JPH11262197A - Charging unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain prompt and efficient recovery of a secondary battery deeply discharged, by forming a means for determining whether the secondary battery is charged rapidly or not, depending on the battery voltage of the secondary battery after trickle charging. SOLUTION: When a secondary battery BAT is trickle charged over the prescribed time, a condition determination part 14 determines whether battery voltage Vbat increases or not. When increase in voltage is detected, the factor of the drop in the battery voltage Vbat is determined as deeply discharged caused by negligence of the secondary battery BAT for a long time. A duty ratio is increased gradually for increasing charging current, and finally the duty ratio reaches 100%, thereby charging the secondary battery BAT rapidly by the constant current supplied from a charging current 3. When any changing does not occur in the battery voltage Vbat of the secondary current BAT, the factor of the drop in the voltage is determined as other than deep discharging. In this case, it is determined that further charging is useless and there is a problem in safety, so that charging processing is stopped at this time.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging device having a function of effectively recovering a deeply discharged secondary battery.

[0002]

2. Related Art Recently, rechargeable secondary batteries such as Ni-MH batteries and Li-ion batteries have been widely used as power sources for various electronic devices. However, when the secondary battery is left for a long period of time, deep discharge occurs, and the voltage of the secondary battery is significantly reduced. In order to recover a secondary battery in which such a deep discharge has occurred, it is unavoidable that a considerable amount of time is required even when quick charging is performed using an ordinary charging device.

That is, the charging of the secondary battery BAT is performed, for example, by a battery voltage detecting circuit 1 as shown in FIG.
The battery voltage Vbat of T is detected, and the constant voltage / constant current control circuit 4 in the charging power supply 3 is operated under the control of the charging control circuit 2 in accordance with the battery voltage Vbat. Is executed by supplying a constant charging current to the.

[0004]

However, in the case where the secondary battery BAT is rapidly charged by the charging device configured as described above, the battery voltage V of the secondary battery BAT is set.
Depending on the cause of the bat reduction, there is a problem with its safety. Therefore, if the cause of the decrease in the battery voltage Vbat is unknown, for example, the secondary battery BAT is once trickle-charged with a current sufficiently lower than a normal charging current, and the battery voltage of the secondary battery BAT is reduced. After Vbat reaches a predetermined recovery voltage, it is desirable that the secondary battery BAT be rapidly charged with the normal charging current. However, when the secondary battery BAT in a deep discharge state is charged with a small trickle current, the time itself until the battery voltage Vbat reaches the above-described recovery voltage is considerably long. Therefore, it takes a considerable amount of time to determine whether the cause of the decrease in the battery voltage Vbat of the secondary battery BAT is a deep discharge, and it is supposed that the cause is determined to be a deep discharge. However, there is a problem in rapidly charging the secondary battery BAT because only quick charging is performed from the time of the determination.

The present invention has been made in view of such circumstances, and has as its object to efficiently determine the cause of a voltage drop in a secondary battery in which the battery voltage has dropped to a deep discharge voltage or less, and to determine a deep discharge state. It is an object of the present invention to provide a charging device which can efficiently charge a secondary battery in a short time.

[0006]

In order to achieve the above-mentioned object, a charging apparatus according to the present invention comprises a voltage detecting circuit for detecting a battery voltage of a secondary battery, and the secondary battery detected by the voltage detecting circuit. A charge control circuit capable of changing a charge current for the secondary battery in accordance with the battery voltage of the battery.In particular, in this charge control circuit, when the battery voltage of the secondary battery is equal to or less than its deep discharge voltage, Means for trickle charging the secondary battery for a predetermined period, and whether to rapidly charge the secondary battery or stop charging the secondary battery according to the battery voltage of the secondary battery after trickle charging. And means for determining.

That is, when the battery voltage of the secondary battery is equal to or lower than its deep discharge voltage, the secondary battery is trickle-charged for a predetermined period, and whether the battery voltage of the secondary battery changes due to the trickle charge is determined. By examining whether or not the drop in battery voltage is due to deep discharge caused by long-term storage,
Alternatively, it is determined whether the charge is caused by another factor, and if the charge is caused by the deep discharge described above, the charge is switched to the quick charge with a constant current immediately. It is characterized by doing.

In a particularly preferred aspect of the present invention, a switch connected in series to the secondary battery is provided as a part of the charge control circuit, and an on / off ratio (duty cycle) of the switch is provided. By changing the ratio, the charging current is varied independently of the charging power supply that outputs a constant current. By setting the on-period shorter than the switch on-off cycle (decreasing the duty ratio), the charging current is reduced, and by gradually increasing the on-period (decreasing the duty ratio), the charging current is reduced. Is gradually increased. By keeping the switch on (duty ratio: 1
00%), the charging current from the charging power supply is supplied to the secondary battery as it is.

The trickle current is defined by claim 3
, The current is set to be sufficiently lower than the rapid charging current of the secondary battery by the constant current.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a charging device according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a schematic configuration diagram of the charging device according to the first embodiment, and the same parts as those of the conventional device shown in FIG. 4 are denoted by the same reference numerals.
This device is characterized in that it comprises a charge control switch 12 connected in series to the secondary battery BAT via a coil 11 and receives the output (detection voltage) of the battery voltage detection circuit 1 so that the charging power supply The charge control circuit 2 for controlling the operation of the constant current / constant voltage control circuit 4 in FIG. 4 is realized as a charge control circuit 10 with an on / off function further having a function of turning on / off the charge control switch 12. There is in the point.

Particularly, the charge control circuit 10 is characterized in that the battery voltage Vbat is equal to or lower than a predetermined deep discharge voltage according to the battery voltage Vbat of the secondary battery BAT detected by the battery voltage detection circuit 1. When the battery is in the overdischarge state, the charging power source 3 is operated, and the duty ratio control unit 13 is operated to drive the charge control switch 12 at a predetermined on / off ratio, thereby setting the secondary battery BAT to a predetermined value. It has the function of trickle charging over time. Further, according to the battery voltage Vbat of the secondary battery BAT detected by the battery voltage detection circuit 1 after the trickle charge, the secondary battery BAT is simply in a deep discharge state, or the battery voltage Vbat is different for another reason. The point is that a state determining means 14 for determining whether the charge control circuit 10 has decreased and controlling the operation of the charge control circuit 10 is provided.

Thus, the duty ratio control unit 13
When the battery voltage Vbat is equal to or lower than a predetermined deep discharge voltage, the charging current from the charging power supply 3 is intermittently turned on and off by driving the charging control switch 12 and supplied to the secondary battery BAT through the coil 11. Thus, the secondary battery BAT is trickle-charged. At this time, the trickle charging current is set to, for example, about several tens mA, which is sufficiently smaller than the normal charging current.
Is determined by the on / off ratio (duty ratio) of

When the secondary battery BAT is trickle-charged for a predetermined period in this way, the state determination unit 14 determines whether or not the battery voltage Vbat has risen. At this time, it is determined that the cause of the decrease in the battery voltage Vbat of the secondary battery BAT is a deep discharge due to leaving the secondary battery BAT for a long period of time. In this case, by gradually increasing the duty ratio, the charging current is increased, and finally, the duty ratio is set to 100%, and the secondary battery BAT is set to a constant current supplied from the charging power supply 3. Charge quickly. The charging process of the secondary battery BAT performed in this manner is performed by the secondary battery BA.
The process is executed until the full charge of T is detected.

On the other hand, if the battery voltage Vbat of the secondary battery BAT does not change despite the trickle charge of the secondary battery BAT for a predetermined time as described above,
It is determined that the cause of the voltage drop of the secondary battery BAT is other than the deep discharge. In this case, it is determined that charging the secondary battery BAT further is useless and there is a problem in terms of safety, and the charging process is stopped at this point. This charging process can be stopped by turning off the switch 12 and then issuing a charge stop command to the constant current / constant voltage control circuit 4. In this case, for example, it is preferable to output a message prompting abnormality or discarding, assuming that the function of the secondary battery BAT is impaired.

Thus, according to the charging device that operates as described above, when the battery voltage Vbat of the secondary battery BAT is greatly reduced, the secondary battery BAT is first supplied with a current sufficiently smaller than the normal charging current. From the battery voltage Vbat at that time, it is determined in a relatively short time whether or not the cause of the voltage drop is due to deep discharge. If it is determined that the charge is caused by deep discharge, the charge current is immediately increased to switch to the quick charge. Therefore, trickle charge with a low current is performed for a long time until the battery voltage Vbat returns to the recovery voltage. Since the charging is not continued, the charging can be efficiently performed.

In particular, when the rise of the battery voltage Vbat due to trickle charging is detected before the battery voltage Vbat reaches the recovery voltage, the on / off ratio (duty ratio) of the switch 12 is gradually increased. Since it is possible to increase the charging current and shift to the rapid charging, the recovery of the battery voltage can be accelerated, and the charging efficiency can be increased.

With the above-described structure, the charging current is controlled by turning on / off the current control switch 12 inserted in series with the secondary battery BAT without changing the function of the charging power supply 3. The charging can be easily and efficiently varied to control the charging. In particular, when the cause of the voltage drop is other than the deep discharge, the charging can be stopped immediately by simply turning off the switch 12, so that the unintentional charging process can be prevented, and the safety can be improved. Can be kept high enough.

By the way, the function of the charging device described above is realized as a part of the function of a fuel gauge (FG) circuit which is integrally packaged with the secondary battery BAT and constitutes the secondary battery device (battery pack). Can also. In this case, for example, as shown in FIG. 2, the function may be realized as a function of the microprocessor pro 20 serving as a control unit of the fuel gauge circuit. That is, in this case, a current control switch (power FET) 21 is provided in series with the secondary battery BAT, and the switch 21 is turned on / off via the driver FET 22. And in the microprocessor 20,
For example, the control program may be constructed to control charging of the secondary battery BAT according to the control procedure shown in FIG.

A case where a secondary battery BAT in which eight nickel-metal hydride batteries are connected in series will be described as an example. First, a timer T for managing the overall processing time of trickle charge control is described.
t is initialized to zero (0) [Step S1], and the secondary battery B
It is determined whether or not the battery voltage Vbat of the AT is less than, for example, 8V. At this time, it is determined at the same time whether or not the charging power supply 3 is operating [Step S2]. If it is confirmed by this determination that the battery voltage Vbat is equal to or higher than the determination threshold value of 8 V, trickle charging is unnecessary, and if the charging power source 3 is not in operation, the charging of the secondary battery BAT itself is performed. , The trickle charging process is terminated.

If the battery voltage Vbat is less than 8 V and the secondary battery BAT can be charged, control parameters Ts1 and Ts2 for trickle charging are set according to the battery voltage Vbat. I do. Specifically, when the battery voltage Vbat is less than 0.2 V, for example, the trickle charge time management parameters Ts1 (on time of the switch 21) and Ts2 (off time of the switch 21) are set to 300 mS and 1300 mS, respectively. [Step S3
a]. Further, when the battery voltage Vbat is 0.2 V or more,
If it is less than 5.8 V, the time management parameters Ts1 and Ts2 are set to 400 mS and 1200 mS, respectively (step S3b). Similarly, the battery voltage Vba
When t is 5.8 V or more and less than 8.0 V, the time management parameters Ts1 and Ts2 are set to 8 respectively.
00 ms and 1000 ms [Step S3
c].

After the time management parameters Ts1 and Ts2 are set according to the battery voltage Vbat as described above, the timer t is set to zero (0) and the switch 21 is turned on to perform trickle charging. [Step S4], the trickle charge is continued until the trickle charge time t reaches the time management parameter Ts1 set as described above, and then the switch 21 is turned off to stop the trickle charge [Step S4]. S5, S6].

After the stop of the trickle charge, a stabilization of the charge voltage Vbat of the secondary battery BAT is waited after a wait time of, for example, 400 ms [Step S7].
It is determined whether or not at has risen to the above-described determination threshold voltage of 8 V or more (step S8). This battery voltage Vbat
Is determined by the time management parameters Ts1, Ts2 described above.
Is repeated until the timer t reaches [Ts1 + 400 + Ts2] (step S9). That is, the time management parameter Ts1
After the trickle charge based on the above, after passing a waiting time of 400 mS and further until a predetermined off-time determined by the time management parameter Ts2 elapses, the battery voltage Vba
Check whether t has increased.

The battery voltage Vbat is thus determined by this determination.
Is restored to 8 V or more, the secondary battery B
It is determined that the charging voltage Vbat of the AT has recovered to a predetermined return voltage, and from this point on, switching is made to rapid charging with a constant current [step S8]. However, the battery voltage Vba
If t does not reach the return voltage of 8 V, it is determined whether or not the timer Tt that manages the overall processing time of the trickle charge control described above has reached 30 minutes. If not, the process from step S2 described above is repeatedly executed [step S10]. When the trickle charging with 2 seconds as one unit is repeated in this way, the time management parameters Ts1 and Ts2 are set according to the battery voltage Vbat at that time. If the battery voltage Vbat does not reach the above-mentioned return voltage of 8 V even after 30 minutes have passed, the battery voltage Vbat is set to the secondary battery B.
It is determined that the AT is abnormal, the disposal of the secondary battery BAT is prompted, and the charging process is terminated.

Thus, under such processing, the secondary battery B
According to the charging device that executes the trickle charge for the AT, the trickle charge is executed for a maximum of 30 minutes in units of 2 seconds according to the battery voltage Vbat. Further, according to the battery voltage Vbat, the on / off ratio (duty ratio) of trickle charging is varied in three steps here, and the charging current value is varied in accordance with the time management parameters Ts1 and Ts2 described above. I have. Then, when the battery voltage is recovered by such three-stage trickle charging, rapid charging is immediately performed. As a result, when the cause of the decrease in the battery voltage Vbat is caused by deep discharge caused by leaving the battery for a long time, the recovery is promptly performed and the rapid charging process is performed.

The present invention is not limited to the above embodiment. For example, the on / off ratio of the charging current and the on / off time width of the charging current when realizing the trickle charging may be determined according to the charging current from the charging power supply 3, the performance of the secondary battery BAT, and the like. Also, the trickle charge control time and the like may be determined according to the specifications, and can be variously modified without departing from the gist of the invention.

[0026]

As described above, according to the present invention, when the battery voltage of the secondary battery is equal to or lower than the deep discharge voltage, the secondary battery is trickle-charged for a predetermined period, and the trickle charge is performed by the trickle charge. By examining whether or not the battery voltage of the secondary battery changes, it is determined whether the decrease in the battery voltage is due to deep discharge caused by leaving for a long period of time or due to other factors. If this is the case, switch to the rapid charging with a constant current promptly, and if it is found to be due to other factors, stop the charging process itself. And it can recover efficiently. In addition, under such a simple control, effects such as recovery can be achieved.

[Brief description of the drawings]

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

FIG. 2 is a diagram showing an implementation example of a charging device according to another embodiment of the present invention.

FIG. 3 is a diagram showing a flow of trickle charge control by the microprocessor shown in FIG. 2;

FIG. 4 is a diagram showing a configuration example of a conventional general charging device.

[Description of Signs] BAT Secondary Battery 1 Battery Voltage Detection Circuit 3 Charging Device 10 Charge Control Circuit 11 Coil 12 Current Control Switch 13 Duty Ratio Control Unit 14 State Judgment Unit 20 Microprocessor 21 Power FET 22 Driver FET

Claims (3)

[Claims] 1. A voltage detection circuit for detecting a battery voltage of a secondary battery, and a charging device capable of changing a charging current for the secondary battery according to the battery voltage of the secondary battery detected by the voltage detection circuit. A control circuit, wherein the charging control circuit is means for trickle-charging the secondary battery for a predetermined period when the battery voltage of the secondary battery is equal to or lower than the deep discharge voltage; and Whether to rapidly charge the secondary battery according to the battery voltage of the secondary battery,
Means for deciding whether to stop charging the secondary battery. 2. The charge control circuit includes a switch connected in series to the secondary battery.
The charging device according to claim 1, wherein the charging current is varied by changing an off ratio. 3. The charging device according to claim 1, wherein the trickle charging is performed with a current sufficiently lower than a rapid charging current of the secondary battery by a constant current.