JPH04308429A - Charger for secondary battery - Google Patents

Abstract

PURPOSE:To prevent charging time for a secondary battery from being unreasonably lengthened while a memory effect of the secondary battery can be effectively eliminated and suppressed. CONSTITUTION:In the case of mounting a secondary battery 2 to a battery terminal 9, terminal voltage of the secondary battery 2 is measured prior to charging. In the case of the terminal voltage in a fixed range in the vicinity of final voltage of the secondary battery 2, a discharge limiting switch 16 is turned on to perform a forced discharge of the secondary battery 2 prior to the charging. The charging is started first when the terminal voltage is decreased surely lower than the final voltage. In the case of the detected terminal voltage out of the above-mentioned range, the charging is instantaneously started. Since the forced discharge of the secondary battery is automatically performed at an adequate period, a memory effect is effectively eliminated and suppressed.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to electronic equipment, and more particularly to a device incorporated into an AC (alternating current) adapter for charging a secondary battery such as a so-called nickel/cadmium battery.

FIG. 3 is a system block diagram of a conventional AC adapter that functions as a charging device for NiCd batteries. Referring to FIG. 3, conventional AC adapter 1
a converts an alternating current given from an external power supply via an AC plug 3 and a fuse 4 into a constant voltage direct current (DC) and supplies it to a DC output terminal 29, and converts it into a constant current source to charge the battery 2. A switching regulator circuit 5 that operates as an AC/DC conversion means for supplying AC/DC to the battery terminal 9, which is a terminal, and a DC output switch 12 and a diode 13 provided between the switching regulator circuit 5 and the DC output terminal 29. It includes a quick charging switch circuit 6, a constant current correction resistor 7, and a diode 8 connected in series between a switching regulator circuit 5 and a battery terminal 9. A trickle charge switch 10 and a trickle charge limiting resistor 11 are connected between the switching regulator circuit 5 and the diode 8 in parallel with the quick charge switch circuit 6 and the constant current correction resistor 7. The functions of the quick charge switch circuit 6, trickle charge switch circuit 10, and DC output switch 12 will be described later.

[0003] The quick charge switch circuit 6, the trickle charge switch circuit 10, and the DC output switch 12 are controlled by a microcomputer 20. The connection line from the switching regulator circuit 5 to the DC output switch 12 branches in the middle and is connected to a switching regulator circuit 24 that operates as DC/DC conversion means. The switching regulator circuit 24 is
15~ output from the switching regulator circuit 5
This is for converting a constant voltage of 6V to a DC voltage of about 5V. The switching regulator circuit 24 includes a charging LED (Lig.
ht Emitting Diode) 27 and charging L
A switch 28 connected between the ED 27 and the ground potential and controlled by the microcomputer 20 is connected.

The AC adapter 1a further has an input connected to a battery terminal 9, and a battery attachment detection circuit 14 for detecting that the battery 2 is attached to the battery terminal 9 and transmitting the detected information to the microcomputer 20. It includes a charging completion detection circuit 15 connected to the battery terminal 9 to detect that charging of the battery 2 is completed and to transmit the detected result to the microcomputer 20 . Both the battery attachment detection circuit 14 and the charging completion detection circuit 15 operate by receiving power from the switching regulator circuit 24 .

The microcomputer 20 further includes a timer 19 provided to prevent damage to the battery 2 due to full charging when the charging completion detection circuit 15 fails to detect the completion of charging the battery 2 for some reason. ,
If the output of the battery attachment detection circuit 14 becomes unstable due to rattling (chattering) when the battery 2 is attached to the battery terminal 9 or due to mischief, the operation mode of the AC adapter 1a becomes unstable. A memory circuit 23 and a power switch 22 connected to the microcomputer 20 are provided to prevent this from happening.

The microcomputer 20 includes a battery attachment detection circuit 14.
In response to the output of the charging completion detection circuit 15, if the battery 2 is not attached to the battery terminal 9, the DC
An AC adapter mode in which DC output is performed to the output terminal 29, a charging mode in which the battery 2 is charged when the battery 2 is attached to the battery terminal 9, and a charging mode in which the battery 2 is charged.
A trickle charge mode in which the battery 2 is charged completely by detecting that the battery 2 has finished charging, and a small current is applied to the battery 2 in order to cover the self-discharge of the battery and to fully charge the battery 2. automatically select each switch 6, 10 according to the selected mode.
, 12.

Referring to FIG. 3, A
The C adapter operates as follows.

AC Adapter Mode When supplying DC power to a portable device or the like, the following connections are made. The AC plug 3 is connected to a commercial AC power outlet. The portable device is connected to the DC output terminal 29 with a DC cable or the like.

The AC adapter mode is selected when the battery 2 is not attached to the battery terminal 9. Whether or not the battery 2 is attached to the battery terminal 9 is detected by the battery attachment detection circuit 14 .

When the battery 2 is not attached to the battery terminal 9, the microcomputer 20 turns on the DC output switch 12 and the quick charge switch circuit 6, and turns off the trickle charge switch 10. The switching regulator circuit 5 converts the AC voltage applied from the AC plug 3 into a specified DC constant voltage B2, and outputs the DC output switch 1.
Give to 2. This constant voltage is turned on when the DC output switch 12 is turned on.
Therefore, it is supplied to a portable device or the like via the diode 13 and the DC output terminal 29. Since the quick charge switch circuit 6 is ON, the battery 2 is connected to the battery terminal 9.
The fact that the battery is attached can be easily detected by the battery attachment detection circuit 14.

Charging Mode In the following discussion, we will discuss batteries that require constant current charging, such as nickel-cadmium batteries, to which the present invention is particularly concerned. A battery attachment detection circuit 14 detects that the battery 2 is attached to the battery terminal 9 and provides this information to the microcomputer 20. Microcomputer 2
0 turns off the DC output switch 12 upon receiving the output of the battery attachment detection circuit 14. The quick charge switch circuit 6 is kept ON and the trickle charge switch 10 is kept OFF.

The switching regulator circuit 5 converts the AC voltage supplied from the plug 3 into a DC constant current of voltage B1 and supplies it to the quick charge switch circuit 6. The magnitude of the constant current is determined by the internal impedance of the quick charge switch circuit 6, the diode 8, the battery 2, and the resistance value r1 of the constant current correction resistor 7. The charging current is transferred from the switching regulator circuit 5 to the quick charge switch circuit 6, constant current correction resistor 7, and diode 8.
is applied to the battery 2 via the battery terminal 9. The battery 2 is then charged by this current.

In the charging mode, the microcomputer 20 turns on the switch 28. The switching regulator circuit 24 converts the voltage of 15 to 6 V outputted from the switch regulator circuit 5 to 5 to 6 V and charges the charging LED 27.
is giving to When the switch 28 is turned on, the charging LED 27 lights up to indicate that charging is in progress.

Trickle Charge Mode When charging of the battery 2 is completed, the operating mode shifts to trickle charge mode. Completion of charging is performed by the charging completion detection circuit 15. This detection is performed as follows. The terminal voltage of the battery 2 gradually increases during charging as shown in the graph of FIG. However, near the completion of charging, there is a point in the terminal voltage of the battery 2 where the voltage decreases, as shown by the charging time t1 in FIG. It is determined that charging is complete by detecting the point in time when this drop amount reaches ΔV. Such a method is called a -ΔV method.

The charging completion detection circuit 15 detects the completion of charging of the battery 2 using the above-mentioned -ΔV method, and the microcomputer 2
A signal indicating the completion of charging is given to 0. When the microcomputer 20 receives a signal indicating the completion of charging, the microcomputer 20 switches the trickle charging switch 1
0 is turned on, and the quick charge switch circuit 6 is turned off. The charging current output from the switching regulator circuit 5 is given to the battery 2 via the trickle charging switch 10, the trickle charging limiting resistor 11 (resistance value r2), the diode 8, and the battery terminal 9, and this current causes the battery 2 to trickle. It will be charged.

As described above, trickle charging is performed for the purpose of fully charging the NiCd battery and for covering the self-discharge of the battery 2. The current used in trickle charging is about 1/30 of the normal charging current.
It is a small current. In the case of NiCd batteries, the activation inside the battery is weak, so even if trickle charging is applied continuously, problems such as leakage due to full charge will not occur. The microcomputer 20 turns off the switch 28 when the charging completion detection circuit 15 detects the completion of charging. As a result, the charging LED 27 turns off.

For some reason, the charging completion detection circuit 15
There is a possibility that a case may occur in which the above-mentioned drop voltage of -ΔV cannot be detected. In such a case, charging continues, and there is a risk that the battery 2 may be damaged due to full charging, that is, fluid leakage may occur due to overcharging. In order to prevent such inconvenience, the charging time may be limited by the timer 19.

The memory circuit 23 is provided to prevent the operation of the charging circuit of the AC adapter 1a from becoming unstable due to rattling of the charging terminal 9 or the like. That is, due to the rattling of the battery terminal 9, the output of the battery attachment detection circuit 14 may vary minutely between a value indicating that the battery is attached and a value indicating that the battery is removed. This is caused not only by the rattling of the battery terminal 9, but also by the operator intentionally inserting the battery 2 into the battery terminal 9.
It can also occur by attaching and detaching the device. Memory circuit 23
is provided to prevent mode switching from occurring until a certain amount of time has elapsed.

FIG. 4 is a diagram showing the flow of charging operation of the battery 2 by the AC adapter 1a. In Figure 4,
Each block can be operated by the operator or by using the AC adapter 1a.
The line connecting each block represents the path through which the state of the AC adapter 1a changes depending on conditions.

Referring to FIG. 4, the AC adapter 1a is
By inserting C plug 3 into the outlet (AC cord included 41), when disconnecting the battery, connect P-O via path A.
When the battery arrives at N42, connect to P-ON via route B.
43 respectively. Battery disconnected state (P-O
After the power switch 22 is turned on in N42),
If the battery remains disconnected, the state shifts to AC adapter mode 49 via route A1. In the AC adapter mode 49, a DC voltage is applied to the outside from the DC output terminal 29 as described above. By turning off the power switch 22 in this state, the state changes to P via path G.
- Return to ON42.

When the battery 2 is attached to the battery terminal 9 after the power switch 22 is turned on in the battery disconnected state (P-ON42), the state of the AC adapter 1a shifts to the quick charging mode 45 via path B'. do. In the quick charging mode 45, charging current is supplied to the battery 2 via the battery terminal 9 as described above, and the charging current is supplied to the battery 2 through the battery terminal 9.
is charged by that current. When the battery is removed in the quick charging mode 45 operating mode, the state of the AC adapter shifts to the AC adapter mode 49 via path A2. When charging is completed in the quick charging mode 45, the AC adapter changes the state to trickle charging mode 46 via path H. If the battery is removed in trickle charge mode 46, the state changes to AC adapter mode 49 via path A3, and if the power is turned off, the state returns to P-ON 43 via path G1.

When the power switch 22 is turned on with the battery connected (P-ON 34), the operation of the AC adapter 1a shifts to the quick charging mode 45. The subsequent operation is P-
Since this is the same as when the state changes from ON42 to quick charge mode 45, the details will be omitted here.

[0023]

[Problems to be Solved by the Invention] However, the above-mentioned secondary battery charging device has the following problems. In the case of NiCd batteries, users have a tendency to want to charge the batteries even after using them for a short period of time, and always want to keep the batteries fully charged. That is, as shown in FIG. 6, short charging and discharging may be repeated. However, in such cases, the battery has a memory effect (Memory effect).
It is known that a phenomenon called "effect" is caused.

Referring to FIG. 7, when the memory effect occurs,
The battery discharge curve (dotted chain line in FIG. 7) is lower than the normal discharge curve (solid line in FIG. 7). Therefore, even if the battery is fully charged, the usable time is shortened. In Figure 7, the battery voltage is the final voltage (1.0V)
The time at which the value decreases to 0.01 moves from t1 to t2. That is, when starting to use a battery from a fully charged state, the usable time will be shorter even though the memory effect has occurred than when the battery does not.

It is known that this memory effect can be eliminated by using up the battery once. This phenomenon is called the memory effect because the battery behaves as if it were remembering the partial discharge.

[0026] Although no unified theory has been established as to the cause of this phenomenon, one way of thinking is as follows. Referring to FIG. 8, it is assumed that the circles shown in FIGS. 8(a) to 8(e) represent the total amount of active material (the source that actually stores and discharges charge) in the battery.

FIG. 8(a) shows the battery before use. No memory effect appears in this battery. After the battery is fully charged as shown in FIG. 8(b), it is partially discharged as shown in FIG. 8(c). Figure 8
In (b) and (c), the shaded area represents the active material storing electricity, and the white area represents the active material that has been discharged.

It is assumed that such partial discharge and charging are repeated many times. Since the reaction of the active material tends to occur in a fixed portion, the electricity stored in the active material within the inner circle in FIG. 8(c) remains unused. As a result, as shown in Fig. 8(d), when this battery is fully charged, the active material in the inner circle has been charged for a long time, while the active material outside the circle has just been charged. A situation may occur where this is the case.

Consider the process of completely discharging this battery as shown in FIG. 8(e). In this case, discharge is first performed from the active material in the area outside the inner circle. The battery voltage at this time is approximately the same as the normal battery voltage. After the discharge in the outer region is completed, discharge from the active material in the inner circle is started. As mentioned above, this part has been charged for a long time. Therefore, when discharging from this portion is occurring, the battery voltage is low. As a result, it is thought that the above-mentioned memory effect is caused.

Such a memory effect can occur not only due to discharge due to use, but also due to repeated natural discharge from a fully charged state. However, this is limited to repeated charging within one month. If left for more than 3 months, the voltage will drop to 1.0V/cell or less.

The phenomenon of usage time due to memory effect is about 1 to 1.5% in one short charging/discharging cycle. It is known that the usage time decreases by about 20% after 20 charging and discharging times, and by a maximum of about 30 to 50% if charging and discharging are repeated more than that.

As can be seen from the above description, in order to improve the memory effect, it is necessary to use up the battery once. In the case of NiCd batteries, the standard set voltage of a single cell is 1.2V. This is the voltage at which it is considered that the discharge is almost completely completed (final voltage), that is, 1.0V.
You can use the battery until it drops below.

In order to solve this problem, there are devices called dischargers for forcibly discharging the battery, and charging devices that incorporate a discharger and forcibly discharging the battery before charging. .

However, if the battery is forcibly discharged in a state close to full charge, the discharge time becomes longer. It can be said that a device in which forced discharge is performed manually is not very desirable commercially. Furthermore, repeated forced discharges may shorten the life of the battery.

Therefore, an object of the present invention is to provide a secondary battery charging device that can automatically suppress the occurrence of the memory effect and that does not unduly lengthen the charging time of the secondary battery. It is.

[0036]

[Means for Solving the Problems] The secondary battery charging device according to claim 1 is capable of attaching and detaching the secondary battery, and provides direct current for charging to the attached secondary battery. Detects the charging terminal and the insertion and removal of the secondary battery to the charging terminal,
When the secondary battery is attached to the charging terminal, the predetermined first value is set, and when the secondary battery is removed, the predetermined second value is set.
battery attachment/detachment detection means for outputting battery attachment/detachment detection signals each having a value of Terminal voltage detection means for detecting terminal voltage of a battery and detecting whether the detected terminal voltage is within a predetermined voltage range whose lower limit is the final voltage of the secondary battery; and terminal voltage detection means. a forced discharge means for forcibly discharging the secondary battery until the terminal voltage becomes equal to or lower than the final voltage when the detected terminal voltage is within the above voltage range; and a terminal voltage detection means. In response to the forced discharge means, it is detected that the detected terminal voltage is outside the above voltage range or that the forced discharge by the forced discharge means has ended, and the secondary battery is pre-charged via the charging terminal. and charging means for charging to a predetermined state of charge.

[0037] The secondary battery charging device according to claim 2 comprises:
In addition to the device according to claim 1, the device further includes a manually operable forced discharge start signal output for outputting a forced discharge start signal for starting forced discharge of the secondary battery attached to the charging terminal. The forced discharging means starts forced discharging of the secondary battery in response to a forced discharge start signal in addition to when the detected terminal voltage is within the voltage range. .

[0038]

In the secondary battery charging apparatus according to the first aspect of the present invention, when the secondary battery is attached to the charging terminal, the terminal voltage of the secondary battery is first measured. When the terminal voltage is outside a predetermined range, charging is started immediately, but in other cases, forced discharge of the secondary battery is performed by the forced discharge means until the terminal voltage falls below the final voltage. Charging is then performed.

In the secondary battery charging device according to the second aspect of the present invention, forced discharge can be started manually by using a forced discharge start signal output means. The discharge is performed by the same forced discharge means that performs forced discharge by detecting the terminal voltage.

[0040]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a system block diagram of an AC adapter 1 equipped with a NiCd battery charging device according to the present invention. The AC adapter 1 shown in FIG. 1 is different from the conventional AC adapter 1a shown in FIG. On/by 20
By being turned off, the discharge switch 16, which is a discharge means for controlling forced discharge of the battery connected to the battery terminal 9, detects the voltage at the connection point between the discharge control switch 16 and the discharge resistor 17. , and a voltage detection circuit 18 which is a terminal voltage detection means for providing the information to the microcomputer 20. Charging device 1 further includes a refresh LED 25 connected in series between switching regulator circuit 24 and ground potential to indicate that forced discharging is in progress, and a switch 26 controlled by microcomputer 20 . In addition to the power switch 22, the microcomputer 20 is connected to a refresh switch 21, which is a forced discharge start signal output means used when the operator wants to forcefully discharge the battery 2.

Identical parts have been given the same reference numerals and names in FIGS. 1 and 3. Their functions are also the same. Therefore, detailed explanations about them will not be repeated here.

Note that the resistance value of the discharge resistor 17 should be approximately 1/3 to 1/3 of the load of the portable device connected to this AC adapter 1, in order to avoid shortening the battery life and causing problems such as heat generation. It is recommended to set it to 1/4.

Referring to FIG. 1, an AC adapter 1 including a charging device according to an embodiment of the present invention operates as follows. The operation of the AC adapter 1 in AC adapter mode is similar to the conventional one already described with reference to FIG. Therefore, the explanation thereof will be omitted here.

Charging of the NiCd battery 2 is performed as follows. When the NiCd battery 2 is attached to the charging terminal 9, the battery attachment detection circuit 14 detects this and gives a signal to the microcomputer 20 indicating that the battery is attached. The microcomputer 20 turns on the forced discharge switch 16 in response to a change in the output of the battery attachment detection circuit 14. The quick charge switch circuit 6 and the DC output switch 12 are turned off. The voltage detection circuit 18 detects the terminal voltage of the battery 2 and provides a signal representing the value to the microcomputer 20.

The microcomputer 20 operates as follows in response to the output of the voltage detection circuit 18. The microcomputer 20 determines that the detected terminal voltage is approximately 0.8 V per cell of the battery 2.
If it is 1.1V, keep switch 16 on. Quick charge switch circuit 6, trickle charge switch circuit 10
, DC output switch 12 are both kept off. As a result, the battery 2 is forcibly discharged via the switch 16 and the discharge resistor 17. As the battery 2 discharges, the terminal voltage of the battery 2 decreases.

The microcomputer 20 turns off the discharge control switch 16 when the terminal voltage of the battery 2 detected by the voltage detection circuit 18 reaches 0.8V. The microcomputer 20 turns on the quick charge switch circuit 6. As a result, rapid charging of the battery 2 is started as in the conventional device.

If the terminal voltage detected by the voltage detection circuit 18 when the battery 2 is installed is below 0.8V per cell, or above 1.1V, the microcomputer 2
0 immediately turns off the discharge control switch 16 and turns on the quick charge switch circuit 6. That is, in this case, charging starts immediately.

The reason why the terminal voltage of the battery 2 is once detected and the battery 2 is forcedly discharged according to the detected value as described above is based on the following concept. As mentioned above, the memory effect occurs when a battery is repeatedly partially discharged and charged. To eliminate the memory effect, it is necessary to nearly discharge the battery. By the way, even if a user uses the battery in a manner that involves repeated partial discharging and charging as described above, the battery may be used for a longer period of time than usual, and the battery may become nearly exhausted. In such a case, the terminal voltage of the battery 2 approaches approximately 1.0V per cell. At this time, the memory effect can be reliably eliminated by automatically discharging to ensure that the terminal voltage is 1.0 V or less per cell. The frequency of forced discharge does not increase, and there is little possibility that the problem of shortening the battery life will occur. Further, as shown by the solid curve in FIG. 7, when the terminal voltage is 1.1 V or less per cell, the slope of the discharge curve is large. Therefore, the time t required for discharge in this part
0 is also short.

That is, a discharge control switch 16, a discharge resistor 17, and a voltage detection circuit 18 are newly provided, and the charging terminal 9
Detects the terminal voltage when battery 2 is attached to the
When this terminal voltage is within a predetermined range, by forcibly discharging the battery 2, the memory effect of the battery 2 is automatically eliminated or its occurrence is suppressed.

[0050] In this case, the problem is in what range of terminal voltage the forced discharge should be automatically performed. Generally, when designing a portable device, the number of battery cells used and the nominal voltage are approximately 1% of the minimum operating voltage of the device.
The voltage is selected to be increased by 0%. This is to reduce the weight of the battery as much as possible.

For example, if the minimum operating voltage of the device is 5.3V
If the minimum operating voltage of the device is approximately 8.8V, use a battery with 8 cells and a nominal voltage of 9.6V if the minimum operating voltage of the device is approximately 8.8V. The design is such that the equipment is driven by the Judging from this value, the voltage per cell of a NiCd battery required for normal operation of the device is approximately 1.1
It can be seen that it is about V. However, if a NiCd battery is charged when the terminal voltage per cell reaches approximately 1.1V, a memory effect may occur. Therefore, in order to eliminate the memory effect, the terminal voltage must be 1.0
It is desirable to discharge the battery until the voltage drops below V. In this example, this voltage was set to about 0.8V to ensure discharge.

Note that even when the battery is automatically discharged as described above, the charging LED 27 is lit in the same way as during normal charging. This is to avoid user confusion.

[0053] The refresh switch 21 connects the charging terminal 9
This is provided to instruct the microcomputer 20 to forcibly discharge the battery installed in the battery regardless of its terminal voltage. The forced discharge of such a battery is
It is called "Refresh". Refresh is battery 2
This is done at the user's will when they feel that a memory effect has occurred.

Refreshing is useful for people who frequently use portable equipment powered by batteries (people who use it as shown in FIG. 6). Under such usage conditions, the terminal voltage of battery 2 is 1 per cell.
．． Discharging and charging are repeated while the voltage is kept above 1V. When charging and discharging are repeated many times in this way, it may be felt that a memory effect has clearly occurred even if the terminal voltage is 1.1V or more. At such times,
Automatic discharge by the voltage detection circuit 18 described above cannot cope with this problem. Refreshing should be performed in such cases.

In the refresh mode, the AC adapter 1 operates as follows. Refresh switch 2
When 1 is pressed, the microcomputer 20 turns off the quick charge switch circuit 6 and the trickle charge switch circuit 10. The discharge control switch 16 is turned on. The battery 2 attached to the battery terminal 9 is forcibly discharged via the discharge control switch 16 and the discharge resistor 17. At this time,
The microcomputer 20 turns on the switch 26 and turns on the switch 28
FF. The refresh LED 25 lights up, allowing the user to know that forced discharge is in progress. The terminal voltage output by the voltage detection circuit 18 is sufficiently low, for example, approximately 0.
．． When the voltage falls below 8V, the microcomputer 20 turns off the forced discharge switch 16 and also turns off the switch 26. Furthermore, since battery 2 should normally be charged, microcontroller 2
0 turns on the quick charge switch circuit 6 and turns on the switch 28 as well. As a result, the battery 2 is charged, and the charging LED 27 lights up to indicate that charging is in progress. The operation of the AC adapter 1 after charging is completed is similar to that of conventional devices. Therefore, detailed explanations about them will not be repeated here.

[0056] In the AC adapter shown in Fig. 1,
The forced discharge circuit for refreshing and the discharge circuit for automatically discharging by detecting the terminal voltage are used. Therefore, an increase in cost can be suppressed compared to a charging device with a refresh function built into a conventional AC adapter.

FIG. 2 is a flowchart showing the operation flow of the AC adapter shown in FIG. The reason that FIG. 2 is different from the flowchart showing the operation of the conventional AC adapter shown in FIG. 4 is that when the power is turned on with the battery 2 attached to the battery terminal 9, the terminal voltage of the battery is detected. process (voltage detection 44), automatic discharge process 47 that is automatically performed when the detected terminal voltage is within a predetermined range, and forced discharge process 48 that is performed when the refresh switch 21 is pressed. This is a new provision.

In FIGS. 2 and 4, identical or corresponding processes are given the same reference numerals and names. The processing performed in them is also the same. Therefore, a description thereof will be omitted here.

Automatic discharge processing 47 and forced discharge processing 48
is executed according to the following flow. When the battery 2 is attached after the P-ON 42 process has been performed on the battery terminal 9, the state of the AC adapter shifts to the voltage detection process 44 via path B1. In the voltage detection 44,
As described above, the terminal voltage of the battery 2 is measured, and the range of the value is determined. When the voltage per battery cell is about 0.8 V or less or about 1.1 V or more, the state of the AC adapter 1 shifts to the rapid charging process 45 via path C. On the other hand, when the voltage per battery cell is approximately 0.8V to 1.1V, AC
The state of the adapter 1 shifts to automatic discharge 47 via path D.

If the terminal voltage of the battery 2 drops to approximately 0.8V per cell during automatic discharge 47, A
The state of the C adapter 1 shifts to the rapid charging process 45 via route E. When the refresh switch 21 is turned on during the process of automatic discharge 47, the state of the AC adapter 1 shifts to the forced discharge state 48 via path F. quick charge 4
The same applies when the refresh switch is pressed during execution of the 5 or trickle charge mode 46.

When the forced discharge of the battery 2 is completed by the process of forced discharge 48, the state of the AC adapter shifts to the state of quick charge 45 via path I.

That is, by providing a path in which the rapid charging process 45 is performed after the automatic discharging process 47 process, the memory effect of the battery 2 can be automatically eliminated. Furthermore, in any of automatic discharge 47, quick charge 45, and trickle charge mode 46, when the refresh switch 21 is pressed, the operation of the AC adapter shifts to forced discharge 48 (F, F1, F2).
. Thereby, the memory effect that cannot be dealt with by the automatic discharge 47 can be eliminated according to the user's intention.

In the above embodiment, the voltage per battery cell to be forcedly discharged is 0.8 to 1.1V.
The range was set to . However, the present invention is not limited to this, and this range may be slightly modified.

[0064]

As described above, in the secondary battery charging apparatus according to the first aspect of the invention, the terminal voltage of the secondary battery is checked prior to starting charging. When the terminal voltage is outside a predetermined range, charging is started immediately, and in other cases, forced discharge of the secondary battery is automatically performed prior to charging. Compared to the case where there is no forced discharge, there is an increased chance that the secondary battery will be completely discharged, and the memory effect can be eliminated. The frequency of forced discharge is lower than when forced discharge is performed unconditionally, and the life of the secondary battery will not be unduly shortened. Furthermore, since forced discharging is performed only when the terminal voltage is close to the final voltage of the secondary battery, discharging can be completed in a short time and the time required for charging will not be unduly prolonged.

The secondary battery charging device according to the second aspect has the following effects in addition to the effects provided by the device according to the first aspect. In this device, the user can manually start the discharge by the forced discharge means. Therefore, it is possible to effectively eliminate the memory effect that cannot be dealt with by automatic forced discharge using the device according to the first aspect. Furthermore, as the forced discharge means itself, the means described in claim 1 can be used as is, and there is no need to make the device unduly complicated.

[Brief explanation of drawings]

FIG. 1: AC having a charging device according to an embodiment of the present invention
FIG. 2 is a system block diagram of an adapter.

FIG. 2 is a flow diagram showing the flow of operation of the apparatus shown in FIG. 1;

FIG. 3 is a system block diagram of an AC adapter incorporating a conventional charging device.

FIG. 4 is a flow diagram showing the operation flow of a conventional AC adapter.

FIG. 5 is a graph showing the relationship between charging time and voltage per cell of a battery.

FIG. 6 is a graph showing the relationship between time and voltage per battery cell when short charging/discharging is performed.

FIG. 7 is a graph showing the relationship between usage time and voltage per cell of the battery, representing the influence of the memory effect of the battery.

FIG. 8 is a schematic diagram for explaining the cause of the memory effect.

[Explanation of symbols]

1 AC adapter 2 NiCd battery 6. Rapid charging switch circuit 9 Battery terminal 10 Trickle charging switch 12 DC output switch 14 Battery installation detection circuit 15 Charge completion detection circuit 16 Discharge control switch 17 Discharge resistance 18 Voltage detection circuit 20 Microcomputer 21 Refresh switch

Claims (2)

[Claims] Claim 1: A charging terminal capable of attaching and detaching a secondary battery, for supplying direct current for charging to the attached secondary battery, and detecting attachment and detachment of the secondary battery to the charging terminal. , battery attachment/detachment detection means for outputting a battery attachment/detachment detection signal that takes a predetermined first value when the secondary battery is attached to the charging terminal and takes a predetermined second value when the secondary battery is removed; and detecting a terminal voltage of a secondary battery attached to the charging terminal in response to a change in the battery attachment/detachment detection signal from the second value to the first value;
terminal voltage detection means for detecting whether or not the detected terminal voltage is within a predetermined voltage range whose lower limit is the final voltage of the secondary battery; a forced discharge means for forcibly discharging the secondary battery until the terminal voltage becomes equal to or less than the final voltage when the terminal voltage is within the voltage range; in response to the forced discharge means, detecting that the detected terminal voltage is outside the voltage range or that the forced discharge by the forced discharge means has ended, and charging the secondary battery via the charging terminal. A charging device for a secondary battery, including a charging means for charging the battery to a predetermined state of charge. 2. A secondary battery charging device according to claim 1, wherein the secondary battery charging device is configured to output a forced discharge start signal for starting forced discharge of the secondary battery attached to the charging terminal. , further comprising manually operable forced discharge start signal output means, wherein the forced discharge means outputs the second output signal in response to the forced discharge start signal, except when the detected terminal voltage is within the voltage range. A secondary battery charging device characterized by starting forced discharge of a secondary battery.