JPH0974691A - Charger for li ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to fully charge an Li ion secondary battery by performing a switching control for a switch depending on a detected signal which has detected a charge current by means of a DC power supply lower than a normal charge voltage and a small current of a voltage booster circuit. SOLUTION: A switch 7 is connected to a-side at a point in time when an Li ion secondary battery 4 has been connected to a charger, a DC power supply 1 is directly connected to a constant voltage circuit 2, and an Li ion secondary battery 4 is charged by current limited by a current, limiting circuit 3. At this time, a relatively large current flows. If the charging is continued in this stage, the charging current decreases gradually. When the charging current becomes lower than a current value set in a charge current detecting circuit 6, the switch 7 is controlled by a detected signal and connected to b-side, and a DC power supply 1 is connected to a constant voltage circuit 2 through a voltage booster circuit 5. At this point in time, a charged current of the Li ion secondary battery has decreased, so that the voltage booster circuit, 5 may supply a small current only.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charger for a rechargeable Li-ion secondary battery pack used in electronic equipment.

[0002]

2. Description of the Related Art A conventional Li-ion secondary battery charger will be described with reference to an example shown in FIG. The charger for the Li-ion secondary battery 4 includes a DC power supply 1 for supplying a charging current to the Li-ion secondary battery 4, a constant voltage circuit 2 for fixing the charging voltage for the Li-ion secondary battery 4 to a specified value, and a Li The current limiting circuit 3 limits the charging current to the ion secondary battery 4.

The Li-ion secondary battery 4 is constructed by connecting battery cells in series or in parallel depending on the required voltage and capacity of the electronic equipment used. Usually, the specified charging voltage per cell of Li-ion secondary battery is about 4.2V. Now, it is assumed that the Li-ion secondary battery 4 has three Li-ion secondary batteries connected in series. Since the Li-ion secondary battery 4 has three cells in series, the specified charging voltage is 12.
It is 6V (4.2V × 3 cells). Therefore, the output voltage of the constant voltage circuit 2 is set to 12.6V. Also, D
The voltage of the C power source 1 is the set voltage (1
It goes without saying that a voltage higher than 2.6 V) is required.

On the other hand, the limiting current of the current limiting circuit 3 is Li
It is determined from the capacity of the ion secondary battery 4 and the charging completion time, and is set to about 1.0 C to 1.5 CmA for quick charging and about 0.5 CmA for normal charging. Now, the capacity of the Li-ion secondary battery 4 is 730 mAh, and the charging current is 1.
Assuming 5 CmA, the limiting current of the current limiting circuit 3 is 109
It is set to 5 mA. As described above, the output voltage of the DC power supply 1 needs to be higher than the set voltage of the constant voltage circuit 2, but if the output voltage of the DC power supply 1 is the constant voltage circuit 2,
When using a voltage lower than the set voltage of, the voltage booster circuit 5 is provided between the DC power source 1 and the constant voltage circuit 2 as shown in FIG. 5, and the output voltage of the constant voltage circuit 2 becomes equal to the set voltage. Need to be.

FIG. 6 shows the charging current characteristics when the Li-ion secondary battery 4 is charged in the conventional Li-ion secondary battery charger configured as described above. The characteristics are shown in FIG. In the conventional Li-ion secondary battery charger shown in FIGS. 4 and 5, the voltage of the DC power supply 1 or the output voltage of the voltage boosting circuit 5 is higher than the set voltage of the constant voltage circuit 2, and the constant voltage circuit 2 sets the voltage. When outputting a voltage, the charging current characteristic and the terminal voltage characteristic of the Li-ion secondary battery 4 are the characteristics shown by A in FIGS. 6 and 7. Further, in the Li-ion secondary battery charger shown in FIG. 4, when the voltage of the DC power supply 1 is low and the output voltage of the constant voltage circuit 2 is lower than the set voltage, the charging current characteristics and the Li-ion secondary battery 4 The terminal voltage characteristic of is the characteristic shown by B in FIGS. 6 and 7. The charging rate of the Li-ion secondary battery 4 is 0 mA in the charging current characteristic shown in FIG.
7 and the terminal voltage of the Li-ion secondary battery 4 shown in FIG.

As described above, in the conventional Li-ion secondary battery charger shown in FIG. 4, when the voltage of the DC power source 1 cannot be set sufficiently higher than the set voltage of the constant voltage circuit 2,
For example, the Li-ion secondary battery 4 has three cells connected in series, the specified charging voltage is about 12.6 V, and D
When the C power source 1 is a car battery and the voltage is less than the specified charging voltage, the Li-ion secondary battery 4 cannot be fully charged.

In the conventional Li-ion secondary battery charger shown in FIG. 5, the output current of the voltage boosting circuit 5 needs to be higher than the current limit of the current limiting circuit 3. For example, in the above-mentioned example, In this case, it is necessary to output about 1.1 A, which means that a large current is handled, so the charger can be made smaller,
It is very disadvantageous in terms of heat and cost.

[0008]

As described above, in the conventional Li-ion secondary battery charger, when charging is performed at a DC power supply voltage lower than the specified charging voltage of the Li-ion secondary battery, There is a problem. It is impossible to fully charge the Li-ion secondary battery. When the voltage booster circuit is used, a large current is handled, and it is impossible to reduce the size of the charger, resulting in a large amount of heat generation, which is disadvantageous in terms of heat and cost.

In view of the above points, the present invention has been made to solve the above problems, and an object thereof is to provide a DC power source that does not meet the specified charging voltage of a Li-ion secondary battery and a voltage of a small current. An object of the present invention is to provide an inexpensive Li-ion secondary battery charger that can fully charge a Li-ion secondary battery by a booster circuit.

[0010]

In order to achieve the above object, the present invention provides a Li-ion secondary battery charger having a power source, a constant voltage circuit, and a current limiting circuit. A charging current detection circuit that detects the charging current,
A Li-ion secondary battery charger is provided with a voltage booster circuit for boosting the power supply voltage and a switch (switching means) for selecting either the power supply output or the voltage booster circuit to connect to the input of the constant voltage circuit. According to the detection signal of the current detection circuit that detects the charging current of the secondary battery, the switch is switched and controlled.

[0011]

Therefore, according to the present invention, it is possible to fully charge the Li-ion secondary battery with a DC power source that does not reach the specified charging voltage of the Li-ion secondary battery and to use the voltage booster circuit with a small current, and to make the Li-ion inexpensive. A secondary battery charger can be provided.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on the embodiments shown in the drawings. FIG. 1 is a diagram showing an embodiment of a Li-ion secondary battery charger according to the present invention. In the figure, a charging current is supplied from the DC power supply 1 to the Li-ion secondary battery 4, and the set voltage of the constant voltage circuit 2 and the limiting current of the current limiting circuit 3 are the same as those of a conventional Li-ion secondary battery charger. It has been decided. In the Li-ion secondary battery charger shown in FIG. 1, the output of the DC power supply 1 is supplied to the constant voltage circuit 2 directly by the switch 7 or via the voltage booster circuit 5, and is fixed to the set voltage, and then the current limit is applied. The current is limited by the circuit 3 and is supplied to the Li-ion secondary battery 4 via the charging current detection circuit 6.

The control of the switch 7 will be described in detail below. When the Li-ion secondary battery 4 is connected to the charger, the switch 7 is connected to the a side, the DC power supply 1 is directly connected to the constant voltage circuit 2, and the Li-ion secondary battery 4 is connected to the current limiting circuit. It is charged by the current limited by 3. The charging current at this time is about 1.0 in rapid charging, as described in the conventional Li-ion secondary battery charger.
C to 1.5 CmA, about 0.5 CmA in normal charging, and a relatively large current flows. If charging is continued in this state, the terminal voltage of the Li-ion secondary battery 4 rises and approaches the voltage set by the constant voltage circuit 2. The charging current gradually decreases from the current limited by the current limiting circuit 3. When the charging current decreases and falls below the current value set by the charging current detection circuit 6, the switch 7 is controlled by the detection signal 8 output from the charging current detection circuit 6 and is connected to the b side, and the DC power supply 1 has a voltage It is connected to the constant voltage circuit 2 via the booster circuit 5. At this point, the charging current of the Li-ion secondary battery 4 is smaller than the current limited by the current limiting circuit 3, so the voltage boosting circuit 5 may supply a small current.

In the charger for the Li-ion secondary battery configured as described above, the voltage of the DC power source 1 is constant voltage circuit 2.
6 is sufficiently higher than the set voltage, the charging current characteristics shown in A of FIG. 6 and the terminal voltage characteristics of the Li-ion secondary battery shown in A of FIG. Becomes The output voltage of the DC power supply 1 is the constant voltage circuit 2
If the set voltage is less than the set voltage,
The terminal voltage characteristics of the ion secondary battery 4 are as shown in FIG. That is, when charging is started, the switch 7 is connected to the side a, and the terminal voltage of the Li-ion secondary battery 4 approaches the set voltage of the constant voltage circuit 2, that is, the voltage less than the specified charging voltage of the Li-ion secondary battery 4. go. The charging current gradually decreases from the current limited by the current limiting circuit 3. Even if this state continues, the Li-ion secondary battery 4 is not fully charged as described in the conventional Li-ion secondary battery charger, but the charging current decreases and the charging current detection circuit 6 decreases. By switching the switch 7 to the b side, the output voltage of the constant voltage circuit 2 becomes a set voltage, and the Li-ion secondary battery 4 can be fully charged.

[0015]

As described above, according to the present invention, L
Provided is an inexpensive Li-ion secondary battery charger that can fully charge a Li-ion secondary battery by using a DC power supply that does not reach the specified charging voltage of the i-ion secondary battery and a small-current voltage booster circuit. It is possible and the effect is remarkable. Further, it is effective when used as a charger for Li-ion secondary batteries for all electronic devices, and its application range is extremely wide.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a charger for a Li-ion secondary battery according to the present invention.

FIG. 2 is a graph showing an example of charging current characteristics of a Li-ion secondary battery charger according to the present invention.

FIG. 3 is a graph showing an example of terminal voltage characteristics of a Li-ion secondary battery in a Li-ion secondary battery charger according to the present invention.

FIG. 4 is a block diagram showing an example of a conventional Li-ion secondary battery charger.

FIG. 5 is a block diagram showing an example of a conventional Li-ion secondary battery charger.

FIG. 6 is a graph showing charging current characteristics of a conventional Li-ion secondary battery charger.

FIG. 7 shows L in a conventional Li-ion secondary battery charger.
The graph which shows the terminal voltage characteristic of an i-ion secondary battery.

[Explanation of Codes] 1 ... DC power supply, 2 ... Constant voltage circuit, 3
... current limiting circuit, 4 ... Li-ion secondary battery, 5 ... voltage boosting circuit, 6 ... charging current detection circuit, 7 ... switch,
8 ... Detection circuit.

Claims (4)

[Claims] 1. A Li-ion secondary battery charger including a power supply, a constant voltage circuit and a current limiting circuit, wherein a charging current detection circuit for detecting a charging current to the Li-ion secondary battery and a Li-ion secondary battery are provided. A charger for boosting the power supply voltage of the charger; and switching means for selectively connecting either the power supply output or the voltage booster circuit output to the input of the constant voltage circuit, A charger for a Li-ion secondary battery, wherein the switching means is configured to switch and control in accordance with a detection signal of a current detection circuit. 2. The charger for a Li-ion secondary battery according to claim 1, wherein the switching means is switched and controlled in accordance with a detection signal of the charging current detection circuit, and the limiting current value of the current limiting circuit is changed. Li characterized by being configured to control
Ion secondary battery charger. 3. The Li-ion secondary battery charger according to claim 1 or 2, wherein the power source is a vehicle-mounted battery. 4. The charger for a Li-ion secondary battery according to claim 3, wherein the Li-ion secondary battery is a 3-cell series connection type.