JP3438751B2 - Overcharge prevention device for rechargeable batteries - 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 over-discharge prevention device which is used in a battery unit equipped with a rechargeable battery, for example, a lithium ion battery, and detects over-discharge of the battery to protect the battery. .

[0002]

2. Description of the Related Art Among rechargeable batteries, especially lithium ion batteries are vulnerable to over-discharge, and therefore an over-discharge preventing device for detecting an over-discharge state and inhibiting discharge is indispensable.

Referring to FIG. 4, a battery unit including a conventional lithium-ion battery equipped with an overdischarge prevention device will be described. In this battery unit, a lithium ion battery (hereinafter, simply referred to as a battery) 100 is provided with an overdischarge detection circuit 41.
0s are connected in parallel. The over-discharge detection circuit 410 is
The terminal voltage of the battery 100 is compared with a threshold voltage, which will be described later, and when the terminal voltage becomes lower than the threshold voltage, it is determined to be overdischarge, and the switch 420 by the semiconductor switch is turned off. As a result, the positive load current line 450p
And the negative side load current line 450n, the load 200 and the battery 100 are disconnected from each other to prohibit discharge. The threshold voltage is set to, for example, about several tens of percent of the terminal voltage when fully charged.

In addition to the overdischarge prevention device, the conventional battery unit usually has an overcharge prevention device for stopping charging when the terminal voltage exceeds a predetermined value during charging, and an overcurrent protection device. An overcurrent detection circuit for inhibiting discharge is provided.

In the over-discharge detection circuit 410, voltage comparison is performed by a comparison circuit as shown in FIG.
This comparison circuit includes a reference voltage generation source E _R for setting a threshold voltage, bleeder resistors R1 and R2, a detection input side resistor R3, a reference voltage side resistor R _G , and a comparator 41.
It is composed of 1.

[0006]

Generally, the terminal voltage of the battery is lowered by the product of the load current and the internal impedance of the battery. Further, the degree of the terminal voltage drop and the degree of the terminal voltage return (the terminal voltage increase) after the discharge is stopped are proportional to the magnitude of the load current at the time of discharge.

Therefore, in the over-discharge prevention device including the example shown in FIG. 4 in which the voltage at which the discharge should be stopped is determined, the above-mentioned threshold voltage and the terminal voltage after the discharge is stopped. It is necessary to set the hysteresis voltage for the recovery of the overdischarge detection circuit with respect to the return of 1 to a value according to the magnitude of the load current. By the way, both the average value and the maximum value of the load current differ depending on the weight of the load connected to the battery unit.

Therefore, it is preferable that the overdischarge prevention device has a threshold voltage according to the weight of the load. But,
Conventional over-discharge prevention devices have a constant threshold voltage and are not configured to operate in consideration of the weight of the load.

For this reason, for example, even when the battery 100 is used up to a state where the remaining capacity is about 10% and the discharge is to be prohibited, the conventional example in which the terminal voltage at which the discharge should be prohibited is set to a constant value As described above, the degree of voltage drop of the terminal voltage varies depending on the weight of the load. Therefore, when the load is light, the remaining capacity is extremely low (the remaining capacity is 10%).
Discharge is prohibited for the first time in a state that is much smaller than that), while it is prohibited even when the remaining capacity is sufficient under heavy load (the state where the remaining capacity is considerably larger than 10%). There is a problem.

SUMMARY OF THE INVENTION An object of the present invention is to provide a rechargeable battery over-discharge prevention device which is excellent in versatility and which can change the voltage at which discharging should be prohibited depending on the weight of the load.

[0011]

According to the present invention, a voltage connected between a rechargeable battery and a load for detecting that the terminal voltage of the battery has dropped to a voltage value at which discharge should be prohibited. An overdischarge detection circuit including a comparison unit, and a rechargeable battery overdischarge prevention device having a switch circuit for stopping power supply from the battery to the load by detection of the overdischarge detection circuit, in which the load is light and heavy. The voltage of a predetermined portion based on a load current that changes in accordance with the detected voltage, further comprising a voltage adjusting circuit for changing the voltage value for which the discharge should be prohibited according to the detected voltage, the voltage of the over-discharge detection circuit The comparing unit is connected to the reference voltage generating source for setting the reference value of the voltage value for which the discharge should be prohibited, a bleeder resistor connected in parallel with the battery to form a predetermined voltage dividing point, and the voltage dividing point. Detected A voltage-side resistor, an input terminal connected to the voltage dividing point via the detection input-side resistor, and a reference voltage input terminal connected to the reference voltage generation source, and the voltage at the input terminal is the reference value. And a comparator formed of an operational amplifier that detects that the terminal voltage of the battery has decreased to a voltage value at which discharge should be prohibited as compared with the voltage of the reference voltage input terminal, and the switch circuit sources the load current line. And a drain connected semiconductor switch, the predetermined portion is between the source / drain of the switch circuit, and the voltage adjusting circuit detects a voltage between the source / drain of the switch circuit and converts the voltage into a current. Then, the overdischarge of the rechargeable battery configured by the voltage / current conversion circuit that supplies the converted current as an adjustment signal to the input terminal side of the comparator. Prevention device can be obtained.

Further, according to the present invention, the voltage adjusting circuit provides the overdischarge preventing device for the rechargeable battery, which supplies the current as the adjusting signal to the upstream side or the downstream side of the detection input side resistor. .

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An overdischarge prevention device for a rechargeable battery according to an embodiment of the present invention will be described below with reference to the drawings. Figure 1
FIG. 3 is a diagram showing a battery unit including an overdischarge prevention device and a lithium ion battery according to the present embodiment. This battery unit also includes an overcharge prevention device and an overcurrent detection circuit as in the conventional case, but since it is not the gist of the present invention, illustration and description thereof will be omitted. FIG. 2 is a circuit diagram showing the overdischarge detection circuit in FIG. 1, in the present battery unit, as in the conventional example shown in FIG. 4, an over-discharge detection circuit 10 is provided in a lithium ion battery (hereinafter simply referred to as a battery) 100.
Are connected in parallel. The over-discharge detection circuit 10 compares the terminal voltage of the battery 100 with a threshold voltage, determines that it is over-discharged when it becomes lower than the threshold voltage, and turns off the switch 20 that is a semiconductor switch, so that the positive side. Discharge is prohibited by disconnecting the connection between the load 200 and the battery 100 connected between the load current line 50p and the negative load current line 50n. Referring to FIG. 2, an overdischarge detection circuit 10
Is the reference voltage generation source E _R , the bleeder resistors R1 and R2, the detection input side resistor R3, as in the conventional example shown in FIG.
It is composed of a reference voltage side resistor R _G and a comparator 11.

With reference to FIG. 1 and FIG. 2 together, the present over-discharge prevention device further detects the voltage V _c at a specific portion based on the load current I _L which changes according to the weight of the load 200, and detects the detected voltage. A voltage that acts as a voltage adjustment circuit that changes the detection-side input voltage of the overdischarge detection circuit 10 according to V _c /
It has a current conversion circuit 30. Here, the voltage V _c is the voltage between the source and drain of the switch 20 which is a semiconductor switch. When the source / drain resistance of the switch 20 is R _ON , V _c = R _ON ×
It is represented by the formula I _L.

The voltage / current conversion circuit 30 is composed of a circuit which detects the voltage V _c and converts it into a current having a magnitude corresponding to the voltage value. Numerically, the voltage V _c is converted into a predetermined coefficient. It is multiplied by k and converted into a current amount having a magnitude represented by k · V _c and output. The output of the voltage / current conversion circuit 30 is connected to the upstream side (I _R3 ) of the detection input side resistor R3 of the comparator 11 of the overdischarge detection circuit 10 in FIG.

[0016] Thus, in the over-discharge detection circuit 10 (comparator 11), a voltage for turning off the switch 20, i.e., the terminal voltage _{V t} to be prohibited _{discharge, V} t =
A variable based on a formula that _{V L} -k · V _c. That is,
The terminal voltage V _{t for} which discharge should be prohibited can be adjusted according to the current flowing from the voltage / current conversion circuit 30. It should be noted that V _L in the equation is when the load 200 is light (the voltage V _{c is} almost 0).
It is a fixed set voltage for prohibiting the discharge of (in case of).

FIG. 3 is a diagram for explaining the operation of the overdischarge prevention device according to the present embodiment, in which the abscissa indicates the usage time of the battery 100 from the fully charged state, and the ordinate indicates the terminal voltage of the battery 100. Indicates. The operation of the overdischarge prevention device according to the present embodiment will be described below with reference to FIGS. In the overdischarge detection circuit 10, the fixed set voltage V _L is, for example,
It is set to 2.8V.

When the load 200 is light, the terminal voltage of the battery 100 drops from the full charge voltage (for example, 4.2 V) as the battery 100 is used, as indicated by the broken line in FIG. The voltage / current conversion circuit 30 detects the voltage V _c according to the load current I _L , and flows the corresponding current I _R3 into the overdischarge detection circuit 10. However, since the load 200 is light,
The current I _R3 is small, and the terminal voltage V _{t for} which discharge should be prohibited is almost the fixed set voltage V _L (2.8 V). Therefore,
When the terminal voltage of the battery 100 drops to about 2.8 V, the control signal is output from the comparator 11, so that the switch 20 is turned off. After that, when the terminal voltage of the battery 100 rises to a predetermined voltage determined by the hysteresis characteristic of the overdischarge detection circuit 10, the switch 20 is connected and the discharge is restarted.

On the other hand, when the load 200 is heavy, as shown by the solid line in FIG. 3, the terminal voltage of the battery 100 drops from the full charge voltage (for example, 4.2V) with use. The voltage / current conversion circuit 30 uses the voltage V corresponding to the unusable current I _L.
c , and the corresponding current I _R3 is detected by the overdischarge detection circuit 1
It flows into 0. Since the load 200 is heavy and the current I _R3 is large to some extent, the terminal voltage V at which discharge should be prohibited
For example, _t becomes 2.2V. Therefore, when the terminal voltage of the battery 100 drops to 2.2V, the comparator 1
The switch 20 is turned off by the signal from 1. After this,
When the terminal voltage of the battery 100 rises to a predetermined voltage,
The switch 20 is connected and the discharge is restarted.

As is apparent from the above description, since the over-discharge prevention device of the present invention automatically adjusts the terminal voltage at which the discharge of the over-discharge detection circuit should be prohibited according to the weight of the load, various types of over-discharge detection circuits can be used. It is easily adaptable to light and heavy loads and has excellent versatility.

In the embodiment, the voltage / current conversion circuit 30 is used.
Flow into the upstream side of the detection input side resistor R3 ( _IR3 )
However, as shown by the alternate long and short dash line in FIG.
The detection input side resistor R3 may be made to flow into the downstream side ( _IR3 ').

Further, the voltage adjusting circuit in the present invention is not limited to the voltage / current converting circuit, but amplifies the voltage of a predetermined portion based on the load current which changes according to the weight of the load and a predetermined portion of the overdischarge detecting circuit. It is also possible to adopt a configuration of an amplifier circuit for applying to the.

Furthermore, it goes without saying that the present invention is applicable not only to lithium ion batteries but also to all rechargeable batteries that require protection from over-discharge.

[0024]

The rechargeable battery over-discharge prevention device according to the present invention should detect the voltage of a predetermined portion based on the load current that changes according to the weight of the load, and prohibit the discharge according to the detected voltage. Since it has a voltage adjustment circuit that changes the voltage value, it can be easily adapted to various loads.
It has excellent versatility.

[Brief description of drawings]

FIG. 1 is a block diagram showing a battery unit to which an overdischarge prevention device for a rechargeable battery according to an exemplary embodiment of the present invention is applied.

FIG. 2 is a circuit diagram showing an overdischarge detection circuit in the overdischarge prevention device shown in FIG.

FIG. 3 is a diagram for explaining the operation of the over-discharge prevention device shown in FIG. 1, in which the horizontal axis represents the usage time of the lithium battery from the fully charged state, and the vertical axis represents the terminal voltage of the lithium battery.

FIG. 4 is a block diagram showing a battery unit to which a rechargeable battery over-discharge prevention device according to a conventional example is applied.

5 is a circuit diagram showing an overdischarge detection circuit in the overdischarge prevention device shown in FIG.

[Explanation of symbols]

100 lithium-ion battery (battery) 10 and 410 overdischarge detecting circuit 11,411 comparator 20,420 switch 30 voltage / current conversion circuit 50p, 450P positive load current line 50n, 450n negative load current lines 200 load E _R reference voltage Source I _L Load current I _R3 , I _R3 'Current R1, R2 Bleeder resistance R3 Detection input side resistance R _G Reference voltage side resistance V _c Voltage

─────────────────────────────────────────────────── ─── Continuation of the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) H02J ^7/ 00-7/12 H02J ⁷ /34-7/36

Claims (2)

(57) [Claims] 1. An over-discharge detection circuit connected between a rechargeable battery and a load, the over-discharge detection circuit including a voltage comparison unit for detecting that the terminal voltage of the battery has dropped to a voltage value at which discharge should be prohibited. A rechargeable battery over-discharge prevention device having a switch circuit for stopping power supply from the battery to the load by detection of the over-discharge detection circuit, wherein a predetermined portion based on a load current that changes according to the weight of the load detecting a voltage, a voltage further comprising <br/> a voltage adjustment circuit for changing a voltage value should be prohibited the discharge in response to which the detected, said voltage comparison section of the over-discharge detection circuit, the discharge Prohibited
Reference voltage generation for setting the reference value of the voltage value to be stopped
And a parallel connection to the battery to form a predetermined voltage dividing point
The bleeder resistance and the detection input side resistance connected to the voltage dividing point.
And connect to the voltage dividing point through the detection input side resistance
Input terminal and the reference voltage connected to the reference voltage source.
A voltage input terminal, and the voltage at the input terminal is the reference value.
The terminal of the battery compared to the voltage at the reference voltage input terminal
Detect that the voltage has dropped to the voltage value at which discharge should be prohibited.
And a comparator formed of an operational amplifier for outputting the source and drain to the load current line.
And a predetermined portion is a source / drain of the switch circuit.
The voltage adjustment circuit is connected to the source / drain of the switch circuit.
It detects the voltage between IN and converts it to current,
It is supplied as an adjustment signal to the input terminal side of the comparator.
An overdischarge prevention device for a rechargeable battery, which is configured by a voltage / current conversion circuit that operates. 2. The overdischarge prevention device for a rechargeable battery according to claim 1, wherein the voltage adjustment circuit supplies a current as the adjustment signal to an upstream side or a downstream side of the detection input side resistor.