JP3426778B2 - Battery charge / discharge control method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a battery charge / discharge control method for preventing overcharge and overdischarge of a battery.

[0002]

2. Description of the Related Art Batteries have the property that their performance deteriorates when they are overcharged. In order to prevent the battery from being overcharged, a charging method has been developed in which the FET connected in series to the battery is turned off when the battery is overcharged (JP-A-4-75431). A circuit that realizes the charging method described in this publication is shown in FIG. Charging FETQ connected in series with battery 1
1, the drain is connected to the negative electrode of the battery, the source is connected to the negative electrode terminal 2, and the gate is connected to the output side of the control circuit 3.
The charging FET Q1 is turned on / off by the control circuit 3. The control circuit 3 detects the battery voltage V1 and turns off the charging FET Q1 when the battery voltage V1 becomes higher than the set value. When the charging FET Q1 is turned off, the battery 1 is no longer charged. Even when the charging FET Q1 is off, the battery 1 can be discharged through the parasitic diode D of the charging FET Q1.

[0003]

The circuit shown in FIG. 1 can charge the battery 1 through the charging FET Q1 and discharge the battery 1 through the parasitic diode D. That is, F for charging
It has the feature that the battery can be discharged by turning off ETQ1. However, when the battery is discharged by the parasitic diode D, the heat generation amount of the charging FET Q1 increases at the time of discharging, and the heat may destroy the charging FET Q1. The amount of heat generated by the charge FET Q1 during discharging is large because the amount of heat generated by the parasitic diode D is in the ON state.
This is because the calorific value is much larger than 1. The heat generation amount of the charging FET Q1 is the product of the internal resistance of the charging FET Q1 and the square of the current. The internal resistance of the charging FET Q1 is as small as several tens of mΩ. Therefore, the charging F in the ON state
The heat generated from ETQ1 is extremely low. On the other hand, the amount of heat generated by the parasitic diode D is a product of the current and about 0.6 V, which is the voltage drop of the diode. Therefore, the amount of heat generation becomes extremely large as the current increases.

Therefore, the method of charging / discharging the battery by the method described in the circuit of FIG. 1 can have a simple circuit configuration, but has a harmful effect that the charging FET Q1 is easily damaged by heat.
In order to prevent this drawback, it is necessary to use a large-capacity FET for charging, which increases the cost of parts.

Further, in the charging method shown in FIG. 1, in order to charge the battery 1, when the battery voltage drops, the charging FET Q
It is necessary to switch 1 to the on state. The control circuit 3
When the battery voltage drops to a predetermined voltage, the charging FETQ
Control 1 to ON state. Control circuit 3 is a charging FET Q1
The reset voltage for switching from OFF to ON is set lower than the overcharge cut voltage for switching from ON to OFF.
If the difference between the return voltage and the overcharge cut voltage is reduced, the charging FET Q1 is repeatedly turned on and off to cause chattering when the battery voltage is in the vicinity. When the difference between the return voltage and the overcharge cut voltage is increased, the parasitic diode D discharges until the battery voltage considerably decreases, so that there is a disadvantage that the amount of heat generation increases. Further, there is a drawback that the output voltage of the battery pack is lowered due to the voltage drop of the parasitic diode.

The present invention was developed for the purpose of solving this drawback. An important object of the present invention is to provide a thermal destruction of the charging and discharging Then Kino FET battery, the charge and discharge control method of a battery that can effectively prevent the chattering of the FET.

[0007]

Battery as claimed in claim 1 and claim 3 of the present invention According to an aspect of the charge and discharge control method, the battery connecting the charging FET to protect overcharge of the battery This is an improved charge / discharge control method. When the battery voltage becomes higher than the overcharge cut voltage, the charging FET is turned off to protect the battery from being overcharged. After that, it detects whether the battery is disconnected from the charger, or whether the battery is in the discharging state, and when the battery is disconnected from the charger or in the discharging state, the charging FET is switched on. Characterize.

The determination as to whether or not the battery is in a discharged state is
This can be determined by detecting the voltage across the charging FET in the off state. This is because when the battery is in the discharged state, a voltage of about 0.6 V is generated by the parasitic diode of the charging FET in the off state.

[0009] Whether batteries are disconnected from the charger determination, for example, it can be determined by detecting the voltage of the electrode terminals 2 of the battery pack. In the battery pack shown in FIG. 3, the voltage of the electrode terminal 2 becomes 0 V when the battery pack is disconnected from the battery charger, and the terminal voltage V is charged when the battery pack is connected to the battery charger.
This is because 2 becomes the output voltage of the charger. However, in order to detect the disconnection of the battery pack from the charger by this method, it is necessary to connect the discharging FET Q2 in series with the charging FET Q1 as shown in FIG. FE for discharge
When the battery voltage V1 rises to the overcharge cut-off voltage VCOFF, TQ2 is controlled to be off together with the charging FET Q1. Since the charging FET Q1 and the discharging FET Q2 are connected in series with each other with the parasitic diode D in the opposite direction, when both FETs are turned off and disconnected from the charger, the inter-terminal voltage V2 becomes 0V. .

Further, the battery charge / discharge control method according to claims 5 and 7 of the present invention is a battery charge / discharge control method to which a discharge FET Q2 for protecting the battery from over-discharge is connected. This is an improvement, and when the battery voltage V1 becomes lower than the overdischarge cutoff voltage, the discharging FET Q2 is turned off to protect the battery from overdischarging. Then, determine whether the battery is connected to the charger or is in a charging state,
When the battery is connected to the charger or is in the charging state, the discharging FET Q2 is turned on.

[0011] decision batteries is whether the state of charge,
This can be determined by detecting the voltage across the discharging FET Q2 in the off state . When batteries are in the charged state, the parasitic diode D of the discharge FETQ2 in the off state, because the voltage of approximately 0.6V is generated.

[0012] Whether batteries is connected to the charger determination, for example, it can be determined by detecting the voltage of the electrode terminals 2 of the battery pack. This is because the voltage of the electrode terminal 2 rises to the charging voltage when the battery pack is connected to the charger. In this way, to detect that the battery pack is disconnected from the charger, the charging FET Q1 is connected in series with the discharging FET Q2.
Need to be connected. When the battery voltage V1 rises to the over-discharge cut voltage, the charging FET Q1 is used for discharging F.
Controlled off with ETQ2.

[0013]

Operation: Charge / discharge control of the battery according to claim 1 of the present invention.
The operating state of the control method will be described with reference to FIG. In the battery pack of this figure, the charging FET Q1 is connected in series with the battery 1. The control circuit 3 charges the battery 1 and when the battery voltage V1 rises to the overcharge cut-off voltage VCOFF, turns off the charging FET Q1. Since the charging FET Q1 has the parasitic diode D, the charging FET Q1 can be turned off to discharge the battery pack. This is because the discharge current flows through the parasitic diode D of the charging FET Q1 as indicated by the solid line indicated by the arrow A. However, in this circuit, when the charging FET Q1 is turned off and the battery is discharged, the parasitic diode D of the charging FET Q1 generates heat.

In order to prevent this adverse effect, the method of the present invention, the charging FETQ1 the battery voltage V1 rises to overcharge cut voltage VCOFF, but switched to the OFF state, when discharging the electricity <br/> Pond Switch to the on state. The method shown in FIG. 2 detects the diode voltage V3 generated across the parasitic diode D of the charging FET Q1 to detect the charging FE.
Turn TQ1 on. When the battery pack is disconnected from the charger and discharged, the parasitic diode D is discharged to about 0.
This is because a voltage of 6V is generated. Diode voltage V3
Is detected by the control circuit 3, and when the diode voltage V3 of about 0.6 V is generated in the parasitic diode D, the control circuit 3 switches the charging FET Q1 to the ON state. The internal resistance of the charging FET Q1 in the ON state is considerably smaller than the internal resistance of the parasitic diode D. Therefore, the heat generation amount of the charging FET Q1 due to the discharge current becomes extremely small, and the thermal destruction is effectively prevented. Further, since the charging FET Q1 is switched to the ON state by detecting the diode voltage V3, chattering of the charging FET Q1 can be effectively prevented.

[0015] charging and discharging of the battery that will be set forth in claim 3 of the present invention
A power control method is illustrated in FIG. In the battery pack shown in this figure, when the battery voltage V1 rises to the overcharge cut voltage VCOFF, the charging FET Q1 and the discharging FET Q2 are turned off to prevent the battery 1 from being overcharged. After that, the inter-terminal voltage V2 of the electrode terminal 2 of the battery pack is detected to detect that the battery pack is disconnected from the charger. In this battery pack, the battery voltage V1 is not output to the electrode terminal 2 when both the charge FET Q1 and the discharge FET Q2 are off. Therefore, when the battery pack is disconnected from the charger, the electrode terminal 2 becomes 0V. When the battery pack is disconnected from the charger, FET Q1 for charging and FET for discharging
Q2 is turned on so that it can be discharged. F for charging
When ETQ1 and discharging FET Q2 are turned on and discharged,
The internal resistance of both FETs is extremely small, and the heat generation amount of the FETs can be reduced.

The charging and discharging of the battery that will be set forth in claim 5 of the present invention
The battery pack used in the power control method is shown in FIG. This battery pack switches the discharge FET Q2 to the off state when the battery 1 is discharged and the voltage becomes lower than the overdischarge cut voltage VDOFF. After that, when the battery pack is connected to a charger and charged, a voltage of about 0.6 V is generated across the parasitic diode D of the discharging FET Q2. The control circuit 3 detects the diode voltage V3, and when this voltage becomes about 0.6V,
The discharging FET Q2 is switched from off to on.

Further, charge / discharge control according to claim 7
The method charges the battery pack shown in FIG. This charge and discharge
The control method is such that the battery is discharged and the voltage is overdischarge cut voltage V.
When it becomes lower than DOFF, discharging FET Q2 and charging FE
Switch TQ1 to the off state. When the battery pack is connected to the charger and the charging voltage is supplied to the electrode terminal 2 of the battery pack, the discharging FET Q2 and the charging FET Q1 are switched on. When the battery pack is charged in this state, the charging current passes through the discharging FET Q2 and the charging FET Q1. Discharging FET Q2 and charging FET in the ON state
The internal resistance of Q1 is considerably smaller than the internal resistance of the parasitic diode D, and the heat generation amount of both FETs can be made extremely small. Further, since the discharging FET Q2 is turned on by detecting the charging voltage applied to the electrode terminal 2 of the battery pack, chattering of the FET can be effectively prevented.

[0018]

EXAMPLES Hereinafter, an embodiment of the present invention have groups Dzu the drawings. However, the examples described below exemplify a battery charge / discharge control method for embodying the technical idea of the present invention, and the present invention does not specify the battery charge / discharge control method to the following. .

Further, in this specification, for easy understanding of the claims, the numbers corresponding to the members shown in the embodiments are referred to as "claims column", "action column", and "action column". It is added to the members shown in the section of "Means for Solving the Problems". However, the members shown in the claims are
It is by no means specific to the members of the examples.

2 to 5 are circuit diagrams of a battery pack used in the charge / discharge control method of the present invention. The battery pack shown in FIG. 2 is a charging FET Q1 that prevents overcharge of the battery 1.
Is connected between the battery 1 and the electrode terminal 2. The charging FET Q1 is an N-channel power MOSFET and has a parasitic diode D connected in parallel.

The charging FET Q1 is on / off controlled by the control circuit 3. The control circuit 3 detects the battery voltage V1 and the parasitic diode D, that is, the diode voltage V3 across the charging FET Q1, and controls the charging FET Q1 to turn on and off. When the battery pack V1 is charged by connecting the battery pack to the charger, the control circuit 3 turns off the charging FET Q1 to prevent the battery 1 from being overcharged when the battery voltage V1 rises to the overcharge cut-off voltage VCOFF. As long as the battery 1 is not discharged, the control circuit 3 keeps the charging FET Q1 in the off state. The diode voltage V3 of the parasitic diode D of the charging FET Q1 is detected to determine whether the battery pack is discharged. This is because when the battery pack is discharged, a voltage of about 0.6 V is generated in the parasitic diode D due to the current flowing in the parasitic diode D in the forward direction. The control circuit 3 detects the diode voltage V3, and when the voltage of the parasitic diode D reaches about 0.6V, switches the charging FET Q1 to the ON state. In this state, the battery pack passes the charging FET Q1 to supply power to the load.

FIG. 6 is a flowchart for charging and discharging the battery pack shown in FIG. The flowchart of this figure charges the battery pack in the following steps. [Step S1] First, as a normal state, the charging FET Q1 is turned on. [Step of S2] Connect the battery pack to the charger. [Step S3] The battery of the battery pack is charged through the charging FET Q1. [Step S4] The control circuit 3 detects the battery voltage V1. The control circuit 3
It is determined whether the battery voltage V1 has exceeded the overcharge cut voltage VCOFF. Battery voltage V1 is overcharge cut voltage VCOFF
If lower than, loop this step. [Step S5] When the battery voltage V1 exceeds the overcharge cut voltage VCOFF, the control circuit 3 switches off the charging FET Q1.

[Step S6] The voltage across the charging FET Q1 is detected. When the battery pack is being charged, when the charging FET Q1 is turned off and connected to the charger, and when the battery pack is removed from the charger, the diode voltage V3 applied across the charging FET Q1 is + or It is 0V. However, when the battery pack is discharged, the diode voltage V3 becomes about -0.6 V when the direction shown in FIG. 2 is +. This is because a current flows through the parasitic diode D in the forward direction. Was it in Tsu, the control circuit 3, FE for charging
When the diode voltage V3 across TQ1 satisfies the following condition, the charging FET Q1 is turned on. Diode voltage V3 ≤ -0.1V In this conditional expression, the diode voltage V3 is -0.1V.
The reason for comparing with the reference voltage is that when the battery pack is discharged, the diode voltage V3 becomes about -0.6 V, which satisfies this conditional expression. However, the reference voltage is 0 V to −0.
It can also be set in the range of 6V. However, if the reference voltage is in the vicinity of 0 V, it is easy to make a mistake in determining whether or not discharging is in progress, and if the reference voltage is in the vicinity of -0.6 V, it is ensured that discharging is in progress due to variations in the diode voltage V3. It may not be detected. Therefore, the reference voltage for comparing the diode voltage V3 is preferably set in the range of -0.01 to -0.5V. The diode voltage V3 does not satisfy the above condition unless the battery pack is discharged. If this condition is not satisfied, the process jumps to step S5 and loops steps S5 and S6.

[Step S7] When the battery pack is discharged, the diode voltage V3 is about −
Since it becomes 0.6V, the control circuit 3 detects this and switches the charging FET Q1 to the ON state. In this state, the battery pack supplies power to a load that is an electric device.

Further, FIG. 4 shows a battery pack provided with a discharging FET Q2 for preventing over-discharge of the battery. In this battery pack, a discharging FET Q2 is connected between the battery and the electrode terminal 2. The discharging FET Q2 is an N-channel power MOSFET and has a parasitic diode D connected in parallel.

The discharge FET Q2 is turned on / off by the control circuit 3. The control circuit 3 detects the battery voltage V1 and the parasitic diode D, that is, the diode voltage V3 across the discharging FET Q2, and controls the discharging FET Q2 to turn on and off. When the battery pack V is connected to a load and discharged, if the battery voltage V1 becomes lower than the overdischarge cut-off voltage VDOFF, the control circuit 3 turns off the discharging FET Q2 to prevent the battery from being overdischarged. As long as the battery 1 is not charged, the control circuit 3 keeps the discharging FET Q2 in the off state. Whether or not the battery pack can be recharged depends on the discharge F
The diode voltage V3 of the parasitic diode D of ETQ2 is detected. When the battery pack is charged, the current flowing in the forward direction of the parasitic diode D causes the parasitic diode D to reach about 0.
This is because a voltage of 6V is generated. The control circuit 3 detects the diode voltage V3, and the voltage of the parasitic diode D is about −
When the voltage reaches 0.6 V, the discharging FET Q2 is switched on. In this state, the battery pack passes through the discharging FET Q2 and supplies power to the load.

FIG. 7 is a flowchart for discharging the battery pack shown in FIG. 4 and then charging it. In the flowchart of this figure, the battery pack is discharged and then charged in the following steps. [Step of S1] First, as a normal state, the discharging FET Q2 is turned on. [Step S2] The battery pack is connected to an electric device that is a load. [Step S3] The battery pack is discharged through the discharging FET Q2. [Step S4] The control circuit 3 detects the battery voltage V1. The control circuit 3
It is determined whether the battery voltage V1 has become lower than the overdischarge cut voltage VDOFF. When the battery voltage V1 is higher than the overdischarge cutoff voltage VDOFF, the steps S3 and S4 are looped. [Step S5] When the battery voltage V1 becomes lower than the overdischarge cutoff voltage VDOFF, the control circuit 3 switches off the discharging FET Q2.

[Step S6] The control circuit 3 detects the voltage across the discharge FET Q2.
When discharging the battery pack, connecting the discharging FET Q2 to the load in the off state, and further removing the battery pack from the electric equipment, the diode voltage V3 applied across the discharging FET Q2 is + or 0V. Is.
However, when the battery pack is charged, if the voltage in the direction shown in FIG.
Is about -0.6V. This is because a current flows through the parasitic diode D in the forward direction. Therefore, the control circuit 3 turns on the discharge FET Q2 when the diode voltage V3 across the discharge FET Q2 satisfies the following condition. Diode voltage V3 ≤ -0.1V Unless the battery pack is charged, the diode voltage V3
Does not satisfy the above. If this condition is not met,
Jump to step S5, and loop steps S5 and S6. [Step of S7] When the battery pack is connected to the charger and charged, the diode voltage V3 becomes about -0.6V, so the control circuit 3 detects this and turns on the discharging FET Q2. Switch.

Further, FIGS. 3 and 5 show a charging FET Q1.
Shows a battery pack in which a discharge FET Q2 is connected to the battery pack. In the battery pack shown in this figure, in order to prevent overcharging and overdischarging of the battery, a discharging FET Q2 and a charging FET Q1 are connected in series between the battery and the electrode terminal 2. Figure 3
A P-channel power MOSFET is used.
1 illustrates a battery pack using a channel power MOSFET. The FET on the upper side in FIG. 3 and the FET on the lower side in FIG. 5 is the charging FET Q1. The lower side of FIG.
The upper FET in FIG. 5 is the discharging FET Q2. The charging FET Q1 and the discharging FET Q2 are in parallel with a parasitic diode D.
Are connected.

The charge FET Q1 and the discharge FET Q2 are on / off controlled by the control circuit 3. The control circuit 3 detects the battery voltage V1 and the inter-terminal voltage V2 of the electrode terminal 2, and controls the charging FET Q1 and the discharging FET Q2 to be turned on and off.
When the battery pack V is connected to a charger and charged, when the battery voltage V1 rises to the overcharge cut voltage VCOFF, the control circuit 3 turns off the charging FET Q1 to prevent the battery from being overcharged. At this time, the discharging FET Q2 can be switched off together with the charging FET Q1. However, the discharging FET Q2 does not necessarily have to be turned off. As long as the battery is fully charged and connected to the charger, the control circuit 3 keeps the charging FET Q1 in the off state. The discharging FET Q2 can be held in the off state together, but the discharging FET Q2 can also be held in the on state.

Whether or not the battery pack is connected to the charger can be determined by detecting the terminal voltage V2. When the battery pack is connected to the charger, the voltage V2 between terminals is 0
This is because it does not become V. When the battery pack is disconnected from the charger, the terminal voltage V2 becomes 0V. Control circuit 3
Detects the inter-terminal voltage V2, and when the inter-terminal voltage V2 becomes lower than the set voltage, turns on the charging FET Q1 and the discharging FET Q2. When the battery pack is mounted on an electric device in this state, electric power is supplied from the battery to the load through the charging FET Q1 and the discharging FET Q2.

When the battery pack is mounted on an electric device and discharged, if the battery voltage becomes lower than the overdischarge cut-off voltage VDOFF, the discharging FET Q2 is turned off to prevent overdischarge. At this time, the charging FET Q1 can also be switched off, but the charging FET Q1 can also be kept on. As long as the battery pack is connected to the load, the discharging FET Q2 is kept off.
Whether or not the battery pack is connected to the load can be determined by the terminal voltage V2. When the battery pack is connected to the load, the terminal voltage V2 becomes 0V. Discharge FET Q2
Is in the off state.

The control circuit 3 detects the voltage V2 between the terminals and holds the discharging FET Q2 in the off state when the load is connected to the battery pack. When the load is removed from the battery pack and connected to the charger, the terminal voltage V2 rises. This is because the voltage of the charger is applied to the electrode terminal 2. The control circuit 3 detects the voltage V2 between the terminals and discharges the FET Q when the battery pack is connected to the charger.
2 and charging FET Q1 are turned on. In this state, the battery pack is charged by passing through the discharging FET Q2 and the charging FET Q1.

FIG. 8 is a diagram showing a flowchart for connecting the battery pack to the charger to charge the battery. The flowchart of this figure charges the battery pack in the following steps. [Step of S1] First, as a normal state, the charging FET Q1 and the discharging F
Turn on ETQ2. [Step of S2] Connect the battery pack to the charger. [Step of S3] The battery is charged by passing through the charging FET Q1 and the discharging FET Q2. [Step S4] The battery voltage V1 is detected, and it is determined whether the battery voltage V1 exceeds the overcharge cut voltage VCOFF. When the battery voltage V1 is lower than the overcharge cut voltage VCOFF, the steps S3 and S4 are looped. [Step S5] When the battery voltage V1 exceeds the overcharge cut voltage VCOFF, the control circuit 3 switches off the charging FET Q1. The discharging FET Q2 is switched off together with the charging FET Q1. [Step S6] It is determined whether the terminal voltage V2 of the battery pack is 0V. As long as the battery pack is connected to the charger, the inter-terminal voltage V2 does not become 0V, so at this time S5
Then, the step S6 is looped to hold the charge FET Q1 and the discharge FET Q2 in the off state. [Step S7] When the battery pack is disconnected from the charger, the voltage V
Since 2 becomes 0 V, the control circuit 3 detects this and switches on both the charging FET Q1 and the discharging FET Q2. In this state, the battery pack is attached to an electric device to supply power to the load.

The charged battery pack is discharged according to the flow chart of FIG. [Step of S1] The battery pack that is fully charged in the above process is a discharging FET.
Q2 and charging FET Q1 are on. [Steps of S2 and S3] Connect the battery pack to an electric device that is a load, and discharge FE
Electric power is supplied from the battery to the load through the TQ2 and the charging FET Q1. [Step S4] With the battery pack supplying power to the load, the control circuit 3 detects the battery voltage V1 and detects the overdischarge cut-off voltage VDOFF.
Compare to. The steps S3 and S4 are looped until the battery voltage V1 becomes equal to or lower than the overdischarge cut voltage VDOFF. [Step S5] When the battery voltage V1 becomes equal to or lower than the overdischarge cut voltage VDOFF,
The control circuit 3 switches off the discharging FET Q2 and the charging FET Q1. This is to prevent over-discharge of the battery.

[Step S6] It is determined whether the inter-terminal voltage V2 is 0V. This step is a step of determining whether or not the battery pack is connected to the charger. This is because when the battery pack is connected to the charger, the terminal voltage V2 becomes the output voltage of the charger. FE for charging when the battery pack is connected to the load
When the TQ1 and the discharging FET Q2 are in the off state, the inter-terminal voltage V2 becomes 0 V, so that the steps S5 and S6 are looped when the battery pack is connected to the load. [Step S7] When the battery pack is connected to the charger, the inter-terminal voltage V2 becomes higher than 0V. Therefore, in this state, the charging FET Q1 and the discharging FET Q2 are switched on.

In the above embodiment, the microcomputer FET is used to control ON / OFF of the charge FET Q1 and the discharge FET Q2. FIG. 10 shows a battery pack that controls the charge FET Q1 and the discharge FET Q2 without using a microcomputer.

In the battery pack of this figure, the battery voltage V1 is compared with the overcharge cut-off voltage VCOFF by the comparator 4.
The + pole of the battery is connected to the + input terminal of the comparator 4. The negative input terminal of the comparator 4 is connected to a reference power source having an overcharge cut voltage VCOFF. The output of the comparator 4 is connected to the base of the transistor Q5. The collector of the transistor Q5 is connected to the latching circuit 5 composed of the transistors Q6 and Q7. Further, the collector of the transistor Q5 is connected to the bases of the transistors Q1 and Q2 which short-circuit the gates of the charging FET Q1 and the discharging FET Q2 to the sources.

The battery pack of this figure operates as follows to prevent overcharging of the battery. (1) Normally, the charge FET Q1 and the discharge FET Q2 are in the ON state. (2) When the battery pack is connected to the charger and charged, the battery voltage V1 rises. (3) The battery voltage V1 is compared with the overcharge cut voltage VCOFF by the comparator 4. (4) When the battery voltage V1 is lower than the overcharge cut voltage VCOFF, the comparator 4 outputs "Low".
The "Low" output of comparator 4 holds transistor Q5 in the off state. When the transistor Q5 is off, the transistors Q3 and Q4 are also off. This is because the base current does not flow in the transistors Q3 and Q4.

(5) Battery voltage V1 is overcharge cut voltage VCO
At the moment when FF is exceeded, the comparator 4 outputs "High". (6) The "High" output of the comparator 4 turns on the transistor Q5. When the transistor Q5 is turned on, the transistors Q6 and Q7 are turned on and the latching circuit 5 is held in this state. (7) Further, when the transistor Q6 of the latching circuit 5 is in the ON state, a base current flows through the transistors Q3 and Q4, and the transistors Q3 and Q4 are held in the ON state. (8) The on-state transistors Q3 and Q4 are F for charging.
The gates of the ETQ1 and the discharge FET Q2 are short-circuited to the source, and both FETs are switched to the OFF state and held in this state. (9) As long as the battery pack is connected to the charger, the transistors Q6 and Q7 of the latching circuit 5 are kept on, and the charging FET Q1 and the discharging FET Q2 are kept off.

(10) When the battery pack is disconnected from the charger, the charging FET Q1 and the discharging FET Q2 are in the off state, so that the base current is not supplied from the transistor Q7 of the latching circuit 5 to the transistor Q6.
Transistor Q6 turns off. (11) When the transistor Q6 is turned off, the transistors Q3 and Q4 are turned off, the charge FET Q1 and the discharge FET Q2 are turned on, and the charge FET Q1 and the discharge F
ETQ2 is reset.

[0042]

The battery charge / discharge control method of the present invention is characterized in that it is possible to prevent chattering of the FET connected in series with the battery and to effectively prevent thermal destruction of the FET. That is, when the battery charge / discharge control method according to claims 1 and 3 of the present invention prevents the overcharge by turning off the charging FET when the battery is fully charged, the battery is discharged. Alternatively, if the charging voltage is no longer applied to the electrode terminals after being disconnected from the charger, the charging FET is turned on. That is, a battery that has been fully charged and then discharged or removed from the charger is a charging FET.
Is in the ON state, the discharge current does not pass through the parasitic diode of the charging FET, but passes through the charging FET in the ON state and in the low resistance state. For this reason, it is possible to effectively prevent thermal destruction caused by the parasitic diode. Further, since the charging FET is switched to the ON state by detecting that the battery has been fully charged and then discharging or being disconnected from the charger, the charging FET does not chatter.

Further, in the battery charge / discharge control method according to the fifth and seventh aspects of the present invention, when discharging the battery, the discharging FET is turned off before the battery is over-discharged. When the discharging FET is turned off, discharging cannot be performed, and thus over-discharging of the battery is prevented. After that, when charging of the battery is started or the battery is connected to the charger, the discharging FET is switched on. When the battery is charged in this state, the charging current does not pass through the parasitic diode of the discharging FET, but passes through the discharging FET in the ON state and in the low resistance state. Therefore, even in the charged state, it is possible to effectively prevent thermal destruction caused by the parasitic diode. Further, after discharging the battery, it is detected that the battery is in a charged state or that the battery is connected to a charger, and the discharging F is detected.
Since the ET is switched to the ON state, the discharging FET does not chatter.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a conventional battery pack that prevents overcharging.

FIG. 2 is a circuit diagram of a battery pack used in a charge / discharge control method according to an embodiment of the present invention.

FIG. 3 is a circuit diagram of a battery pack used in a charge / discharge control method according to another embodiment of the present invention.

FIG. 4 is a circuit diagram of a battery pack used in a charge / discharge control method according to another embodiment of the present invention.

FIG. 5 is a circuit diagram of a battery pack used in a charge / discharge control method according to another embodiment of the present invention.

FIG. 6 is a flowchart showing charging and discharging states of the battery pack shown in FIG.

FIG. 7 is a flowchart showing a state in which the battery pack shown in FIG. 4 is charged after being discharged.

FIG. 8 is a flowchart showing the state of charge of the battery pack shown in FIG.

9 is a flow chart diagram showing a discharged state of the battery pack shown in FIG.

FIG. 10 is a circuit diagram of a battery pack used in a charge / discharge control method according to another embodiment of the present invention.

[Explanation of symbols]

1 ... Battery 2 ... Electrode terminal 3 ... Control circuit 4 ... Comparator 5 ... Latching circuit Q1 ... FET for charging Q2 ... FET for discharging D ... Parasitic diode

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-4-75430 (JP, A) JP-A-4-75431 (JP, A) JP-A-6-197468 (JP, A) JP-A-2- 250636 (JP, A) JP 53-21747 (JP, A) JP 4-33271 (JP, A) JP 8-265985 (JP, A) JP 8-103029 (JP, A) JP-A-8-111941 (JP, A) JP-A-8-154341 (JP, A) JP-A-8-190936 (JP, A) JP-A-8-214460 (JP, A) JP-A-8-237875 (JP, A) JP-A-8-237872 (JP, A) JP-A-8-65907 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H02J 7/00-7 / 10 H01M 10/44

Claims (8)

(57) [Claims] 1. A charging / discharging control method for a battery, to which a charging FET for protecting the battery from being overcharged is connected. When the battery voltage becomes higher than an overcharge cut-off voltage, a charging F
Turn off ET (Q1) to prevent overcharging of battery (1) ,
After that, it is detected whether or not the battery is discharged, and when the battery is discharged, the charging FET (Q1) is turned on to discharge the battery. 2. Both ends of the charging FET (Q1) in the off state
Voltage is detected to determine if the battery is in a discharged state
The charge / discharge control method for a battery according to claim 1. 3. A charging / discharging control method for a battery, to which a charging FET for protecting the battery from being overcharged is connected. When the battery voltage becomes higher than an overcharge cut voltage, a charging F
Turn off ET (Q1) to prevent overcharging of battery (1) ,
After that, it detects that the battery is disconnected from the charger,
With the battery disconnected from the charger, the charging FET (Q
A charging / discharging control method for a battery, characterized in that 1) is turned on and discharging is performed. 4. The voltage of the electrode terminal (2) of the battery is detected,
A contract to determine if the battery has been disconnected from the charger.
The battery charge / discharge control method according to claim 3. 5. A charging / discharging control method for a battery to which a discharging FET for protecting the battery from over-discharging is connected, wherein when the battery voltage becomes lower than an over-discharge cut-off voltage, a discharging F
Turn off ET (Q2 ) to prevent over discharge of battery (1) ,
After that, it is detected whether or not the battery is charged, and when the battery is charged, the discharging FET (Q2) is turned on to charge the battery. 6. Both ends of the discharging FET (Q2) in the off state.
Voltage to determine if the battery is charged.
The charging / discharging control method of the battery according to claim 5, which is defined. 7. A charging / discharging control method for a battery to which a discharging FET for protecting the battery from over-discharging is connected, wherein when the battery voltage becomes lower than an over-discharge cut-off voltage, a discharging F
Turn off ET (Q2) to prevent over discharge of battery (1) ,
Then detect if the battery is connected to the charger,
A charging / discharging control method for a battery, comprising charging the discharging FET (Q2) in an ON state when the battery is connected to a charger. 8. A battery by detecting the voltage of an electrode terminal of the battery.
The method according to claim 7, wherein it is determined whether or not is connected to the charger.
A battery charge / discharge control method described.