JP2675053B2 - Charge control circuit - Google Patents

Description

TECHNICAL FIELD The present invention relates to a charge control circuit for nickel-cadmium batteries used in video equipment, audio equipment, small television equipment and their related equipment.

[Conventional technology]

Conventionally, various methods have been provided for a charge control circuit for charging a sealed nickel-cadmium storage battery (hereinafter, simply referred to as a battery). Among them, the -ΔV charge control method is widely used. . This is a system in which the charging is completed when the DC voltage applied to the battery is slightly lower than the peak value, and this system will be described below with reference to FIG.

In the figure, when a constant charging current I is applied to such a battery to charge it, the charging voltage V _B of the battery due to this increases with time t as shown in the figure. Then, the charging voltage V _B finally reaches the peak value V _BP (the time at this time is defined as t _P with reference to the start of charging), but thereafter decreases. Then, when the charging voltage V _B drops by a certain value ΔV from the peak value V _BP (this time is defined as t _S ), the charging current I is cut off and the charging is completed. Voltage V at this time
_BS (= V _BP −ΔV) is the charged voltage of the battery.

In the conventional charging control circuit using such a method, Δ
The V value was fixed at a constant value. In this case, the peak value V _BP
Is constant, the charging voltage of the battery when charging is completed
_VBS is constant, but when the ambient temperature is different and the peak value _VBP is different, or when it is shared by batteries with different numbers of cells,
Insufficient charging or overcharging will greatly affect the life of the battery, and will also significantly affect the amount of charge.

For this purpose, for example, "National Technical Report
Issued by Ohmsha Co., Ltd. Vol. 32, No. 5 (October 1986) p
As described in “5. Relative voltage drop (relative −ΔV) charge control circuit” on p.696-697, ΔV for each cell of the battery
A charge control circuit has been proposed in which the value is relatively constant, the resistance that determines the ΔV value is temperature-dependent, and the ΔV is variable depending on the ambient temperature.

[Problems to be solved by the invention]

By the way, in the nickel-cadmium battery, the peak value V _BP of the voltage V _B during charging may vary depending on not only the ambient temperature but also the conditions under which the battery is left.
Charging characteristics according to standing conditions are as shown in FIGS. 3, 4, and 5. Fig. 3 shows the charging characteristics of a battery that has been completely discharged after being left as it is after it has been in a used state due to an unusable voltage. Fig. 4 shows the charging characteristics of a battery in this used state. 5 shows the charging characteristics of the battery in the fully charged state immediately after charging as described in FIG.

As shown in FIG. 3 to FIG. 5, the peak value V _BP of the voltage V _{B in} the charging characteristic varies depending on the ambient temperature, but even at the same ambient temperature, depending on the standing condition, it is possible to change the peak value V _BP from FIG. 3 to FIG. The peak value V _BP of the voltage V _B may differ between the charging characteristics shown in.

In the above conventional charging control circuit, the condition of leaving the battery is not taken into consideration, and if the peak value V _BP of the charging voltage of the battery to be charged differs depending on the leaving condition, insufficient charging or overcharging will occur. Not only can the battery performance not be fully utilized, but it will also have a great impact on the battery life.

It is an object of the present invention to provide a charging control circuit which solves the above problems and can prevent undercharging or overcharging due to a battery leaving condition.

[Means for solving the problem]

In order to achieve the above object, the present invention provides a voltage dividing circuit for dividing an applied voltage of a battery to be charged into a divided voltage of a high voltage value and a divided voltage of a low voltage value, and a peak value of the divided voltage of the low voltage value. Comparing the output of the peak voltage holding circuit with the divided voltage of the high voltage value, and when the divided voltage of the high voltage value drops to the output voltage value of the peak voltage holding circuit, A comparator for turning off the switch to terminate the charging of the battery, and a second switch for turning on the battery when the battery is attached and supplying a charging current to the battery through the first switch and turning off the battery when the battery is removed. A switch and a discharge circuit for discharging the holding voltage of the peak voltage holding circuit when the second switch is turned off,
The output of the comparator is the control voltage of the first switch that turns on and off the charging current of the battery.

[Action]

The time when the divided voltage of the low voltage value reaches the peak value coincides with the time when the voltage applied to the battery reaches the peak value. The divided voltage of the high voltage value also reaches the peak value at this time, but at the time when the magnitude relationship with the peak of the low voltage value held in the high voltage peak voltage holding circuit is reversed, the voltage applied to the battery reaches the peak value. It is a time point when the voltage value has passed to a certain voltage value. At this time point, the first switch is turned off by the output of the comparator, and the charging of the battery is completed.

Therefore, the charging voltage of this battery is equal to the voltage value of the applied voltage of this battery when the divided voltage of the high voltage value and the peak value of the divided voltage of the low voltage value held in the peak voltage holding circuit match. The difference between the voltage value and the peak value of the voltage applied to the battery is the ΔV value. This ΔV value is proportional to the peak value of the applied voltage to the battery. Therefore, when the peak value of the applied voltage to the battery is large depending on the condition of leaving the battery, the ΔV value is ΔV.
The value is large, and the ΔV value is small when this peak value is small. From this fact, the charging voltage of the battery is almost constant regardless of the standing condition.

Then, when charging is completed and the battery is removed, the discharge circuit operates and the holding voltage of the peak voltage holding circuit is discharged,
Prepare for the next battery charge.

〔Example〕

FIG. 1 is a circuit diagram showing an embodiment of a charging control circuit according to the present invention, in which 1 is a rectifier circuit, 2 is a switching switch, and 3 is a switching switch.
Is a voltage dividing circuit, 4 is a discharging circuit, 5 is a peak voltage holding circuit, 6 is a comparator circuit, 7 is a switch, 8 is an output terminal, 9 is a battery, 10 is a coil of a transformer, 11, 12 are diodes, 13 and 14 Is a capacitor, 15 to 23 are resistors, 24 is a PNP transistor, 25 and 26 are comparators, 27 is a plus line, and 28 is a minus line.

In the figure, in the rectifier circuit 1, the output AC voltage of the coil 10 is rectified by the diode 11 and further smoothed by the capacitor 13 to form the DC voltage V _B. The output terminal 8 is configured so that the battery 9 to be charged can be attached and detached. The switching switch 2 is closed to the A side when the battery 9 is not connected to the output terminal 8 to close the rectifying circuit 1 and the voltage dividing circuit 3.
When the battery 9 is connected to the output terminal 8,
The rectifier circuit 1 and the voltage dividing circuit 3 are connected by closing on the B side. The switch 7 is closed when the output of the comparator 26 in the comparator circuit 6 is "L" (low level), and is opened when this output is "H" (high level). The power supply voltage V _CC is supplied to the comparator circuit 6.

Therefore, when the output terminal 8 is connected to the battery 9, the switching switch 2 is closed to the B side, and the switch 7 is connected to the switch 7 as described later.
Also, the DC voltage V _B generated in the rectifier circuit 1 causes a constant charging current I to flow in the battery 9 through the switching switch 2, the voltage dividing circuit 3, the switch 7, and the output terminal 8. At this time, the DC voltage V _B basically changes as shown in FIG. 2, but changes as shown in FIGS. 3 to 5 depending on the standing condition, ambient temperature and the like.

The voltage dividing circuit 3 includes three resistors 15, 16 and 17 connected in series between the positive line 27 and the negative line 28, and the resistors 16 and 1
From the connection point of 7, connect the divided voltage V _B1 of the DC voltage V _B to the resistors 15, 16
Similarly, the divided voltage V _B2 is output from the connection point of. Here, if the resistance values of the resistors ₁₅ , ₁₆ and ₁₇ are R ₁₅ , R ₁₆ and R ₁₇ , And V _B1 <V _B2 .

This division voltage V _B1 is supplied to the comparator 25 in the comparator circuit 6 as a non-inverting input, and the division voltage V _B2
Is supplied to the comparator 26 as an inverting input. Then, the comparator 25 compares the divided voltage V _B1 with the charging voltage V _C of the capacitor 14 in the peak voltage holding circuit 5, and the comparator 26 compares the divided voltage V _B2 with the charging voltage V _{C of the} capacitor 14. .

Therefore, it is now assumed that the battery 9 is connected to the output terminal 8 and the charging is started, and in order to simplify the explanation, it is assumed that the DC voltage V _B changes as shown in FIG. The operation of the embodiment will be described.

The DC voltage V _B supplied from the rectifier circuit 1 is the peak value V _BP
This DC voltage V _B gradually increases until time t _P
Therefore, the division voltages V _B1 and V _B2 also sequentially increase. Also,
At the start of charging the battery 9, the charging voltage V _C of the capacitor 14 is zero due to the action of the discharging circuit 4 described later. Therefore, since V _B1 > V _C , the output of the comparator 25 becomes “H”, and this is supplied to the capacitor 14 via the diode 12 and the resistor 21. At this time, the output of the comparator 25 is also supplied from the resistor 21 to the emitter of the PNP transistor 24 via the resistor 20, but the base of the PNP transistor 24 is supplied with “H” of the DC voltage V _B by the resistors 18 and 19. A division voltage is applied, which causes the PNP transistor 24 to be off. For this reason, the division voltage V
During the period when _B1 rises, V _B1 > V _C , and therefore,
The output of comparator 25 is held at “H” and capacitor 14
Charging continues.

Similarly, during the period when the DC voltage V _B rises, V _C <V _B1 <V _B2 , and therefore the output of the comparator 26 is biased by the bias of the power supply voltage V _CC via the resistor 23. It becomes "L". Therefore, switch 7 is closed,
The charging current I flows into the battery 9.

In this way, the capacitor 14 are sequentially charged, but rises its charge voltage V _C, the DC voltage V _B at time t _P reaches the peak value, the subsequent DC voltage V _B is lowered Then, the division voltages V _B1 and V _B2 also decrease. Even at this time, the discharge circuit 4 does not operate, so that when the divided voltage V _B1 reaches the peak value, the charging voltage V _C of the capacitor 14 becomes the divided voltage V _B1.
It becomes the peak voltage V _{B1P of B1} . The peak voltage V _CP at this capacitor 14 is Is represented by When the divided voltage V _{B1 drops} from this peak voltage V _B1P , V _B1 <V _CP , so the output of the comparator 25 becomes “L”, the diode 12 is turned off, and the capacitor 14 _receives this peak voltage V _B1P. Retained.

On the other hand, the division voltage V _B2 also reaches the peak value when the DC voltage V _B reaches the peak value, and then decreases with the decrease of the DC voltage V _B , but since V _B1 <V _B2 , the division voltage V _B2
Peak value V _B2P of _B2 is higher than the peak value V _B1P divided voltage V _B1. Therefore, even if the divided voltage V _B2 starts to fall from the peak value V _B2P , the output of the comparator 26 is “L” and the switch 7 continues until it becomes equal to the peak voltage V _CP held in the capacitor 14. Is kept closed.

When the divided voltage V _B2 sequentially decreases and becomes equal to the peak voltage V _CP held in the capacitor 14 (time t _S ), the output of the comparator 26 becomes “H”, the switch 7 opens and the charging of the battery 9 ends. To do.

That is, when V _B2 = V _CP , charging of the battery 9 is completed, and the value V _BS of the DC voltage V _B at this time is V _BS = V _BP −ΔV (4) The battery 9 has been charged to V _BS .

Here, since the voltage value V _BS of the DC voltage V _{B is} the voltage value when the divided voltage V _B2 becomes equal to the peak voltage V _cp held in the capacitor 14, the above formulas (2) and (3) are used. , Therefore, And according to equations (4) and (5), Becomes That is, the charging voltage V _BS of the battery 9 is lower than the peak value V _BP of the DC voltage V _B applied to the battery 9 by ΔV represented by the equation (6).

Therefore, as is clear from equation (6), the ΔV value is the resistance
It is determined by the voltage division ratio of 16, 17 and the peak value V _BP of the DC voltage V _B. As described above with reference to FIGS. 3 to 4, the peak value V _BP may vary depending on the condition of the battery being left untreated, but according to the equation (6), the ΔV value has a high peak voltage V _BP. It is sometimes large and small when the peak voltage V _BP is low. Therefore, if the ambient temperature during charging is the same,
Regardless of the conditions under which the battery is left, the charging voltage of the battery is almost constant, and variations are reduced.

Further, by using a resistor such as a posistor having a temperature-dependent resistance value as the resistors 16 and 17, the voltage division ratio of the resistors 16 and 17 can be changed according to the ambient temperature. Therefore, when the peak value V _BP changes according to the ambient temperature as shown in FIGS. 3 to 4, the temperature characteristics of the resistance values of the resistors 16 and 17 are appropriately set to change the ambient temperature to different ambient temperatures. In contrast, the ΔV value can be changed so that the charging voltage V _BS of the battery 9 is almost constant.

As described above, undercharging and overcharging can be prevented and charging can be performed so that the charging voltage becomes almost constant, regardless of the conditions under which the battery is left and the ambient temperature.

Now, in FIG. 1, when charging is completed and the battery 9 is removed from the output terminal 8, the switching switch 2 is switched to the A side, and the rectifying circuit 1 and the voltage dividing circuit 3 are disconnected. As a result, no voltage is applied to the resistors 18 and 19 in the discharge circuit 4, and the base potential of the PNP transistor 24 becomes zero. However, the charging voltage V _C of “H” of capacitor 14
Is applied to the emitter of the PNP transistor 24 via the resistor 20, which causes the capacitor 14 to discharge via the resistor 20 and the PNP transistor 24. As a result, when the battery is next connected to the output terminal 8 for charging, the capacitor 14
Is reset so that its charging voltage V _C becomes zero, and the above charging operation can be performed.

When charging the battery in the fully discharged state, as shown in FIG. 3, the voltage V _B applied to the temporary battery immediately after the start of charging, and accordingly, the divided voltages V _B1 , V _B2 are It may fall. But this drop is small,
Moreover, since the divided voltage V _B2 can be always set higher than the charging voltage held in the capacitor 14 before the drop, the output of the comparator 26 is not held at “L” and the switch 7 does not open after the start of charging. , Are continuously charged.

〔The invention's effect〕

As described above, according to the present invention, the charging voltage of the battery can be constantly charged regardless of the discharge condition of the battery, and further, regardless of the ambient temperature, and the insufficient charge or overcharge can be prevented. As a result, the battery performance can be fully utilized and the battery life can be extended.

[Brief description of the drawings]

1 is a circuit diagram showing an embodiment of a charge control circuit according to the present invention, FIG. 2 is a charge characteristic diagram of a nickel-cadmium battery in a charge control circuit of a −ΔV charge control system, and FIG. 3 is a fully discharged state. FIG. 4 is a charging characteristic diagram of the Atsushi nickel-cadmium battery, FIG. 4 is a charging characteristic diagram of the used nickel-cadmium battery, and FIG. 5 is a charging characteristic diagram of the fully-charged nickel-cadmium battery. 1 ... Rectifier circuit, 2 ... Switching switch, 3 ... Voltage dividing circuit, 4 ... Discharge circuit, 5 ... Peak voltage holding circuit, 6
...... Comparator circuit, 7 ...... Switch, 8 ...... Output terminal, 9 ...... Battery, 14 ...... Capacitor, 15 to 23 ...... Resistance,
24 …… PNP transistor, 25,26 …… Comparator.

 ─────────────────────────────────────────────────── ─── Continuation of front page (56) References JP-A-58-33940 (JP, A) JP-A-63-224632 (JP, A) JP-A-1-97141 (JP, A) JP-A-56- 25341 (JP, A)

Claims (1)

(57) [Claims] 1. A charging control circuit for supplying a direct current to a battery detachably attached to an output terminal via a first switch to charge the battery, wherein the battery is attached to the output terminal. A second electric current which is supplied to the battery through the first switch when the battery is removed from the output terminal and is closed when the battery is removed from the output terminal; Switch, a voltage dividing circuit that divides the charging voltage of the battery and outputs a first divided voltage and a second divided voltage higher than this voltage, and a peak voltage that holds the peak voltage of the first divided voltage. The holding circuit and the output voltage of the peak voltage holding circuit are level-compared with the second divided voltage, and when the second divided voltage becomes equal to or lower than the output voltage of the peak voltage holding circuit, the first switch is turned on. Open to cut off the direct current And a battery that is attached to the output terminal to close the second switch, start the voltage holding operation of the peak voltage holding circuit, and remove the battery from the output terminal. And a discharge circuit for allowing the holding voltage of the peak voltage holding circuit to stand when the switch is opened.