JP2002165373A - Over discharge prevention circuit of battery and over discharge preventive method of battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent discharge in a period when recharge is necessary after a battery is discharged and over discharge. SOLUTION: The over discharge prevention circuit includes a first switching element 13 which is disposed between an electronic circuit 7 and a battery 2 and connected to the first pole side 3 of the battery 2, and a voltage divider resistance circuit 8 which is disposed between the plus and minus poles 3, 4 of the battery 2. The switching element 13 has a first switching voltage V1 which is operated with a higher voltage than the partial voltage of the battery voltage divided by the voltage divider resistance circuit 8, and it further includes a second switching element 14 which short-circuits a voltage dividing point 12 divided by the voltage divider resistance circuit 8, when the switching element 13 is operated, to the second pole side 4 of the battery 2. The first switching element 13 does not operate at a lower voltage than the predetermined voltage V1, and no current flows from the battery to the electronic circuit 7. If the battery voltage drops to a voltage at which voltage supply required by the electronic circuit can not be made, the voltage supply to the battery is completely stopped and useless current flow can be almost prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a circuit for preventing overdischarge of a battery and a method for preventing overdischarge of a battery, and more particularly to a circuit for preventing overdischarge of a battery that supplies a voltage to an electronic circuit. And a method for preventing overdischarge of a battery.

[0002]

2. Description of the Related Art An abundance of electronic devices having an electronic circuit to which a voltage is supplied from a battery are provided. With the miniaturization of the electronic equipment, high performance and large capacity are promoted. It is required to extend the life and continuous operation time of the battery used there, and it is desired that overdischarge is prevented as much as possible.
Generally, a rechargeable battery has a property that the battery charge decreases due to long-term use, and accordingly, the internal resistance increases and the output voltage decreases. Prevention of overdischarge of a battery is known from Japanese Patent Application Laid-Open No. H11-299121.

[0005] As shown in FIG. 5, the battery voltage VBAT decreases due to prolonged use, and when the battery voltage VBAT falls below a voltage required for the operation of the electronic circuit, the electronic circuit is stopped and the battery is stopped. Discharge stops. By stopping the battery discharge, the voltage drop due to the internal resistance of the battery disappears, and the battery voltage temporarily increases,
The electronic circuit operates again, so that current is drawn from the battery. Such a current causes a voltage drop due to the internal resistance again, and the battery voltage drops again.
When such a decrease occurs, the operating voltage required for the electronic circuit becomes insufficient, and a repeated phenomenon that the electronic circuit stops again occurs. When such repetition continues, the battery charge decreases and the battery voltage cannot rise to a voltage required for the operation of the electronic circuit, and finally the current supply to the electronic circuit stops.

An electronic circuit generally has a bias circuit for operating an internal active element. Even after the function of the electronic circuit is stopped, a leakage current from the battery continues to flow into the internal bias circuit. That is, since the input resistance viewed from the power supply terminal of the electronic circuit is finite, such a leakage current flows even at a low voltage at which the circuit cannot operate normally. For this reason, if the notification is performed for a long time after the operation of the electronic circuit is stopped, the leakage current continues to flow and the battery is finally emptied.

[0005] There are many other problems besides emptying the battery. There is a danger that the discharge current from the battery is repeatedly turned on and off in a burst manner and flows into the electronic circuit as an inrush current, thereby damaging the electronic circuit. Useless discharge increases the recharge time. The operation / stop is repeated by monitoring the power state.
Blink ED. It has been pointed out that there are many problems with complete discharge, such as reducing the number of times of recovery by recharging and shortening battery life.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a battery over-discharge prevention circuit capable of preventing discharge or over-discharge during a period when the battery is discharged and needs to be recharged, and a battery over-discharge circuit. It is to provide a prevention method.

[0007]

Means for solving the problem are described as follows. The technical items appearing in the expression are appended with numbers, symbols, and the like in parentheses (). The numbers, symbols, etc. are technical items that constitute at least one embodiment or a plurality of examples of the embodiments or examples of the present invention, in particular, the embodiments or the examples. Corresponds to the reference numerals, reference symbols, and the like assigned to the technical matters expressed in the drawings corresponding to the above. Such reference numbers and reference symbols clarify the correspondence and bridging between the technical matters described in the claims and the technical matters of the embodiments or examples. Such correspondence / bridge does not mean that the technical matters described in the claims are interpreted as being limited to the technical matters of the embodiments or the examples.

The battery over-discharge prevention circuit according to the present invention is provided between the electronic circuit (7) and the battery (2) and connected to the first pole of the battery (2). And a voltage dividing resistance circuit (8) interposed between the positive and negative electrodes of the battery (2), wherein the first switching element (13) has a first switching voltage and has a voltage dividing resistance circuit (8). Operates under the condition that the divided voltage of the battery voltage divided by the first switching voltage is higher than the first switching voltage. If the first switching element (13) operates, the voltage dividing resistor circuit (8)
And a second switching element (14) that short-circuits the voltage dividing point (12) to the second pole side of the battery (2), and the second switching element (14) has a second switching voltage. The first switching element (13) operates under the condition that the terminal voltage on the electronic circuit side is higher than the second switching voltage. Discharge during periods when the battery needs to be recharged is substantially completely prevented.

At a voltage lower than the prescribed voltage (V1), the first switching element (13) does not operate, no current flows from the battery to the electronic circuit (7), and no on / off is repeated. . At a moment when a voltage lower than that required for the electronic circuit (7) is about to be supplied to the electronic circuit (7), the supply of the voltage is almost completely stopped, and the unnecessary current flows to almost completely zero. Battery voltage (V
BAT), the first switching element (13) stops responding and reacts quickly, and the flow of useless current is more effectively prevented.

The first switching element is formed by a first transistor (13), and the second switching element is formed by a second transistor (14). The terminal voltage of the first switching element is a voltage on the drain side of the first transistor (13). is there. The first switching voltage is a gate cut voltage of the first transistor (13), and the second switching voltage is a gate cut voltage of the second transistor (14). The gate cut voltage of the first transistor (13) corresponds to the rising point and the falling point of the voltage of the battery (2) with high accuracy, so that the supply of the battery voltage (VBAT) is started with high accuracy at an appropriate time, and , Can be stopped.

The first transistor (13) is a p-channel MOS transistor or an n-channel MOS transistor, and the second transistor (14) is an n-channel MOS transistor.
It is an OS transistor or a p-channel MOS transistor, and starts and stops operation instantaneously. in this case,
The source of the first transistor (13) is connected to the positive or negative electrode of the battery, and the source of the second transistor (14) is connected to the negative or positive electrode of the battery. The voltage dividing point (12) is connected to the first transistor (1
3) is connected to the gate of the second transistor (14) and the drain of the first transistor (13) is connected to the second transistor (14).
It is connected to the gate of the transistor (14).

According to the method for preventing overdischarge of a battery according to the present invention, power is supplied from a battery (2) to an electronic circuit (7) via a switching element (13). 7) via a switching element (13), the battery voltage (VBA
At a time t1 when T) rises to a prescribed voltage, the conduction of the switching element (13) starts sharply, and at a time t2 when the battery voltage (VBAT) falls to a prescribed voltage.
And the conduction of the switching element (13) is rapidly stopped.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Corresponding to the drawings, an embodiment of a circuit for preventing overdischarge of a battery according to the present invention has an overdischarge prevention circuit provided between a BAT (battery) and a CKT (electronic circuit). I have. As shown in FIG. 1, the overdischarge prevention circuit 1 has a positive terminal 3 connected to the positive electrode of the BAT 2.
And BAT2 via a negative terminal 4 connected to the negative electrode of BAT2. The overdischarge prevention circuit 1 is connected to the CK through a positive output terminal 5 and a negative output terminal 6.
Connected to T7.

A voltage dividing resistor circuit 8 is provided between the positive and negative electrodes of the BAT 2. The voltage dividing resistor circuit 8 is formed by connecting a high-resistance first resistor 9 and a high-resistance second resistor 11 in series. The first resistor 9 is disposed on the positive electrode side,
The second resistor 11 is arranged on the negative electrode side. First resistor 9
The battery voltage VBAT is divided by the first resistor 9 and the second resistor 11, and a voltage dividing point 12 is formed between the first resistor 9 and the second resistor 11.

A complementary transistor pair is interposed between the positive terminal 3 and the negative terminal 4 in a complementary manner. The complementary transistor pair includes a first transistor 13 and a second transistor 14. The first transistor 13 is exemplified by a p-channel MOS transistor. The second transistor 14 is an n-channel MO
An S transistor is illustrated.

The source of the first transistor 13 is directly connected to the positive terminal 3. First transistor 13
Are connected directly to the positive output terminal 5. The source of the second transistor 14 is directly connected to the negative terminal 4 and the negative output terminal 6. The gate of the second transistor 14 is directly connected to the positive output terminal 5. The gate of the first transistor 13 and the drain of the second transistor 14 are directly connected to the voltage dividing point 12. Therefore, the gate of the second transistor 14 is directly connected to the drain of the first transistor 13,
The divided voltage at the dividing point 12 is applied to the gate of the first transistor 13 and the drain of the second transistor 14.

The voltage dividing resistor circuit 8 includes a first transistor 13
The first resistor 9 and the second resistor 11 are appropriately supplied with a high resistance R1 and a high resistance R2, respectively, for supplying a bias voltage to the first resistor 9 and not for supplying a bias current. Have been. If R1 + R2 = 1 MΩ, the battery voltage VBAT is assumed to be 12 V on average, and 12 μA (= 12 V / 1 M
Ω). The battery capacity is normally 600 mAH, and the current value in this case is 5 in terms of discharge time.
This corresponds to 10,000 hours (= 600 mAH / 12 μA), which is negligibly small in an assumed normal use situation.

FIG. 2 shows current characteristics of the first transistor 13. The horizontal axis is the source-gate voltage Vs
g, and the vertical axis indicates the drain current Id.
If the source-gate voltage Vsg exceeds the gate cut voltage V1, the drain current Id flows. If the source-gate voltage Vsg is less than the gate cut voltage V1, the first transistor 13 is off and no drain current flows.
Such a gate cut voltage V of the first transistor 13
1 is set to be equal to or lower than the voltage at the voltage dividing point 12 at which the charging voltage value of the battery voltage VBAT is divided by the resistance.
The condition for turning on the first transistor 13 is that the source-gate voltage Vsg, which is the voltage at the voltage dividing point 12, exceeds the gate cut voltage V1 set in this way.

The gate cut voltage V2 of the second transistor 14 is set to be lower than a value obtained by subtracting the ON voltage of the first transistor 13 from the charging voltage of the battery voltage VBAT. The value obtained by subtracting the source-drain voltage of the first transistor 13 from the charge voltage of the battery voltage VBAT is the gate cut voltage V2 of the second transistor 14.
The condition of 2 or more is a condition for turning on the second transistor 14. ON voltage V of first transistor 13
There is no restriction on the magnitude relationship between the first voltage and the ON voltage V2 of the second transistor.

FIG. 3 shows an embodiment of a method for preventing overdischarge of a battery according to the present invention. FIG. 3A shows a time waveform of the battery voltage VBAT and the source-gate voltage Vsg of the first transistor 13. FIG. 3 (b)
Is a current (CK) supplied from the battery 2 to the electronic circuit 7.
T current). At time t0, the battery is connected to CKT7 via overdischarge prevention circuit 1. The first transistor 13 is off until time t1. The battery voltage VB is applied between the source and the gate of the first transistor 13.
An AT resistance division voltage (voltage at voltage dividing point 12) is applied. The following equation holds for the first transistor 13. Vsg = VBAT · R1 / (R1 + R2) (1)

When the voltage applied to the first transistor 13 from the battery rises and the source-gate voltage Vsg1 exceeds the gate cut-off voltage V1 at time t1, the first transistor 13
The transistor 13 is turned on, and a current flows through the CKT 7 via the positive output terminal 5. Until time t1, the second transistor 14 to which no voltage is applied to its gate is off, but if the first transistor 13 is on, the second transistor 14 is off.
A voltage is applied to the gate of the transistor 14. Since the gate cut voltage V2 of the second transistor 14 is set lower than the voltage applied to the gate of the second transistor 14 at this time, the second transistor 14 is also turned on.
When the second transistor 14 is turned on, the second resistor 11 is short-circuited by the second transistor 14, and a potential substantially equal to the negative electrode potential of the battery is applied to the gate of the first transistor 13. At this time, most of the current flowing from the positive electrode of the battery 2 to the first resistor 9 flows from the drain to the source of the second transistor 14 without passing through the second resistor 11, and returns to the negative electrode of the BAT2. Therefore, after time t1, most of the battery voltage VBAT is applied to the first resistor 9, and the following equation is established. Vsg1 ≒ VBAT (2)

Generally, the interval from time t0 to time t1 is a very short time. If the battery voltage VBAT decreases with the lapse of time and the source / gate voltage Vsg of the first transistor 13 becomes lower than the gate cut voltage V1 again at time t2, the first transistor 13 is turned off and the first transistor 13 Is stopped, the gate voltage of the second transistor 14 drops, becomes lower than the gate cut voltage V2, and the second transistor 14 also turns off. Since the second transistor 14 that is turned off cannot short-circuit the second resistor 11, the voltage between the source and the gate of the first transistor 13 returns to the resistance-divided value represented by the equation (1). Therefore, the source-gate voltage Vsg of the first transistor 13 decreases instantaneously at time t2. After such time t2, CKT
The power supply to 7 stops.

With this stop, the discharge of BAT2 stops, the voltage drop due to the internal resistance stops, and the output voltage rises transiently. Since the source-gate voltage of the first transistor 13 which rises with such a transient rise is set lower than the gate cut voltage V1, the first transistor 13 does not turn on. First
Unless the transistor 13 is turned on, the second transistor 1
4 does not turn on, so that the gate-source voltage of the first transistor 13 does not switch and expand.

In such a state, since the first transistor 13 and the second transistor 14, which are MOS transistors, have a high impedance, the discharge current of the BAT 2 flows through the first and second high-resistance resistors 9 and 11, and leaks. Only the current, and the leakage current is negligibly small as described above. When the battery is recharged and the battery voltage is restored, the power supply to the CKT 7 is resumed as described above.

FIG. 4 shows another embodiment of the battery over-discharge prevention circuit according to the present invention. This embodiment is the same as the above-described embodiment except that the channel types are switched between the first transistor 13 and the second transistor 14, and that the positive and negative electrodes of the BAT 2 are connected in reverse. This is the same as the above-described embodiment. The first transistor 13 'is an n-channel MOS transistor, and the second transistor 14' is a p-channel MOS transistor. In this case, the positive output terminal of the above-described embodiment is changed to a negative output terminal, and the negative output terminal is changed to a positive output terminal.

[0026]

According to the battery over-discharge prevention circuit and the battery over-discharge prevention method of the present invention, the battery discharge can be almost completely stopped in an unnecessary time zone.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of a circuit for preventing overdischarge of a battery according to the present invention.

FIG. 2 is a graph showing an operating voltage of a transistor.

FIG. 3 is a time chart showing the operation of the method for preventing overdischarge of a battery according to the present invention.

FIG. 4 is a circuit diagram showing another embodiment of the battery over-discharge prevention circuit according to the present invention.

FIG. 5 is a time chart showing known voltages and currents.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Over-discharge prevention circuit 2 ... Battery 3 ... First pole side 4 ... Second pole side 5.6 ... Electronic circuit side terminal 7 ... Electronic circuit 8 ... Voltage dividing resistor circuit 9 ... High resistance R1 10 ... High resistance R2 12: voltage dividing point 13: first switching element (first transistor) 14: second switching element (second transistor) V1: first switching voltage V2: second switching voltage t0, t1, t2: time

Claims (8)

[Claims] 1. A first switching element interposed between an electronic circuit and a battery and connected to a first pole side of the battery, and a voltage dividing resistance circuit interposed between a positive electrode and a negative electrode of the battery. The first switching element has a first switching voltage, and operates under a condition that a divided voltage of a battery voltage divided by the voltage dividing resistor circuit is higher than the first switching voltage; A second switching element for short-circuiting a voltage dividing point divided by the voltage dividing resistor circuit to a second pole side of the battery when the element operates, the second switching element having a second switching voltage; An overdischarge prevention circuit for a battery that operates under the condition that the terminal voltage of the first switching element on the electronic circuit side is higher than the second switching voltage. 2. The first switching element is formed by a first transistor; the second switching element is formed by a second transistor; the terminal voltage is a voltage on a drain side of the first transistor; The circuit according to claim 1, wherein the switching voltage is a gate cut voltage of the first transistor, and the second switching voltage is a gate cut voltage of the second transistor. 3. The first transistor is a p-channel MO.
An S transistor; wherein the second transistor is an n-channel MOS transistor; a source of the first transistor is connected to a positive electrode of the battery; a source of the second transistor is connected to a negative electrode of the battery; 3. The overdischarge prevention circuit for a battery according to claim 2, wherein the voltage dividing point is connected to a gate of the first transistor and a drain of the second transistor, and a drain of the first transistor is connected to a gate of the second transistor. . 4. The first transistor is an n-channel MO.
An S transistor, wherein the second transistor is a p-channel MOS transistor, a source of the first transistor is connected to a negative electrode side of the battery, a source of the second transistor is connected to a positive electrode side of the battery, 3. The overdischarge prevention circuit for a battery according to claim 2, wherein the voltage dividing point is connected to a gate of the first transistor and a drain of the second transistor, and a drain of the first transistor is connected to a gate of the second transistor. . 5. A power supply from a battery to an electronic circuit via a switching element, connecting a battery to the electronic circuit at a time t0 via the switching element, and raising the battery voltage to a prescribed voltage. Time t1
A steep start of conduction of the switching element at time t2 when the battery voltage falls to a prescribed voltage
And abruptly stopping conduction of the switching element. 6. The method according to claim 5, wherein said switching element is a MOS transistor. 7. The method according to claim 5, wherein the operating voltage is a divided voltage obtained by dividing the battery voltage. 8. The method for preventing overdischarge of a battery according to claim 7, further comprising short-circuiting a voltage dividing point for dividing the battery voltage to the battery at the time t1.