JPH07312231A - Charging device for secondary battery - Google Patents

Abstract

PURPOSE:To provide a charging device for secondary battery in which the cycle life of a battery can be extended, and a user feels no abnormal heat by prohibiting the quick charge to the battery laid in full charge state or in a state close thereto. CONSTITUTION:The temperature of a secondary battery is detected through a thermistor, an A/D converter 41, and a battery temperature calculating part 43, and a timer 49 for measuring the elapsed time after the end of quick charge of the secondary battery is provided. This charging device also has a charge control part 50 for prohibiting the quick charge when the detected battery temperature is a prescribed value or more when the secondary battery is set to the charging device, and the elapsed time measured by the timer 49 is less than a prescribed value.

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 rapid charging of an alkaline secondary battery such as a nickel-cadmium secondary battery or a nickel-hydrogen secondary battery.

[0002]

2. Description of the Related Art In a quick charger for charging a secondary battery in a short time, generally, when the battery is set, the rapid charging is started, and when the battery is fully charged, the rapid charging is ended. As a method for setting the battery in the quick charger, there are a mode in which the battery pack is set alone in the charger and a mode in which a device such as a mobile phone in which the battery pack is incorporated is set in the charger.

By the way, in the conventional quick charger, the fully charged battery after the quick charging is removed from the charger,
If you do not use the battery at all, or use it for a very short time such as a few minutes and then set it again in the charger,
The battery is configured to perform rapid charging again even when the battery is fully charged. In this case, if the battery is an alkaline secondary battery, such as a nickel-cadmium secondary battery or a nickel-hydrogen secondary battery, it will be overcharged or the battery temperature will rise again after rapid charging, There is a problem that the battery temperature further rises due to the rapid charging, and the cycle life of the battery is shortened. In addition, in such a state where the temperature of the battery is greatly increased (for example, 50 ° C.
If you use a device such as a mobile phone,
The user feels unusual heat and causes complaints.

[0004]

As described above, in the conventional quick charger, the battery in the fully charged state after the quick charging is removed from the charger and the battery is not used at all.
Alternatively, even if the battery is used for an extremely short time and then recharged, the battery will be overcharged or the temperature will rise abnormally, resulting in a shorter cycle life of the battery. Also, there is a problem that the user feels abnormal heat.

The present invention has been made in order to solve the above-mentioned problems of the conventional quick charger. By not performing the quick charge on a battery which is fully charged or is close to it. An object of the present invention is to provide a charging device for a secondary battery, which can prolong the cycle life of the battery and which does not cause the user to feel abnormal heat.

[0006]

A charging device for a secondary battery according to a first aspect of the present invention measures a temperature detecting means for detecting a temperature of the secondary battery, and an elapsed time after completion of rapid charging of the secondary battery. If the temperature detected by the temperature detecting means when the secondary battery is set in the charging device and the time measuring means is equal to or higher than a predetermined value, and the elapsed time measured by the time measuring means is less than the predetermined value, And a charge control means for prohibiting rapid charging.

A secondary battery charging device according to a second aspect of the present invention is
Voltage detecting means for detecting the voltage of the secondary battery, and prohibiting quick charging when the voltage detected by the voltage detecting means when the secondary battery is set in the charging device is equal to or higher than a predetermined threshold voltage. And a charging control means.

In the rechargeable battery charging device according to the second aspect of the invention, there is provided temperature detecting means for detecting the temperature of the rechargeable battery, and the temperature detecting means for detecting when the rechargeable battery is set in the charging device. And a correction unit that corrects the threshold voltage according to the temperature that has been set.

Further, in the rechargeable battery charging device according to the second aspect of the invention, there is provided temperature detecting means for detecting the temperature of the rechargeable battery, voltage detected by the voltage detecting means and temperature detecting means at the end of the rapid charging, and It further comprises a correction means for correcting the threshold voltage according to the temperature.

[0010]

According to the first aspect of the invention, when the secondary battery is set in the charging device, the battery temperature is equal to or higher than the predetermined value, and the elapsed time from the end of the previous rapid charging is less than the predetermined value, the battery is not charged. It is determined that the battery is fully charged and rapid charging is prohibited. As a result, overcharging due to rapid charging of the fully charged battery is prevented and abnormal temperature rise of the battery is prevented.

If it is determined whether or not the battery is to be rapidly charged only by the battery temperature, there is a possibility that the battery will not be rapidly charged even if the battery is not overcharged, for example, when the ambient temperature is high. Also, if it is determined whether or not to perform quick charging only from the time elapsed from the end of the previous quick charging, when the battery is quickly depleted in a short time, the battery is still not overcharged. However, it may not be charged quickly. According to the second aspect of the invention, it is possible to prohibit the rapid charging only when the battery is almost overcharged because it is determined whether or not the rapid charging is performed based on both the battery temperature and the elapsed time.

According to the second aspect of the invention, when the secondary battery is set in the charging device and the battery voltage is equal to or higher than a predetermined threshold voltage, it is determined that the battery is fully charged and rapid charging is prohibited. To be done. That is, after the rapid charge is completed, the battery is relatively high when the battery is rarely used and is almost fully charged, and the battery voltage exceeds a certain threshold voltage. Therefore, the rapid charge is prohibited in such a case. As a result, overcharging due to rapid charging of the fully charged battery is prevented and abnormal temperature rise of the battery is prevented.

Here, the threshold voltage is set to a value close to 100% of the charge capacity of the battery, for example, a value corresponding to the battery voltage of 97%, which is a battery voltage-battery temperature characteristic. Changes according to the battery temperature, and also changes according to the battery voltage and battery temperature at the end of rapid charging due to the cycle characteristics of the battery. Therefore, in the second invention, the threshold voltage is corrected by correcting the threshold voltage according to the battery temperature when the battery is set in the charging device and the battery voltage and the battery temperature at the end of quick charging. By doing so, it is possible to accurately determine whether or not to perform quick charging.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit configuration diagram of a secondary battery charging device showing an embodiment according to the first invention. In FIG. 1, a battery pack 1 includes a secondary battery (hereinafter, simply referred to as a battery) 2 such as an alkaline secondary battery and a thermistor 3 for temperature measurement arranged near the battery 2 in a housing. is there. FIG. 1 shows a state in which the battery pack 1 is set in the charging device 4. A mobile phone or other device in which the battery pack 1 is incorporated may be set in the charging device 4.

The charging device 4 is constructed as follows. The charging device 4 has a commercial AC power source 5 (for example, 100V)
Power from is input and filter 6 for noise removal
After being converted into a direct current by the rectifying / smoothing circuit 7 via, the signal is supplied to the primary side of the transformer 8. On the primary side of the transformer 8,
A switching transistor 9 composed of a power MOS transistor is connected via a resistor 10. The switching transistor 9 is a PWM (pulse width modulation) circuit 1
It is switched by the output of 1. As a result, a pulse current flows in the primary side of the transformer 8 and energy is transmitted to the secondary side of the transformer 8. The output generated on the secondary side of the transformer 8 is converted into a direct current by the rectifying and smoothing circuit 12,
It is supplied as a charging current to the battery 2 through the quick charging transistor 13 or the series circuit of the trickle charging transistor 14 and the resistor 15 and further through the backflow prevention diode 16. The output of the rectifying / smoothing circuit 12 is also supplied to the light emitting element 18 of the photocoupler 17, and the output of the light receiving element 19 of the photocoupler 17 is input to the PWM circuit 11.

The microcontroller 20 is mainly composed of a microcomputer, and controls the rapid charging transistor 13, the trickle charging transistor 14, the photocoupler 17 and the LED 31. This microcontroller 20 has a voltage at the connection point between the resistor 21 and the thermistor 3 (hereinafter referred to as the thermistor voltage).
Vt and a voltage Vb obtained by dividing the voltage VB of the battery 2 by the resistors 22 and 23 (hereinafter, referred to as a battery voltage division value) Vb are input.

The resistors 24-29 and the operational amplifier 30 are
It is provided for controlling the charging current to be constant. The inverting input terminal of the operational amplifier 30 receives the terminal voltage of the resistor 24 that is inserted in series in the charging path and detects the charging current via the resistor 27, and the non-inverting input terminal of + 5V.
A voltage (reference voltage) obtained by dividing the power supply voltage of 2 by the resistors 25 and 26 is input via the resistor 28. Operational amplifier 30
A resistor 29 is connected between the inverting input terminal and the output terminal, and the gain of the operational amplifier 30 is determined by the resistors 27 and 29. The output terminal of the operational amplifier 30 is connected to the side of the light emitting element 18 of the photocoupler 17 opposite to the side connected to the output terminal of the rectifying / smoothing circuit 12. With such a configuration, feedback control is performed so that the inverting input terminal and the non-inverting input terminal of the operational amplifier 30 have the same potential.

For example, when the charging current of the battery 2 is large and the terminal voltage of the current detection resistor 24 is large, the inverting input terminal of the operational amplifier 30 has a higher potential than the non-inverting input terminal thereof, so that the operational amplifier 30 has a higher potential. Output voltage decreases, and the current flowing through the light emitting element 18 increases. As a result, the output pulse width of the PWM circuit 11, that is, the on-time width of the switching transistor 9 is shortened, the energy transmitted to the secondary side of the transformer 8 is reduced, and the charging current is reduced.

On the contrary, when the charging current of the battery 2 is small,
Since the inverting input terminal of the operational amplifier 30 has a lower potential than the non-inverting input terminal thereof, the output voltage of the operational amplifier 30 increases and the current flowing through the light emitting element 18 decreases, so that the PWM
The output pulse width of the circuit 11, that is, the on-time width of the switching transistor 9 increases, and the energy transmitted to the secondary side of the transformer 8 increases, so that the charging current increases.

In this way, the resistance 2 corresponding to the charging current
Feedback control is performed so that the terminal voltage of No. 4 and the reference voltage obtained by the resistors 25 and 26 become equal to each other, and the charging current is subjected to constant current control.

The microcontroller 20 controls by software processing using a microcomputer. FIG. 2 shows a functional block diagram of the microcontroller 20.

In FIG. 2, the thermistor voltage Vt and the battery voltage division value Vb are converted into digital values by the A / D converters 41 and 42, respectively, and then the battery temperature calculation unit 4
3 and the battery voltage detector 44, respectively, to obtain the battery temperature TB and the battery voltage VB. The output of the battery temperature calculation unit 43 is input to the battery temperature determination unit 45 and the temperature differential calculation unit 46. The battery temperature determination unit 45 determines in what temperature range the battery voltage is.
The temperature differential calculation unit 46 calculates the differential of the battery temperature, that is, the amount of temperature rise per unit time. The output of the battery voltage detection unit 44 is input to the battery state determination unit 47. The battery state determination unit 47 determines whether the battery 2 is normal based on the battery voltage. The output of the A / D converter 41 is
It is also input to the battery pack set detection unit 48. The battery pack set detection unit 48 detects whether or not the battery pack 1 is set in the charging device 4.

A / D converter 41, battery temperature determination unit 45,
The outputs of the temperature differential calculation unit 46, the battery state determination unit 47, and the battery pack set detection unit 48 are input to the charging control unit 50, and the charging control unit 50 measures these outputs and the elapsed time after the end of quick charging 49. On the basis of the output (timer value), the quick charge control signal 51 to the quick charge transistor 13, the trickle charge control signal 52 to the trickle charge transistor 14, and the charge start signal 53 are generated. The charge start signal 53 is the resistance 2 in FIG.
8 is supplied to one end.

Next, the operation of this embodiment will be described with reference to the flow chart shown in FIG. First, the thermistor voltage V
t is read via the A / D converter 41 (step 101). When the battery pack 1 is set in the charging device 4, the thermistor voltage Vt decreases from + 5V until then due to the partial pressure of the thermistor 3 and the resistor 21. here,
When the thermistor voltage Vt becomes equal to or lower than a predetermined value (for example, 4.8 V), the battery pack set detection unit 48 detects that the battery pack 1 is set in the charging device 4 (step 102).

When the set of the battery pack 1 is detected in step 102, the battery temperature calculator 43 converts the thermistor voltage Vt into temperature data to calculate the battery temperature TB (step 103), and then the battery temperature determiner 4
According to 5, it is determined whether the battery temperature TB is in the range of 0 ° C. or higher and 40 ° C. or lower (step 104). When the battery temperature TB falls within the range of 0 ° C ≤ TB ≤ 40 ° C, the battery temperature determination unit 45 subsequently determines whether TB exceeds 35 ° C (step 105).

When the battery temperature TB exceeds 35 ° C., the timer value after the final quick charge is calculated (step 106). The timer 49 starts at the time when the last quick charging of the battery 2 in the battery pack 1 set in the charging device 4 ends, and measures the elapsed time from this time, and this time is the charging control unit 50. Is taken into. next,
It is determined whether the timer value indicating this elapsed time exceeds a predetermined time, for example, 15 minutes (step 107),
If it does not exceed 15 minutes, the process ends and quick charging is not performed. That is, the elapsed time after the final quick charge is 15
If it is within a minute, the battery 2 is not used at all or is used very little. Therefore, it is determined that the battery 2 is fully charged or close to it, and even if the battery pack 1 is set, Do not charge. This allows the battery 2
It is possible to avoid overcharging and abnormal temperature rise.

On the other hand, in step 105, the battery temperature T
When B is less than 35 ° C., the trickle charge control signal 52 output from the charge control unit 50 becomes “L” level, the trickle charge transistor 14 is turned on, and trickle charge is performed. (Step 10
8). After this, the battery voltage division value Vb is changed to the A / D converter 42.
(Step 109), the battery voltage detection unit 44 obtains the battery voltage VB, and the battery state determination unit 47 determines whether the battery 2 is normal or not from the battery voltage VB (Step 110). Here, if the battery 2 is not normal, the process ends and rapid charging is not performed. When the battery 2 is normal, the quick charge control signal 51 output from the charge control unit 50 becomes “L” level, the transistor 13 for quick charge is turned on, and the charge start signal 53 is “L”. When the level is reached, rapid charging is performed (step 111). During this period, the LED 31 is controlled by the microcontroller 20 and lights up to indicate that the rapid charging is being performed. Further, during this rapid charging, the charging current is kept constant by the above-mentioned feedback control.

Further, during the rapid charging, the temperature differential calculation unit 46 calculates the temperature differential of the battery temperature TB, that is, the temperature increase rate per unit time (for example, 1 minute), and the temperature differential is set to a predetermined value (for example, 1). (° C / 1 minute) or more, the battery 2 is determined to be fully charged (step 112). Battery 2
When it is determined that the battery is fully charged, the charging control unit 50 resets the timer 49 (step 113), restarts the timer 49, and both the quick charging control signal 51 and the charging start signal 53 become "H" level. As a result, the quick charge ends.

FIG. 4 shows changes with time in the battery voltage VB, the battery temperature TB and the rapid charging current I. When the rapid charging is started at time t0, the battery voltage VB and the battery temperature TB increase as shown in the figure as the charging progresses, the battery temperature TB rapidly increases, and the temperature differential is 1 ° C. / At time ta, which has reached 1 minute, the rapid charging is completed. The battery temperature TB is, for example, 25 ° C. at time t0, 40 ° C. at time ta, and increases by 15 ° C.

Now, at time ta, the battery pack 1 is charged by the charging device 4
It is assumed that the battery pack 1 is not used at all and is reset in the charging device 4 at a time point tb 5 minutes after the removal. In this case, in the conventional quick charger, since the battery is charged rapidly even though the battery is fully charged, the battery temperature T
B rapidly rises as shown by the solid line, and the temperature differential of the battery temperature is 1 ° C. /
It is detected that 1 minute has been reached, and the rapid charging is stopped.
At this time, the battery temperature TB is 35 ° C. at time tb,
In c, it reaches 50 ° C.

On the other hand, in this embodiment, when the battery pack 1 is set at the time tb, it is determined whether or not a predetermined time, that is, 15 minutes in this example, has elapsed from the quick charging end time ta. If it has not elapsed, do not perform quick charging. Therefore, after tb, the battery temperature TB decreases as shown by the broken line, and the temperature does not rise abnormally as in the conventional case.

FIG. 5 shows the cycle life of the battery, where the horizontal axis represents the number of cycles and the vertical axis represents the battery capacity. As shown in the figure, according to the present invention, the cycle life is extended as compared with the conventional case. This is because if you set the battery in the quick charger without using the battery or after almost no use after the quick charge, the quick charge will be performed even if the battery is full or close to the conventional state. As a result, the battery is overcharged as a result, but in the present invention, as shown in the above embodiment, when the battery is set in a short time after the end of rapid charging, the battery is fully charged or close to it. This is because the battery is not overcharged because it is determined that the battery is in the state and rapid charging is not performed.

FIG. 6 is a circuit configuration diagram of a secondary battery charging device showing an embodiment according to the second invention. In FIG. 6, the portions corresponding to those in FIG. 1 are designated by the same reference numerals, and the description will focus on the differences from the previous embodiment. In FIG. 6, a discharging transistor 32 is added. The discharging transistor 32 is for discharging the battery 2 at a constant current for a fixed time when storing the battery voltage at the end of rapid charging described later, and the collector is a charging terminal to which the + terminal of the battery 2 is connected. Is connected to the microcontroller 20 via a resistor 33, the emitter is grounded, the base is connected to a +5 V power source via the resistor 34, and is also connected to the microcontroller 20.

Further, in this embodiment, the configuration of the microcontroller 20 is different from that of the previous embodiments. FIG. 7 shows a functional block diagram of the microcontroller 20 in this embodiment.

In FIG. 7, the thermistor voltage Vt and the battery voltage division value Vb are converted into digital values by the A / D converters 41 and 42, respectively, and then the battery temperature calculation unit 4
3 and the battery voltage detector 44, respectively, to obtain the battery temperature TB and the battery voltage VB. The output of the battery temperature calculation unit 43 is input to the battery temperature determination unit 45 and the temperature differential calculation unit 46. The battery temperature determination unit 45 determines in what temperature range the battery voltage is.
The temperature differential calculation unit 46 obtains a differential value of the battery temperature, that is, a temperature increase amount per unit time. The output of the battery voltage detection unit 44 is input to the battery state determination unit 47.
The battery state determination unit 47 determines whether the battery 2 is normal based on the battery voltage. The output of the A / D converter 41 is also input to the battery pack set detection unit 48. In the battery pack set detection unit 48, the battery pack 1 is the charging device 4
It is to detect whether it is set to.

A / D converter 41, battery temperature determination unit 45,
The outputs of the temperature differential value calculation unit 46, the battery state determination unit 47, and the battery pack set detection unit 48 are input to the charging control unit 50, and the charging control unit 50 refers to these outputs and the threshold voltage correction table 54, Transistor 1 for quick charging
3 to generate a quick charge control signal 51 to the trickle charge control signal 52, a trickle charge control signal 52 to the trickle charge transistor 14, a charge start signal 53, and a discharge control signal 55. The charge start signal 53 is supplied to one end of the resistor 28 in FIG. 6, and the discharge control signal 55 is supplied to the base of the discharging transistor 32 in FIG.

In the threshold voltage correction table 54, the threshold voltage Vth for determining the battery voltage VB is set to (1) battery temperature, (2) battery voltage and battery temperature at the end of rapid charging, etc., as described later. Is a memory that stores in advance data for correction according to the above, and is realized by a ROM.

Next, the operation of this embodiment will be described with reference to the flow chart shown in FIG. First, the thermistor voltage V
t is read via the A / D converter 41 (step 201). When the battery pack 1 is set in the charging device 4, the thermistor voltage Vt decreases from + 5V until then due to the partial pressure of the thermistor 3 and the resistor 21. here,
When the thermistor voltage Vt becomes equal to or lower than a predetermined value (for example, 4.8V), the battery pack set detection unit 48 detects that the battery pack 1 is set in the charging device 4 (step 202).

When the set of the battery pack 1 is detected in step 202, the battery temperature calculation unit 43 converts the thermistor voltage Vt into temperature data to calculate the battery temperature TB (step 203), and then the battery temperature determination unit 4
According to 5, it is determined whether the battery temperature TB is in the range of 0 ° C. or higher and 40 ° C. or lower (step 204). When the battery TB enters the range of 0 ° C. ≦ TB ≦ 40 ° C., the battery voltage division value Vb is continuously read through the A / D converter 42 (step 205), and the battery voltage detection unit 44 determines the battery voltage VB. Desired.

Next, the threshold voltage Vth for determining whether or not to perform the rapid charge is the threshold voltage correction table 5
4 is calculated (step 206). And
The battery voltage VB and the threshold value Vth are compared (step 2
07), if VB ≧ Vth, the process is terminated and rapid charging is not performed. That is, the battery voltage VB is the threshold voltage V
If it is th or more, it is determined that the battery 2 is not used at all or is used very little, and it is determined that the battery 2 is fully charged or close to it, and quick charging is not performed even when the battery pack 1 is set. . As a result, overcharging of the battery 2 and abnormal temperature rise can be avoided. The threshold voltage Vth is set to a value (for example, 1.35V) corresponding to the battery voltage VB when the charging capacity of the battery 2 reaches 97%.

On the other hand, in step 207, the battery voltage V
When B is less than the threshold voltage Vth, the trickle charge control signal 52 output from the charge controller 50 is “L”.
When the level becomes the level, the trickle charging transistor 14 is turned on and trickle charging is performed (step 208). After that, the battery voltage division value Vb is read through the A / D converter 42 (step 209), the battery voltage VB is obtained by the battery voltage detection unit 44, and the battery voltage VB is obtained from the battery state determination unit 47. It is determined whether the battery 2 is normal (step 210). here,
If the battery 2 is not normal, the process ends and rapid charging is not performed. When the battery 2 is normal, the quick charge control signal 51 output from the charge control unit 50 becomes “L” level, the transistor 13 for quick charge is turned on, and the charge start signal 53 is “L”. When the level is reached, rapid charging is performed (step 211). During this period, the LED 31 is controlled by the microcontroller 20 and lights up to indicate that the rapid charging is being performed.
Further, during this rapid charging, the charging current is kept constant by the above-mentioned feedback control.

Further, during this rapid charging, the temperature differential calculation unit 46 calculates the temperature differential of the battery temperature TB, that is, the temperature increase rate per unit time (for example, 1 minute), and this temperature differential is set to a predetermined value (for example, 1). (° C / 1 minute) or more, the battery 2 is determined to be fully charged (step 212). Battery 2
When it is determined that the battery is fully charged, both the quick charge control signal 51 and the charge start signal 53 output from the charge control unit 50 become the “H” level, and the quick charge ends. Further, the battery temperature TB and the battery voltage VB at the end of the rapid charging are adjusted by the charge control unit 5 in order to correct the threshold voltage Vth.
0 is stored in the memory.

FIG. 9 shows open circuit voltage characteristics of the battery 2 after rapid charging. As shown in the figure, when the rapid charging is started at the time t0 and the rapid charging is ended at the time ta, the battery voltage VB becomes steep because the charging current is turned off for a short time after the completion of the rapid charging. It shows a voltage drop and then a gentle voltage drop.

FIG. 10 shows a 1C discharge voltage characteristic when the battery 2 is left for a certain period of time after the end of the rapid charging. As shown in the figure, the battery voltage VB is ta after the end of the rapid charging.
Shows a sharp voltage drop for a short period of time up to th, and then t
During the period from h to td, the voltage decreases gently. Next, when 1C discharge is started at time td, a sharp voltage drop is shown immediately after that, followed by a gentle drop and then a large voltage drop again, and at time tg, the end voltage = 1.0 V (battery 1 Per cell).

Here, if it is assumed that the devices used (including the battery pack 1) operate at power-on at time th,
As the battery 2 starts to discharge, the battery voltage VB decreases as shown by the broken line, and when the power source of the device is turned off at time tj, the battery voltage VB becomes an open voltage and Vth = 1.35.
The voltage is higher than V. The time from th to tj is long, and the battery 2
When the discharge energy of is relatively large, time tj
The battery voltage VB at is also lower. Therefore, even at the time td when the battery pack 1 is set in the charging device 4, the battery voltage VB is lower than Vth = 1.35V. On the contrary, when the time from th to tj is short, the battery voltage V
B also has a higher battery voltage VB at time tj.

Here, in the conventional case, when the charging device 4 and the battery pack 1 are set, the battery voltage VB is set at the time td.
Although the rapid charging was started regardless of the above, in the present embodiment, it is determined at time td whether the battery voltage VB is equal to or higher than the threshold voltage Vth (Vth = 1.35V in the illustrated example). It is determined whether or not to perform quick charge, and when VB is Vth or more, t
Since the time from h to tj is short, it is determined that the battery 2 is in a fully charged state, and rapid charging is prohibited.

In the present embodiment, the threshold voltage Vth may be a constant value that is predetermined according to the device used, such as a mobile phone, but if it is set to a lower value, when the charge capacity of the battery 2 is small ( For example, 90% or less) may be insufficiently charged and the required charging capacity may not be secured. vice versa,
When the threshold voltage Vth is set to be higher, when the battery pack 1 is set in the charging device 4, rapid charging is performed in most cases, resulting in overcharging.

In order to prevent such overcharge and undercharge when the threshold voltage Vth is kept constant, it is desirable to correct the threshold voltage Vth by the following methods (1) and (2), for example.

(1) Method of Correcting Threshold Voltage Vth Based on Battery Temperature FIG. 11 shows battery voltage-battery temperature characteristics when the battery 2 is charged and discharged at 1C. As shown in the figure, during charging, the battery voltage difference at time ta is about 60 mV in the temperature range of 20 ° C. to 0 ° C. and about −60 mV in the temperature range of 20 ° C. to 45 ° C.
Is. On the other hand, during discharge, the battery voltage difference is about −30 mV in the temperature range of 20 ° C. to 0 ° C. and about 20 mV in the temperature range of 20 ° C. to 45 ° C. Therefore, the threshold voltage Vth is corrected in consideration of such a battery voltage-battery temperature characteristic. In this case, the threshold voltage correction table 54 contains
The relationship between the battery temperature and the correction value of the threshold voltage Vth is obtained in advance and stored.

In the microcontroller 20 shown in FIG. 7, the battery temperature calculation unit 4 is connected via the A / D converter 41.
The current battery temperature TB obtained in 3 is taken into the charge control unit 50. Here, for example, the current battery temperature is TB = 35.
And the threshold voltage Vth at 20 ° C. is, for example, 1.
If it is 35V, the correction value when TB = 35 ° C =
By searching -0.03V from the threshold voltage correction table 54, the temperature-corrected threshold voltage Vth is obtained as Vth = 1.35V-0.03V = 1.32V.

(2) Method of correcting the threshold voltage Vth according to the battery voltage and the battery temperature at the end of rapid charging As the cycle characteristics of the secondary battery, as the battery voltage at the end of rapid charging overlaps the number of cycles. There are batteries that have characteristics that gradually increase. In this case, the relationship between the battery voltage VB and the battery temperature TB at the end of the final quick charge and the correction value of the threshold voltage Vth is stored in the threshold voltage correction table 54. Then, the battery voltage VB and the battery temperature TB obtained at the end of the rapid charge are stored in a non-volatile memory in the charge control unit 50, and when the battery pack 1 is set, VB and T read from the memory are stored.
A correction value is retrieved from the threshold voltage table 54 using the value of B as a key, and the threshold voltage Vth is corrected using this value.

The battery temperature shown in FIG. 11 can be obtained by correcting the threshold voltage Vth by performing the correction methods such as the above (1) and (2) independently or by using both of them together.
It is possible to reliably determine whether or not the battery 2 is fully charged regardless of the battery voltage characteristic and the battery cycle characteristic.

At the time tj in FIG. 10, when the power of the equipment used is turned off and the load current is set to zero, the battery voltage VB rises to an open circuit voltage as shown by the broken line, which rises in the order of milliseconds. It is on the order of seconds, not short times. Therefore, when the time width between tj and td changes, the battery voltage VB at the time td when the battery pack 1 is set in the charging device 4 changes, and a detection error of the battery voltage VB occurs. Therefore, based on the comparison between the battery voltage VB and the threshold voltage Vth in step 207, for example, a determination error may occur when determining whether or not to perform rapid charging with the charge capacity of 97% as a boundary. .

Therefore, in this embodiment, when the battery pack 1 is set in the charging device 4, the discharge control signal 55 output from the microcontroller 20 is set to "H" level to turn on the discharge transistor 32 for a very short time. To discharge the battery 2 and to turn on the trickle charging transistor 14 to flow the trickle charging current, so that the battery voltage VB and the threshold voltage in step 207 are not affected by the time width between tj and td. It is possible to accurately determine whether or not to perform quick charging by comparing with Vth. The current value and time width during this discharge are arbitrary, and the discharge transistor 32 may be switched to flow a pulsed discharge current.

[0055]

As described above, according to the present invention, rapid charging is prohibited for a fully charged battery or a battery close to it, thereby preventing overcharging and extending the cycle life of the battery. It is also possible to obtain the effect that the user does not feel abnormal heat due to the temperature rise of the battery due to overcharging.

[Brief description of drawings]

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

FIG. 2 is a functional block diagram of the microcontroller in FIG.

FIG. 3 is a flowchart for explaining the operation of the embodiment.

FIG. 4 is a diagram showing changes with time of a battery voltage, a battery temperature and a rapid charging current for explaining the operation of the embodiment.

FIG. 5 is a diagram showing cycle life characteristics of the present invention and a conventional one.

FIG. 6 is a circuit configuration diagram of a secondary battery charging device according to another embodiment of the present invention.

FIG. 7 is a functional block diagram of the microcontroller in FIG.

FIG. 8 is a flowchart for explaining the operation of the embodiment.

FIG. 9 is a diagram showing open circuit voltage characteristics after rapid charging in the example.

FIG. 10 is a diagram showing a 1C discharge voltage characteristic when left for a certain period of time after completion of rapid charging in the example.

FIG. 11 is a diagram showing battery voltage-battery temperature characteristics during charging / discharging in the same Example.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Battery pack 2 ... Secondary battery 3 ... Thermistor 4 ... Charging device 5 ... Commercial AC power supply 6 ... Filter 7 ... Rectification smoothing circuit 8 ... Transformer 9 ... Switching transistor 11 ... Pulse width modulation circuit 12 ... Rectification smoothing circuit 13 ... Rapid Charge transistor 14 ... Trickle charge transistor 16 ... Backflow prevention diode 17 ... Photocoupler 20 ... Microcontroller 30 ... Operational amplifier 32 ... Discharge transistor 41 ... A / D converter 42 ... A / D converter 43 ... Battery temperature Calculation unit 44 ... Battery voltage detection unit 45 ... Battery temperature determination unit 46 ... Temperature differential calculation unit 47 ... Battery state determination unit 48 ... Battery pack set detection unit 49 ... Timer 50 ... Charge control unit 51 ... Rapid charge control signal 52 ... Trickle Charge control signal 53 ... Charge start signal 54 ... Threshold voltage correction table

Claims (4)

[Claims] 1. A charging device having a function of rapidly charging a secondary battery, comprising: a temperature detecting means for detecting a temperature of the secondary battery; and a time for measuring an elapsed time after completion of the rapid charging of the secondary battery. When the temperature detected by the temperature detecting means when the secondary battery is set in the charging device is a predetermined value or more, and the elapsed time measured by the time measuring means is less than a predetermined value, Is a charging device for a secondary battery, comprising: a charging control unit that prohibits quick charging. 2. A charging device having a function of rapidly charging a secondary battery, the voltage detecting means for detecting a voltage of the secondary battery, and the voltage detection when the secondary battery is set in the charging device. A charging device for a secondary battery, comprising: a charging control means for prohibiting rapid charging when the voltage detected by the means is equal to or higher than a predetermined threshold voltage. 3. A temperature detecting means for detecting the temperature of the secondary battery, and the threshold voltage according to the temperature detected by the temperature detecting means when the secondary battery is set in the charging device. The charging device for the secondary battery according to claim 2, further comprising: a correction unit that corrects 4. A temperature detecting means for detecting the temperature of the secondary battery, and correcting the threshold voltage in accordance with the voltage and temperature detected by the voltage detecting means and the temperature detecting means at the end of rapid charging. The charging device for a secondary battery according to claim 2, further comprising a correction unit.