JPH07308028A - Charger for series battery - Google Patents

Abstract

PURPOSE:To full charge all batteries with good balance within a time as short as possible without causing overcharge in any battery. CONSTITUTION:Batteries Bl, B2 are connected in series with the output terminal of a variable voltage power supply circuit 1 and voltage detectors 5a, 5b are connected across respective batteries B1, B2. The battery charger is constituted such that the output level of the voltage detector varies abruptly when the difference between the battery voltage and a preset full charge voltage approaches zero. When the voltage of each battery is increasing through charging operation, a selection circuit 6 extracts an output exhibiting a largest level variation among a plurality of voltage detectors. Output signal from the selection circuit is employed as a control signal for a power supply circuit 1 and a feedback control loop is established. When the voltages of the batteries B1, B2 reach the full charge voltage, bypass current paths 7a, 8a and 7b, 8b are formed so that the charging current bypasses the batteries B1, B2 and fed to another battery.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging device for charging a lithium secondary battery or the like by connecting them in series. In particular, all the batteries are fully charged in a short time as possible without overcharging. The present invention relates to charge control for charging.

[0002]

2. Description of the Related Art A typical example of a series battery charger for a lithium secondary battery is disclosed in Japanese Patent Laid-Open No. 4-331425. In this conventional charging device, a switching element is inserted in the charging current path from the charging power source to the series battery, and the terminal voltage of each battery connected in series is input to each individual voltage detector. When the terminal voltage of any one of the batteries reaches the set value (charging end voltage) during charging of the series battery,
The switching element is turned off by the detection signal from the corresponding voltage detector, and the charging path to the battery group is cut off. In this way, overcharging is prevented. In addition, the voltage detector is configured to detect the voltage of the overcharge level of each battery, and for the battery in which overcharge is detected, not only charging is stopped, but also the battery is appropriately discharged to Charging devices designed to correct the capacity balance are also known.

[0003]

In the above-mentioned conventional battery charger for series batteries, the charging of the entire battery is stopped when at least one battery voltage exceeds the set value, so that the remaining capacity and characteristics of each battery vary. As a result, the charging time is limited by the battery that is the fastest to be fully charged, and it is not possible to fully charge another battery having a sufficient capacity. In order to solve this problem, it is conceivable to detect that the series voltage of the battery group has reached the total value of the charge completion voltage of each battery and stop the charging. However, in such a case, it is likely that a certain battery is overcharged and continues to be charged. Further, the configuration in which the capacity balance of each battery is corrected by discharging the overcharged battery leads to the overcharged state of the battery, which is a very unfavorable method depending on the type of the battery.

The present invention has been made in view of the above-mentioned conventional problems, and an object thereof is to fully charge all the batteries in the shortest possible time without overcharging any of the batteries and to determine the capacity of each battery. An object of the present invention is to provide a series battery charging device which also has a function of adjusting the balance.

[0005]

Therefore, in the present invention, a plurality of batteries to be charged are connected in series to the output terminal of a variable voltage power supply circuit whose DC output voltage changes in response to a control signal.
A voltage detector is connected between each terminal of these batteries, and the output level of the corresponding voltage detector is configured to change suddenly when the difference between the battery voltage and the set charge end voltage becomes zero. In the process of increasing the voltage of each of the batteries due to charging, the output that causes the largest level change among the outputs of the plurality of voltage detectors is extracted by the selection circuit, and the output signal of the selection circuit is directly or indirectly By using the control signal of the power supply circuit, the output voltage of the power supply circuit is controlled so that the corresponding battery voltage in the voltage detector whose output is extracted by the selection circuit becomes substantially equal to the charge completion voltage. And a feedback control loop that, when the voltage detector detects that the corresponding battery voltage has reached the charge end voltage, responds to the output signal thereof. Bypass current path is formed, and configured so as to bypass the corresponding cell flow the charging current to the other batteries. In this configuration, the bypass current path may be included as a part of the voltage detector. Further, the conduction resistance value of the bypass current path may be varied according to the corresponding battery voltage.

[0006]

When a plurality of batteries are charged in series, the terminal voltages of the batteries usually differ due to variations in the capacities and remaining capacities of the batteries. In the above charging device according to the present invention, attention is paid to the battery having the highest terminal voltage during charging, and the output voltage of the power supply circuit is feedback-controlled so that the battery voltage becomes substantially equal to the charging completion voltage. At the same time, a bypass current path for bypassing the battery that has reached the charge completion voltage is formed. Bypassing the battery, a charging current for another battery is supplied. In other words, neither battery will ever be overcharged,
Charging proceeds while the capacity balance of each battery is corrected, and the charging voltage (output voltage of the power supply circuit) is kept at the maximum within the range of the conditions. Therefore, each battery can be charged in a well-balanced manner in a short time with an efficiency close to that of the constant voltage charging method for a single battery.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The construction of a charging device according to an embodiment of the present invention is shown in FIGS. In this embodiment, two lithium secondary batteries B1 and B2 are charged in series. The variable voltage power supply circuit for charging is the chopper-controlled DC-DC converter 1. The direct current generated by the rectifier circuit 3 and the smoothing circuit 4 from the AC power source 2 becomes the input of the DC-DC converter 1. The DC-DC converter 1 includes a switching element Q1 which is turned on / off at a high frequency by a switching control circuit 1a, an inductor L1 and a capacitor C1 which are connected in series with the switching element Q1 to a smoothing circuit 4, and L1 and C1. It includes a diode D1 connected in parallel and obtains a smoothed DC output from the capacitor C1. As is well known, the switching control circuit 1a changes the duty ratio of the switching pulse of the switching element Q1 in response to the voltage control signal, and changes the output voltage Vout of the DC-DC converter 1 according to the change. The series batteries B1 and B2 are connected to the output terminal of the DC-DC converter 1 via an initial current limiting resistor R1 for preventing an excessive current from flowing at the initial stage of charging.

A voltage detector 5 is provided between the terminals of the battery B1.
a is connected, and the voltage detector 5b is connected between the terminals of the battery B2. As shown in FIG. 2, the voltage detectors 5a and 5b have the same configuration, and the input voltage (V1 or V2)
With the comparator 51 operating as a power source, and the input voltage divided by resistors R2 and R3 (Vx or V
y) is applied to the plus terminal of the comparator 51, and the constant voltage Vf generated by the constant voltage generator 52 is applied to the comparator 5
It is a configuration in which it is applied to the negative terminal of 1.

In this example, the charge end voltage of the batteries B1 and B2 is 4.2 volts. Then, when the terminal voltage V1 of the battery B1 rises to reach 4.2 volts, the divided input voltage Vx in the voltage detector 5a becomes substantially equal to the set voltage Vf, and the output of the comparator 51 becomes low before and after this state. Sudden change from level to high level.

In exactly the same way, the terminal voltage V2 of the battery B2
Rises to 4.2 volts, the divided input voltage Vy in the voltage detector 5b becomes substantially equal to the set voltage Vf, and the output of the comparator 51 suddenly changes from low level to high level before and after this state.

A series circuit of a switch 7a serving as a bypass current path and a resistor 8a is connected in parallel to the battery B1, and a switch 7b serving as a bypass current path and a resistor 8 are connected to the battery B2.
b series circuits are connected in parallel. Switches 7a and 7
b is normally off, and when the output of the voltage detector 5a is inverted to a high level, the switch 7a is turned on and the voltage detector 5b is turned on.
When the output of is inverted to a high level, the switch 7b is turned on.

As shown in FIG. 2, the selection circuit 6 includes two diodes D2 and D3 for connecting the outputs of the two comparators 51 in a wired-OR connection, and a buffer amplifier for inputting the voltage at the connection point of the diodes D2 and D3. 6a.
The selection circuit 6 extracts a signal having a higher level from the output of the voltage comparator 5a and the output of the voltage comparator 5b. The extracted signal is input to the switching control circuit 1a as a voltage control signal for the DC-DC converter 1 via the buffer amplifier 6a. This makes DC-
A feedback control loop that controls the voltage of the DC converter 1 is configured.

The switching control circuit 1a has a characteristic that linear control is performed by the feedback control loop in a transient state in which the output level of the comparator 51 suddenly changes.

In the above configuration, the series batteries B1 and B2
When the charging of the battery is started, the battery voltage V
1 and V2 rise rapidly. Then, for example, the terminal voltage V1 of one battery B1 rises earlier than the other battery voltage V2, and the battery voltage V1 is almost equal to the charging end voltage (4.2).
Bolt). Then, the output of the comparator 51 of the voltage detector 5a suddenly changes from the low level to the high level, and the output level becomes the voltage control signal of the DC-DC converter 1 via the selection circuit 6. Then, as a result of performing the linear control in the transient state of the output level change of the comparator 51, DC
-The output voltage Vout of the DC converter 1 is the battery voltage V1.
Is feedback-controlled so that the voltage substantially matches the charge end voltage (4.2 V). That is, the feedback control loop functions so that the state of the following equation is maintained.

Vout = 4.2 + V2 At the same time, the switch 7a is turned on in response to the output of the comparator 51 of the voltage detector 5a being inverted to a high level, and the bypass consisting of the switch 7a bypassing the battery B1 and the resistor 8a. A current path is formed and the charging current for the other battery B2 will flow through this bypass current path. Therefore, the battery B1 is charged at the highest voltage Vout within the range where it is not overcharged, and finally,
The charging current is reduced to almost zero. As a result, charging is continuously performed until both the two batteries B1 and B2 are well-balanced and fully charged.

FIG. 3 shows the configuration of the essential parts of another embodiment of the present invention. The feature of this embodiment is that each battery B1 (B2)
The voltage detector 5a (5b) for detecting the voltage is included as a part of the bypass current path. That is, the voltage detector 5a (same for 5b) is configured using the shunt regulator 53. The shunt regulator 53 is an IC in which an operational amplifier and a Zener diode are connected as shown in the figure (for example, product number HA1743).
1). The voltage of the battery B1 is divided by resistors R4 and R5 and applied to the reference terminal R of the shunt regulator 53, the anode terminal A of the shunt regulator 53 is connected to the negative side of the battery B1, and the cathode terminal K is connected to the series resistors R6 and R7. Is connected to the positive side of the battery B1 via. The middle point of the resistors R6 and R7 is connected to the base of the open collector type output transistor 54, and the collector of the transistor 54 is connected to the selection circuit 6.

In this configuration, when the battery B1 reaches the charge completion voltage first during the charging process, the shunt regulator 5
3 becomes conductive, a current flows from the cathode K to the anode A, and the output transistor 54 which has been off until then is turned on. Then, the shunt regulator 53 itself serves as the bypass current path, and the charging current to the other battery B2 bypasses the battery B1 to bypass the shunt regulator 5.
It will flow through 3. With this configuration, the number of circuit elements can be reduced.

In the above two embodiments, the conduction resistance when the bypass current path was formed was constant (in the example of FIG. 1, it is almost determined by the resistors 8a and 8b, and in the example of FIG. Almost determined by R6 and R7),
The present invention is not limited to such an embodiment,
You may comprise as follows. If the battery B1 reaches the charge end voltage first and a bypass current path that bypasses the battery B1 is formed, the conduction resistance of the bypass current path at this time is changed according to the voltage difference between the batteries B1 and B2, and B2
It is configured to appropriately control the charging current to the battery. In this case, a microcomputer is used, the voltage of each battery is applied to the input port with an A / D converter, and the voltage of each battery is monitored by the microcomputer.
It controls the converter and the bypass current path as described above. Then, a large number of current limiting resistors having different values are provided in the bypass current path, and the microcomputer switches the analog switch so that the current limiting resistance having an appropriate value is incorporated in the bypass current path according to the voltage monitoring result. The configuration such as to do will be adopted.

[0019]

As described in detail above, according to the series battery charging device of the present invention, neither battery is overcharged and the safety is extremely high. Can fully charge multiple batteries in a short time with good balance.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram of a charging device according to an embodiment of the present invention.

FIG. 2 is a configuration diagram showing details of a main part of the apparatus according to the above embodiment.

FIG. 3 is a configuration diagram showing details of a main part of another embodiment of the present invention.

[Explanation of symbols]

 1 DC-DC converter (variable voltage power supply circuit) 1a Switching control circuit 5a, 5b Voltage detector 6 Selection circuit 7a, 7b Bypass current path switch 8a, 8b Bypass current path resistance 53 Shunt regulator B1, B2 Battery

Claims (3)

[Claims] 1. A plurality of batteries to be charged are connected in series to an output terminal of a variable voltage power supply circuit whose DC output voltage changes in response to a control signal, and a voltage detector is provided between each terminal of these batteries. Connected, configured so that the output level of the corresponding voltage detector suddenly changes in the vicinity of the difference between the battery voltage and the set charge expiration voltage becomes zero, in the process of increasing the voltage of each battery by charging,
By extracting the output having the largest level change among the outputs of the plurality of voltage detectors by the selection circuit, and directly or indirectly using the output signal of the selection circuit as the control signal of the power supply circuit, In the voltage detector whose output is extracted by the selection circuit, a feedback control loop that controls the output voltage of the power supply circuit is configured so that the corresponding battery voltage is substantially equal to the charge end voltage, and the voltage detector When it is detected that the corresponding battery voltage has reached the charge completion voltage, a bypass current path is formed in response to the output signal, and the corresponding battery is bypassed to flow the charging current to other batteries. A series battery charging device characterized in that 2. The series battery charging device according to claim 1, wherein the bypass current path is included as a part of the voltage detector. 3. The conduction resistance value of the bypass current path is variable according to the corresponding battery voltage.
Alternatively, the series battery charging device according to claim 2.