JPH0956080A - Battery charger - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable a battery charger for charging a secondary battery, such as a lithium ion battery, etc., which is to be charged with a constant voltage to effectively utilize the capacity of the battery without deteriorating it. SOLUTION: A battery charger is constituted in such a way that the voltage supplied to a secondary battery can be switched between a first voltage V1 and a second voltage V2 which is lower than the first voltage V1 and, when the fully charged state of the battery is detected, the voltage is switched to the second voltage V2 from the first voltage V1 . In addition, when a charging current larger than a prescribed current value I2 is detected while the second voltage V2 is supplied, the voltage supplied to the battery is returned to the first voltage V1 (or a voltage between the second and first voltages V2 and V1 ).

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 a secondary battery, and more particularly to a charging device suitable for being applied to a secondary battery requiring constant voltage charging such as a lithium ion battery.

[0002]

2. Description of the Related Art Conventionally, lithium ion batteries have been developed as rechargeable batteries that require constant voltage charging. This lithium-ion battery
For example, the battery is charged with the characteristics shown in FIG. FIG. 12 is a characteristic diagram of charging current / voltage vs. elapsed time of a general lithium-ion battery. Charging is performed with the charging current I as a constant current from the start of charging until the battery voltage reaches a predetermined potential. By performing the constant current charging, when the battery voltage V rises and exceeds a predetermined value, the mode is switched to the constant voltage charging. At this time,
For example supplying the voltages V ₁ corresponding to the battery voltage during full charge of the lithium ion battery (i.e. when 100% charge). By performing the constant voltage charging, are charged lithium ion battery, but the battery voltage rises to the voltage V _1, according to this charging is performed, the charging current I is reduced. Here, when the charging current I decreases to a predetermined value, it is determined that the lithium ion battery has been charged to 100% (or charged to a state close to 100%), and the supply of the charging current is stopped.

[0003] By charging in this way, a lithium ion battery can be efficiently charged up to 100%.

[0004]

Incidentally, the characteristics of a lithium ion battery charged up to 100% in this way may be degraded depending on the state of charge thereafter. That is, the voltages V ₁ corresponding to the full battery voltage during charging of the lithium ion battery, always applied as the charging voltage of the lithium ion battery has been charged 100 percent from the charging apparatus, when to perform repeated charging of small power, Even if there is self-discharge, the state of charge can be maintained at almost 100%. However, if the state of almost 100% continues, the lithium ion battery has a characteristic that the chargeable capacity gradually decreases, and the characteristic as a secondary battery is deteriorated.

In order to prevent the characteristic deterioration due to the continuation of the 100% charged state, for example, 9% of the charging capacity is used.
Although it is conceivable to stop the charging at about 0%, there is a disadvantage that the capacity prepared as the secondary battery is not effectively utilized in this case.

Further, the lithium-ion battery has the disadvantage that when the temperature of the battery itself rises, the capacity that can be charged decreases and the battery characteristics deteriorate quickly. Therefore, the temperature rises when the battery temperature rises during charging. There is an inconvenience that it is not preferable to charge the battery to full charge under the same conditions as when there is no.

In view of these points, the present invention has an object to make it possible to effectively utilize the battery capacity without degrading the battery.

[0008]

According to the present invention, a voltage supplied to a secondary battery can be switched between a first voltage and a second voltage lower than the first voltage, which corresponds to full charge. When it detects a state of charging, the first voltage is switched to the second voltage, and when the current of the second charging current or more is detected in the state of supplying the second voltage, the voltage returns to the first voltage. It was done like this.

According to the present invention having such a configuration, the second charging voltage, which is lower than the first voltage after the fully charged state, is set.
However, when the battery voltage drops due to discharging to the second voltage, some charging current flows from the charging circuit side of the charging device to the secondary battery. At this time,
When the charging current is equal to or higher than the predetermined value, it is determined that the remaining capacity of the secondary battery is equal to or lower than the predetermined capacity, and the charging voltage is returned to the first voltage. Is fully charged.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will now be described with reference to FIGS.
This will be described with reference to FIG.

FIG. 1 is a block diagram showing the configuration of the charging device of this embodiment, in which an AC 100V power source from a commercial AC power source 1 is supplied to a transformer / rectifier circuit 2 to form a DC low voltage power source. This DC low voltage power supply is supplied to the constant current circuit 3 to obtain a constant current output. Then, the output of this constant current is supplied to the movable contact 4m of the changeover switch 4. The first and second fixed contacts 4a and 4b of the changeover switch 4 are connected to constant voltage circuits 5 and 6, respectively, and a constant voltage is applied from the constant voltage circuit 5 or 6 on the side to which the movable contact 4m is connected. Is output. Here, the constant voltage circuit 5 is set to output 4.2V, and the constant voltage circuit 6 is set to output 4.0V.

Then, the output voltage of the constant voltage circuit 5 or 6 is supplied to the positive electrode side of the secondary battery 7 mounted in this charging device. In this case, a lithium ion battery is used as the secondary battery 7 in this example. The lithium-ion battery used here has a characteristic that the battery voltage when fully charged (fully charged) is 4.2V.

Then, the potential difference between the positive electrode side and the negative electrode side of the secondary battery 7 is detected by the voltage detection circuit 8. The data of the voltage value detected by the voltage detection circuit 8 is supplied to the control circuit 11 described later.

Then, the negative electrode side of the secondary battery 7 is connected to the transformer / rectifier circuit 2 through the current detecting resistor 9 to form a charging circuit for the secondary battery 7. Then, the current flowing through the resistor 9 is detected by the current detection circuit 10 based on the potential difference between the one end and the other end of the current detection resistor 9. The current value detected by the current detection circuit 10 corresponds to the charging current supplied to the secondary battery 7. Then, the current value data detected by the current detection circuit 10 is supplied to the control circuit 11. The control circuit 11 is composed of a microcomputer and controls the charging operation.
Based on the comparison between the data of the current value detected in ₁ and the current value I ₁ previously stored in the control circuit 11, the changeover switch 4
The connection state of the movable contact 4m is controlled. Here, as the current value I ₁ , the secondary battery 7 has a charging voltage of 4.2 V
This is the charging current value when the battery is charged to 100%.

A load circuit 18 may be connected to the secondary battery 7.

Next, the process of charging a secondary battery (lithium ion battery) with this charging device will be described with reference to the flowchart of FIG.

First, the control circuit 11 detects the presence / absence of the secondary battery 7 (that is, whether or not it is attached to the charging device) (step 101). The presence / absence of the battery 7 may be determined electrically by detecting the battery voltage, or mechanically. Either detection may be performed.

Then, it is judged whether or not this detection result indicates that the battery is present (step 102). If the battery is present,
The movable contact 4m of the changeover switch 4 is connected to the first fixed contact 4a, and the battery 7 is charged by the charging voltage V ₁ of 4.2V output from the first constant voltage circuit 5 (step 1
03). Then, at this time, the current detection circuit 10 detects the charging current (step 104), and determines whether or not the detected charging current value is equal to or less than a preset predetermined value I ₁ (step 105).

Here, if the value exceeds the set value I ₁ , the process returns to step 103 and the charging voltage V _{1 of} 4.2V is obtained.
Continue charging in. When it is determined in step 105 that the value is less than or equal to the set value I ₁ , processing for stopping charging is performed (step 106), and the movable contact 4m of the changeover switch 4 is moved from the first fixed contact 4a to the second fixed contact 4a. The fixed contact 4b is switched to, and the charging voltage V _{2 of} 4.0 V output from the second constant voltage circuit 6 is applied to the secondary battery 7 (step 107).

Then, in this state, the charging current is detected by the current detection circuit 10 (step 108), and the detected charging current value I ₂ is compared with a preset predetermined value I ₁ (step 109) to determine the charging current. If the value I ₂ is less than or equal to the set value I ₁ , the process returns to step 108 and current detection is continued. When the current value I ₂ is equal to or greater than the set value I ₁ in this current detection (that is, when I ₂ ≧ I ₁ ), the movable contact 4m of the changeover switch 4 is moved from the second fixed contact 4b to the first fixed contact 4b. , And the charging voltage V _{1 of} 4.2 V output from the first constant voltage circuit 5 is applied to the secondary battery 7.
Charging is executed at the charging voltage V ₁ of 4.2V (step 110). And then, returning to step 104,
The current detection circuit 10 detects the charging current.

By controlling the charging operation by the control circuit 11 as shown in the flow chart of FIG. 2, charging is performed with the characteristics shown in FIG. FIG. 3 is a characteristic diagram of charging current / voltage vs. elapsed time. From the start of charging until the battery voltage reaches a predetermined potential, constant current charging with constant charging current I is performed (constant current charging in this example. The configuration for carrying out is omitted), after which the voltage is switched to constant voltage charging and 4.2V
Charging is performed with the charging voltage V ₁ of By performing the constant voltage charging, the battery voltage V becomes equal to the charging voltage V ₁ , but the charging current I gradually decreases, and the charging current I becomes equal to or less than the preset current value I _1. Value. The secondary battery (lithium ion battery) is 100% charged when the current value is less than or equal to I ₁ .

The timing of 100% charge, that is, the timing T at which the charging current becomes less than the current value I _{1
In 1} , the changeover switch 4 moves from the first fixed contact 4a to the second fixed contact 4a.
The fixed voltage is switched to the fixed contact 4b side and the charging voltage is 4.2V.
The voltage is switched from (V ₁ ) to 4.0 V (V ₂ ) (charging voltage V ₀ shown by the broken line in FIG. 3). Thus, the charging voltage is 4.
When the voltage becomes 0 V, the battery voltage V is 4.2 V, so that the secondary battery 7 is not charged and the charging current stops flowing.

If the secondary battery 7 is left in this state,
The battery voltage V gradually decreases due to self-discharge of the battery (or discharge to the connected load 8). However, when the battery voltage V decreases to 4.0V which is the charging voltage, the secondary battery 7 is discharged from the charging circuit side.
The charging current I comes to flow into the. For example, if the battery voltage V drops to 4.0 V at timing T ₃ in FIG. 3, a charging current I ₂ is generated, and this charging current I ₂ is detected by the current detection circuit 10. At this time, the charging current I ₂ is compared with a preset current value I _1, and when the value is equal to or more than the set value I ₁ , the charging voltage is switched from 4.0V to 4.2V (indicated by a broken line in FIG. 3). (Indicated increase in charging voltage V ₀ ). Due to this increase in the charging voltage, the charging current I becomes higher and charging is performed. Then, when the state of 100% charge is approached by this charging, the charging current decreases as in the first charging, and when the charging current I becomes equal to or less than the set value I ₁ , the charging voltage becomes 4. The voltage drops to 0V and the charging operation stops.

By thus performing the charging operation of the secondary battery which is a lithium ion battery, the secondary battery can be efficiently maintained in a state close to 100% charge. That is, when performing a charging operation, charging is performed at an appropriate charging voltage of 4.2 V, charging is performed until 100% charging is performed, and after this 100% charging, the charging voltage is 4.2 V.
Is 4.0V, which is a voltage slightly lower than, and when the battery voltage V drops to 4.0V due to self-discharge (or discharge to the load), the charging voltage rises to 4.2V again and reaches 100%. The operation of charging up to is repeated.
Therefore, once charged to a fully charged state, each time the remaining amount of the battery decreases to a predetermined amount, charging until full charge is repeatedly performed, and the state of charge of the lithium ion battery is constantly set to a state close to full charge. In addition to maintaining the battery voltage, the battery voltage of 4.0 V, which is lower than the battery voltage of 4.2 V when the battery is fully charged, is applied to the battery except when the battery is charged up to the full charge. Since charging is not performed until the battery is lowered, the lithium-ion battery does not continuously enter the full-charge state, and deterioration of the performance of the lithium-ion battery due to the continuous full-charge state can be prevented.

In this example, the charging current I ₂ detected at the time of recharging is compared with the current set value I ₁ used for the judgment of charging stop, but the charging current I ₂ detected at the time of recharging is compared.
₂ is compared with the current value set separately from the set value I ₁ ,
The charging voltage may be switched to 4.2V when a current value equal to or higher than the set current value is detected.

In the above example, the charging current is the predetermined value I.
When it becomes ₁ or less, although the secondary battery 7 is to be determined to be 100% charge, after reaching a predetermined value I ₁ or less,
It may be determined that the battery is fully charged after a predetermined time has elapsed. That is, as shown in the flowchart of FIG. 4, when the charging current I detected by the current detection circuit 10 in step 105 becomes less than or equal to a predetermined value I ₁ , the control circuit 11
When the timer circuit inside is operated (step 111) and this timer circuit has counted for a predetermined time, step 107
Alternatively, the charging voltage may be lowered from V ₁ to V ₂ . The other steps of the flowchart of FIG. 4 are the same as the processing described in FIG.

In the above example, the charging current is detected by 1
I tried to judge the state of being charged to 00%, but
100% charged when the battery voltage was detected by the output circuit 8.
You may make it detect a state. That is, the flow of FIG.
As shown in the chart, the charging voltage is set to V in step 103.
₁After setting to, the battery voltage is detected by the voltage detection circuit 8.
(Step 113), this detected value corresponds to full charge
Voltage V which is the voltage value ₁Is detected (step 11
4) Go to step 107 and set the charging voltage to V₁To V₂
You may make it lower. Flow chart of FIG.
Other steps are the same as the processing described in FIG.
You.

Further, in the case of detecting the state of 100% charged with the battery voltage as in the flow chart of FIG. 5, when the predetermined time elapses after the predetermined battery voltage is detected, it is determined that the battery is fully charged. You may make a judgment.
That is, as shown in the flowchart of FIG.
After the charging voltage is set to V ₁ in 03, the battery voltage is detected by the voltage detection circuit 8 (step 113), and the detected value is a voltage V ₃ which is slightly lower than the voltage value V ₁ corresponding to full charge. Is detected (step 114), it is determined that the battery is fully charged, and the process proceeds to step 107, where the charging voltage is V
_You may make it fall from ₁ to V ₂ . The other steps of the flowchart of FIG. 6 are the same as the processing described in FIG.

In each of the flowcharts of FIGS. 2, 4, 5 and 6, the temperature of the surface or the inside of the secondary battery 7 is detected instead of directly reducing the charging voltage to V ₂ in step 107. Then, the voltage value to be reduced may be selected according to the detected temperature. That is, the process of the flowchart of FIG. 7 may be performed instead of step 107 of each diagram. In the process of FIG. 7, a temperature sensor provided in the charging device has a predetermined temperature (here, 50 ° C.) as the temperature of the surface of the secondary battery 7 or the like.
It is determined whether or not the above is detected (step 131), 50
If the temperature is less than or equal to ℃, the charging voltage is lowered to the above-mentioned voltage value V ₂ (for example, 4.0 V) (step 132), and 50 ℃.
If it exceeds, the charging voltage is reduced to a voltage value (for example, 3.9V) obtained by subtracting a predetermined value ΔV (for example, 0.1V) from the above-mentioned voltage value V ₂ (step 133), and the process proceeds to the next step. May be. By doing so, an appropriate charging voltage can be set according to the temperature. In this case, in addition to the circuit of FIG. 1, it is necessary to prepare a temperature sensor and a constant voltage circuit for generating a voltage value [V ₂ −ΔV].

Next, another embodiment of the present invention will be described with reference to FIGS.
This will be described with reference to FIG. In this example, the temperature of the battery is detected and the charging voltage at the time of recharging is changed, and the charging device is configured as shown in FIG. 8, parts corresponding to those in FIG. 1 are designated by the same reference numerals, and detailed description thereof will be omitted.

In this example, the output of the constant current circuit 3 is switched.
It is supplied to the movable contact 12m of the switch 12, and this switching switch
1st, 2nd and 3rd fixed contacts 12a, 12b
And 12c are connected to constant voltage circuits 13, 14 and 15 respectively.
Connect to. Here, the constant voltage circuit 13 has a constant voltage of 4.2V.
The constant voltage circuit 14 has a voltage of 4.1V.
The constant voltage circuit 15 has a constant voltage output of 4.0.
This is a circuit that can obtain a constant voltage output of V. And each
The outputs of the constant voltage circuits 13, 14 and 15 are connected to a lithium battery.
It is supplied to the positive electrode side of the secondary battery 7, which is an on-battery. Soshi
The current detection resistor connected to the negative side of the secondary battery 7.
The current flowing through the container 9 is detected by the current detection circuit 10 and the current is detected.
The flow value detection data is set as a reference by the control circuit 16.
Current value I ₁And the switching switch based on the comparison result.
The switch 12 is controlled. Also connected to this charger
Temperature or surface temperature of secondary battery 7 or secondary battery
The temperature in the vicinity of 7 should be detected by the temperature sensor 17.
And the detected temperature data is supplied to the control circuit 16.
The detected temperature is equal to or higher than the set temperature Ta.
When controlling the changeover switch 12 based on the judgment of
Change the switching state of. As the set temperature Ta,
For example, it is set to 50 ° C.

The other parts are constructed in the same manner as the charging device shown in FIG. Although not shown, a load circuit may be connected to the secondary battery in this charging device as well.

Next, the operation of charging by the charging device of this example will be described with reference to the flowchart of FIG.
In the flowchart of FIG. 9, step 109
The processing up to (that is, the step of comparing the charging current value I ₂ detected after being charged to 100% once and the set value I ₁ ) is the same as that of the flowchart shown in FIG. 2, and the description thereof will be omitted. However, the charging voltage V ₁ set in step 103 is 4.2V by the constant voltage circuit 13 (that is, the movable contact 12m of the changeover switch 12 is the first fixed contact 1).
2a), and the charging voltage V ₂ set in step 107 is 4.0V by the constant voltage circuit 15 (that is, the movable contact 12m of the changeover switch 12 is connected to the third fixed contact 12c). Is.

When the detected charging current value I ₂ is greater than or equal to the set value I ₁ (that is, I ₂ ≧ I ₁ ) in the comparison in step 109, the temperature detected by the temperature sensor 17 is judged. Then, it is determined whether the detected temperature is equal to or higher than the set temperature Ta (for example, 50 ° C.) (step 121). Here, when the detected temperature is equal to or higher than the set temperature Ta, the changeover switch 1
The second movable contact 12m is switched from the third fixed contact 12c to the second fixed contact 12b, and the charging voltage of 4.1V output from the second constant voltage circuit 14 (this charging voltage is V ₁ -Δ
V) is applied to the secondary battery 7, and charging is executed at the charging voltage V ₁ −ΔV of 4.1 V (step 12).
2). Next, returning to step 104, the current detection circuit 10 detects the charging current.

When the detected temperature is lower than the set temperature Ta in step 121, the movable contact 12m of the changeover switch 12 is switched from the third fixed contact 12c to the first fixed contact 12a, and the first fixed contact 12m is changed. The charging voltage V _{1 of} 4.2V output from the voltage circuit 13 is applied to the secondary battery 7, and the charging is performed at the charging voltage V ₁ of 4.2V (step 123). Next, returning to step 104, the current detection circuit 10 detects the charging current.

By controlling the charging operation by the control circuit 11 as shown in the flow chart of FIG. 9, charging is performed with the characteristics shown in FIG. FIG. 10 is a characteristic diagram of charging current / voltage vs. elapsed time. After constant voltage charging is started after charging is started, charging is performed at a charging voltage V ₁ of 4.2V. By performing this constant voltage charging, the battery voltage V becomes equal to the charging voltage V ₁ , but the charging current I gradually decreases and the charging current I is set to a preset current value I ₁ or less. Becomes the value of 100 and the secondary battery (lithium ion battery) becomes 100
% Charged. Then, at the timing T _{1 when the} battery is 100% charged, the changeover switch 12 moves the first fixed contact 12a.
Is switched to the third fixed contact 12c side, and the charging voltage is switched from 4.2 V (V ₁ ) to 4.0 V (V ₂ ) (reduction of charging voltage V ₀ shown by the broken line in FIG. 10). In this way, the charging voltage becomes 4.0 V, so that the battery voltage V becomes 4.
Since it is 2V, the secondary battery 7 is not charged and the charging current stops flowing. Up to this point, the state is the same as that described with reference to FIG.

If the secondary battery 7 is left in this state,
Although the battery voltage V gradually decreases due to the self-discharge of the battery (or the discharge to the connected load), when the battery voltage V decreases to 4.0V which is the charging voltage (timing T _{2 in} FIG. 10), the charging circuit side outputs 2 The charging current I ₂ flows through the secondary battery 7. Then, the charging current I ₂ is detected by the current detection circuit 10 and compared with the set value I ₁ to obtain the set value I _2.
When it is ₁ or more, the process of increasing the charging voltage is performed. The charging voltage to be switched is V ₁ depending on whether the temperature detected by the temperature sensor 17 at this time is the set temperature Ta or higher.
(4.2V) or V ₁ −ΔV (4.1V).

That is, the detected temperature at this time is the set temperature Ta.
In the above case, the charging voltage is 4.1V, and the charging voltage of 4.1V is charged until the battery voltage becomes 4.1V (state of battery voltage Va shown in FIG. 10). Since the battery voltage of 4.1V is slightly lower than the battery voltage of 4.2V when the battery is 100% charged, the voltage is 10V.
Charging stops when the battery is charged a little lower than 0% (for example, 90%). When the detected temperature is lower than the set temperature Ta, the charging voltage is set to 4.2V, and the battery voltage becomes 4.2V at the charging voltage of 4.2V.
It is charged to 0% (state of battery voltage Vb shown in FIG. 10).

By changing the charging voltage in the case of recharging after being fully charged in this way, the battery is protected when the temperature is high by changing the charging voltage according to the temperature of the battery or its surroundings. That is, when the temperature of the lithium-ion battery is high,
Since there is a disadvantage that the characteristic deterioration (that is, the reduction of the charge capacity) when charged to 00% is faster than that at the normal time, it is not preferable to charge to 100%. Here, in the case of the present example, when the battery temperature is high, the charging is stopped immediately before 100% charging, so it is possible to prevent characteristic deterioration due to 100% charging at high temperature. Then, when the battery temperature is not high, the battery is charged to 100%. Therefore, when the protection by temperature is not required, the secondary battery is charged until the capacity of the secondary battery can be utilized to the maximum, and efficient charging is performed. Done. The charging operation when the temperature is lower than the set temperature Ta is exactly the same as the charging operation of the embodiment described in FIG. 3, and has the same effect as that of the embodiment.

In the examples described with reference to FIGS. 8 to 10, the charging voltage at the time of recharging is switched to two types based on the judgment as to whether or not the temperature is equal to or higher than the set temperature Ta, but the temperature is detected more finely. The charging voltage may be finely controlled based on the result. For example, instead of the temperature judgment in step 121 in the flowchart of FIG. 9 and the charging voltage setting in steps 122 and 123 based on the judgment,
As shown in the flowchart of FIG. 11, the temperature determination may be performed in two stages and the charging voltage at the time of recharging may be switched in three stages.

That is, as shown in the flow chart of FIG. 11, first, it is judged whether or not the temperature detected by the temperature sensor 17 is 50 ° C. or higher (step 124). If it is 50 ° C. or higher, the temperature is further 60 ° C. It is determined whether or not the above (step 125). When it is determined that the temperature is 60 ° C. or higher, [V ₁ −2ΔV] is set as the charging voltage (step 126). Here, for example, V ₁ is 4.2 V, Δ
When V is 0.1 V, 4.0 V is set (the charging voltage does not change when V ₂ is 4.0 V).

When it is determined in step 125 that the temperature is lower than 60 ° C., the charging voltage [V ₁ −Δ
V] is set (step 127). Here, assuming the values of V ₁ and ΔV described above, 4.1V will be set.

When it is determined in step 124 that the temperature is lower than 50 ° C., V ₁ is set as the charging voltage (step 128). Here, assuming the value of V ₁ described above, 4.2V is set.

By controlling the voltage more finely according to the temperature as described above, there is an effect that the secondary battery can be protected more accurately by the temperature. In addition to the stepwise change, the voltage value at the time of recharging may be continuously changed according to the detected temperature.

Although the specific configuration of the temperature sensor 17 for detecting the temperature of the secondary battery 7 is not described here, temperature sensors having various configurations can be applied. For example, the surface temperature of the secondary battery may be detected by an infrared sensor, or the internal temperature may be detected via a temperature detection terminal provided on the secondary battery. You may make it detect the temperature of the attachment part of a secondary battery using a detection element.

Further, in each of the above-mentioned embodiments, the case where the lithium ion battery is charged as the secondary battery has been described, but it can be applied to other similar secondary battery charging devices which require constant voltage charging. Of course. Further, the value of the voltage to be charged until the battery is fully charged may be appropriately selected according to the voltage characteristics of the battery to be used, and is not limited to the values in the above-described embodiments.

[0047]

According to the present invention, once the battery is fully charged, the charging voltage is switched to the second voltage, which is lower than the first voltage, so that the battery voltage is reduced to the second voltage. At this time, some charging current flows from the charging circuit side of the charging device to the secondary battery. When the charging current is equal to or higher than a predetermined value, the charging voltage is returned to the first voltage, so that the remaining battery level is reduced. Is charged to the fully charged state by the first charging voltage only when the voltage has decreased to a predetermined amount. Therefore, after the battery is once charged to the full charge state, the charge until the full charge is repeatedly performed every time the remaining amount of the battery decreases to a predetermined amount, and the state of charge of the secondary battery is always close to the full charge state. The second voltage, which is lower than the first voltage, is applied to the battery except when the battery can be maintained and fully charged until it is fully charged. It is possible to prevent the performance of the secondary battery from deteriorating due to the continuous charging.

In this case, the charging voltage is changed from the first voltage to the second voltage.
The first charging current used for the determination when switching to the second voltage and the second charging current used for the determination when switching the charging voltage from the second voltage to the first voltage have the same value. Thus, good charge state control is possible.

Further, when the temperature detected by the temperature detecting means is equal to or higher than the predetermined temperature, instead of returning the charging voltage from the second voltage to the first voltage, a third voltage between the first voltage and the second voltage is used. By setting the voltage to, it is possible to suppress the deterioration of the secondary battery performance due to the temperature rise.

[Brief description of drawings]

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

FIG. 2 is a flowchart showing a charging process according to an embodiment.

FIG. 3 is a characteristic diagram showing a state of charge according to an embodiment.

FIG. 4 is a flowchart showing a charging process when full charge detection is performed by another process in an embodiment.

FIG. 5 is a flowchart showing a charging process when full charge detection is performed in still another process in an embodiment.

FIG. 6 is a flowchart showing a charging process when full charge detection is performed in still another process in an embodiment.

FIG. 7 is a flow chart in the case where the control at full charge of the charging process of one embodiment is performed by temperature.

FIG. 8 is a configuration diagram showing a configuration of a charging device according to another embodiment of the present invention.

9 is a flowchart showing a charging process according to the example of FIG.

FIG. 10 is a characteristic diagram showing a state of charge according to the example of FIG.

FIG. 11 is a flowchart showing a charging process when the voltage is changed in three stages depending on the temperature in the example of FIG.

FIG. 12 is an explanatory diagram showing an example of charging characteristics of a lithium ion storage battery.

[Explanation of symbols]

 1 Commercial AC power supply 2 Transformer / rectifier circuit 3 Constant current circuit 4 Changeover switch 5,6 Constant voltage circuit 7 Secondary battery 8 Voltage detection circuit 9 Current detection resistor 10 Current detection circuit 11 Control circuit 12 Changeover switch 13, 14, 15 constant voltage circuit 16 control circuit 17 temperature sensor 18 load circuit

Claims (5)

[Claims] 1. A charging device for charging a secondary battery that is charged by a constant charging voltage, comprising: a first voltage supply means for supplying a first voltage to the secondary battery; and a secondary battery for the secondary battery. A second voltage supply means for supplying a second voltage lower than the first voltage; a current detection means for detecting a charging current to the secondary battery; and a detection result by the current detection means. And a control means for switching between the supply by the first voltage supply means and the supply by the second voltage supply means, which corresponds to a state in which the secondary battery is almost fully charged by the current detection means. When the first charging current is detected, the above 2
A state where the supply to the secondary battery is switched from the first voltage supply means to the second voltage supply means, and the second voltage is supplied from the second voltage supply means to the secondary battery by this switching. Then, the current detection means is the second
The charging device configured to switch to the supply by the first voltage supply means when a current equal to or higher than the charging current is detected. 2. The charging device according to claim 1, wherein the second charging current and the first charging current have the same value. 3. A third voltage supply means for supplying a third voltage having a potential between the first and second voltages to the secondary battery, and a temperature inside or near the secondary battery is detected. When the temperature detected by the temperature detecting means is equal to or higher than a predetermined temperature, the second voltage supplying means is switched to the third voltage supplying means instead of the first voltage supplying means. The charging device according to claim 1, configured as described above. 4. A charging device for charging a secondary battery, which is charged by a constant-voltage charging voltage, comprising: first voltage supply means for supplying a first voltage to the secondary battery; Second voltage supply means for supplying a second voltage lower than the first voltage, current detection means for detecting a charging current to the secondary battery, and voltage detection for detecting a voltage of the secondary battery. Means and a control means for switching between the supply by the first voltage supply means and the supply by the second voltage supply means based on the detection result of the voltage detection means. When a predetermined voltage corresponding to a state where the secondary battery is almost fully charged is detected, the supply to the secondary battery is switched from the first voltage supply means to the second voltage supply means, and By this switching, the second voltage supply means In a state where the secondary voltage is supplied to the secondary battery, the charging device is configured to switch to the supply by the first voltage supply unit when the current detection unit detects a current higher than a predetermined charging current. . 5. A third voltage supply means for supplying a third voltage having a potential between the first and second voltages to the secondary battery, and a temperature inside or near the secondary battery is detected. When the temperature detected by the temperature detecting means is equal to or higher than a predetermined temperature, the second voltage supplying means is switched to the third voltage supplying means instead of the first voltage supplying means. The charging device according to claim 4, wherein.