut off, and the microswitch 9 is turned off and the energization from the secondary battery 1 to the voltage detection control circuit 2 is cut off. Useless power consumption by the voltage detection control circuit 2 is suppressed, and the discharge current of the secondary battery 1 when not in use is only self-discharge inside the battery element, and the time to reach an overdischarge state is longer than before. Become.

In the fourth embodiment, the operation start switch 42 of the host device 40 is a slide switch. However, the operation start switch 42 is not limited to this, and the operation start switch 42 is a push button type, seesaw type or rotary type. Even in this case, the same effect can be obtained by configuring the micro switch 9 so that it can be turned on and off according to the on / off state of the switch.

In the first to fourth embodiments described above, the reed switch 6 or the micro switch 9 is provided between the voltage detection control circuit 2 and the positive electrode of the secondary battery 1, but it is provided between the negative electrode and the negative electrode. Also has the same effect. Further, the power control circuit 3 may be provided on the positive electrode side.

In this embodiment, one secondary battery 1 is used, and the battery packs 10 and 30 are provided with one voltage detection control circuit 2 corresponding thereto, but the present invention is not limited to this. However, when a plurality of secondary batteries 1 are provided and a plurality of voltage detection control circuits 2 are provided corresponding thereto, as shown in FIG. 9, a reed switch 6 or a micro switch is provided for each of these voltage detection control circuits 2. By providing the switch 9, the same effect can be obtained.

Further, as shown in FIG. 10, the charging path and the discharging path are different from each other, and a charging power control circuit 3a and a discharging power control circuit 3b are provided correspondingly, and control from the voltage detection control circuit is performed. Even when the operation of the charging and discharging power control circuits 3a and 3b is controlled by the signal,
A similar effect can be obtained by providing the reed switch 6 or the micro switch 9 between the secondary battery 1 and the voltage detection control circuit 2.

[0050]

As described above, according to the secondary battery over-discharge prevention method of the first aspect of the present invention, when the secondary battery is not energized, the voltage detection control circuit Since the switch between the secondary battery and the secondary battery is turned off, and the power supply from the secondary battery to the voltage detection control circuit is cut off, power is not consumed when the secondary battery is not used. In addition, the characteristics of the secondary battery can be prevented from being deteriorated without reaching the over-discharged state.

According to the secondary battery over-discharge prevention method of the second aspect, the switch is turned on when the secondary battery housed in the case is attached to the host device. To the voltage detection control circuit, the terminal voltage of the secondary battery is detected by the voltage detection control circuit to control the current from the secondary battery to the host device, and the case of the secondary battery is the host device. When the device is not mounted, the switch between the voltage detection control circuit and the secondary battery is turned off, and the power supply from the secondary battery to the voltage detection control circuit is cut off. When the secondary battery is not used, the power is not consumed, the over-discharge state is not reached, and the characteristic deterioration of the secondary battery can be prevented.

According to the secondary battery over-discharge prevention method of the third aspect, when the secondary battery housed in the case is attached to the host device, the magnet provided in the host device is removed. The reed switch provided in the case is turned on by the magnetic force, and the voltage detection control circuit is energized from the secondary battery, and the voltage between the terminals of the secondary battery is detected by the voltage detection control circuit, and the secondary battery is connected to the upper layer. When the current to the device is controlled and the case of the secondary battery is not attached to the host device, the magnetic force of the magnet of the host device does not affect the reed switch. Since the secondary battery is turned off and the power supply from the secondary battery to the voltage detection control circuit is cut off, power is not consumed when the secondary battery is not used, and over-discharge occurs. Without leading to state, it is possible to prevent deterioration of the characteristics of the secondary battery.

According to the charge / discharge control circuit of the fourth aspect, when the secondary battery is not in use, the switch between the voltage detection control circuit and the secondary battery is turned off.
Since the energization from the secondary battery to the voltage detection control circuit is cut off, the power of the secondary battery is not consumed, the over-discharge state is not reached, and the characteristic deterioration of the secondary battery is prevented. Can be prevented.

According to the battery pack of the fifth aspect, when the secondary battery is not used, the switch provided between the voltage detection control circuit and the secondary battery is turned off. Since the energization from the secondary battery to the voltage detection control circuit is cut off, the power of the secondary battery is not consumed, the over-discharge state is not reached, and the characteristic deterioration of the secondary battery is prevented. Can be prevented.

According to the battery pack of the sixth aspect, in addition to the above effects, the on / off state of the reed switch can be changed by the magnetic force from the magnetic force generating means provided corresponding to the reed switch. Since it can be used only by a charger or a higher-level device suitable for the battery pack, accidents due to misuse can be prevented and safety can be improved.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a battery pack according to a first embodiment of the present invention.

FIG. 2 is a configuration diagram showing a conventional example.

FIG. 3 is a diagram for explaining the structure and operation of the first embodiment of the present invention.

FIG. 4 is a diagram for explaining the operation of the first embodiment of the present invention.

FIG. 5 is a configuration diagram showing a second embodiment of the present invention.

FIG. 6 is a configuration diagram showing a battery pack according to a third embodiment of the present invention.

FIG. 7 is a diagram for explaining the structure and operation of the third embodiment of the present invention.

FIG. 8 is a diagram for explaining the structure and operation of the fourth embodiment of the present invention.

FIG. 9 is a configuration diagram showing another embodiment of the present invention.

FIG. 10 is a block diagram showing another embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Secondary battery, 2 ... Voltage detection control circuit, 3 ... Power control circuit, 3a ... Charging power control circuit, 3b ... Discharge power control circuit, 4a, 4b ... Output terminal, 5 ... Charge / discharge control circuit, 6
... Reed switch, 7 ... Charge / discharge control circuit, 8 ... Case,
9 ... Micro switch, 10, 30 ... Battery pack, 20, 40 ... Host device, 21 ... Magnet, 22, 42 ...
Operation start switch, 31 ... Case, 31a ... Opening part, 4
1 ... Projection part, 43 ... Opening part.

Claims (6)

[Claims] 1. A secondary battery connected to a charge / discharge control circuit for detecting a voltage between terminals of the secondary battery by a voltage detection control circuit and controlling a current from the secondary battery to a load based on the detection result. In the over-discharge prevention method, a switch is provided between the voltage detection control circuit and the secondary battery, and the switch is turned off when the secondary battery does not energize the load. And a method for preventing over-discharge of a secondary battery. 2. A secondary battery housed in a case detachably attached to a host device to which power is supplied, the voltage between terminals of the secondary battery is detected by a voltage detection control circuit, and the secondary battery is detected based on the detection result. From the overcharge prevention method of the secondary battery connected to the charge / discharge control circuit for controlling the current from the load to the load, a switch is provided between the voltage detection control circuit and the secondary battery, and the secondary battery is A method of preventing over-discharge of a secondary battery, wherein the switch is turned off when the device is not attached to the host device. 3. The switch comprises a reed switch, and a magnet is provided at a rechargeable battery mounting position of the host device so as to correspond to the reed switch, and the magnet is provided when the rechargeable battery is mounted on the host device. The overdischarge prevention method for a secondary battery according to claim 2, wherein the reed switch is turned on by a magnetic force of a magnet. 4. A charging / discharging control circuit connected between a power supply terminal and a secondary battery to prevent over-discharging and over-charging of the secondary battery, wherein a positive electrode terminal and a negative electrode terminal of the secondary battery are connected. Connected in between,
A voltage detection control circuit that detects a voltage between terminals of the secondary battery and outputs a control signal based on the voltage between the terminals, is connected between the secondary battery and a power supply terminal, and is based on the control signal. A power control circuit that controls a current between the secondary battery and the power supply terminal, and at least one switch provided between the voltage detection control circuit and the secondary battery. Charge and discharge control circuit. 5. A battery pack provided with a charge / discharge control circuit, which is connected between a power supply terminal provided in a case and a secondary battery and prevents over-discharge and over-charge of the secondary battery, The charge / discharge control circuit is connected between a positive electrode terminal and a negative electrode terminal of the secondary battery, detects a voltage between terminals of the secondary battery, and outputs a control signal based on the voltage between terminals. A power control circuit that is connected between the secondary battery and a power supply terminal and that controls the current between the secondary battery and the power supply terminal based on the control signal; And a at least one switch provided between the secondary battery and the secondary battery. 6. The battery pack according to claim 5, wherein the switch is a reed switch.