JP2000253590A - Charging and discharging control circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a charging and discharging control circuit for controlling a battery, which does not fully charge the battery under high temperature conditions. SOLUTION: A charging and discharging control circuit 1, which controls a battery 2 according to the voltage of the battery, is provided with a temperature detection circuit 6 which detects the ambient temperature Ts of the battery 2, a transistor Q2 for discharging which brings the battery 2 in dischargeable state according to the temperature detected through the temperature detection circuit 6, a charging voltage detection circuit 5 which detects the charging voltage of the battery 2, and a transistor Q1 for discharging which is series- connected with the transistor Q2 for discharging and brings the battery 2 in dischargeable state, according to the charging voltage which is detected through the charging voltage detection circuit 5.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a charge / discharge control circuit, and more particularly, to a charge / discharge control circuit for controlling charging / discharging of a battery.

[0002]

2. Description of the Related Art Secondary batteries such as lithium ion batteries and lithium polymer batteries are used as rechargeable batteries. Lithium ion batteries, lithium polymer batteries, and the like are easily damaged by overcharge and overdischarge.
Therefore, control is performed by a charge / discharge control circuit so as not to be overcharged or overdischarged.

FIG. 5 is a block diagram showing an example of a conventional charge / discharge control circuit. A conventional charge / discharge control circuit 100 is connected between a battery 101 and a charging voltage Vp,
1 is charged by the charging voltage Vp. Charge / discharge control circuit 10
0 is mainly a charge / discharge control IC 102, a discharge control transistor Q21, a charge control transistor Q22, a discharge control IC 10
3

[0004] A battery 101 is connected between battery terminals T21 and T22. The positive terminal of the battery 101 is connected to the battery terminal T21, and the negative electrode of the battery 101 is connected to the battery terminal T22. The charging voltage Vp is applied between the power supply terminals T23 and T24. Note that the positive electrode of the battery 101 is connected to the output terminal T25 via the resistor R21. An output load is connected between the output terminal T25 and the power supply terminal T24 to generate an output voltage Vout.

A battery terminal T21 and a power supply terminal T23 are connected to a resistor R
21, connected to the charge / discharge control IC 102 via the capacitor C21. The charge / discharge control IC 102 includes an overdischarge detection circuit 1
04, an overcharge detection circuit 105, a discharge control unit 106, a charge control unit 107, a comparator 108, a hysteresis setting unit 109, a diode D11, a resistor R22, and a PNP transistor Q23.

[0006] The overdischarge detection circuit 104 detects the voltage of the battery terminal T21 via a resistor R21, thereby detecting the battery 10
1 is detected. The over-discharge detection circuit 104
When overdischarge of the battery 101 is detected, a detection signal is supplied to the discharge control unit 106. When the detection signal is supplied from the over-discharge detection circuit 104, the discharge control unit 106 turns off the discharge control transistor Q21.

The overcharge detection circuit 105 detects the overcharge state of the battery 101 by detecting the voltage of the battery terminal T21 via a resistor R21. Overcharge detection circuit 105
Supplies a detection signal to the charging control unit 107 when detecting an overcharged state of the battery 101. When receiving the detection signal from the overcharge detection circuit 105, the charge control unit 107 turns on the transistor Q23. When the transistor Q23 is turned on, a discharge control signal is supplied to the discharge control IC 103.

[0008] The discharge control IC 103 comprises an NPN transistor Q24, resistors R23 to R27, and a diode D12. The discharge control signal output from the transistor Q23 is
The voltage is supplied to the base of the transistor Q24 via the resistor R23. The transistor Q24 has a collector connected to the battery terminal T21 and the power supply terminal T23 via the resistor R26. The base of the transistor Q24 is biased by resistors R24 and R25 and a diode D12. The emitter of the transistor Q24 is grounded.

Therefore, when the transistor Q24 is turned on by the discharge control signal output from the transistor Q23, the battery terminal T21 is grounded via the resistor R26. The battery terminal T21, the power terminal T23 and the power terminal T
A capacitor C23 is connected between the capacitor 24 and the capacitor 24 to absorb fluctuations in the charging voltage Vp. The transistor Q21 and the transistor Q22 are composed of MOS-FETs.
The transistors Q21 and Q22 have a drain
The source is connected in series between the battery terminal T22 and the power supply terminal T24. The transistor Q21 is switched by a discharge control signal supplied from the charge / discharge control IC 102 at the time of overdischarge. The transistor Q22 is switched by the discharge control IC 103 at the time of overcharge.

Further, the transistor Q21 and the transistor Q
The connection point with 22 is connected to the charge / discharge control IC 102 via a resistor R27 built in the discharge control IC 103. The charge / discharge control IC 102 compares the voltage at the connection point between the transistor Q21 and the transistor Q22 with the reference voltage generated by the resistor R22 and the Zener diode D11.
08, and according to the comparison result, the discharge control unit 1
06 is controlled. The voltage at the connection point between the transistor Q21 and the transistor Q22 is
Is supplied to the overdischarge detection circuit 104 as a start.

In the conventional charge / discharge control circuit 100, the battery 1
When 01 is overcharged or overdischarged, transistors Q21 and Q21
When the battery 22 is turned off, the connection between the battery 101 and the power supply or the output load is disconnected, thereby preventing the battery 101 from being overcharged or overdischarged.

[0012]

However, the conventional charge / discharge control circuit simply monitors the charge voltage of the battery, controls the charge / discharge according to the charge voltage of the battery, and monitors the state of the ambient temperature of the battery. Therefore, there is a possibility that the battery may be left under a high-temperature condition in a state near full charge. The present invention has been made in view of the above points, and has as its object to provide a charge / discharge control circuit that does not fully charge a battery under high-temperature conditions.

[0013]

According to the present invention, a charge / discharge control circuit 1 for controlling the charge / discharge of a battery according to the voltage of the battery 2 includes:
A temperature detecting means 6 for detecting an ambient temperature Ts of the battery 2 and a first discharging means Q2 for discharging the battery 2 in accordance with the temperature detected by the temperature detecting means 6 are provided.

According to the present invention, when the ambient temperature of the battery is higher than the predetermined temperature, the battery can be discharged. Therefore, it is possible to prevent the battery from being exposed to a high temperature condition at a full charge voltage. The present invention also provides a charging voltage detecting means 5 for detecting a charging voltage of the battery 2 and a first discharging means Q
And a second discharging means Q1 which is connected in series to the battery 2 and is capable of discharging the battery 2 in accordance with the charging voltage detected by the charging voltage detecting means 5.

According to the present invention, even when the ambient temperature of the battery is equal to or higher than the predetermined temperature, the battery is not discharged when the charging voltage is equal to or lower than the predetermined voltage. Further, under conditions other than the high temperature condition, the battery is not discharged, so that unnecessary discharge of the battery can be prevented. Further, the present invention has a thermistor TH1 having a temperature detecting means 6 at one end to which the voltage of the battery 2 is applied, and a resistor R3 having one end connected to the other end of the thermistor TH1 and the other end grounded. The voltage Vs2 at the connection point between TH1 and the resistor R3 is output as a temperature detection result.

According to the present invention, the temperature can be easily detected by using a thermistor and a resistor. Further, the present invention includes a load resistor RL which is connected in series to the first discharging means Q2 and limits the discharging current of the battery 2. According to the present invention, by providing the load resistance, the discharge current of the battery can be limited.

Further, according to the present invention, a backflow preventing means D1 connected to the first discharging means Q2 for preventing a backflow of the discharge current.
Is provided. According to the present invention, since the backflow of the discharge current can be prevented by providing the backflow prevention means, the battery is not damaged.

[0018]

FIG. 1 is a block diagram showing an embodiment of the present invention. In the charge / discharge circuit 1 of this embodiment, a battery 2 is connected between battery connection terminals T1 and T2, and a power supply terminal T3
, T4, the power supply voltage Vp is applied.
To charge the battery 2. An output voltage is output between the output terminal T5 and the power supply terminal T4.

The charge / discharge circuit 1 comprises a charge / discharge control circuit 3 and a temperature protection circuit 4. Charge / discharge control circuit 3
Is the same as that of the conventional charge / discharge circuit shown in FIG. 5, the same components as those in FIG. 5 are denoted by the same reference numerals, and description thereof will be omitted. The temperature protection circuit section 4 includes a charging voltage detection circuit 5, a temperature detection circuit 6, discharging transistors Q1, Q2, a load resistor RL, and a diode D1. The charging voltage detecting circuit 5 detects the charging voltage of the battery 2 and controls the switching of the discharging transistor Q1 according to the detected charging voltage. The temperature detecting circuit 6 detects the ambient temperature of the battery 2 and controls the switching of the discharging transistor Q2.

The temperature protection circuit section 4 turns on both the discharging transistors Q1 and Q2 when the charging voltage is equal to or higher than the predetermined charging voltage and equal to or higher than the predetermined temperature, via the load resistance RL and the backflow preventing diode D1. The battery 2 is discharged. The load resistance RL limits the discharge current of the battery 2. Further, the diode D1 prevents the backflow of the current. FIG. 2 is a block diagram showing a temperature protection circuit according to an embodiment of the present invention. In the figure, the same components as those in FIG. 1 are denoted by the same reference numerals.

The charge detection circuit 5 comprises a reset IC 7, a resistor R1, and a capacitor C1. Reset IC7
Are a detection terminal T11, an output terminal T12, and a ground terminal T13.
And outputs a high or low level output signal from the output terminal T12 according to the voltage applied to the detection terminal T11.
The output signal output from the output terminal T12 of the reset IC 7 absorbs unnecessary fluctuations by the resistor R1 and the capacitor C1, and is supplied to the gate of the discharging transistor Q1.

FIG. 3 is a block diagram showing a reset IC according to an embodiment of the present invention. The reset IC 7 includes a current source 8,
It comprises a Zener diode D11, resistors R11 to R13, a comparator 9, and transistors Q11 to Q14. The current source 8 supplies a current to the Zener diode D11 according to the power supply voltage Vp supplied to the detection terminal T11. The Zener diode D11 generates a reference voltage Vref based on the current supplied from the current source 8 and applies it to the non-inverting input terminal of the comparator 9. A voltage obtained by dividing the voltage applied to the detection terminal T11 by the resistors R11 and R12 is applied to the inverting input terminal of the comparator 9.

The comparator 9 compares the detection voltage at the detection terminal T11 with the reference voltage Vref generated by the current source 8 and the Zener diode D11. If the voltage at the detection terminal T11 is higher than the reference voltage Vref, the comparator 9 detects a low level. If the voltage at the terminal T11 is smaller than the reference voltage Vref, a high-level output signal is output. The output signal of the comparator 9 is
It is supplied to the base of transistor Q11.

The transistors Q11 to Q14 and the resistor R13 are
An output circuit is formed, and an output signal obtained by inverting the output signal of the comparator 9 is output from an output terminal T12. That is, if the voltage obtained by dividing the detection voltage Vs1 of the detection terminal T11 is higher than the reference voltage Vref, the output signal output from the output terminal T12 becomes high level, and the voltage obtained by dividing the detection voltage Vs1 of the detection terminal T11 becomes If the voltage is lower than the reference voltage Vref, the output signal output from the output terminal T12 becomes low level.

The output terminal T12 of the reset IC 7 is connected to a resistor R
1 and the capacitor C1. Resistance R1
And the capacitor C1 is connected to the terminal T to which the charging voltage Vp is applied.
Connected in series between 1 and ground. The fluctuation of the output signal at the output terminal T12 of the reset IC 7 is absorbed by the resistor R1 and the capacitor C1. The connection point between the resistor R1 and the capacitor C1 is connected to the gate of the discharging transistor Q1. The transistor Q1 is constituted by a power MOS field effect transistor (FET). The drain of the transistor Q1 is connected to the battery terminal T1 to which the charging voltage Vp is applied, and the source is connected to the drain of the transistor Q2.

The discharging transistor Q1 is turned on when the charging voltage becomes higher than a predetermined level and the output signal of the output terminal T12 of the reset IC 7 becomes high level, the charging voltage becomes lower than the predetermined level, and the output of the reset IC 7 becomes lower. When the output signal of the terminal T12 is at a low level, the signal is turned off when the signal goes to a low level. The reset IC 7 and the reset IC 8 have the same circuit configuration.

Next, the temperature detection circuit 6 will be described.
The temperature detection circuit 6 includes a thermistor TH1 as shown in FIG.
, Resistors R2, R3, reset IC8, capacitor C2
Consists of Since the reset IC 8 has the same configuration as the reset IC 7 of the charging voltage detection circuit 5, the description thereof is omitted. The thermistor TH1 has an NTC (Negative Temperature Coeffic) whose resistance decreases according to the temperature.
ient) composed of a thermistor. The thermistor TH1 and the resistor R3 are connected in series between the battery terminal T1 and ground. At the connection point between the thermistor TH1 and the resistor R3, a temperature detection voltage that rises with temperature is generated.

The connection point between the thermistor TH1 and the resistor R3 is connected to the detection terminal T11 of the reset IC 8. The reset IC 8 goes to a high level if the voltage obtained by dividing the temperature detection voltage Vs2 at the connection point between the thermistor TH1 and the resistor R3 is higher than the internally generated reference voltage Vref. If the compressed voltage is lower than the reference voltage Vref, an output signal which becomes low level is output from the output terminal T12.

The output terminal T12 of the reset IC 8 is connected to a resistor R
2 and the capacitor C2. Resistance R2
And the capacitor C2 is connected to the terminal T to which the charging voltage Vp is applied.
Connected in series between 1 and ground. The fluctuation of the output signal at the output terminal T12 of the reset IC 8 is absorbed by the resistor R2 and the capacitor C2. The connection point between the resistor R2 and the capacitor C2 is connected to the gate of the discharging transistor Q2. The transistor Q2 is constituted by a power MOS field effect transistor (FET). The drain of the discharging transistor Q2 is connected to the source of the discharging transistor Q1, and the source is connected to the battery terminal T2 via the load resistor RL and the backflow preventing diode D1.

The discharging transistor Q2 is turned on when the temperature around the battery 2 becomes higher than the predetermined temperature and the output signal of the output terminal T12 of the reset IC 8 becomes high level, and the temperature around the battery 2 becomes the predetermined temperature. Lower than the temperature,
When the output signal of the output terminal T12 of the reset IC 8 becomes low level, it is turned off. When the charging voltage becomes higher than the predetermined voltage, the discharging transistor Q1 turns on, and the temperature around the battery 2 rises above the predetermined temperature and the discharging transistor Q2 turns on, the battery terminals T1 and T2 are loaded. The battery 2 is connected through the resistor RL and the diode D1, and discharges the battery 2. At this time, the discharge current of the battery 2 is limited by the load resistance RL. Also, the backflow is prevented by the diode D1.

Next, the operation of the protection circuit section 4 of this embodiment will be described with reference to the drawings. FIG. 4 is a diagram for explaining the operation of the protection circuit unit according to one embodiment of the present invention. FIG. 4A shows the charging voltage Vp,
4 (B) shows the output signal of the reset IC 7, FIG. 4 (C) shows the state of the discharging transistor Q1, FIG. 4 (D) shows the ambient temperature of the battery 2, and FIG. 4 (E) shows the output signal of the reset IC 8. 4 (F) is the state of the discharging transistor Q2, FIG.
Indicates the discharged state of the battery.

As shown in FIG. 4A, at time t1, the battery 2
When the charging voltage Vp reaches a predetermined voltage V0 set near the full charging voltage Vf of the battery 2, the output signal of the reset IC 7 changes from a low level to a high level as shown in FIG. When the reset IC 7 becomes high level, FIG.
As shown in (C), the discharging transistor Q1 turns on.

At this time, as shown in FIG.
If the ambient temperature Ts is smaller than the predetermined temperature T0,
As shown in FIG. 4E, the output signal of the reset IC 8 remains at the low level, and the discharge transistor Q2 is in the off state as shown in FIG. in this way,
Even if the discharge transistor Q1 is turned on when the battery 2 is at or above a predetermined voltage V0 near the full charge voltage, if the ambient temperature Ts of the battery 2 is at or below the predetermined temperature T0, the discharge transistor Q2
Is turned off, so that the battery 2 is not discharged.

At time t2, the charge voltage Vp of the battery 2 is
When the ambient temperature Ts of the battery 2 becomes higher than the predetermined temperature T0 when the output signal of the reset IC 7 is at a high level and the discharging transistor Q1 is turned on, the state shown in FIG. As shown, the output signal of the reset IC 8 changes from a low level to a high level. Reset I
When the output signal of C8 changes from low level to high level,
As shown in FIG. 4F, the discharging transistor Q2 turns on.

At time t2, when the discharging transistor Q2 turns on, the discharging transistor Q1 has already turned on, so that both the discharging transistors Q1 and Q2 turn on.
The battery terminal T1 to which the battery 2 is connected and the battery terminal T2 are connected via a load resistor RL and a diode D1. When the battery terminal T1 and the battery terminal T2 are connected via the load resistance RL and the diode D1, the battery 2 is discharged.

The ambient temperature Ts of the battery 2 is equal to a predetermined temperature T
0, the charging voltage Vp of the battery 2 is higher than the predetermined voltage Vp.
If it is smaller than 0, the discharging transistor Q1 is turned off, so that no discharging is performed. As described above, according to the present embodiment, when the ambient temperature of the battery 2 becomes equal to or higher than the predetermined temperature while the battery 2 is near the full charge voltage, the battery 2 is discharged, and the battery 2 is discharged.
, The expansion of the battery 2 is suppressed.

[0037]

As described above, according to the present invention, when the ambient temperature of the battery becomes higher than the predetermined temperature, the battery can be discharged. Therefore, the battery is exposed to a high temperature condition at a full charge voltage. It has features such as being able to prevent that.
According to the present invention, even when the ambient temperature of the battery is equal to or higher than the predetermined temperature, the battery is not discharged when the charging voltage is equal to or lower than the predetermined voltage. Under the conditions other than the conditions described above, the battery is not discharged, so that there is an advantage that unnecessary discharge of the battery can be prevented.

According to the present invention, the temperature sensor can be easily detected by using a thermistor and a resistor. ADVANTAGE OF THE INVENTION According to this invention, it has the characteristics that discharge current of a battery can be limited by providing a load resistance. According to the present invention, since the backflow prevention means is provided, the backflow of the discharge current can be prevented, so that there is a feature that the battery is not damaged.

[Brief description of the drawings]

FIG. 1 is a block diagram of an embodiment of the present invention.

FIG. 2 is a block diagram of a protection circuit unit according to one embodiment of the present invention.

FIG. 3 is a block diagram of a reset IC according to an embodiment of the present invention.

FIG. 4 is an explanatory diagram of an operation of the protection circuit unit according to one embodiment of the present invention.

FIG. 5 is a block diagram of a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Charge / discharge control circuit 2 Battery 3 Charge / discharge control circuit unit 4 Protection circuit unit 5 Charge voltage detection circuit 6 Temperature detection circuit 102 Charge / discharge control IC 103 Charge control IC Q1, Q2 Discharge transistor RL Load resistance D1 Diode R21 Resistance Q21, Q22 Transistor C21 ~ C23 Capacitor

Claims (5)

[Claims] 1. A charge / discharge control circuit for controlling charging / discharging of a battery according to a voltage of the battery, wherein the temperature detecting means detects an ambient temperature of the battery, and the temperature is detected by the temperature detecting means. And a first discharging means for setting the battery in a dischargeable state. 2. A charging voltage detecting means for detecting a charging voltage of the battery, and a battery connected in series with the first discharging means, and discharging the battery in accordance with the charging voltage detected by the charging voltage detecting means. 2. The charge / discharge control circuit according to claim 1, further comprising a second discharge unit that is enabled. 3. The temperature detecting means has one end to which one voltage of the battery is applied, one end connected to the other end of the thermistor, and the other end applied to the other voltage of the battery. The charge / discharge control circuit according to claim 1, further comprising a resistor, wherein a voltage at a connection point between the thermistor and the resistor is output as a temperature detection result. 4. The first discharging means is connected in series with the first discharging means,
The charge / discharge control circuit according to claim 1, further comprising a load resistor for limiting a discharge current of the battery. 5. The charge / discharge control circuit according to claim 1, further comprising backflow prevention means connected to said first discharge means for preventing a backflow of said discharge current.