JP2001275271A - Secondary cell charging device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a secondary cell charging device for charging a secondary cell via a charging circuit with constant-voltage constant-current charging. SOLUTION: The secondary cell charging device charges the secondary cell via the charging circuit the constant-voltage constant-current charging. The charging device comprises a current limiting means inserted between the cell and the charging circuit to limxt the charging current by a control signal, and a voltage monitor means for monitoring the terminal voltage of the cell to output a control signal with a predetermined threshold as a reference.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a secondary battery charger for charging a secondary battery by performing constant current and constant voltage charging via a charging circuit.

[0002]

2. Description of the Related Art A lithium ion secondary battery has a very small charge capacity, and if constant current charging is performed in an overdischarged state, an excessive current flows through a charging circuit and the secondary battery.

When an excessive current flows, not only the rechargeable battery but also the elements of the charging circuit are burdened, and it is necessary to increase the withstand current of the elements of the charging circuit. The scale is large and the cost is high.

Therefore, conventionally, as shown in FIG.
A DC / DC converter is used, and a detection resistor is inserted in the circuit through which the charging current flows, and the transistor is turned on / off using the detection voltage generated across the detection resistor to control the DC / DC converter. A secondary battery charger is used.

[0005] The charging circuit 10 has a power supply 11 such as an AC adapter for converting alternating current to direct current connected to one end through terminals T1 and T2, and a secondary battery 12 such as a lithium ion battery connected to a terminal T3 at the other end. And T4, and the secondary battery 12 is charged by the charging circuit 10 at a constant voltage and a constant current.

A DC / D is provided between the terminal T1 and the terminal T2.
A C converter 13 is connected, the emitter of the transistor Q1 is connected to the terminal T1, and the base is connected to the DC / DC converter 1
3, the terminal T2 is connected to the terminal T2, and the terminal T2 is connected to the terminal T4.

The collector of the transistor Q1 is connected to one end of a smoothing circuit 14, and the other end of the smoothing circuit 14 is connected to a terminal T3 via a detecting resistor R1.
The base and the emitter of the transistor Q2 are connected to both ends of 1 respectively.

Further, the collector of the transistor Q2 is
It is connected to a voltage dividing point of a series circuit of a voltage dividing resistor R2 and a volume R3 connected between the other end of the smoothing circuit 14 and the terminal T2.

The midpoint of the volume R3 is that the feedback voltage V1 related to the terminal voltage E1 across the secondary battery 12 is D.
The input state is input to the C / DC converter 13, and the operation state of the DC / DC converter 13 is controlled by the feedback voltage V1 to be a constant voltage or a constant current.

With the above configuration, when charging is started, the charging current I1 flows through the detection resistor R1 according to the time t as shown in FIG. 6B, so that the charging current I1 causes As shown, the terminal voltage E1 of the secondary battery 12 increases with time t.

In FIG. 6A, the horizontal axis represents the elapsed time t.
The vertical axis indicates the terminal voltage E1 of the secondary battery 12, and in FIG. 6B, the horizontal axis indicates the elapsed time t, and the vertical axis indicates the charging current I1 flowing through the secondary battery 12.

Then, the potential difference generated by the charging current I1 between the base and the emitter of the transistor Q2 increases, and the transistor Q2 is turned on. Therefore, both ends of the voltage dividing resistor R2 are short-circuited, and the feedback voltage V1 increases. Become
The constant current charging is performed on the secondary battery 12 without performing the voltage control.

When the charging proceeds and the charging current I1 to the secondary battery 12 decreases as shown in FIG. 6B, the potential difference across the detection resistor R1 decreases, and the transistor Q2 turns off. As a result, the feedback voltage V1 decreases, and DC /
The DC converter 13 enters a stable operation region and performs constant voltage charging.

[0014]

However, when an overdischarged secondary battery is connected and the charging operation is started in the above-described secondary battery charging device, the internal impedance of the secondary battery is low. Large current flows until the charging capacity reaches

For this reason, not only the secondary battery 12 but also the elements of the charging circuit 10 and the AC adapter on the power supply side are burdened, and the problem of heat generation needs to be considered.

[0016]

According to the present invention, as a configuration of a secondary battery charging device for solving the above-mentioned problems, a secondary battery is charged by performing constant current and constant voltage charging via a charging circuit. A current limiting means inserted between the secondary battery and the charging circuit to limit a charging current by a control signal, and a predetermined threshold value for monitoring a terminal voltage of the secondary battery and Voltage monitoring means for outputting the control signal on the basis of a voltage.

According to the present invention, even when the secondary battery to be charged is in an overcharged state, the terminal voltage of the secondary battery is monitored and the current limiting means is activated, so that the secondary battery or the charging circuit is not overcharged. Current can be prevented from flowing, and a charging system can be realized with a minimum necessary size for a circuit element of a charging circuit, an AC adapter serving as a power supply source, and the like.

Further, even if any element in the charging circuit fails and the power supply side and the output of the charging circuit are short-circuited, the current limiting means prevents excessive current from flowing to the secondary battery. And the system can be advantageously operated from the viewpoint of system security.

Further, even at the beginning of the circuit operation and even when the charging circuit is not operating, the current limiting means, especially only the limiting resistor, is always inserted between the charging circuit and the secondary battery, so that the current limiting is performed. Therefore, the system can be advantageously operated from the viewpoint of system security management.

In addition, in the present invention, in the present invention, the secondary battery is a lithium ion battery, and the current limiting means is connected to a limiting resistor inserted in series in the charging circuit and in parallel with the limiting resistor. The additional requirements include that the current control element is controlled and that the voltage monitoring means is constituted by a microcomputer or a comparator.

In the above additional requirements, the present invention is effective when applied to the charging of a lithium ion battery as a secondary battery, and the use of a limiting resistor, which is a passive element, as a part of the current limiting means is a safety management. In other words, when a microcomputer is used, it can be used in combination with other functions, and when a comparator which is a discrete element is used, it can be realized at low cost.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the secondary battery charging device according to the present invention will be described below with reference to the drawings. FIG. 1 is an overall configuration diagram schematically showing one embodiment of the present invention. For easy understanding, the same parts as those of the conventional secondary battery charger are denoted by the same reference numerals and described.

The terminals T3 and T4 on the output side of the charging circuit 10,
And between the terminal T5 and the terminal T6 of the secondary battery 12,
A current limiting circuit 20 functioning as current limiting means is connected.

The current limiting circuit 20 includes a limiting resistor R4 and a current controlling element Q3, for example, a transistor or a field effect transistor, connected in parallel with the limiting resistor R4. This parallel circuit connects the terminals T3 and T5. Connected between them.

A terminal voltage E2 between the terminal T5 and the terminal T6 to which the secondary battery 12 is connected is applied to an input terminal of a microcomputer 21 having a built-in threshold value ER for controlling the circuit and functioning as voltage monitoring means. ing.

The microcomputer 21 incorporated in the system compares the threshold value ER and, based on the result, passes through the circuit control element 22 the current control element Q3 in the current limiting circuit 20, for example, the gate of a field effect transistor. The charging current I2 supplied to the secondary battery 12 is limited by applying a voltage to the secondary battery and controlling its internal resistance.

Next, the operation of the secondary battery charger 23 configured as described above will be described. First, the microcomputer 21 operates the step ST1 shown in FIG.
In the initial setting, the gate voltage of the field-effect transistor of the current control element Q3 is controlled to turn off the field-effect transistor, thereby setting the current control state.

In the current limiting state, the limiting resistor R4 is inserted between the charging circuit 10 and the secondary battery 12, so that the charging current I2 is limited to the secondary battery 12 in the limited state. Flowing.

On the other hand, the microcomputer 21 performs a voltage monitoring operation of the terminal voltage E2 of the secondary battery 12 as shown in step ST2.
At 3, it is determined whether or not the secondary battery 12 is in the overdischarged state.

A secondary battery 12 such as a lithium ion battery
Has a correlation between the charging capacity and the terminal voltage,
By monitoring the terminal voltage using this characteristic, it is possible to flexibly deal with the charging circuit side.

Therefore, whether or not the secondary battery 12 is in the overdischarge state is determined by whether or not the terminal voltage E2 of the secondary battery 12 exceeds a preset threshold value ER built in the microcomputer 21. Can be.

In step ST3, as shown in FIG.
When the terminal voltage E2 is lower than R at the point P, it is determined to be in the overdischarge state.

In FIG. 4A, the elapsed time t is plotted on the horizontal axis.
The vertical axis indicates the terminal voltage E2 of the secondary battery 12, and in FIG. 4B, the horizontal axis indicates the elapsed time t, and the vertical axis indicates the charging current I2 flowing through the secondary battery 12.

In this overdischarge state, as shown in FIG. 4A, since the current is in the current limiting section A and the limiting resistor R4 is inserted, the charging circuit 10 is turned off as shown in step ST4. The secondary battery 12 is driven at a constant voltage, and the charging current I2 flows in a current-limited state.

Since the terminal voltage E2 tends to advance and increase with the passage of the charging time, the microcomputer 21 returns to step T2 to determine whether or not the terminal voltage E2 has escaped from the current limiting section A, and performs the voltage monitoring operation. to continue.

As a result of continuing the constant voltage charging, the microcomputer 21 sets the terminal voltage E2 of the secondary battery 12 to
As shown in (A), when the threshold value ER is reached, it is determined that the overdischarge state has been released, and the process proceeds to step ST5.

First, the gate voltage of the field effect transistor of the current controlling element Q3 is controlled to be off by controlling the gate voltage of the current controlling element Q3 via the circuit control element 22, and thereafter, the charging by the constant current charging is performed from the charging circuit 10 by the voltage rise of the circuit. The current I2 flows.

When the charge current I2 exceeds the threshold value ER, as shown in FIG. 4B, the charge current I2 rapidly rises to a predetermined value IM to charge the secondary battery 12. The charging current I2 gradually decreases in a curve indicated by the charging current I2.

On the other hand, when the terminal voltage E2 of the secondary battery 12 exceeds the threshold value ER as shown in FIG.
2 increases, the voltage rise rate becomes larger than in the case of the current limit section A, rises in a large curve indicated by the terminal voltage E2, and the constant current charging operation is performed.

As the charging proceeds, the charging current I2 to the secondary battery 12 decreases, so that the potential difference between both ends of the limiting resistor R1 shown in FIG.
2 is turned off, the feedback voltage V1 decreases, and D
The C / DC converter 13 enters the stable operation region and performs constant voltage charging.

FIG. 2 is a block diagram showing another embodiment of the secondary battery charging device according to the present invention. In this case, the secondary battery charging device is constituted by discrete circuit elements. For ease of understanding, circuit elements having the same functions as those shown in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted.

In this case, the terminal voltage E3 of the secondary battery 12
In order to monitor the threshold voltage ER, a comparator 24, which is a logic element functioning as a voltage monitoring means, is used instead of the microcomputer 21. Is used to constitute the secondary battery charger 26.

Even with such a configuration, the same operation as the operation shown in the flowchart shown in FIG. 3 is performed similarly to the secondary battery charger 23 having the configuration shown in FIG. 1, and the terminal voltage E3 is shown in FIG. The terminal voltage E2 and the charging current I3 correspond to the charging current I2 shown in FIG.

That is, the terminal voltage E3 of the secondary battery 12
Is constantly input to the comparator 24. However, when the terminal voltage E3 exceeds the threshold voltage ERV input from the reference voltage generator 25, the polarity of the voltage at the output terminal is inverted.

This polarity inversion is applied to the gate of the field effect transistor functioning as the current control element Q3 via the circuit control element 22A, and performs control to turn on and off the drain and source of the field effect transistor. Then, the limitation of the charging current I3 is canceled or the current is limited by short-circuiting or opening the limitation resistor R4.

[0046]

As described above, according to the secondary battery charger of the present invention, the terminal voltage of the secondary battery is monitored even when the secondary battery to be charged is in an overdischarged state. By activating the current limiting means, an excessive current can be prevented from flowing through the secondary battery and the charging circuit, and the circuit elements of the charging circuit and the AC adapter serving as a power supply source have a minimum necessary size. Thus, a charging system can be realized.

In addition, even if some element in the charging circuit fails and the power supply side and the output of the charging circuit are short-circuited, the current limiting means prevents excessive current from flowing to the secondary battery. And the system can be advantageously operated from the viewpoint of system security.

Further, even in the initial stage of the circuit operation, even when the charging circuit is not operating, the current limiting means, especially only the limiting resistor, is always inserted between the charging circuit and the secondary battery, so that the current limiting is performed. Therefore, the system can be advantageously operated from the viewpoint of system security management.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment according to the present invention.

FIG. 2 is a block diagram showing another embodiment according to the present invention.

FIG. 3 is a flowchart for explaining the operation of the embodiment shown in FIGS. 1 and 2;

FIG. 4 is a characteristic diagram for explaining the operation of the embodiment shown in FIGS. 1 and 2;

FIG. 5 is a block diagram showing a configuration of a conventional secondary battery charging device.

6 is a characteristic diagram illustrating the operation of the secondary battery charging device shown in FIG.

[Explanation of symbols]

10; charging device; 11; power supply; 12; secondary battery; 13;
DC / DC converter, 14; smoothing circuit, 20; current limiting circuit, 21; microcomputer, 22; circuit control element, 23; secondary battery charger, 24; comparator,
25; reference voltage generator, 26; secondary battery charger, E
R: Threshold, ERV: Threshold voltage, Q1 to Q2; Transistor, Q3: Current control element, R1: Detection resistor, R2: Voltage dividing resistor, R3: Volume, R4: Limiting resistor, V1: Feedback voltage, E1 to E3 Terminal voltage, I1 to I3; charging current,
A: Current limit section

Claims (5)

[Claims] 1. A secondary battery charger for charging a secondary battery by performing constant current and constant voltage charging via a charging circuit, wherein the charging device is inserted between the secondary battery and the charging circuit. A secondary battery charging device comprising: a current limiting unit configured to limit a charging current according to a control signal; and a voltage monitoring unit configured to monitor a terminal voltage of the secondary battery and output the control signal based on a predetermined threshold. apparatus. 2. The secondary battery charging device according to claim 1, wherein the secondary battery is a lithium ion battery. 3. The current limiting device according to claim 1, wherein said current limiting means comprises a limiting resistor inserted in series in a charging circuit, and a current control element connected in parallel to said limiting resistor and controlled by said control signal. Next battery charger. 4. The secondary battery charger according to claim 1, wherein said voltage monitoring means is constituted by a microcomputer. 5. The secondary battery charging device according to claim 1, wherein said voltage monitoring means comprises a comparator for comparing said threshold value with said terminal voltage.