JPS62250831A - Secondary battery charging controller - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a secondary battery charging control circuit used for charging a secondary battery.

BACKGROUND OF THE INVENTION In recent years, secondary batteries such as sealed nickel-cadmium batteries and lead-sealed batteries have come into widespread use as power supplies for portable videos and hand-belt computers. Typical examples of circuits for detecting the end of charging of these secondary batteries include a method of detecting the upper limit of the charging voltage and a method of detecting the peak point of the charging voltage.

Hereinafter, a conventional charging control circuit that detects the end of charging of a secondary battery by detecting the peak of the charging voltage as described above will be described with reference to the drawings.

Figure 4 shows a conventional circuit for detecting the completion of charging.
A circuit for detecting a peak point p of the battery charging voltage characteristics shown in the figure is provided. In FIG. 4, 21 is a DC stabilized power supply, 22 is a charging current control circuit, 23 is a comparator, 24 is a diode, 25 is a capacitor that stores the peak point of the charging voltage characteristics of the battery, and 26 is a capacitor 25. A switch for discharging the charge, 2 is a secondary battery to be charged, and 28 is a resistor.

The operation of the charging control circuit configured as shown in FIG. 4 and having a circuit for detecting the peak point of the charging voltage characteristic of the battery as a circuit for detecting the completion of charging will be described below.

First, the discharged secondary battery 27 is connected as shown in FIG. 4, and after the charge of the capacitor 26 is discharged by the switch 26, the switch 26 is opened and a charging current is supplied from the DC stabilized power supply 21. The electric charge of the battery 27 charges the capacitor 25 through the resistor 28 and the diode 24. In this case, the comparator 23 outputs a high level because the non-inverting input is biased higher than the inverting input by the forward voltage of the diode 23, and the charging current control circuit 2
2 becomes active and performs charging. The battery voltage during charging continues to rise until a peak point p, as shown in FIG. 2, and then falls. The voltage of the capacitor 25 continues to rise following the battery voltage, eventually reaching a peak point p and maintaining that value. During the period when the battery voltage is rising, the resistor 28
, since the capacitor 24 is charged through the diode 24, the diode 24 is biased in the forward direction, and the non-inverting input side of the comparator 23 is also biased higher than the inverting input side, outputting a high level and controlling the charging current. The circuit charges the battery 27. Eventually, as charging approaches completion and the battery voltage begins to drop from the peak point p, the voltage of the capacitor 25 becomes higher than the voltage of the battery 27, and the charge in the capacitor 26 reverse biases the diode 24.

Therefore, the inverting input of the comparator 23 is biased at a higher potential than the non-inverting input, the output is low level, and charging is terminated by the charging current control circuit.

Problems to be Solved by the Invention However, in the above configuration, the voltage drop △V of the battery voltage from the voltage peak point p in FIG. This has disadvantages in that variations occur and charging starts again.

These causes will be explained with reference to FIG. First, consider the temperature characteristics of the forward voltage of the diode 24. This is because the peak detection means of the battery is detected by switching the forward bias of the diode 24 to the reverse bias, so that the value of the voltage drop ΔV also varies due to the variation in the forward voltage of the diode 24. Second,
Leakage current from the diode 24 and capacitor 26 is considered. This is because after detecting the peak voltage of the battery 27, the diode 24 is reverse biased and the output of the comparator 23 becomes low level, but if it is left for a long time, the voltage of the capacitor 26 will decrease due to leakage current between the diode 24 and itself. When the voltage decreases and eventually becomes lower than the voltage of the battery 27, the diode 24 is forward biased and the output of the comparator 23 is set to zero again so that the battery is charged again. In particular, the above phenomenon occurs most frequently when charging batteries with a small capacity, because when batteries of different capacities are charged with one charger, the charging time limit is determined according to the battery with the largest capacity. ing.

In view of the above drawbacks, the present invention provides a charging control circuit equipped with means for accurately detecting the voltage drop ΔV from the voltage peak point p of the battery 27, which is means for detecting the end of charging.

Means for Solving the Problem In order to achieve this object, the charging control circuit of the present invention includes means for charging a capacitor with the battery voltage, and a means for charging a capacitor with a low level when the voltage on the capacitor becomes higher than a reference voltage. a comparator for outputting, a means for counting the time until the comparator is inverted, a storage means for storing the minimum value of the count value, and a comparison means for comparing the count value and the stored value;
It is comprised of means for controlling the charging current and completing charging when the count value continuously increases from the stored value.

Function: With this configuration, the capacitor is charged in accordance with the battery voltage, and the current battery voltage is calculated relatively by means of counting the time until the capacitor is charged, and the current battery voltage is continuously calculated from the minimum count value. By determining that charging is complete when the battery voltage increases, unlike conventional charging circuits, there is no need to store the peak value of the battery voltage in the capacitor, and charging can be completed accurately without being affected by the performance of electronic components or the surrounding environment. It will have a detection function.

EXAMPLE Hereinafter, an example of the present invention will be described with reference to the drawings. Figure 1 shows a charging control circuit equipped with a circuit that detects the completion of charging by calculating the charging voltage of the battery from the count time and detecting the peak of the charging voltage of the battery. This shows the configuration. In FIG. 1, 11 is a secondary battery charged by a charging circuit. 8 is a means N for charging the capacitor 9 with the voltage of the battery 11; 9 is a capacitor charged with the voltage of the battery 11; 1o is a reset circuit for resetting the capacitor 9. 7 is comparator 6
This is a reference voltage generation circuit connected to the non-inverting input of. 6
is a comparator for comparing the reference voltage generated by the reference voltage generating circuit 7 and the voltage of the capacitor 9. 6 is capacitor 9
This is a counting means for counting the time from the start of charging until the inverted output of the comparator 6 is output. 4 is a storage means for storing the minimum count value counted by the counting means 6; 3 is a storage means for comparing the minimum count value stored by the storage means 4 with the current count value by the counting means 5; It is a means of comparison. 2 is a means for controlling the charging current to complete charging when the comparison means 3 determines that the count value by the counting means 5 has continuously increased from the minimum count value stored by the storage means; 1 is a means for controlling the charging current and completing charging; This is a DC stabilized power supply for charging the 11.

The operation of the charging control circuit configured as described above will be described below.

First, connect the discharged secondary battery 11 as shown in Fig. 1, start charging the battery 11 with the DC stabilized power supply 1, turn off the reset circuit 1o, and at the same time start counting by the counting means 6. let In this case, the capacitor 9 is charged by the battery voltage through the charging means 8, and when the voltage of the capacitor 9 becomes higher than the voltage of the reference voltage generating circuit 7, the output of the comparator 6 becomes an inverted output. Here, the counting means 6 stops counting and at the same time sends a signal to the reset circuit 10 to discharge the capacitor 9. Next, the comparison means 3 compares the count value stored in the storage means 4 with the current count value, and if the value counted by the counting means is smaller, that value is stored in the storage means 4. When this is repeated and the battery 11 is continued to be charged, the battery voltage during charging continues to rise to a peak value as shown in FIG. 2, and then falls. Correspondingly, the value counted by the counting means 6 becomes minimum at the peak point of the battery 11, and then increases. During the period when the battery voltage is rising, the value counted by the counting means is always smaller than the value stored in the storage means 4, and the charging current control means continues to charge the battery 11. Eventually, when charging approaches completion and the battery voltage begins to drop below the peak point p, the value stored in the storage means 4 becomes smaller than the value counted by the counting means, and this continues continuously. This is recognized by the comparison means 3, and the charging is terminated by the charging current control means. FIG. 3 shows this control in the form of a flowchart, and in this embodiment, each of the means 2.3 and 4.5 in FIG. 1 was realized by a microcomputer.

As described above, this embodiment includes means for relatively converting battery voltage into count time, and means for comparing the minimum count value by the storage means and the count value by the count means, so that the count value is continuous. By terminating charging when the battery voltage increases, there is no need to hold the peak value of the battery voltage for a long time using diodes and capacitors as in the past, and the end of charging can be accurately detected without relying on component performance. The battery can be equipped with a function to prevent charging from occurring again.

Effects of the Invention As described above, the present invention includes a means for calculating a count value relatively from the battery voltage, a means for storing a minimum count value, and a means for comparing the minimum count value and the current count value to calculate the count value. By providing a means for controlling the charging current by continuous increase, it is possible to accurately detect the end of charging without depending on the surrounding environment and circuit performance.
Some devices can be equipped with a function to prevent charging from starting again after charging is completed.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the secondary battery charging control circuit of the present invention, FIG. 2 is a characteristic diagram showing the charging voltage of the secondary battery and a relative count value in the present invention, and FIG. The figure is a flowchart explaining the secondary battery charging control of the present invention, and FIG. 4 is a circuit diagram showing a conventional charging control circuit. 1... DC stabilized power supply, 2... Charging current control circuit, 3... Comparison means, 4...
Count value storage means, 6...Counting means, 6
... Comparator, 7 ... Reference voltage generation circuit, 8 ... Means for charging capacitor 9 with battery voltage, 9 ... Capacitor, 10 ... ...
・Reset circuit, 11... Secondary battery. Name of agent: Patent attorney Toshio Nakao and 1 other person
2 Figure □ nm6 Figure 3

Claims (1)

[Claims] A capacitor connected across the battery, a means for charging the capacitor in accordance with the battery voltage, a reset circuit for the capacitor, a comparator that receives the capacitor voltage as input, a reference voltage generation circuit that serves as a reference for comparison, and a comparison circuit. a time counting means connected to the output of the device, a storage means for storing the minimum value of the count value of the counting means, and a comparison means for comparing the count value and the stored value, and the count value is the stored value. A secondary battery charging control circuit that controls the charging current and completes charging when the current increases above a set value.