JP2000102182A - Overcharge/overdischarge preventive circuit for secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an overcharge/overdischarge preventive circuit of a small loss for a secondary battery. SOLUTION: A secondary battery Bat is serially connected with a bidirectionally conducting field effect transistor Q1. The bidirectionally conducting field effect transistor Q is turned on and off by a control signal accommodating the voltage level of the secondary battery Bat to prevent the overcharge and overdischarge of the secondary battery Bat. A switch for allowing charging and discharging current to flow and cutting it off is constituted only of the bidirectionally conducting field effect transistor. Due to this structure, a loss can be reduced and the size can also be reduced more than the conventional battery.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a circuit for preventing overcharge and overdischarge of a secondary battery.

[0002]

2. Description of the Related Art Generally, when a secondary battery is overcharged or overdischarged, its characteristics are deteriorated, and it is necessary to prevent such deterioration. In particular, lithium-ion rechargeable batteries may be ignited or exploded if overcharged.
An overdischarge prevention function is indispensable. As a measure to prevent overcharge and overdischarge of the secondary battery, the correlation between the battery voltage and the charge / discharge energy is used. When the battery voltage exceeds the set upper limit, the charge current is cut off. The blocking method is widely used.

FIG. 11 shows a conventional overcharge / overdischarge prevention circuit. MOSFET switches MS1 and MS2 are connected in series to the secondary battery Bat. The diodes D1 and D2 are elements built in the switches MS1 and MS2, respectively. A charging circuit or a load is connected to the terminals V + and V-. The gates of the switches MS1 and MS2 are connected to a battery protection IC. The battery protection IC detects the voltage of the secondary battery Bat, and determines that the voltage is equal to or higher than the set upper limit voltage, determines that the battery is overcharged, and turns off the switch MS2. As a result, the charging current is cut off and overcharging is prevented. When the battery voltage falls below the design lower limit, the battery protection IC determines that the battery is overdischarged and turns off the switch MS1. As a result, the discharge current is cut off and overdischarge is prevented.

[0004]

In the above prior art, the charge / discharge current always flows through the two switches MS1 and MS2, so that the loss due to these switches becomes a problem. That is, besides the energy stored in the battery during charging,
This is because the energy consumed by the two switches must be supplied, and a part of the battery power is discharged by the two switches during discharging, which hinders the effective use of energy. Therefore, it is necessary to reduce the loss of the protection circuit as much as possible. Switch element 2
Since one IC and one IC are used, there is a problem in reducing the size and cost.

An object of the present invention is to provide a circuit for preventing overcharge and overdischarge of a secondary battery which can be reduced in size and reduced in loss.

[0006]

An overcharge / overdischarge prevention circuit for a secondary battery according to the present invention which solves the above-mentioned problems is provided by connecting a bidirectional conduction type MOSFET in series to the secondary battery and controlling the voltage of the secondary battery. The control signal according to the level turns on and off the bidirectional conductive field effect transistor to prevent overcharge and overdischarge of the secondary battery.

[0007]

FIG. 1 shows an overcharge / overdischarge prevention circuit for a secondary battery according to a first embodiment of the present invention. A four-terminal depletion-type N-channel MOSFET Q1 capable of conducting and shutting off bidirectionally is connected in series to the positive electrode side of the secondary battery Bat. A charging circuit or a load is connected to the terminals V + and V-, and a charging / discharging current is supplied to or discharged from the secondary battery Bat through these terminals. The control circuit detects the voltages of the secondary battery Bat and the MOSFET Q1, and controls on / off of the switches M1, M2, and M3 according to the values.

FIG. 2 is a sectional structural view of a depletion-type N-channel MOSFET Q1 used in the first embodiment of the present invention. When the potential of the gate electrode G is equal to or higher than the negative threshold voltage, bidirectional conduction is possible between the drain electrode D and the source electrode S. When the potential of the gate electrode G is equal to or lower than the threshold voltage, the drain electrode D and the source electrode During S, it is off.

First, the overcharge prevention function will be described. When the charging circuit is connected between the terminals V + and V-, the voltage Vds between the drain electrode D and the source electrode S of the MOSFET Q1 becomes a positive value. The control circuit detects that Vds is positive, turns off the switches M1 and M2, and turns on the switch M3. As a result, a positive voltage Vds is applied between the gate electrode G and the source electrode S of the MOSFET Q1, and the MOSFET Q1 is turned on.

When the secondary battery is charged and the battery voltage reaches the set upper limit, the control circuit turns on the switch M1, and the switch M
2. Turn off M3. Then, the gate electrode of the MOSFET Q1 becomes lower in potential than the source electrode S by the voltage of the secondary battery Bat, and the MOSFET Q1 is turned off. As a result, the charging current is cut off, and the secondary battery Bat is prevented from being overcharged.

When the charging current is cut off, the voltage drop due to the internal resistance is eliminated, so that the voltage of the secondary battery Bat decreases. In order to prevent the charging from being started again due to the voltage drop, after the charging is prohibited, the charging prohibited state may be maintained until the secondary battery Bat is discharged to some extent and the voltage becomes equal to or lower than the set value. . When a load is connected between the terminals V + and V- in the charging prohibited state, Vds switches from positive to negative. The control circuit switches M so as to discharge when Vds is negative and to cut off the charging current when Vds is positive.
What is necessary is just to control 1-M3.

In the above description, the switches M1 and M
2 was turned off, and the switch M3 was turned on. However, if the switch M1 is turned off and at least one of the switches M2 and M3 is turned on, charging can be performed similarly. Switch M2
Is turned on, the gate electrode G has the same potential as the source electrode S regardless of the on / off state of the switch M3.
This is because ET Q1 is energized.

As described above, when the switch M3 is turned on and the switch M2 is turned off, the voltage between the gate electrode G and the source electrode S becomes Vds and is positively biased, which is advantageous in terms of reducing loss. It is. Switches M2 and M
When both of them are turned on, discharge is possible as described later. Therefore, it is not necessary to switch the switch when switching between charging and discharging. Further, when charging is prohibited as described above, and when discharging is to be described later, the switch M
2 and M3 are both off, and the two switches are always on or off at the same time. Therefore, switch M
It is not necessary to independently control M2 and M3, and the configuration of the control circuit can be simplified.

Next, the overdischarge prevention function will be described. When a load is connected between the terminals V + and V-, the voltage Vds between the drain electrode D and the source electrode S of the MOSFET Q1 becomes a negative value. The control circuit detects that Vds is negative, turns off the switches M1 and M3, and turns on the switch M2. As a result, a positive bias -Vds is applied between the drain electrode D and the gate electrode G of the MOSFET Q1, and the MOSFET Q1 is turned on.

When the discharge of the secondary battery proceeds and the battery voltage reaches the set lower limit, the control circuit turns on the switch M1 and turns off the switches M2 and M3. Then, the gate electrode of the MOSFET Q1 becomes lower than the drain electrode D by the voltage of the secondary battery Bat, and the MOSFET Q1 is turned off. As a result, the discharge current is cut off, and the secondary battery Bat is prevented from being over-discharged.

When the discharge current is cut off, the voltage drop due to the internal resistance is eliminated, so that the voltage of the secondary battery Bat increases. In order to prevent the discharge from being started again due to this voltage rise, after the discharge is prohibited, the discharge prohibited state may be maintained until the secondary battery Bat is charged to some extent and the voltage becomes equal to or higher than the set value. When a charging circuit is connected between the terminals V + and V- in the discharge prohibited state, Vds switches from negative to positive. The control circuit switches the switch M so as to charge when Vds is positive, and to cut off the discharge current when Vds is negative.
What is necessary is just to control 1-M3.

In the above description, the switches M1, M
3 is turned off and the switch M2 is turned on. However, if the switch M1 is turned off and at least one of the switches M2 and M3 is turned on, the discharge can be performed similarly. Switch M3
Is turned on, the gate electrode G has the same potential as the drain electrode D irrespective of the on / off state of the switch M2.
This is because the SFET Q1 is turned on. As described above, when the switch M2 is turned on and the switch M3 is turned off, the voltage between the gate electrode G and the drain electrode D becomes -Vds
Is positively biased, which is advantageous in reducing the loss. Further, when the switches M2 and M3 are both turned on, as described above, it is not necessary to switch the switches at the time of switching between charging and discharging.
3 need not be controlled independently, and the configuration of the control circuit can be simplified.

Diodes D1 and D2 are formed between the substrate electrode Sb of the MOSFET Q1 and the drain electrode D and the source electrode S, respectively. Since the substrate electrode Sb is connected to the negative electrode side of the secondary battery Bat, it is always reverse biased. Therefore, the diodes D1 and D2 do not conduct, and do not affect the protection operation described above.

The MOSFET Q1 shown in FIG. 2 has a horizontal structure, and it is easy to configure the MOSFET Q1 and the control circuit with one IC. Therefore, since the overcharge / overdischarge protection circuit, which conventionally has been configured with one IC and two switches, can be configured with one IC, downsizing and cost reduction can be achieved.

FIG. 3 is a sectional structural view of a depletion-type N-channel MOSFET Q1 used in an overcharge / overdischarge prevention circuit for a secondary battery according to a second embodiment of the present invention. The configuration of the overcharge / overdischarge prevention circuit for the secondary battery is the same as that of FIG. 1 which is the first embodiment of the present invention. Gate electrode G as in FIG.
Is greater than or equal to the negative threshold voltage, bidirectional conduction is possible between the drain electrode D and the source electrode S, and when the gate electrode G is less than the threshold voltage, the drain electrode D and the source electrode S are turned off. In this embodiment, the depression type N-channel MOSFET Q1 has a vertical structure. Therefore, lower loss can be achieved as compared with the lateral MOSFET of FIG.

FIG. 4 shows an overcharge / overdischarge prevention circuit for a secondary battery according to a third embodiment of the present invention. A four-terminal depletion-type P-channel MOSFET Q1 capable of conducting and shutting off bidirectionally is connected in series to the negative electrode side of the secondary battery Bat. Terminal V
A charging circuit or a load is connected to + and V-, and a charging / discharging current is supplied to or discharged from the secondary battery Bat through this terminal. The control circuit is a rechargeable battery Bat and MOSFET Q
1 is detected, and switches M1, M
2, ON / OFF of M3 is controlled. When the potential of the gate electrode G is equal to or lower than the positive threshold voltage, the MOSFET Q1 can conduct electricity bidirectionally between the drain electrode D and the source electrode S. When the potential of the gate electrode G exceeds the threshold voltage, the drain electrode D And the source electrode S is turned off.

First, the overcharge prevention function will be described. When the charging circuit is connected between the terminals V + and V-, the voltage Vds between the drain electrode D and the source electrode S of the MOSFET Q1 becomes a positive value. The control circuit detects that Vds is positive, turns off the switches M1 and M3, and turns on the switch M2. As a result, a negative voltage -Vds is applied between the gate electrode G and the drain electrode D of the MOSFET Q1, and the MOSFET Q1 is turned on.

When the secondary battery is charged and the battery voltage reaches the set upper limit value, the control circuit turns on the switch M1, and the switch M
2. Turn off M3. Then, the gate electrode of the MOSFET Q1 becomes higher than the drain electrode D by the voltage of the secondary battery Bat, and the MOSFET Q1 is turned off. As a result, the charging current is cut off, and the secondary battery Bat is prevented from being overcharged.

When the charging current is cut off, the voltage drop due to the internal resistance is eliminated, so that the voltage of the secondary battery Bat decreases. In order to prevent the charging from being started again due to the voltage drop, after the charging is prohibited, the charging prohibited state may be maintained until the secondary battery Bat is discharged to some extent and the voltage becomes equal to or lower than the set value. When a load is connected between the terminals V + and V- in the charging prohibited state, Vds switches from positive to negative. The control circuit switches M1 to M so as to discharge when Vds is negative and to cut off the charging current when Vds is positive.
3 may be controlled.

In the above description, the switches M1, M
3 was turned off, and the switch M2 was turned on. However, if the switch M1 is turned off and at least one of the switches M2 and M3 is turned on, charging can be performed similarly. When the switch M3 is turned on, regardless of whether the switch M2 is on or off,
The gate electrode G has the same potential as the drain electrode D, and the MOSFET
This is because Q1 is energized.

As described above, when the switch M2 is turned on and the switch M3 is turned off, the voltage between the gate electrode G and the drain electrode D becomes -Vds, which is negatively biased. It is advantageous. Also switch M
When both M3 and M3 are turned on, discharge is possible as described later. Therefore, it is not necessary to switch the switch when switching between charging and discharging. Further, when charging is prohibited as described above and when discharging is to be described later, the switches M2 and M3 are both off, and the two switches are always on or off at the same time. Therefore, there is no need to independently control the switches M2 and M3, and the configuration of the control circuit can be simplified.

Next, the overdischarge prevention function will be described. When a load is connected between the terminals V + and V-, the voltage Vds between the drain electrode D and the source electrode S of the MOSFET Q1 becomes a negative value. The control circuit detects that Vds is negative, turns off the switches M1 and M2, and turns on the switch M3. As a result, a negative bias Vds is applied between the source electrode S and the gate electrode G of the MOSFET Q1, and the MOSFET Q1 is turned on.

When the discharge of the secondary battery proceeds and the battery voltage reaches the set lower limit, the control circuit turns on the switch M1 and turns off the switches M2 and M3. Then, the gate electrode of the MOSFET Q1 becomes higher in potential than the source electrode S by the voltage of the secondary battery Bat, and the MOSFET Q1 is turned off. As a result, the discharge current is cut off, and the secondary battery Bat is prevented from being over-discharged.

When the discharge current is cut off, the voltage drop due to the internal resistance is eliminated, so that the voltage of the secondary battery Bat increases. In order to prevent the discharge from being started again due to this voltage rise, after the discharge is prohibited, the discharge prohibited state may be maintained until the secondary battery Bat is charged to some extent and the voltage becomes equal to or higher than the set value. When a charging circuit is connected between the terminals V + and V- in the discharge prohibited state, Vds switches from negative to positive. The control circuit switches the switch M so as to charge when Vds is positive, and to cut off the discharge current when Vds is negative.
What is necessary is just to control 1-M3.

In the above description, the switches M1, M
2 was turned off, and the switch M3 was turned on. However, if the switch M1 is turned off and at least one of the switches M2 and M3 is turned on, the discharge can be performed similarly. When the switch M2 is turned on, the gate electrode G has the same potential as the source electrode S regardless of whether the switch M3 is on or off.
This is because ET Q1 is energized. As described above, when the switch M3 is turned on and the switch M2 is turned off, the voltage between the gate electrode G and the source electrode S becomes Vds and is negatively biased, which is advantageous in reducing loss. Further, when the switches M2 and M3 are both turned on, as described above, there is no need to switch the switches at the time of switching between charging and discharging.
Need not be controlled independently, and the configuration of the control circuit can be simplified.

Diodes D1 and D2 are formed between the substrate electrode Sb and the drain electrode D and the source electrode S of the MOSFET Q1, respectively. Since the substrate electrode Sb is connected to the positive electrode side of the secondary battery Bat, it is always reverse biased. Therefore, the diodes D1 and D2 do not conduct, and do not affect the protection operation described above.

As in the first embodiment of the present invention, the MOSFET Q1 may have a horizontal structure or a vertical structure. With the horizontal structure, it is easy to configure the MOSFET Q1 and the control circuit with one IC. Therefore, one conventional IC and switch 2
Since the overcharge / overdischarge protection circuit, which has been configured as a single unit, can be configured with a single IC, downsizing and cost reduction can be achieved. On the other hand, the vertical structure can reduce the loss compared to the horizontal structure.

FIG. 5 shows an overcharge / overdischarge prevention circuit for a secondary battery according to a fourth embodiment of the present invention. A four-terminal enhancement-type N-channel MOSFET Q1 capable of conducting and shutting off bidirectionally is connected in series to the positive electrode side of the secondary battery Bat. A charging circuit or a load is connected to the terminals V + and V-, and a charging / discharging current is supplied to or discharged from the secondary battery Bat through these terminals. Control circuit is rechargeable battery Bat and MOSFET
The voltage of Q1 is detected, and switches M1 to M
5 is turned on and off. When the potential of the gate electrode G is equal to or higher than the positive threshold voltage, the MOSFET Q1 can conduct current bidirectionally between the drain electrode D and the source electrode S. When the potential of the gate electrode G becomes equal to or lower than the threshold voltage, the drain electrode D And the source electrode S is turned off.

First, the overcharge prevention function will be described. When the charging circuit is connected between the terminals V + and V-, the voltage Vds between the drain electrode D and the source electrode S of the MOSFET Q1 becomes a positive value. The control circuit detects that Vds is positive, and first turns on the switches M1 and M4, and switches M2, M3 and M
Turn 5 off. Then, the positive voltage Vc is applied to the capacitor C1.
Is applied. Here, the sign of Vc is assumed to be in the direction shown in the figure. At this time, since the gate electrode G and the source electrode S of the MOSFET Q1 are short-circuited by the switch M4, they have the same potential and are in an off state. Next, after a sufficient time has elapsed for charging the capacitor C1, the switch M2 is turned on, and the switches M1, M3 to M5 are turned off. As a result, a positive voltage Vc is applied between the gate electrode G and the source electrode S of the MOSFET Q1, and the MOSFET Q1 is turned on. At this time, the diode DI1 prevents the charge of the capacitor C1 from being discharged through the built-in diode of the switch M4 and the switch M2.

When the secondary battery is charged and the battery voltage reaches the set upper limit, the control circuit turns on the switches M2 and M5 and turns off the switches M1, M3 and M4. Then capacitor C
At the same time as the negative voltage is applied to 1, the gate electrode G of the MOSFET Q1 becomes lower in potential than the source electrode S by the voltage of the secondary battery Bat, and the MOSFET Q1 is turned off. As a result, the charging current is cut off, and the secondary battery Bat is prevented from being overcharged.

When the charging current is cut off, the voltage drop due to the internal resistance is eliminated, so that the voltage of the secondary battery Bat decreases. In order to prevent the charging from being started again due to the voltage drop, after the charging is prohibited, the charging prohibited state may be maintained until the secondary battery Bat is discharged to some extent and the voltage becomes equal to or lower than the set value. When a load is connected between the terminals V + and V- in the charging prohibited state, Vds switches from positive to negative. The control circuit switches M1 to M so as to discharge when Vds is negative and to cut off the charging current when Vds is positive.
5 may be controlled.

In the above description, the switch M4 is turned off at the time of charging, but it can be charged similarly when it is turned on. Switch M
4 is turned on, the diode DI1 is connected to the capacitor C1 through the built-in diode of the switch M4 and the switch M2.
Is prevented from being discharged, Vc is applied between the gate electrode G and the source electrode S, and the MOSFET Q1 is turned on. When charging is stopped, switch M2
M5 was turned on and switches M1, M3 and M4 were turned off,
Turn on switch M5 and turn off the other, or switch M
1, M4 can be turned on and the others can be turned off to stop charging.

When the switch M5 is turned on and the others are turned off,
The electric charge charged in the capacitor C1 is discharged through the built-in diodes of the switches M5 and M1, the gate electrode G of the MOSFET is lower in potential than the source electrode S by the voltage of the secondary battery Bat, and the MOSFET Q1 is turned off. It is. When the switches M1 and M4 are turned on, the gate electrode G of the MOSFET is set to the same potential as the source electrode S by the switch M4 and the diode DI1 biased in the forward direction.
This is because the MOSFET Q1 is turned off.

Next, the overdischarge prevention function will be described. When a load is connected between the terminals V + and V-, the voltage Vds between the drain electrode D and the source electrode S of the MOSFET Q1 becomes a negative value. The control circuit detects that Vds is negative, turns on the switches M1 and M4, and turns off the switches M2, M3 and M5. Then, a positive voltage Vc is applied to the capacitor C1. At this time, since the gate electrode G and the source electrode S of the MOSFET Q1 are short-circuited by the switch M4, they have the same potential and are in an off state. Next, after a sufficient time has elapsed for the capacitor C1 to be charged, the switch M3 is turned on.
The switches M1, M2, M4, M5 are turned off. As a result, a positive voltage Vc is applied between the gate electrode G and the drain electrode D of the MOSFET Q1, and the MOSFET Q1 is turned on. At this time, the diode DI1 prevents the charge of the capacitor C1 from being discharged through the built-in diode of the switch M4 and the switch M3.

When the discharge of the secondary battery proceeds and the battery voltage reaches the set lower limit, the control circuit turns on the switches M3 and M5 and turns off the switches M1, M2 and M4. Then, at the same time when a negative voltage is applied to the capacitor C1, the gate electrode G of the MOSFET Q1 becomes lower in potential than the drain electrode D by the voltage of the secondary battery Bat, and the MOSFET Q1 is turned off. As a result, the discharge current is cut off, and the secondary battery Bat is prevented from being over-discharged.

When the discharge current is cut off, the voltage drop due to the internal resistance is eliminated, so that the voltage of the secondary battery Bat increases. In order to prevent the discharge from being started again due to this voltage rise, after the discharge is prohibited, the discharge prohibited state may be maintained until the secondary battery Bat is charged to some extent and the voltage becomes equal to or higher than the set value. When a charging circuit is connected between the terminals V + and V- in the discharge prohibited state, Vds switches from negative to positive. The control circuit switches the switch M so as to charge when Vds is positive, and to cut off the discharge current when Vds is negative.
What is necessary is just to control 1-M5.

In the above description, the switch M4 is turned off at the time of discharging, but it can be discharged similarly when it is turned on. Switch M
4 is turned on, the diode DI1 is connected to the capacitor C1 through the built-in diode of the switch M4 and the switch M3.
Is prevented from being discharged, Vc is applied between the gate electrode G and the drain electrode D, and the MOSFET Q1 is turned on.

When the discharge is stopped, the switches M3 and M5 are turned on and the switches M1, M2 and M4 are turned off. However, the switch M5 is turned on and the others are turned off, or the switches M1 and M5 are turned off.
Similarly, the discharge can be stopped by turning on the switch 4 and turning off the other switches. When the switch M5 is turned on and the others are turned off, the electric charge charged in the capacitor C1 is changed to the switches M5 and M
1 through the internal diode, the gate electrode G of the MOSFET becomes lower than the drain electrode D by the voltage of the secondary battery Bat, and the MOSFET Q1 is turned off.
When the switches M1 and M4 are turned on, the switch M4
And the forward biased diode DI1
The gate electrode G of the SFET becomes the same potential as the source electrode S and becomes MOSF
This is because ET Q1 is turned off.

Diodes D1 and D2 are formed between the substrate electrode Sb and the drain electrode D and the source electrode S of the MOSFET Q1, respectively. Since the substrate electrode Sb is connected to the negative electrode side of the secondary battery Bat, it is always reverse biased. Therefore, the diodes D1 and D2 do not conduct, and do not affect the protection operation described above.

As in the first embodiment of the present invention described above, the MOSFET Q1 may have a horizontal structure or a vertical structure. With the horizontal structure, it is easy to configure the MOSFET Q1 and the control circuit with one IC. Therefore, one conventional IC and switch 2
Since the overcharge / overdischarge protection circuit, which has been configured as a single unit, can be configured with a single IC, downsizing and cost reduction can be achieved. On the other hand, the vertical structure can reduce the loss compared to the horizontal structure.

FIG. 6 shows a circuit for preventing overcharge and overdischarge of a secondary battery according to a fifth embodiment of the present invention. A four-terminal enhancement-type P-channel MOSFET Q1 capable of conducting and shutting off bidirectionally is connected in series to the negative electrode side of the secondary battery Bat. A charging circuit or a load is connected to the terminals V + and V-, and a charging / discharging current is supplied to or discharged from the secondary battery Bat through these terminals. Control circuit is rechargeable battery Bat and MOSFET
The voltage of Q1 is detected, and switches M1 to M
5 is turned on and off. When the potential of the gate electrode G is equal to or lower than the negative threshold voltage, the MOSFET Q1 can conduct electricity bidirectionally between the drain electrode D and the source electrode S. When the potential of the gate electrode G exceeds the threshold voltage, the drain electrode D And the source electrode S is turned off.

First, the overcharge prevention function will be described. When the charging circuit is connected between the terminals V + and V-, the voltage Vds between the drain electrode D and the source electrode S of the MOSFET Q1 becomes a positive value. The control circuit detects that Vds is positive, and first turns on the switches M1 and M4, and switches M2, M3 and M
Turn 5 off. Then, the positive voltage Vc is applied to the capacitor C1.
Is applied. Here, the sign of Vc is assumed to be in the direction shown in the figure. At this time, since the gate electrode G and the drain electrode D of the MOSFET Q1 are short-circuited by the switch M4, they have the same potential and are in an off state. Next, after a sufficient time has elapsed for the capacitor C1 to be charged, the switch M2
And switches M1 and M3 to M5 are turned off. As a result, a negative voltage -Vc is applied between the gate electrode G and the drain electrode D of the MOSFET Q1, and the MOSFET Q1 is turned on. At this time, the diode DI1 prevents the charge of the capacitor C1 from being discharged through the built-in diode of the switch M4 and the switch M2.

When the secondary battery is charged and the battery voltage reaches the set upper limit, the control circuit turns on the switches M2 and M5 and turns off the switches M1, M3 and M4. Then capacitor C
At the same time as the negative voltage is applied to 1, the gate electrode G of the MOSFET Q1 becomes higher in potential than the drain electrode D by the voltage of the secondary battery Bat, and the MOSFET Q1 is turned off. As a result, the charging current is cut off, and the secondary battery Bat is prevented from being overcharged.

When the charging current is cut off, the voltage drop due to the internal resistance is eliminated, so that the voltage of the secondary battery Bat decreases. In order to prevent the charging from being started again due to the voltage drop, after the charging is prohibited, the charging prohibited state may be maintained until the secondary battery Bat is discharged to some extent and the voltage becomes equal to or lower than the set value. When a load is connected between the terminals V + and V- in the charging prohibited state, Vds switches from positive to negative. The control circuit switches M1 to M so as to discharge when Vds is negative and to cut off the charging current when Vds is positive.
5 may be controlled.

In the above description, the switch M4 is turned off at the time of charging, but it can be charged similarly when it is turned on. Switch M
4 is turned on, the diode DI1 is connected to the capacitor C1 through the built-in diode of the switch M4 and the switch M2.
Is prevented from being discharged, -Vc is applied between the gate electrode G and the drain electrode D, and the MOSFET Q1 is turned on. When charging is stopped, switch M
2, M5 is turned on, and switches M1, M3, and M4 are turned off. However, charging can be stopped similarly by turning on switch M5 and turning off the other, or turning on switches M1 and M4 and turning off the other. When the switch M5 is turned on and the others are turned off, the charge stored in the capacitor C1 is changed to the switch M5,
Discharge through the built-in diode of switch M1, MOSFET
Is higher than the drain electrode D by the voltage of the secondary battery Bat, and the MOSFET Q1 is turned off. When the switches M1 and M4 are turned on, the switch M4 and the forward-biased diode DI1 are turned on.
As a result, the gate electrode G of the MOSFET has the same potential as the drain electrode D, and the MOSFET Q1 is turned off. Next, the overdischarge prevention function will be described. Load is applied to terminals V +, V-
When connected between them, the voltage Vds between the drain electrode D and the source electrode S of the MOSFET Q1 becomes a negative value. The control circuit is Vds
Is negative, switches M1 and M4 are turned on, and switches M2, M3 and M5 are turned off. Then, a positive voltage Vc is applied to the capacitor C1. At this time MO
The gate electrode G and drain electrode D of SFET Q1 are switches M
4, since they are short-circuited, they have the same potential and are in an off state. Next, after a sufficient time has elapsed for charging the capacitor C1, the switch M3 is turned on, and the switches M1 and M
2, M4 and M5 are turned off. As a result, a negative voltage -Vc is applied between the gate electrode G and the source electrode S of the MOSFET Q1, and the MOSFET Q1 is turned on. At this time, the diode DI1 prevents the charge of the capacitor C1 from being discharged through the built-in diode of the switch M4 and the switch M3.

When the discharge of the secondary battery proceeds and the battery voltage reaches the set lower limit, the control circuit turns on the switches M3 and M5 and turns off the switches M1, M2 and M4. Then, at the same time as the negative voltage is applied to the capacitor C1, the gate electrode G of the MOSFET Q1 becomes higher in potential than the source electrode S by the voltage of the secondary battery Bat, and the MOSFET Q1 is turned off. As a result, the discharge current is cut off, and the secondary battery Bat is prevented from being over-discharged.

When the discharge current is cut off, the voltage drop due to the internal resistance is eliminated, so that the voltage of the secondary battery Bat increases. In order to prevent the discharge from being started again due to this voltage rise, after the discharge is prohibited, the discharge prohibited state may be maintained until the secondary battery Bat is charged to some extent and the voltage becomes equal to or higher than the set value. When a charging circuit is connected between the terminals V + and V- in the discharge prohibited state, Vds switches from negative to positive. The control circuit switches the switch M so as to charge when Vds is positive, and to cut off the discharge current when Vds is negative.
What is necessary is just to control 1-M5.

In the above description, the switch M4 is turned off at the time of discharging, but it can be discharged even when it is turned on. Switch M
4 is turned on, the diode DI1 is connected to the capacitor C1 through the built-in diode of the switch M4 and the switch M3.
Is prevented from being discharged, Vc is applied between the gate electrode G and the drain electrode D, and the MOSFET Q1 is turned on.

When the discharge is stopped, the switches M3 and M5 are turned on and the switches M1, M2 and M4 are turned off. However, the switch M5 is turned on and the others are turned off or the switches M1 and M5 are turned off.
Similarly, the discharge can be stopped by turning on the switch 4 and turning off the other switches. When the switch M5 is turned on and the others are turned off, the electric charge charged in the capacitor C1 is changed to the switches M5 and M
This is because the discharge through the internal diode 1 causes the gate electrode G of the MOSFET to be higher than the source electrode s by the voltage of the secondary battery Bat, and the MOSFET Q1 is turned off. When the switches M1 and M4 are turned on, the MOSF is turned on by the switch M4 and the diode DI1 biased in the forward direction.
The gate electrode G of the ET becomes the same potential as the source electrode S, and the MOSFET
This is because Q1 is turned off.

Diodes D1 and D2 are formed between the substrate electrode Sb and the drain electrode D and the source electrode S of the MOSFET Q1, respectively. Since the substrate electrode Sb is connected to the positive electrode side of the secondary battery Bat, it is always reverse biased. Therefore, the diodes D1 and D2 do not conduct, and do not affect the protection operation described above.

As in the first embodiment of the present invention described above, the MOSFET Q1 may have a horizontal structure or a vertical structure. With the horizontal structure, it is easy to configure the MOSFET Q1 and the control circuit with one IC. Therefore, the overcharge / overdischarge protection circuit conventionally constituted by one IC and two switches is replaced by the IC1.
Since it can be constituted by individual components, it is possible to reduce the size and cost. On the other hand, the vertical structure can reduce the loss compared to the horizontal structure.

FIG. 7 shows an overcharge / overdischarge prevention circuit for a secondary battery according to a sixth embodiment of the present invention. A four-terminal enhancement-type N-channel MOSFET Q1 capable of conducting and shutting off bidirectionally is connected in series to the positive electrode side of the secondary battery Bat. A charging circuit or a load is connected to the terminals V + and V-, and a charging / discharging current is supplied to or discharged from the secondary battery Bat through these terminals. Control circuit is rechargeable battery Bat and MOSFET
The voltage of Q1 is detected, and switches M1, M
2 is turned on and off. When the potential of the gate electrode G is equal to or higher than the positive threshold voltage, the MOSFET Q1 can conduct current bidirectionally between the drain electrode D and the source electrode S. When the potential of the gate electrode G becomes equal to or lower than the threshold voltage, the drain electrode D And the source electrode S is turned off.

First, the overcharge prevention function will be described. When the charging circuit is connected between the terminals V + and V-, the voltage Vds between the drain electrode D and the source electrode S of the MOSFET Q1 becomes a positive value. The control circuit detects that Vds is positive, and first turns on the switches M1 and M2. Then reactor L1
A current IL flows in the illustrated direction. At this time, the MOSFET
Since the switch M2 is on, the gate electrode G of Q1 has a lower potential than the source electrode S by the voltage of the secondary battery Bat, and is in an off state. Next, after a certain amount of current IL flows through reactor L1, switch M1 is turned on and switch M2 is turned off. Then, the current IL becomes the diode DI1,
The current flows into the gate electrode G of the MOSFET Q1 through the damping resistor R1. With this current, the parasitic capacitance of the MOSFET is charged, and the gate electrode G becomes higher in potential than the source electrode S.
MOSFET Q1 is energized. At this time, the diode DI
1 prevents the current IL from flowing backward to lower the potential of the gate electrode G.

When the secondary battery is charged and the battery voltage reaches the set upper limit, the control circuit turns on the switch M2,
Turn 1 off. Then, the charge stored in the gate electrode G is discharged, and the gate electrode G is separated from the source electrode S by the secondary battery Ba.
The potential becomes lower by the voltage of t, and the MOSFET Q1 is turned off. As a result, the charging current is cut off, and the secondary battery Bat is prevented from being overcharged.

When the charging current is cut off, the voltage drop due to the internal resistance is eliminated, so that the voltage of the secondary battery Bat decreases. In order to prevent the charging from being started again due to the voltage drop, after the charging is prohibited, the charging prohibited state may be maintained until the secondary battery Bat is discharged to some extent and the voltage becomes equal to or lower than the set value. . When a load is connected between the terminals V + and V- in the charging prohibited state, Vds switches from positive to negative. The control circuit discharges when Vds is negative,
In the positive case, the switches M1,
M2 may be controlled.

Next, the overdischarge prevention function will be described. When a load is connected between the terminals V + and V-, the voltage Vds between the drain electrode D and the source electrode S of the MOSFET Q1 becomes a negative value. The control circuit detects that Vds is negative, and turns on the switches M1 and M2. Then, current IL flows in reactor L1 in the illustrated direction. At this time, since the switch M2 is on, the gate electrode G of the MOSFET Q1 becomes lower in potential than the source electrode S by the voltage of the secondary battery Bat, and is in the off state. Next, a certain amount of current I flows through reactor L1.
After L flows, the switch M1 is turned on and the switch M2 is turned off.

Then, the current IL flows into the gate electrode G of the MOSFET Q1 through the diode DI1 and the damping resistor R1. With this current, the parasitic capacitance of the MOSFET is charged, and the potential of the gate electrode G becomes higher than that of the drain electrode D.
SFET Q1 is turned on. At this time, the diode DI1
Prevents the current IL from flowing backward and the potential of the gate electrode G from lowering.

When the discharge of the secondary battery proceeds and the battery voltage reaches the set lower limit, the control circuit turns on the switch M2 and turns off the switch M1. Then, the charge stored in the gate electrode G is discharged, the gate electrode G becomes lower in potential than the drain electrode D by the voltage of the secondary battery Bat, and the MOSFET Q1 is turned off. As a result, the discharge current is cut off and the secondary battery Bat
To prevent overdischarge.

When the discharge current is cut off, the voltage drop due to the internal resistance is eliminated, so that the voltage of the secondary battery Bat increases. In order to prevent the discharge from being started again due to this voltage rise, after the discharge is prohibited, the discharge prohibited state may be maintained until the secondary battery Bat is charged to some extent and the voltage becomes equal to or higher than the set value. When a charging circuit is connected between the terminals V + and V- in the discharge prohibited state, Vds switches from negative to positive. The control circuit switches the switch M so as to charge when Vds is positive, and to cut off the discharge current when Vds is negative.
1, M2 may be controlled.

Diodes D1 and D2 are formed between the substrate electrode Sb and the drain electrode D and the source electrode S of the MOSFET Q1, respectively. Since the substrate electrode Sb is connected to the negative electrode side of the secondary battery Bat, it is always reverse biased. Therefore, the diodes D1 and D2 do not conduct, and do not affect the protection operation described above.

As in the first embodiment of the present invention, the MOSFET Q1 may have a horizontal structure or a vertical structure. With the horizontal structure, it is easy to configure the MOSFET Q1 and the control circuit with one IC. Therefore, one conventional IC and switch 2
Since the overcharge / overdischarge protection circuit, which has been configured as a single unit, can be configured with a single IC, downsizing and cost reduction can be achieved. On the other hand, the vertical structure can reduce the loss compared to the horizontal structure.

FIG. 8 shows a circuit for preventing overcharge and overdischarge of a secondary battery according to a seventh embodiment of the present invention. A four-terminal enhancement-type P-channel MOSFET Q1 capable of conducting and shutting off bidirectionally is connected in series to the negative electrode side of the secondary battery Bat. A charging circuit or a load is connected to the terminals V + and V-, and a charging / discharging current is supplied to or discharged from the secondary battery Bat through these terminals. Control circuit is rechargeable battery Bat and MOSFET
The voltage of Q1 is detected, and switches M1, M
2 is turned on and off. When the potential of the gate electrode G is equal to or lower than the negative threshold voltage, the MOSFET Q1 can conduct electricity bidirectionally between the drain electrode D and the source electrode S. When the potential of the gate electrode G exceeds the threshold voltage, the drain electrode D And the source electrode S is turned off.

First, the overcharge prevention function will be described. When the charging circuit is connected between the terminals V + and V-, the voltage Vds between the drain electrode D and the source electrode S of the MOSFET Q1 becomes a positive value. The control circuit detects that Vds is positive, and first turns on the switches M1 and M2. Then reactor L1
A current IL flows in the illustrated direction. At this time, the MOSFET
Since the switch M2 is on, the gate electrode G of Q1 has a higher potential than the source electrode S by the voltage of the secondary battery Bat, and is off. Next, after a certain amount of current IL flows through reactor L1, switch M1 is turned on and switch M2 is turned off. Then, the current IL becomes the diode DI
1, flows out from the gate electrode G of the MOSFET Q1 through the damping resistor R1. This current charges the parasitic capacitance of the MOSFET, the gate electrode G becomes lower in potential than the source electrode S, and the MOSFET Q1 is turned on. At this time, the diode DI1 prevents the current IL from flowing backward and the potential of the gate electrode G from rising.

When the secondary battery is charged and the battery voltage reaches the set upper limit, the control circuit turns on the switch M2,
Turn 1 off. Then, the charge stored in the gate electrode G is discharged, and the gate electrode G is separated from the source electrode S by the secondary battery Ba.
The potential becomes high by the voltage of t, and the MOSFET Q1 is turned off. As a result, the charging current is cut off, and the secondary battery Bat is prevented from being overcharged.

When the charging current is cut off, the voltage drop due to the internal resistance is eliminated, so that the voltage of the secondary battery Bat decreases. In order to prevent the charging from being started again due to the voltage drop, after the charging is prohibited, the charging prohibited state may be maintained until the secondary battery Bat is discharged to some extent and the voltage becomes equal to or lower than the set value. . When a load is connected between the terminals V + and V- in the charging prohibited state, Vds switches from positive to negative. The control circuit discharges when Vds is negative,
In the positive case, the switches M1,
M2 may be controlled.

Next, the overdischarge prevention function will be described. When a load is connected between the terminals V + and V-, the voltage Vds between the drain electrode D and the source electrode S of the MOSFET Q1 becomes a negative value. The control circuit detects that Vds is negative, and turns on the switches M1 and M2. Then, current IL flows in reactor L1 in the illustrated direction. At this time, since the switch M2 is on, the gate electrode G of the MOSFET Q1 becomes higher in potential than the source electrode S by the voltage of the secondary battery Bat, and is off. Next, a certain amount of current I flows through reactor L1.
After L flows, the switch M1 is turned on and the switch M2 is turned off. Then, the current IL flows out of the gate electrode G of the MOSFET Q1 through the diode DI1 and the damping resistor R1. This current charges the parasitic capacitance of the MOSFET, causing the gate electrode G to have a lower potential than the drain electrode D and
SFET Q1 is turned on. At this time, the diode DI1
Prevents the current IL from flowing backward and the potential of the gate electrode G from lowering.

When the discharge of the secondary battery proceeds and the battery voltage reaches the set lower limit, the control circuit turns on the switch M2 and turns off the switch M1. Then, the charge stored in the gate electrode G is discharged, the gate electrode G becomes lower in potential than the drain electrode D by the voltage of the secondary battery Bat, and the MOSFET Q1 is turned off. As a result, the discharge current is cut off and the secondary battery Bat
To prevent overdischarge.

When the discharge current is cut off, the voltage drop due to the internal resistance is eliminated, so that the voltage of the secondary battery Bat increases. In order to prevent the discharge from being started again due to this voltage rise, after the discharge is prohibited, the discharge prohibited state may be maintained until the secondary battery Bat is charged to some extent and the voltage becomes equal to or higher than the set value. When a charging circuit is connected between the terminals V + and V- in the discharge prohibited state, Vds switches from negative to positive. The control circuit switches the switch M so as to charge when Vds is positive, and to cut off the discharge current when Vds is negative.
1, M2 may be controlled.

Diodes D1 and D2 are formed between the substrate electrode Sb and the drain electrode D and the source electrode S of the MOSFET Q1, respectively. Since the substrate electrode Sb is connected to the negative electrode side of the secondary battery Bat, it is always reverse biased. Therefore, the diodes D1 and D2 do not conduct, and do not affect the protection operation described above.

As in the first embodiment of the present invention, the MOSFET Q1 may have a horizontal structure or a vertical structure. With the horizontal structure, it is easy to configure the MOSFET Q1 and the control circuit with one IC. Therefore, one conventional IC and switch 2
Since the overcharge / overdischarge protection circuit, which has been configured as a single unit, can be configured with a single IC, downsizing and cost reduction can be achieved. On the other hand, the vertical structure can reduce the loss compared to the horizontal structure.

FIG. 9 shows an overcharge / overdischarge prevention circuit for a secondary battery according to an eighth embodiment of the present invention. An enhancement-type N-channel MOSFET Q1 that can be turned on and off bidirectionally is connected in series to the negative electrode side of the secondary battery Bat. A charging circuit or a load is connected to the terminals V + and V-, and a charging / discharging current is supplied to or discharged from the secondary battery Bat through these terminals. The control circuit detects the voltage of the secondary battery Bat and the voltage of the MOSFET Q1, and switches M1, M2, M3 according to the detected values.
On and off. MOSFET Q1 has a gate electrode G
Is more than the positive threshold voltage, bidirectional conduction is possible between the drain electrode D and the source electrode S, and the gate electrode G
Becomes lower than the threshold voltage, the drain electrode D and the source electrode S are turned off.

First, the overcharge prevention function will be described. When the charging circuit is connected between the terminals V + and V-, the voltage Vds between the drain electrode D and the source electrode S of the MOSFET Q1 becomes a positive value. The control circuit detects that Vds is positive, turns on the switch M1, and turns off the switches M2 and M3. As a result, the gate electrode of MOSFET Q1 is 2
The potential becomes higher by the voltage of the secondary battery Bat, and the MOSFET Q1 is turned on.

When the secondary battery is charged and the battery voltage reaches the set upper limit, the control circuit turns off the switch M1,
2. Turn on M3. Then the gate electrode G of MOSFET Q1
Becomes the same potential as the source electrode S, and the MOSFET Q1 is turned off. As a result, the charging current is cut off, and the secondary battery Bat is prevented from being overcharged. At this time, the diode D
I2 becomes reverse-biased and switches M2 and M3
Prevents current from flowing through.

When the charging current is cut off, the voltage drop due to the internal resistance is eliminated, so that the voltage of the secondary battery Bat decreases. In order to prevent the charging from being started again due to the voltage drop, after the charging is prohibited, the charging prohibited state may be maintained until the secondary battery Bat is discharged to some extent and the voltage becomes equal to or lower than the set value. When a load is connected between the terminals V + and V- in the charging prohibited state, Vds switches from positive to negative. The control circuit switches M1 to M so as to discharge when Vds is negative and to cut off the charging current when Vds is positive.
3 may be controlled.

In the above description, when charging is stopped, the switch M
2 and M3 were both turned on. However, even if the switch M3 is turned off, charging can be stopped similarly. Regardless of whether the switch M3 is on or off, the gate electrode G has the same potential as the source electrode S because the switch M2 is on, and the MOSFET Q
1 is off. Also, the current flowing through the switches M2 and M3 is cut off by the diode DI2.

However, both the switches M2 and M3 are off during the charging described above and during the discharging described below. Therefore, when the charging is stopped, the switches M2 and M3 are both turned on. As will be described later, even when the discharging is stopped, the switches M2 and M3 are turned off.
If both M3 are on, the two switches are always on or off at the same time. Therefore, switch M
It is not necessary to independently control M2 and M3, and the configuration of the control circuit can be simplified.

Next, the overdischarge prevention function will be described. When a load is connected between the terminals V + and V-, the voltage Vds between the drain electrode D and the source electrode S of the MOSFET Q1 becomes a negative value. The control circuit detects that Vds is negative, turns on the switch M1, and turns off the switches M2 and M3. As a result, the gate electrode of MOSFET Q1 is two
The potential becomes higher by the voltage of the secondary battery Bat, and the MOSFET Q1 is turned on.

When the discharge of the secondary battery proceeds and the battery voltage reaches the set lower limit, the control circuit turns off the switch M1 and turns on the switches M2 and M3. Then, the gate electrode G of the MOSFET Q1 has the same potential as the drain electrode D, and the MOSFET Q1 is turned off. As a result, the discharge current is cut off and the secondary battery Ba
t is prevented from being over-discharged. At this time, the diode DI1 is reverse-biased to prevent a current from flowing through the switches M3 and M2.

When the discharge current is cut off, the voltage drop due to the internal resistance is eliminated, so that the voltage of the secondary battery Bat increases. In order to prevent the discharge from being started again due to this voltage rise, after the discharge is prohibited, the discharge prohibited state may be maintained until the secondary battery Bat is charged to some extent and the voltage becomes equal to or higher than the set value. . When a charging circuit is connected between the terminals V + and V- in the discharge prohibited state, Vds switches from negative to positive. The control circuit switches the switch M so as to charge when Vds is positive, and to cut off the discharge current when Vds is negative.
What is necessary is just to control 1-M3.

In the above description, when the discharge is stopped, the switch M
2 and M3 were both turned on. However, even when the switch M2 is turned off, the discharge can be stopped similarly. Since the switch M3 is on regardless of whether the switch M2 is on or off, the gate electrode G has the same potential as the drain electrode D, and the MOSFET
Q1 is turned off. Also, the current flowing through the switches M2 and M3 is cut off by the diode DI1.

However, if the switches M2 and M3 are both turned on when the discharge is stopped, the two switches are always turned on or off simultaneously as described above. Therefore, there is no need to independently control the switches M2 and M3, and the configuration of the control circuit can be simplified.

MOSFET Q1 has built-in diodes D1 and D
2 are formed. However, they are connected in series in the reverse direction, do not conduct, and do not affect the protection operation described above.

As in the first embodiment of the present invention, the MOSFET Q1 may have a horizontal structure or a vertical structure. With the horizontal structure, it is easy to configure the MOSFET Q1 and the control circuit with one IC. Therefore, one conventional IC and switch 2
Since the overcharge / overdischarge protection circuit, which has been configured as a single unit, can be configured with a single IC, downsizing and cost reduction can be achieved. On the other hand, the vertical structure can reduce the loss compared to the horizontal structure.

FIG. 10 shows an overcharge / overdischarge prevention circuit for a secondary battery according to a ninth embodiment of the present invention. Secondary battery Bat
An enhancement-type P-channel MOSFET Q1 that can be turned on and off bidirectionally is connected in series to the positive electrode side of. A charging circuit or a load is connected to the terminals V + and V-, and a charging / discharging current is supplied to or discharged from the secondary battery Bat through these terminals. The control circuit detects the voltage of the secondary battery Bat and the voltage of the MOSFET Q1, and switches M1, M2, M
3 is turned on and off. When the potential of the gate electrode G is equal to or lower than the negative threshold voltage, the MOSFET Q1 can conduct electricity bidirectionally between the drain electrode D and the source electrode S. When the potential of the gate electrode G exceeds the threshold voltage, the drain electrode D And the source electrode S is turned off.

First, the overcharge prevention function will be described. When the charging circuit is connected between the terminals V + and V-, the voltage Vds between the drain electrode D and the source electrode S of the MOSFET Q1 becomes a positive value. The control circuit detects that Vds is positive, turns on the switch M1, and turns off the switches M2 and M3. As a result, the gate electrode of the MOSFET Q1 becomes lower in potential than the drain electrode D by the voltage of the secondary battery Bat, and the MOSFET Q1 is turned on.

When the secondary battery is charged and the battery voltage reaches the set upper limit, the control circuit turns off the switch M1,
2. Turn on M3. Then the gate electrode G of MOSFET Q1
Becomes the same potential as the drain electrode D, and the MOSFET Q1 is turned off. As a result, the charging current is cut off and the secondary battery Bat
To prevent overcharging. At this time, the diode DI2 is reverse-biased and the switches M2 and M
3 prevents current from flowing.

When the charging current is cut off, the voltage drop due to the internal resistance is eliminated, so that the voltage of the secondary battery Bat decreases. In order to prevent the charging from being started again due to the voltage drop, after the charging is prohibited, the charging prohibited state may be maintained until the secondary battery Bat is discharged to some extent and the voltage becomes equal to or lower than the set value. . When a load is connected between the terminals V + and V- in the charging prohibited state, Vds switches from positive to negative. The control circuit discharges when Vds is negative,
In the positive case, the switches M1
What is necessary is just to control M3.

In the above description, when charging is stopped, the switch M
2 and M3 were both turned on. However, even if the switch M2 is turned off, charging can be stopped similarly. Since the switch M3 is on regardless of whether the switch M2 is on or off, the gate electrode G has the same potential as the drain electrode D, and the MOSFET
Q1 is off. Also, the current flowing through the switches M2 and M3 is cut off by the diode DI2.

However, the switches M2 and M3 are both off during the charging described above and during the discharging described later. Therefore, when the charging is stopped, the switches M2 and M3 are both turned on. As will be described later, even when the discharging is stopped, the switches M2 and M3 are turned off.
If both M3 are on, the two switches are always on or off at the same time. Therefore, switch M2,
It is not necessary to control M3 independently, and the configuration of the control circuit can be simplified.

Next, the overdischarge prevention function will be described. When a load is connected between the terminals V + and V-, the voltage Vds between the drain electrode D and the source electrode S of the MOSFET Q1 becomes a negative value. The control circuit detects that Vds is negative, turns on the switch M1, and turns off the switches M2 and M3. As a result, the gate electrode of the MOSFET Q1 becomes lower in potential than the source electrode S by the voltage of the secondary battery Bat, and the MOSFET Q1 is turned on.

When the discharge of the secondary battery proceeds and the battery voltage reaches the set lower limit, the control circuit turns off the switch M1 and turns on the switches M2 and M3. Then, the gate electrode G of the MOSFET Q1 has the same potential as the source electrode S, and the MOSFET Q1 is turned off. As a result, the discharge current is cut off and the secondary battery Bat
To prevent overdischarge. At this time, the diode DI1 is reverse-biased and the switches M3 and M
2 to prevent current from flowing.

When the discharge current is cut off, the voltage drop due to the internal resistance is eliminated, so that the voltage of the secondary battery Bat increases. In order to prevent the discharge from being started again due to this voltage rise, after the discharge is prohibited, the discharge prohibited state may be maintained until the secondary battery Bat is charged to some extent and the voltage becomes equal to or higher than the set value. When a charging circuit is connected between the terminals V + and V- in the discharge prohibited state, Vds switches from negative to positive. The control circuit switches the switch M so as to charge when Vds is positive, and to cut off the discharge current when Vds is negative.
What is necessary is just to control 1-M3.

In the above description, when the discharge is stopped, the switch M
2 and M3 were both turned on. However, even when the switch M3 is turned off, the discharge can be stopped similarly. Regardless of whether the switch M3 is on or off, the gate electrode G has the same potential as the source electrode S because the switch M2 is on, and the MOSFET Q
1 is off. Also, the current flowing through the switches M2 and M3 is cut off by the diode DI1.

However, if the switches M2 and M3 are both turned on when the discharge is stopped, the two switches are always turned on or off simultaneously as described above. Therefore, there is no need to independently control the switches M2 and M3, and the configuration of the control circuit can be simplified.

MOSFET Q1 has built-in diodes D1 and D
2 are formed. However, they are connected in series in the reverse direction, do not conduct, and do not affect the protection operation described above.

As in the first embodiment of the present invention, the MOSFET Q1 may have a horizontal structure or a vertical structure. With the horizontal structure, it is easy to configure the MOSFET Q1 and the control circuit with one IC. Therefore, one conventional IC and switch 2
Since the overcharge / overdischarge protection circuit, which has been configured as a single unit, can be configured with a single IC, downsizing and cost reduction can be achieved. On the other hand, the vertical structure can reduce the loss compared to the horizontal structure.

[0102]

As described above with reference to the drawings, the overcharge / overdischarge prevention circuit for a secondary battery according to the present invention comprises connecting a bidirectional MOSFET in series with the secondary battery, and controlling the voltage of the secondary battery. The control signal according to the level turns on and off the bidirectional conductive field effect transistor to prevent overcharge and overdischarge of the secondary battery. In the present invention, which has conventionally been constituted by two field effect transistors, but is constituted by one bidirectional conduction field effect transistor, the size and loss can be reduced. Furthermore, if a lateral bidirectional conduction field-effect transistor is used, it can be constituted by a single IC including a control circuit, and the size can be significantly reduced.

[Brief description of the drawings]

FIG. 1 is an overcharge / overdischarge prevention circuit diagram of a secondary battery according to a first embodiment of the present invention.

FIG. 2 is a sectional view of a bidirectional conducting lateral field effect transistor used in the first embodiment of the present invention.

FIG. 3 is a cross-sectional view of a bidirectional conducting vertical field effect transistor used in a second embodiment of the present invention.

FIG. 4 is an overcharge / overdischarge prevention circuit diagram of a secondary battery according to a third embodiment of the present invention.

FIG. 5 is an overcharge / overdischarge prevention circuit diagram of a secondary battery according to a fourth embodiment of the present invention.

FIG. 6 is a circuit diagram of an overcharge / overdischarge prevention circuit for a secondary battery according to a fifth embodiment of the present invention.

FIG. 7 is a circuit diagram of an overcharge / overdischarge prevention circuit for a secondary battery according to a sixth embodiment of the present invention.

FIG. 8 is an overcharge / overdischarge prevention circuit diagram of a secondary battery according to a seventh embodiment of the present invention.

FIG. 9 is a circuit diagram of an overcharge / overdischarge prevention circuit for a secondary battery according to an eighth embodiment of the present invention.

FIG. 10 is a circuit diagram of an overcharge / overdischarge prevention circuit for a secondary battery according to a ninth embodiment of the present invention.

FIG. 11 is a circuit diagram of a conventional overcharge / overdischarge prevention of a secondary battery.

[Explanation of symbols]

Bat: secondary battery, Q1: bidirectional conductive field effect transistor, D: drain electrode, S: source electrode, G: gate electrode, Sb: substrate electrode, D1, D2: diode with built-in field effect transistor, DI1, DI2 ...
Diode, M1 to M3, MS1, MS2 ... MOSFET, V
+, V -... terminals.

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Hideki Miyazaki 7-1-1, Omika-cho, Hitachi City, Ibaraki Prefecture F-term in Hitachi Research Laboratory, Hitachi Ltd. 5G003 AA01 BA01 CA14 CC02 DA07 DA13 GA01

Claims (8)

[Claims] 1. A rechargeable battery, a four-terminal depletion-type N-channel MOSFET connected in series to a positive electrode of the rechargeable battery and capable of conducting and shutting off bidirectionally, and the voltage corresponding to the voltage of the rechargeable battery. Means for energizing or deactivating the depletion type N-channel MOSFET;
An overcharge / overdischarge prevention circuit for a secondary battery, wherein a substrate electrode of a channel MOSFET is connected to a negative electrode side of the secondary battery. 2. A rechargeable battery, a four-terminal depletion-type P-channel MOSFET connected in series to a negative electrode of the rechargeable battery and capable of conducting and shutting off bidirectionally, and the voltage corresponding to the voltage of the rechargeable battery. Means for turning on or off the depletion-type P-channel MOSFET;
An overcharge / overdischarge prevention circuit for a secondary battery, wherein a substrate electrode of a channel MOSFET is connected to a positive electrode side of the secondary battery. 3. A rechargeable battery, a four-terminal enhancement-type N-channel MOSFET connected in series to a positive electrode of the rechargeable battery and capable of conducting and shutting off bidirectionally, a capacitor, and
Means for positively or negatively charging the capacitor with the voltage of the secondary battery, and applying the voltage of the capacitor charged positively or negatively according to the voltage of the secondary battery to the gate electrode of the enhancement N-channel MOSFET. An overcharge / overdischarge prevention circuit for a secondary battery, comprising: means for applying a voltage, wherein a substrate electrode of the enhancement type N-channel MOSFET is connected to a negative electrode side of the secondary battery. 4. A rechargeable battery, a four-terminal enhancement-type P-channel MOSFET connected in series with a negative electrode of the rechargeable battery and capable of conducting and shutting off bidirectionally, and a capacitor and a capacitor connected to the rechargeable battery. Means for positively or negatively charging a voltage, and means for applying a voltage of the capacitor positively or negatively charged according to a voltage of the secondary battery to a gate electrode of the enhancement type P-channel MOSFET, An overcharge / overdischarge prevention circuit for a secondary battery, wherein a substrate electrode of a type P-channel MOSFET is connected to a positive electrode side of the secondary battery. 5. A rechargeable battery, a four-terminal enhancement-type N-channel MOSFET connected in series with a positive electrode of the rechargeable battery and capable of bidirectional conduction and cutoff, a current source, and a voltage of the rechargeable battery. Means for flowing the current of the current source to the gate electrode of the enhancement N-channel MOSFET in accordance with
Wherein the substrate electrode is connected to the negative electrode side of the secondary battery. 6. A rechargeable battery, a four-terminal enhancement-type jP-channel MOSFET connected in series with a negative electrode of the rechargeable battery and capable of bidirectional conduction and cutoff, a current source, and a voltage of the rechargeable battery. Means for flowing the current of the current source to the gate electrode of the enhancement-type P-channel MOSFET in accordance with
An overcharge / overdischarge prevention circuit for a secondary battery, wherein a substrate electrode of the ET is connected to a positive electrode side of the secondary battery. 7. A rechargeable battery, an enhancement N-channel MOSFET connected in series to a negative electrode of the rechargeable battery and capable of conducting and shutting off bidirectionally, and the enhancement N-type MOSFET according to a voltage of the rechargeable battery. An overcharge / overdischarge prevention circuit for a secondary battery, comprising: means for energizing or interrupting a channel MOSFET, wherein a substrate of the enhancement type N-channel MOSFET is floating. 8. A rechargeable battery, an enhancement-type P-channel MOSFET connected in series to the positive electrode of the rechargeable battery and capable of conducting and shutting off bidirectionally, and the enhancement-type P-channel MOSFET according to the voltage of the rechargeable battery. An overcharge / overdischarge prevention circuit for a secondary battery, comprising means for energizing or interrupting a channel MOSFET, wherein a substrate of the enhancement type P-channel MOSFET is floating.