JPH09261882A - Charging method and charging apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To keep, to a certain degree, the time until full charging condition is recovered in order to prevent deterioration of a secondary battery by starting again the charging of the secondary battery after the predetermined time has passed from the detecting time when it is detected that the secondary battery reaches the predetermined condition after the full charging of the secondary battery is detected and charging is stopped. SOLUTION: A control circuit 7 controls supply of an output voltage of a constant voltage circuit 4 to a secondary battery 5 based on a detected value of the voltage detecting circuit 6 and a detected value of the current detecting circuit 9. Here, when charging is continued and the battery voltage reaches the full charging voltage value, charging to the secondary battery is stopped. Thereafter, when a battery voltage is lowered due to self-discharging to reach the reference voltage, a timer in the control circuit 7 is activated to restart the charging to the secondary battery 5 after the predetermined time has passed to continue the recharging until the battery voltage reaches the full charging voltage. Thereby, even if the detected battery voltage includes an error, good charging can be made to prevent characteristic deterioration of the secondary battery 5.

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. 11 is a characteristic diagram of charging current / voltage vs. elapsed time of a general lithium-ion battery, and 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.

By performing charging in this manner, it is possible to obtain a lithium-ion battery having a characteristic requiring constant voltage charging to almost 1
It can be charged efficiently up to 00%.

[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.

Here, the conventional lithium ion battery is replaced by 10
An example of the charge control state in the case of 0% charge is shown in FIG. 12, for example, when a lithium ion battery having a voltage of V ₁ at the time of full charge is charged and the battery voltage of this battery is V at a certain timing t _{1. Suppose} it becomes ₁ . At this time, it is determined that the lithium ion battery is fully charged, and the supply of charging current is stopped. By stopping the charging, the battery voltage of the lithium ion battery gradually decreases due to self-discharge or discharge to the load circuit.

Here, the charging circuit is set to restart charging when the battery voltage reaches a predetermined voltage V ₂ . When the timing t ₂ in the charging circuit is that it has detected the battery voltage V _2, the charging at a timing t ₂ is resumed, to rise again as shown the battery voltage is the characteristic Vx, it is fully charged .

By setting in this way, the battery voltage is maintained at a voltage close to full charge. Here, by setting the voltage V ₂ for resuming charging to a voltage value extremely close to the battery voltage V ₁ at the time of full charge, the lithium-ion battery is always kept at approximately 100
However, if this is done, the deterioration of the battery is accelerated. Therefore, the voltage V ₂ for restarting charging is set to a voltage slightly lower than the battery voltage V ₁ at the time of full charge,
The deterioration of the battery is prevented by changing the remaining amount of the battery within a certain range.

In general, however, it is difficult for a voltage detection circuit of a relatively simple structure incorporated in a charger of this type to accurately detect the voltage V ₂ at all times, and the detected value of the voltage has an error ΔV. Will occur. Here, as shown in FIG. 12, a voltage higher than the actual set value by an error ΔV is set to the voltage V
_When it is determined to be ₂ (timing t ₂ ′), as shown by the characteristic Vy indicated by the broken line, the battery is returned to the full charge state earlier than the originally set state (state according to the characteristic Vx), and the battery characteristic Will be accelerated.

It is an object of the present invention to provide a charging method and a charging device which can favorably charge a battery without degrading the battery even if there is a detection error of the battery state.

[0010]

According to the present invention, when it is detected that the secondary battery is in a predetermined state after the secondary battery is almost fully charged and the charging is stopped, it is detected from this detection. The charging of the secondary battery is restarted after a predetermined time has elapsed.

By doing so, the time from when the battery is once in the fully-charged state (or a state close to the fully-charged state) until when the charging is restarted is from the fully-charged state to the predetermined state. The time can be set to a time obtained by adding a predetermined time, and even if there is an error in the detection of the battery state, it is possible to secure a certain amount of time before returning to the fully charged state,
It is possible to prevent the deterioration of the characteristics of the secondary battery.

Further, according to the present invention, when the secondary battery is almost fully charged and the charging is stopped, the secondary battery is charged at a predetermined interval of about 2 seconds.
The state of the secondary battery is detected, and the charging is restarted when the detected state is a predetermined state.

By doing this, until the battery is once fully charged and the charging is stopped, the charging is restarted.
At least a predetermined time can be provided, a certain amount of time before returning to the fully charged state can be secured, and deterioration of the characteristics of the secondary battery can be prevented.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to FIGS.

FIG. 1 is a block diagram showing a configuration of a charging device applied to each embodiment of the present invention. In each embodiment described below, charging is performed by the charging device having the configuration shown in FIG. However, the control state of charging differs in each embodiment.

First, the structure of the charging device shown in FIG. 1 will be described. An AC power source (for example, AC100V) having a predetermined voltage from the commercial AC power source 1 is supplied to the transformer / rectifier circuit 2 to form a DC low voltage power source. Then, this DC low-voltage power supply is supplied to the constant current circuit 3 to obtain a constant current output. Then, the output of the constant current is supplied to the constant voltage circuit 4 so that the output of the constant voltage is obtained. In this case, the constant voltage circuit 4 can set a constant voltage output of 4.2V and a constant voltage output of 4.0V. This output voltage is controlled to 4.2V and 4.V by the control of the control circuit 7 described later.
Either of 0 V can be selected (however, a constant voltage output of 4.0 V may not be necessary depending on the embodiment).

Then, the output voltage of the constant voltage circuit 4 is supplied to the positive electrode side of the secondary battery 5 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 voltage detection circuit 6 detects the potential difference between the positive electrode side and the negative electrode side of the secondary battery 5. The data of the voltage value detected by the voltage detection circuit 6 is supplied to the control circuit 7.

Then, the negative electrode side of the secondary battery 5 is connected to the transformer / rectifier circuit 2 through the current detecting resistor 8 to form a charging circuit for the secondary battery 5. Then, the current flowing through the resistor 8 is detected by the current detection circuit 9 based on the potential difference between the one end and the other end of the current detection resistor 8. The current value detected by the current detection circuit 9 corresponds to the charging current supplied to the secondary battery 5. Then, the current value data detected by the current detection circuit 9 is supplied to the control circuit 7. The control circuit 7 is a circuit configured of a microcomputer to control the charging operation, and based on the battery voltage data detected by the voltage detection circuit 6 and the current value data detected by the current detection circuit 9, The supply of the charging power source from the constant voltage circuit 4 to the secondary battery 5 is controlled. Further, the control circuit 7 of the present example has a built-in timer circuit (not shown) so that the elapse of a preset time can be determined.

A load circuit 10 may be connected to the secondary battery 5.

Next, the charging process of the first embodiment for charging a secondary battery (lithium ion battery) using the charging device having the configuration shown in FIG. 1 will be described with reference to the flowchart of FIG. To do.

The charging control of this example is carried out under the control of the control circuit 7. When the charging operation is started and the battery is charged to some extent, the constant voltage circuit 4 outputs 4.2V.
Is output to perform constant voltage charging (step 101). Then, during this charging, the control circuit 7 determines whether or not it has become fully charged (or a state close to full charge) (step 10).
2). As for the determination of the fully charged state, for example, based on the detection data of the current detection circuit 9, it is determined whether or not the charging current corresponding to the full charge is reduced. Here, when it is determined that the battery is fully charged, the control circuit 7 controls the output of the constant voltage circuit 4 of 4.2 V to stop the charging (step 103). Note that the charging may be stopped when a predetermined time (for example, one hour) has elapsed after detecting the current or voltage corresponding to full charge.

After the charging is stopped, the battery voltage of the secondary battery 5 is detected by the voltage detection circuit 6 (step 104). Here, the detected voltage value is the control circuit 7
It is determined whether or not the voltage value is equal to or lower than the reference voltage V ₂ set in advance (step 105). Here, the reference voltage V ₂ is set to 4.0 V, and in the processing of step 105, the control circuit 7 determines whether or not it is 4.0 V or less. And 4.
If it is not 0 V or less, the battery voltage detection in step 104 is repeatedly executed.

In the comparison processing of the detected voltages in step 105, 4.2V output from the constant voltage circuit 4 is used as a reference voltage, and 4.2V is detected by the voltage detection circuit 6. The control circuit 7 determines the voltage difference from the battery voltage. Then, it is determined whether or not the voltage difference exceeds 0.2 V, and a process of determining whether or not the battery voltage becomes 4.0 V or less is performed.

Alternatively, as another comparison process of the voltage in step 105, the control circuit 7 is caused to set 4.0 V as a reference voltage with a voltage with the ground potential (that is, 0 V) as a reference. Then, the battery voltage detected by the voltage detection circuit 6 and the reference voltage (4.0 V) may be compared to perform a process of determining whether or not the battery voltage is equal to or lower than the reference voltage.

Then, in step 105, the battery voltage is 4.0.
When it is determined that the voltage is V or less, the timer set in the control circuit 7 is activated (step 106). Then, after activating this timer, it is judged whether or not a predetermined time n ₁ has elapsed (step 107).
The time n ₁ is, eg, 30 minutes.

[0026] Then, the control circuit 7 time after the determination (i.e. battery voltage over time n ₁ is equal to or less than 4.0V n ₁
(Determination that has passed), the process returns to step 101 to start the charging operation. As the charging operation at this time, 4.2V is output from the constant voltage circuit 4 based on the control of the control circuit 7, and the constant voltage charging by 4.2V is performed. Then, the processing after step 101 is repeated.

Here, the flowchart of FIG. 2 is shown.
The charging processing state of this example will be described with reference to FIG. This figure
The voltage characteristic Va shown in 3 shows the change in battery voltage,
The battery voltage Va is the voltage V when fully charged₁Close to
Therefore, the voltage V when fully charged ₁(4.2V)
Imming t₁₁Then, stop the output of the constant voltage circuit 4, and
The charging of the secondary battery 5 is stopped. By stopping this charging,
Imming t₁₁From the self-discharge of the battery (or to the load circuit
(Discharge) causes the battery voltage Va to gradually decrease.

In this charging stopped state, it is assumed that the battery voltage Va is sequentially detected and the battery voltage Va becomes lower than the reference voltage V ₂ (4.0V) at the timing t ₁₂ .
At this time, the timer circuit in the control circuit 7 is activated at the timing t ₁₂ , and the time n ₁ (for example, 3
0 min) at the timing t ₁₃ has elapsed, the charging of the secondary battery 5 is resumed, the battery voltage Va is charged to the timing t ₁₄ to the V ₁ again.

By charging in this way, the timing for resuming charging is set appropriately, and even if there is a detection error in the battery voltage, recharging can be performed well, and it is close to a fully charged state. It is possible to prevent the deterioration of the battery characteristics due to the continuous state. That is, the battery voltage Va
If the battery is accurately detected, the battery voltage becomes a voltage sufficiently lower than the reference voltage V ₂ at the timing t ₁₃ when charging is restarted. Assuming that there is a battery voltage detection error ΔV as shown in FIG. 3, this error Δ
The timer circuit operates when the battery voltage is higher than the voltage V ₂ by V, and when the time n ₁ elapses from the start of the operation, charging is resumed (voltage Vb indicated by a broken line). Therefore, even if there is an error in the detection of the battery voltage, it is possible to secure a sufficient time for the charging to be restarted and to return to full charge, and the battery due to the continued full charge state of the secondary battery (lithium ion battery) Can be prevented from deteriorating.

In this case, in this example, 4.2V output from the constant voltage circuit 4 is used as the judgment of the detected battery voltage.
The voltage difference between the 4.2V and the battery voltage detected by the voltage detection circuit 6 is judged in the control circuit 7 with (the 4.2V is the battery voltage at full charge) as a reference voltage, By determining the decrease of the battery voltage by 4.0 V or less, the battery voltage can be accurately determined with a small error, and the charge control of the secondary battery can be better performed.

Further, when the voltage of 4.0 V is judged with the voltage based on the ground potential (that is, 0 V) instead of the battery voltage at the time of full charge as a reference, the control circuit 7 The battery voltage can be determined by directly determining the detection data of the voltage detection circuit 6, and the battery voltage can be determined with a simple configuration. In this case as well, the time until the charging is restarted and the battery is returned to full charge as described above. Can be sufficiently ensured, and the deterioration of the battery due to the continuation of the fully charged state of the secondary battery can be effectively prevented.

In the processing of the first embodiment described above, the judgment at the restart of charging is made by detecting the battery voltage, but the judgment at the restart of charging may be made by detecting the charging current. good. The flowchart of FIG. 4 shows the charging process in this case, which will be described below.

First, the charging operation is performed under the control of the control circuit 7 (step 201). At this time, when the secondary battery 5 is charged to some extent, the constant voltage circuit 4 outputs 4.2V to perform constant voltage charging. Then, during this charging, the control circuit 7 causes the current detection circuit 9 to detect the charging current (step 202), and the control circuit 7 determines whether the detected charging current is 100 mA or less (step 203). Here, when the charging current exceeds 100 mA, it is determined that the secondary battery 5 is not yet in the fully charged state, and the charging in step 201 is continued. When it is determined that the charging current is 100 mA or less, 2
Secondary battery 5 is fully charged (or close to fully charged)
Then, the output voltage of the constant voltage circuit 4 is switched to 4.0 V by the control of the control circuit 7 (step 20).
4).

Then, while the constant voltage of 4.0 V is applied to the secondary battery 5, the charging current at that time is detected by the current detection circuit 9 (step 205). Then, the control circuit 7 determines whether the detected charging current is 30 mA or more (step 206). Here, when the charging current is not 30 mA or more, the charging current is repeatedly detected in step 205 while continuously supplying the constant voltage of 4.0 V in step 204.

When it is determined that the charging current is 30 mA or more, the timer circuit in the control circuit 7 is activated (step 207). Then, after activating this timer, it is determined whether or not a predetermined time n ₁ has elapsed (step 208). The time n ₁ is, eg, 30 minutes.

[0036] Then, the control circuit 7 is time from when the elapsed time n ₁ determined (i.e. the charging current is more than 30 mA n ₁
(Determination that has passed), the process returns to step 201 to start the charging operation. As the charging operation at this time, the output of the constant voltage circuit 4 is switched to 4.2V based on the control of the control circuit 7, and the constant voltage charging by 4.2V is performed. Then, the processing from step 201 onward is repeated.

It should be noted that the charging may be stopped when a predetermined time (for example, 1 hour) has elapsed after the charging current corresponding to the full charge was detected in step 203.

Here, the charge processing state of this example shown in the flow chart of FIG. 4 will be described with reference to FIG. This FIG. 5 shows changes in the battery voltage Va and the charging current I. When charging is performed, the battery voltage Va approaches the voltage V ₁ at the time of full charge, but the charging current I gradually decreases when approaching this full charge. To do. Then, at the timing t ₂₁ when the charging current I reaches 100 mA (I ₁ ), the charging voltage V from the constant voltage circuit 4
₀ is switched to 4.0 V (V ₂ ). This 4.0V
When the battery voltage is 4.0 V or more in the state where the charging voltage is supplied, the charging current hardly flows. Then, when the battery voltage Va drops to 4.0 V, a detectable charging current is generated, and when the charging current is 30 mA (I ₂ ) or more (timing T ₂₂ ), the timer circuit in the control circuit 7 Operate. Then, the timing t when the time n ₁ (for example, 30 minutes) has elapsed from the start of the operation of the timer circuit
_{At 23} , the output voltage of the constant voltage circuit 4 is returned to 4.2V, the charging of the secondary battery 5 by the charging voltage of 4.2V is restarted, and the secondary battery 5 is charged until the charging current becomes 100 mA or less.

By charging in this way, the timing at which charging is restarted is set to a good level, and a state close to a full-charged state is achieved, as in the case of voltage detection described above (during processing according to the flowchart of FIG. 2). It is possible to prevent the deterioration of the characteristics of the secondary battery (lithium ion battery) due to the continuation.

Next, a second embodiment of the present invention will be described.
Also in the case of the second embodiment, charging is performed by the charging device having the configuration shown in FIG. 1, and the control of the charging by the control circuit 7 is performed according to the flowchart of FIG. The process will be described below. First, the charging operation is performed under the control of the control circuit 7 (step 301). At this time, when the secondary battery 5 is charged to some extent, the constant voltage circuit 4 outputs 4.2V to perform constant voltage charging. Then, during this charging, the control circuit 7 causes the current detection circuit 9 to detect the charging current (step 302), and the control circuit 7 determines whether the detected charging current is 100 mA or less (step 303). Here, the charging current is 100m
If it exceeds A, it is determined that the secondary battery 5 is not in a fully charged state and the charging in step 301 is continued. When it is determined that the charging current is 100 mA or less, it is determined that the secondary battery 5 is in the fully charged state (or a state close to the fully charged state), and the output of the constant voltage circuit 4 is controlled by the control circuit 7. The voltage is stopped to stop charging (step 304). Note that the charging may be stopped when a predetermined time (for example, one hour) has elapsed after detecting the current corresponding to full charge.

At the same time when this charging is stopped,
The timer circuit in the control circuit 7 is activated (step 3
05). Then, it is determined whether or not a preset time n ₂ (for example, 30 minutes) has elapsed since the timer circuit was activated (step 306). And this time n ₂
When elapses, the control circuit 7 controls the constant voltage circuit 4 to output a charging voltage of 4.2 V to temporarily restart the charging operation (step 307). Then, the charging current at this time is detected by the current detection circuit 9 (step 308). Then, the control circuit 7 determines whether the charging current detected at this time is 200 mA or more (step 3).
09). When the charging current is not 200 mA or more, the process returns to step 304, the output voltage of the constant voltage circuit 4 is stopped, and the charging is stopped. Then, the timer circuit is activated in step 305, and the charging operation and the detection of the charging current at that time are repeated every time n ₂ has elapsed from the activation.

Then, in step 309, the charging current is set to 20.
If it is determined to be 0 mA or more, step 30
Returning to 1, the charging for resuming the fully charged state is restarted.

Here, the charging state by the charging process shown in the flowchart of FIG. 6 will be described with reference to FIG.
This FIG. 5 shows the battery voltage Va, the charging voltage V ₀ and the charging current I.
The battery voltage Va approaches the voltage V ₁ at the time of full charge due to the charging, but the charging current I gradually decreases when approaching this full charge. Then, the charging current I is 10
At timing t ₃₁ when 0 mA (I ₁ ) is reached, the supply of the charging voltage V ₀ of 4.2 V from the constant voltage circuit 4 is stopped.

At the same time when this charging is stopped, the control circuit 7
The internal timer circuit operates, and the output of 4.2 V from the constant voltage circuit 4 is temporarily restarted at the timing t _{32 when} time n ₂ (for example, 30 minutes) has elapsed from the start of operation of this timer circuit. Then, the charging current I at this time is detected. Then, it is determined whether or not the charging current I is 200 mA (I ₃ ) or more. When it is 200 mA or less, the supply of the charging voltage V ₀ is stopped, and the next time n ₂ by the timer circuit elapses ( Wait until timing t ₃₃ ).

Then, while the detection of the temporary charging current is repeated every time the time n ₂ has elapsed, the secondary battery 5 is no longer fully charged due to self-discharge or the like, and the predetermined remaining amount is reached. 200mA at a charging voltage of 4.2V
(When time t ₃₄₎ (I ₃₎ or more of the charging current is detected, charging of the secondary battery 5 by a constant voltage of 4.2V is performed. And the charging current I is 100m by this charging.
At the timing t ₃₅ became A (I _1), it is determined that the fully charged state, to stop the supply of the charge voltage V ₀ which 4.2V from the constant voltage circuit 4.

As a result of being charged in this way, at least a predetermined time n ₂ (for example, 30 minutes) is reached after the battery has once become a fully charged state (or a state close to a fully charged state) and charging has stopped.
The charging is not restarted unless the time elapses, and the charging current is detected at every predetermined time period n ₂ and the charging is not restarted when the remaining amount of the battery is close to the fully charged state. Unless the charging is resumed unless otherwise, the characteristics of the secondary battery (lithium ion battery) can be prevented from deteriorating due to the continuous state close to the fully charged state.

In the process shown in the flowchart of FIG. 6, only 4.2V, which is the battery voltage when the secondary battery 5 is fully charged, is supplied as the output of the constant voltage circuit 4, but it is temporary. A lower charging voltage may be used when detecting the charging current. The flowchart of FIG. 8 shows the processing when the charging voltage is changed in the case of the second embodiment.

The process will be described below. First, the charging operation is performed under the control of the control circuit 7 (step 401). At this time, when the secondary battery 5 is charged to some extent, the constant voltage circuit 4 outputs 4.2V to perform constant voltage charging. Then, during this charging, the control circuit 7 causes the current detection circuit 9 to detect the charging current (step 402), and the control circuit 7 determines whether the detected charging current is 100 mA or less (step 403). here,
If the charging current exceeds 100 mA, it is determined that the secondary battery 5 is not yet in the fully charged state, and step 401
To continue charging. And the charging current is 100mA
When it is determined that it is below, it is determined that the secondary battery 5 is in a fully charged state (or a state close to a fully charged state),
The output voltage of the constant voltage circuit 4 is stopped by the control of the control circuit 7 to stop the charging (step 404). In addition,
The charging may be stopped when a predetermined time (for example, one hour) has elapsed after detecting the current corresponding to the full charge.

At the same time when this charging is stopped,
The timer circuit in the control circuit 7 is activated (step 4
05). Then, it is determined whether or not a preset time n ₂ (for example, 30 minutes) has elapsed since the timer circuit was activated (step 406). And this time n ₂
When elapses, the control circuit 7 controls the constant voltage circuit 4 to output a charging voltage of 4.0 V, and temporarily restarts the charging operation with the charging voltage of 4.0 V (step 407). Then, the charging current at this time is detected by the current detection circuit 9 (step 408). Then, the control circuit 7 determines whether or not the charging current detected at this time is 30 mA or more (step 409). Then, when the charging current is not 30 mA or more, the process returns to step 404, the output voltage of the constant voltage circuit 4 is stopped, and the charging by the supply of the charging voltage of 4.0 V is stopped. Then, the timer circuit is started in step 405, and the charging operation and the detection of the charging current at that time are repeated every time n ₂ has elapsed from the start.

Then, in step 409, the charging current is set to 30.
If it is determined that the current is equal to or higher than mA, step 401
Then, 4.2V is output from the constant voltage circuit 4 to perform constant voltage charging, and charging to bring the battery into a fully charged state is restarted.

In this way, when the battery state is detected, the charging voltage is set to 4.0V, which is lower than the battery voltage 4.2V when the secondary battery 5 is fully charged. The state of the battery can be detected, and the state of the battery (remaining amount) can be accurately detected while the load on the secondary battery is small. From this point as well, deterioration of the battery can be prevented.

Next, an example of the case where the charging process based on the second embodiment is performed by detecting the battery voltage will be described with reference to the flowchart of FIG. First, when the charging operation is started and the battery is charged to a certain extent, the constant voltage circuit 4 outputs 4.2V to perform constant voltage charging (step 501). Then, during this charging, the control circuit 7 determines whether or not it has become fully charged (or a state close to full charge) (step 502). As for the determination of the fully charged state, for example, based on the detection data of the current detection circuit 9, it is determined whether or not the charging current corresponding to the full charge is reduced. When it is determined that the battery is fully charged, the control circuit 7 controls the output of 4.2 V from the constant voltage circuit 4 to stop the charging (step 50).
3). Note that the charging may be stopped when a predetermined time (for example, one hour) has elapsed after detecting the current or voltage corresponding to full charge.

At the same time when this charging is stopped,
The timer circuit in the control circuit 7 is activated (step 5).
04). Then, it is determined whether or not a preset time n ₂ (for example, 30 minutes) has elapsed since the timer circuit was activated (step 505). And this time n ₂
When has passed, the control circuit 7 controls the voltage detection circuit 6 to detect the battery voltage of the secondary battery 5 (step 506). Then, it is determined whether or not the battery voltage at this time is 4.0 V or less (step 507).

Here, if it is not 4.0 V or less, the control circuit 7
When it is determined that the battery is still fully charged, only the energy required to detect the battery voltage at this time is charged (step 508). That is, the charging voltage of 4.2V from the constant voltage circuit 4 for a preset time (this time is a relatively short time proportional to the power consumed by the voltage detection circuit 6 in step 506). Is supplied to the secondary battery 5 to be charged by the amount discharged by the detection of the battery state. Alternatively, it may be charged a little more than that. Then, at the same time when the charging is stopped in step 508, the process returns to step 504, the timer circuit is activated, and the battery voltage is repeatedly detected every time the time n ₂ elapses.

Then, in the detection of the battery voltage in step 507, if 4.0 V or less is detected, the secondary battery 5
Is judged to be enough to charge the battery, step 5
Returning to 01, the constant voltage circuit 4 outputs 4.2 V to restart the constant voltage charging.

By performing the charging process in this manner, the time until the charging is restarted is at least the predetermined time n, as in the process shown in the flowchart of FIG.
It can be longer than ₂ (for example, 30 minutes), the charge state of the secondary battery can be appropriately maintained, and deterioration of the characteristics of the secondary battery can be effectively prevented.

In the process shown in the flow chart of FIG. 9, the battery voltage detection process in step 506 uses 4.2V output from the constant voltage circuit 4 as a reference voltage and 4.2V. The control circuit 7 determines the voltage difference from the battery voltage detected by the voltage detection circuit 6. Then, it is judged whether the voltage difference exceeds 0.2 V,
A process of determining whether or not the battery voltage has become 4.0 V or less is performed.

Alternatively, as another comparison process of the voltages, the control circuit 7 is set with a voltage with reference to the ground potential (that is, 0V) and 4.0V as the reference voltage. Then, the battery voltage detected by the voltage detection circuit 6 and this reference voltage (4.0 V)
It is also possible to perform a process of comparing whether the battery voltage is equal to or lower than the reference voltage by comparing with.

Next, a third embodiment of the present invention will be described.
Also in the case of the third embodiment, charging is performed by the charging device having the configuration shown in FIG. 1, and the control of the charging by the control circuit 7 is performed according to the flowchart of FIG. In the case of the third embodiment, the control for waiting the predetermined time n ₁ described in the first embodiment to start recharging and the predetermined time n ₂ after the charging stop described in the second embodiment are performed. Is combined with control for detecting the battery state.

The process will be described below. First,
The charging operation is performed under the control of the control circuit 7 (step 601). At this time, when the secondary battery 5 is charged to some extent, the constant voltage circuit 4 outputs 4.2V to perform constant voltage charging. Then, during this charging, the control circuit 7 causes the current detection circuit 9 to detect the charging current (step 602), and the control circuit 7 determines whether the detected charging current is 100 mA or less (step 603). here,
If the charging current exceeds 100 mA, it is determined that the secondary battery 5 is not yet in a fully charged state, and step 601
To continue charging. And the charging current is 100mA
When it is determined that it is below, it is determined that the secondary battery 5 is in a fully charged state (or a state close to a fully charged state),
The output voltage of the constant voltage circuit 4 is stopped by the control of the control circuit 7 to stop the charging (step 604). In addition,
The charging may be stopped when a predetermined time (for example, one hour) has elapsed after detecting the current corresponding to the full charge.

At the same time when this charging is stopped,
The timer circuit in the control circuit 7 is activated (step 6).
05). Then, it is determined whether or not a preset time n ₂ (for example, 30 minutes) has elapsed since the timer circuit was activated (step 606). And this time n ₂
When elapses, the control circuit 7 controls the constant voltage circuit 4 to output a charging voltage of 4.2 V to temporarily restart the charging operation (step 607). Then, the charging current at this time is detected by the current detection circuit 9 (step 608). Then, the control circuit 7 determines whether the charging current detected at this time is 200 mA or more (step 6).
09). When the charging current is not 200 mA or more, the process returns to step 604, the output voltage of the constant voltage circuit 4 is stopped, and the charging is stopped. Then, the timer circuit is activated in step 605, and the charging operation and the detection of the charging current at that time are repeated every time n ₂ has elapsed from the activation.

Then, in step 609, the charging current is set to 20.
If it is determined to be 0 mA or more, the timer circuit in the control circuit 7 is activated again (step 610).
Then, after activating the timer in step 610, it is determined whether or not a predetermined time n ₁ has elapsed (step 611). The time n ₁ is, for example, 3
0 minutes.

Then, the control circuit 7 judges that the time n ₁ has passed (that is, the time n has passed since the charging current exceeded 200 mA).
(Determination that ₁ has elapsed), the process returns to step 601 to start the charging operation. As the charging operation at this time, the output of the constant voltage circuit 4 is switched to 4.2V based on the control of the control circuit 7, and the constant voltage charging by 4.2V is performed. Then, the processing from step 201 onward is repeated.

By performing the charging process in this manner, the process of detecting the state of the secondary battery after the charging of the secondary battery is stopped is performed by the timer circuit every time the time n ₂ elapses. The control for properly maintaining the state of charge of the secondary battery is satisfactorily performed, and the detection is performed at each time n ₂ .
If it is determined that the battery level is rechargeable,
Since the recharging is started after waiting the elapse of time n ₁ by the timer circuit, the period until the secondary battery returns to the fully charged state should always be kept good regardless of the detection accuracy at that time. From this point as well, control is performed to keep the state of charge of the secondary battery proper.

In the third embodiment, the charging voltage at the time of temporary charging after the stop of charging is 4.2 V, which is the same as that at the time of normal charging, but the charging voltage at the time of temporary charging is A low voltage such as 4.0 V may be used. By doing so, it is possible to reduce the load on the secondary battery when the battery state is detected.

Further, instead of detecting the state of the secondary battery by the current value, the state of the secondary battery may be detected by the battery voltage. When detecting this battery voltage,
When the battery voltage is detected in this charging stopped state, the energy discharged from the secondary battery may be charged for this detection.

In each of the above-described embodiments, the case of charging a lithium ion battery as a secondary battery has been described, but the present invention is also applied to other similar secondary battery charging methods and devices that require constant voltage charging. Of course you can. Also, the voltage to be charged until full charge, the voltage value at the time of detection, the current value, and the value such as the time set by each timer circuit may be appropriately selected according to the voltage characteristics and capacity of the battery used, It is not limited to the values in the above-mentioned respective embodiments.

[0068]

According to the present invention, when it is detected that the secondary battery is in a predetermined state after the secondary battery is almost fully charged and the charging is stopped, a predetermined time elapses from this detection. After recharging the secondary battery, the time from when the battery is once fully charged (or close to fully charged) to when charging is restarted is It is possible to set the time until the predetermined state is added to the predetermined time, and even if there is an error in the detection of the battery state, it is possible to secure a certain amount of time before returning to the fully charged state. It is possible to prevent the deterioration of the characteristics of the secondary battery due to the continuous charge state.

In this case, as the detection of the predetermined state, it is detected that the battery voltage of the secondary battery has decreased by a predetermined value from the voltage value with the charging voltage as a reference. It is possible to detect a significant drop in battery voltage and accurately control the state of the secondary battery.

Further, as the detection of the predetermined state, by detecting that the battery voltage from the voltage value with reference to the ground potential of the secondary battery has reached the predetermined voltage, a relatively simple voltage detection can be performed. Then, it becomes possible to properly control the state of the secondary battery.

Further, as the detection of the predetermined state, by detecting that the charging current reaches a predetermined value when a predetermined voltage is applied to the secondary battery, the secondary current is detected based on the detection of the current value. It becomes possible to properly control the state of charge of the battery.

Further, when it is detected that the charging current has reached the predetermined value, the load applied to the secondary battery is reduced by setting the predetermined voltage applied to the secondary battery to a voltage lower than the charging voltage. Then, the battery state can be properly detected.

Further, according to the present invention, the state of the secondary battery is detected at almost every predetermined time after the secondary battery is almost fully charged and the charging is stopped, and the detected state is predetermined. By restarting charging when the battery is in the state, it is possible to wait at least a predetermined time until the battery is fully charged and then stopped, and then restart charging again. A certain amount of time can be secured, and deterioration of the characteristics of the secondary battery can be prevented.

In this case, by restarting the charging after a certain time has passed after the detection of the predetermined state, the time until the fully charged state is returned can be secured more effectively, and the secondary battery can be secured. The effect of preventing the deterioration of the characteristics can be further enhanced.

Further, when the charging voltage or a voltage lower than this charging voltage is applied to the secondary battery as the detection of the predetermined state, it is detected that the charging current exceeds the predetermined value. As a result, the state of the secondary battery can be accurately detected.

Further, by detecting that the battery voltage of the secondary battery has reached the predetermined voltage as the detection of the predetermined state, the state of the secondary battery can be accurately detected by the battery voltage.

Further, when the battery voltage is detected, if the battery voltage does not reach the predetermined voltage and the charging is not restarted, at least the energy required for detecting the battery voltage is charged in the secondary battery. As a result, it is possible to effectively prevent a decrease in the remaining charge amount due to the detection of the battery state being repeated every predetermined time.

Further, as the detection of the predetermined voltage, it is possible to accurately detect the decrease of the battery voltage based on the charging voltage by detecting the decrease of the predetermined value from the voltage value based on the charging voltage. As a result, the state of the secondary battery can be controlled accurately.

Further, as the detection of the predetermined voltage, by detecting that the battery voltage from the voltage with reference to the ground potential of the secondary battery has reached a predetermined voltage value, a relatively simple voltage can be obtained. By the detection, the state of the secondary battery can be properly controlled.

[Brief description of drawings]

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

FIG. 2 is a flowchart illustrating a charging process according to the first embodiment.

FIG. 3 is a characteristic diagram showing a charge state according to the first embodiment.

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

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

FIG. 6 is a flowchart showing a charging process according to the second embodiment.

FIG. 7 is a characteristic diagram showing a state of charge according to a second embodiment.

FIG. 8 is a flowchart showing a charging process when full charge detection is performed by another process in the second embodiment.

FIG. 9 is a flowchart showing a charging process when full charge detection is performed in still another process in the second embodiment.

FIG. 10 is a characteristic diagram showing a state of charge according to a third embodiment.

FIG. 11 is an explanatory diagram showing an example of charging characteristics of a lithium ion battery.

FIG. 12 is a characteristic diagram showing an example of a recharged state of a conventional lithium-ion battery.

[Explanation of symbols]

1 commercial AC power supply, 2 transformer / rectifier circuit, 3 constant current circuit, 4 constant voltage circuit, 5 secondary battery, 6 voltage detection circuit, 7 control circuit, 8 current detection resistor, 9 current detection circuit, 10 load circuit

Claims (21)

[Claims] 1. A charging method for charging a secondary battery that is charged by a constant-voltage charging voltage, wherein after the secondary battery is almost fully charged and the charging is stopped, the secondary battery is set to a predetermined state. A charging method in which, when it is detected that the state has been reached, charging of the secondary battery is restarted after a predetermined time has elapsed from the detection. 2. The charging method according to claim 1, wherein, as the detection of the predetermined state, it is detected that the battery voltage of the secondary battery has decreased by a predetermined value from a voltage value based on the charging voltage. 3. The charging method according to claim 1, wherein as the detection of the predetermined state, it is detected that the battery voltage from a voltage value with reference to the ground potential of the secondary battery has reached a predetermined voltage. . 4. The charging method according to claim 1, wherein, as the detection of the predetermined state, it is detected that the charging current reaches a predetermined value when a predetermined voltage is applied to the secondary battery. 5. The charging method according to claim 4, wherein the predetermined voltage is lower than the charging voltage of the constant voltage. 6. A charging method for charging a secondary battery, which is charged by a constant-voltage charging voltage, wherein the secondary battery is charged almost every predetermined time after detection of almost full charge and stopping of charging. A charging method in which the state of the secondary battery is detected, and charging is restarted when the detected state is a predetermined state. 7. The charging method according to claim 6, wherein the charging is restarted after a lapse of a predetermined time from the detection of the predetermined state. 8. The detection of the predetermined state, wherein the charging current exceeds a predetermined value when the charging voltage or a voltage lower than the charging voltage is applied to the secondary battery. 6. The charging method according to 6. 9. The charging method according to claim 6, wherein as the detection of the predetermined state, it is detected that the battery voltage of the secondary battery has reached a predetermined voltage. 10. The secondary battery is charged with at least the energy required to detect the battery voltage when the battery voltage of the secondary battery does not reach a predetermined voltage and charging is not restarted. The charging method described. 11. The charging method according to claim 9, wherein, as the detection of the predetermined voltage, it is detected that the voltage value has decreased by a predetermined value from a voltage value based on the charging voltage. 12. The detection of the predetermined voltage is performed by detecting that the battery voltage from a voltage with reference to the ground potential of the secondary battery has reached a predetermined voltage value.
The charging method described. 13. A charging device for charging a secondary battery that is charged by a constant charging voltage, a constant voltage means for supplying the charging voltage to the secondary battery, and a state of the secondary battery is detected. Battery state detection means, charge control means for controlling charging by the constant voltage means, and timer means that operates when the battery state detection means detects a predetermined state of the secondary battery, the timer means operating When a predetermined time has passed from the start,
A charging device in which the charging control means starts charging by the constant voltage means. 14. The charging device according to claim 13, wherein, as the detection of the predetermined state by the battery state detection means, it is detected that the battery voltage of the secondary battery has reached a predetermined voltage. 15. The charging according to claim 13, wherein, as the detection of the predetermined state by the battery state detection means, it is detected that the charging current has reached a predetermined value when a predetermined voltage is applied to the secondary battery. apparatus. 16. A constant voltage for precharging, which is lower than the charging voltage, can be supplied as the constant voltage means, and the constant voltage for precharge is used as the predetermined voltage applied to the secondary battery. Charging device. 17. A charging device for charging a secondary battery charged by a constant charging voltage, wherein a constant voltage means for supplying the charging voltage to the secondary battery and a state of the secondary battery are detected. A battery state detecting means; a charging control means for controlling charging by the constant voltage means; and a timer means that operates when the battery state detecting means detects a substantially full charge of the secondary battery. Every time a predetermined time elapses from the start of operation, the charging control means causes the battery state detection means to perform
A charging device configured to detect the state of the secondary battery and restart the charging by the constant voltage means when the detected state is a predetermined state. 18. The charging device according to claim 17, wherein when the predetermined state is detected, charging by the constant voltage means is restarted after a predetermined time has elapsed from the detection. 19. The detection of the predetermined state by the battery state detection means is to detect that the charging current when the charging voltage or a voltage lower than the charging voltage is applied to the secondary battery exceeds a predetermined value. The charging device according to claim 17, wherein 20. The charging device according to claim 17, wherein the detection of the predetermined state by the battery state detection means detects that the battery voltage of the secondary battery has reached a predetermined voltage. 21. When the battery voltage of the secondary battery is not a predetermined voltage and charging is not restarted, at least energy required for detecting the battery voltage is supplied to the secondary battery by the control of the charge control means. The charging device according to claim 20, wherein the charging device is configured to be charged.