JP3429511B2 - Rechargeable battery charging circuit - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging circuit for secondary batteries, and more particularly to a charging circuit for charging a plurality of secondary batteries in series.

[0002]

2. Description of the Related Art There are various types of charging methods for secondary batteries. For example, Japanese Patent Application Laid-Open No. 2-60073 discloses a method of charging a secondary battery so that the maximum terminal voltage is within a predetermined range. Have been described.

In this conventional charging method, when a non-aqueous electrolyte secondary battery using a lithium metal as a negative electrode active material and a manganese oxide as a positive electrode active material is charged, the maximum terminal of the secondary battery is charged. Voltage is 3.50-4.10.
By charging the battery within the range of (V), the cycle life is extended.

[0004]

In the conventional charging method described above, when a plurality (n) of secondary batteries are connected in series for charging, the maximum terminal voltage of the series circuit of n secondary batteries is 3 or less. Charging is performed so as to be in the range of 0.50 × n to 4.10 × n (V). When charging is performed by such a method, if there is a variation in the electric capacity between the individual secondary batteries, the terminal voltage of the battery having a relatively small electric capacity is 3.
The maximum terminal voltage range of 50 to 4.10 (V) will be exceeded. If the battery is charged in excess of the maximum terminal voltage determined in this way, the battery will be deteriorated or damaged, resulting in a shorter battery life.

In order to avoid this problem, a method may be considered in which the electric capacities of the individual secondary batteries are measured in advance, and a plurality of batteries are connected in series with a combination of batteries having uniform electric capacities for charging. However, this method not only requires the complicated work of selecting batteries with uniform electric capacities, but also spreads the dispersion of electric capacities of individual secondary batteries during repeated charging cycles, which is the root cause of the above problem. Is not an effective solution.

The present invention has been made in order to solve such a conventional problem. When a plurality of secondary batteries are connected in series for charging, the electric capacity of each secondary battery varies. It is an object of the present invention to provide a charging circuit for a secondary battery which does not cause deterioration or damage of the battery.

[0007]

In order to solve the above problems, a secondary battery charging circuit according to the present invention comprises a charging power source for charging a plurality of secondary batteries connected in series, and A plurality of voltage detection means for detecting the terminal voltage of the plurality of secondary batteries, and an output terminal for the plurality of voltage detection means.
Each input terminal is connected and each output terminal is common
Consisting of multiple ideal diode circuits connected to
Number of ideal diodes to the common output terminal
The output of the signal processing means is connected between the signal processing means for generating an output corresponding to the highest voltage among the outputs of the pressure detecting means, and the charging power source and the series circuit of the plurality of secondary batteries. Is supplied to the plurality of secondary batteries for a period of time less than the set value, and after reaching the set value, the charge current is controlled so that the output of the signal processing means maintains the set value or less. And a control means for controlling the operation.

[0008]

As described above, according to the present invention, constant current charging is performed for a plurality of secondary batteries connected in series while the output of the voltage detecting means corresponding to the highest terminal voltage is below the set value. After reaching the set value, the charging current is controlled so that the terminal voltage of all batteries does not exceed the set value, and for example, constant voltage charging is performed, resulting in variations in the electric capacity of the secondary battery. However, the battery will not be deteriorated or damaged.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram of a charging circuit for a secondary battery according to an embodiment of the present invention. In the figure, one end of the charging power source 1 is connected to the input terminal IN of the control circuit 2. Between the output terminal OUT of the control circuit 2 and the other end of the charging power source 1, a plurality (two in this example) of secondary batteries (for example, lithium secondary batteries, hereinafter simply referred to as batteries) 3, 4 Are connected in series. As the charging power source 1, a power source for rectifying the output of an AC power source to obtain a direct current or another battery having a relatively large capacity is used.

When the voltage applied to the control terminal C is lower than the reference voltage Vref (described later), the control circuit 2 supplies a preset constant charging current to the batteries 3 and 4 to perform so-called constant current charging. When the voltage applied to the control terminal C rises and reaches the reference voltage Vref, the voltage is applied to the control terminal C.
That controls the charging current so that the voltage to be to maintain a constant voltage corresponding to Vref or Vref.

The voltage detection circuits 5 and 7 are for detecting the terminal voltages of the voltages 3 and 4, and the voltage detection circuit 5 is composed of a differential amplifier composed of resistors R1 to R4 and an operational amplifier 6, and similarly. The voltage detection circuit 7 is composed of a differential amplifier including resistors R5 to R8 and an operational amplifier 8. The input terminals a1 and b1 of the voltage detection circuit 5 are connected to the positive electrode terminal and the negative electrode terminal of the battery 3, respectively, and the resistance R
1 and R2 are connected to the inverting input terminal and the non-inverting input terminal of the operational amplifier 6, respectively. Operational amplifier 6
The inverting input terminal is connected to the output terminal via the resistor R3, and the non-inverting input terminal is grounded via the resistor R4. The output terminal of the operational amplifier 6 is connected to the output terminal c1 of the voltage detection circuit 5.

Similarly, the input terminals a2 and a2 of the voltage detection circuit 7 are
b2 is connected to the positive electrode terminal and the negative electrode terminal of the battery 4, respectively, and is also connected to the inverting input terminal and the non-inverting input terminal of the operational amplifier 8 via the resistors R5 and R6. The inverting input terminal of the operational amplifier 8 is connected to the output terminal via the resistor R7, and the non-inverting input terminal is grounded via the resistor R8. The output terminal of the operational amplifier 8 is connected to the output terminal c2 of the voltage detection circuit 7.

Therefore, the output terminals c of the voltage detection circuits 5 and 7
Output voltages Vt1 and Vt2 corresponding to the terminal voltages of the batteries 3 and 4 are obtained at 1 and c2, respectively. The output voltages Vt1 and Vt2 of these voltage detection circuits 5 and 7 are
The terminal voltages of V1 and V2, and resistors R1, R2, R3
The resistance values of R4, R5, R6, R7, and R8 are r1, r2, and
r3, r4, r5, r6, r7, r8, and r1 =
If r2 = r3 = r4 = r5 = r6 = r7 = r8, then Vt1 = -V1 (1) Vt2 = -V2 (2).

Output terminals c1 and c2 of the voltage detection circuits 5 and 7
Are connected to the two input terminals d1 and d2 of the signal processing circuit 9. The signal processing circuit 9 outputs the output voltage Vtm corresponding to the lower one of the voltages input to the input terminals d1 and d2.
Is generated from the output terminal e. As shown in the equations (1) and (2), the output voltages Vt1 and Vt2 of the voltage detection circuits 5 and 7 are inverted with respect to the terminal voltages V1 and V2 of the batteries 3 and 4, so that the signal processing circuit is eventually ended. The voltage Vtm generated at the output terminal e of the battery 9 is a voltage corresponding to the higher one of the terminal voltages V1 and V2 of the batteries 3 and 4.

The signal processing circuit 9 is composed of two ideal diode circuits 10 and 11. The first ideal diode circuit 10 includes resistors R9 and R10 and a diode D.
1 and D2 and an operational amplifier 12, one end of the resistor R9 is connected to the input terminal d1 of the signal processing circuit 9 and the other end is connected to the inverting input terminal of the operational amplifier 12, and the non-inverting input terminal of the operational amplifier 12 is grounded. The inverting input terminal of the operational amplifier 12 is further connected to the anode of the diode D1 and the resistor R.
10, the cathode of the diode D1 is connected to the output terminal of the operational amplifier 12 and the anode of the diode D2, and the cathode of the diode D2 and the other end of the resistor R10 are connected to the output terminal e of the signal processing circuit 9. There is.

Similarly, the second ideal diode circuit 11
Is composed of resistors R11 and R12, diodes D3 and D4, and an operational amplifier 13. One end of the resistor R11 is connected to the input terminal d2 of the signal processing circuit 9 and the other end is connected to the inverting input terminal of the operational amplifier 13. The non-inverting input terminal of 13 is grounded, the inverting input terminal of the operational amplifier 13 is further connected to the anode of the diode D3 and one end of the resistor R12, and the cathode of the diode D3 is the operational amplifier 13.
Is connected to the anode of the diode D4, and the cathode of the diode D4 and the other end of the resistor R12 are connected to the output terminal e of the signal processing circuit 9.

Now, the input terminals d1 and d2 of the signal processing circuit 9
The output voltages of the voltage detection circuits 5 and 6 input to the terminals are Vt1 and Vt2 as described above, and the resistors R9, R10, R11 and R
Assuming that the resistance values of 12 are r9, r10, r11 and r12 and the outputs of the ideal diode circuits 10 and 11 are not connected to each other, the output voltages Vx1 and Vx2 of the ideal diode circuits 10 and 11 are Vx1 = −, respectively. Vt1 × (r10 / r9) (3) Vx2 = −Vt2 × (r12 / r11) (4) Here, assuming that r9 = r10 and r11 = r12, the output voltages Vx1 and Vx2 of the ideal diode circuits 10 and 11 when the outputs are not connected to each other are −Vt1 and −Vt2, respectively.

Assuming that the relationship between the terminal voltages V1 and V2 of the voltages 3 and 4 is V1> V2, Vt1>Vt2> 0. Therefore, the output voltage Vx1 of the ideal diode circuit 10 (=-
Vt1) is the output voltage Vx of the ideal diode circuit 11
2 (= -Vt2). As a result, when the output terminals of the ideal diode circuits 10 and 11 are commonly connected to the output terminal e of the signal processing circuit 9 as shown in FIG. 1, the higher output voltage −Vt1 is output as the output voltage Vtm of the signal processing circuit 9. To be done. That is, Vtm = -Vt1 = V1 (5), and the voltage corresponding to the higher voltage V1 of the terminal voltages V1 and V2 of the batteries 3 and 4 is output as Vtm.
The output Vtm of the signal processing circuit 9 is input to the control terminal C of the control circuit 2.

Next, the operation of the charging circuit of FIG. 1 will be described with reference to the waveform diagram of FIG. 2 showing its charging characteristic. In FIG. 2, (a) shows the terminal voltages V1 and V2 of the batteries 3 and 4 and their series combined voltage, and (b) shows the charging current I flowing through the batteries 3 and 4, respectively.

When charging is started, a constant charging current is supplied from the charging power source 1 to the batteries 3 and 4 via the control circuit 2. For example, in the case where the batteries 3 and 4 are lithium secondary batteries, when the constant current charging is performed in this way, the terminal voltages V1 and V2 increase almost linearly as shown in FIG. Both V1 and V2 are lower than the reference voltage Vref.

Assuming that the battery 3 has a smaller electric capacity than the battery 4, the terminal voltage V1 of the battery 3 is higher than the terminal voltage V2 of the battery 4, so that the signal processing circuit as shown in the equation (5) is used. The output voltage V corresponding to V1 is applied to the output terminal e of 9
tm occurs. The output voltage Vtm is input to the control terminal C of the control circuit 2.

Now, when the output voltage Vtm of the signal processing circuit 9 is Vref> Vtm = V1, the control circuit 2 charges the batteries 3 and 4 with a constant current, but the charging proceeds and the terminal voltage of the batteries 3 and 4 increases. After time t = t1 when Vref = Vtm is reached, the charging current is reduced as shown in FIG. 2 (b) so that the terminal voltage V1 of the battery 3 is constant Vref, that is, constant voltage charging is performed. Charge 3 and 4.

On the other hand, the terminal voltage V2 of the battery 4 is shown in FIG.
As shown in, the terminal voltage V of the battery 3 during the period of 0 <t <t1
Although lower than 1, the slope shows almost the same voltage change. After this, when t1 ≦ t, the rising slope of the terminal voltage V2 becomes gentle and approaches V1 with the lapse of time.

In this way, the terminal voltages V1,
During a period in which the higher voltage of V2 does not reach the set value corresponding to the reference voltage Vref, the batteries 3 and 4 are charged with a constant current, and the higher voltage of the terminal voltages V1 and V2 reaches the set value. After that, by charging the batteries 3 and 4 at a constant voltage, even if the electric capacities of the batteries 3 and 4 vary, the battery having the smaller electric capacity is not applied with a voltage higher than the set value, and the battery is deteriorated. And damage can be prevented.

FIG. 3 shows a concrete example of the control circuit 2 shown in FIG. The control terminal C is connected to the inverting input terminal of the operational amplifier 14, and the reference voltage V is applied to the non-inverting input terminal of the operational amplifier 14.
ref is being applied. The output terminal of the operational amplifier 14 is connected to the base of the transistor Q1 and the collector of the transistor Q2 via the resistor R13. The collector of the transistor Q1 is connected to the input terminal IN, and the emitter is connected to the base of the transistor Q2 and one end of the resistor R14. The emitter of the transistor Q2 has a resistor R
It is connected to the output terminal OUT together with the other end of 14.

Now, the voltage input to the control terminal C, that is, the output voltage Vtm of the signal processing circuit 9 is the reference voltage Vref.
If it is lower, the output of the operational amplifier 13 becomes high level, and a large current flows through the base of the transistor Q1.
At this time, assuming that the base-emitter voltage of the transistor Q2 is V _BE and the resistance value of the resistor R14 is r14, a relatively large constant current expressed by V _BE / r14 flows in the transistor Q1, Constant current charging is performed on the batteries 3 and 4. On the other hand, when the output voltage of the signal processing circuit 9 reaches the reference voltage Vref, the output of the operational amplifier 14 becomes low level, so that the current flowing through the base of the transistor Q1 decreases and the battery 3 is kept so that Vtm does not exceed Vref. , 4 are subjected to constant voltage charging. The present invention is not limited to the above embodiments, but can be modified in various ways as follows.

(1) In the embodiment, when controlling the charging current in the control circuit 2, the resistance value of the transistor Q1 is changed to convert the extra power into heat in the configuration as shown in FIG. The charging current may be controlled by a control method. By doing so, the loss in the transistor is reduced and heat generation can be reduced.

(2) In the embodiment, the charging control is performed only on the basis of the terminal voltage of the battery. However, timer control may be combined, or temperature control for detecting a chargeable temperature range may be combined.

(3) In the embodiment, the control circuit 2 controls the charging current so that Vtm maintains Vref after the output voltage Vtm of the signal processing circuit 9 reaches the reference voltage Vref, but this is not always necessary. Absent. For example, after Vtm reaches Vref, the charging current may be simply reduced in steps, that is, the charging current may be controlled so that Vtm is maintained at a voltage equal to or lower than Vref. (4) In the embodiment, the example in which the battery and the voltage detection circuit are two sets is shown, but the number may be three or more.

(5) In the embodiment, the terminal voltage of each of a plurality of batteries connected in series is detected and the output corresponding to the maximum voltage among them is less than the set value or has reached the set value. Although the charging current of the batteries is controlled, if the number of batteries connected in series is larger, the batteries may be divided into a plurality of groups and the terminal voltage may be detected for each group. In that case, if the amplification degree of the voltage detection circuit or the signal processing circuit is selected, it is possible to control even if the number of batteries in each group is not the same. With such a configuration in which the terminal voltage is detected in units of groups, it is possible to reduce the number of voltage detection circuits and ideal diode circuits and reduce the overall circuit scale even when the number of batteries connected in series is large. .

(6) In the embodiment, a lithium secondary battery is used as the secondary battery, but the charging circuit of the present invention can be applied to the case where another secondary battery such as a lead storage battery is used. Is.

(7) In the embodiment, the voltage detecting means and the signal processing means are realized by hardware using resistors, diodes, operational amplifiers, etc., but part or all of them are programmed by using a microcomputer or the like. Processed with
It may be realized by software. In addition, the present invention can be variously modified and implemented without departing from the scope of the invention.

[0033]

As described above, according to the present invention, the terminal voltages of a plurality of secondary batteries are detected by the voltage detecting means, and the output terminals of the voltage detecting means are detected.
Each input terminal is connected and each output terminal is
It consists of multiple ideal diode circuits connected in common,
A plurality of electric currents are connected to the common output terminals of the plurality of ideal diode circuits.
A signal processing means for generating an output corresponding to the highest voltage among the outputs of the pressure detecting means is provided, and a constant charging current is supplied to the plurality of secondary batteries while the output of the signal processing means is less than the set value. By controlling the charging current so that the output of the signal processing means maintains the set value or less after reaching the set value, the deterioration or damage of the battery is caused even if the electric capacity of the secondary battery varies. Can be charged without. Therefore, it is not necessary to select a uniform battery capacity by measuring the electrical capacitance of the pre-cell and an even greater variation in capacitance by repeating the charge cycle, it is possible to perform appropriate charging.

Therefore, it is not necessary to measure the electric capacity of the batteries in advance to select batteries having a uniform capacity, and it is possible to perform appropriate charging even if there are wide variations in electric capacity due to repeated charging cycles. Is.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a charging circuit for a secondary battery according to an embodiment of the present invention.

2 is a waveform diagram for explaining the operation of the charging circuit of FIG.

FIG. 3 is a circuit diagram showing a specific example of a control circuit in FIG.

[Explanation of symbols]

1 ... Charging power source 2 ... Control circuit 3, 4 ... Secondary battery 5, 7 ... Voltage detection circuit 9 ... Signal processing circuit 10, 11 ... Ideal diode circuit

─────────────────────────────────────────────────── ─── Continuation of front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) H02J 7/00

Claims (2)

(57) [Claims] 1. A charging power source for charging a plurality of rechargeable batteries connected in series, a plurality of voltage detection means for detecting a terminal voltage of the plurality of rechargeable batteries, and a plurality of these voltage detection devices. Each input to the output terminal of the means
Terminals are connected and each output terminal is connected in common.
A plurality of ideal diode circuits,
The plurality of voltage detecting means are provided at a common output terminal of the ion circuit.
A signal processing means for generating a corresponding output to the highest voltage of the output, is connected between the series circuit of the secondary battery of the plurality and the charging power supply, the output of the signal processing means preset value Control means for supplying a constant charging current to the plurality of secondary batteries for a period of less than, and for controlling the charging current so that the output of the signal processing means maintains the set value or less after reaching the set value. A charging circuit for a secondary battery, comprising: 2. Each of the ideal diode circuits is non-inverted.
The operational amplifier whose input terminal is grounded, and the operational amplifier
Between the input terminal and the input terminal of the ideal diode circuit
The connected first resistor and the inverting input of the operational amplifier
A second resistor connected between the child and the common output terminal
And the anode is connected to the inverting input terminal of the operational amplifier.
And the cathode was connected to the output terminal of the operational amplifier.
An anode is connected to the first diode and the output terminal of the operational amplifier.
Connected to the cathode and the cathode to the common output terminal.
2. The secondary battery according to claim 1, comprising a second diode
Pond charging circuit.