JPH0779531B2 - Secondary battery charge control circuit - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a secondary battery charge control circuit used for charging a secondary battery.

2. Description of the Related Art In recent years, secondary batteries such as sealed nickel-cadmium batteries and lead-sealed batteries have been widely used as power sources for portable video and handheld 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 charge control circuit that detects the end of charging of the secondary battery by detecting the peak of the charging voltage as described above will be described with reference to the drawings.

FIG. 4 shows a second conventional circuit for detecting the completion of charging.
A circuit for detecting the peak point p of the battery charging voltage characteristics shown in the figure is provided. In FIG. 4, 21 is a stabilized direct current power supply, 22 is a charging current control circuit, 23 is a comparator, 24 is a diode, 25 is a circuit for storing the peak point of the charging voltage characteristic of a battery, and 26 is a capacitor 25. A switch for discharging electric charge, 27 is a secondary battery to be charged, and 28 is a resistor.

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

First, the discharged secondary battery 27 is connected as shown in FIG. 4, the charge of the capacitor 25 is discharged by the switch 26, the switch 26 is opened, and the charging current is supplied from the stabilized DC 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, since the non-inverting input side of the comparator 23 is biased higher than the inverting input by the forward voltage of the diode 23, the output outputs a high level and the charging current control circuit 22 becomes the active state to charge the battery. I do. The battery voltage during charging continues to rise up to the peak point p and then falls, as shown in FIG. The voltage of the capacitor 25 continues to increase following the battery voltage, and eventually reaches the peak point p and holds that value. Since the capacitor 24 is charged through the resistor 28 and the diode 24 during the period when the battery voltage is rising, the diode 24 is forward biased, and the comparator 23 is also biased at the non-inverting input side higher than the inverting input, and the output Outputs a high level to charge the battery 27 by the charging current control circuit. Eventually, when the charging approaches the completion and the battery voltage starts 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 of the capacitor 25 reverse biases the diode 24. Therefore, the inverting input side of the comparator 23 is biased to a higher potential than the non-inverting input side, the output outputs a low level, and the charging current control circuit ends the charging.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention However, in the above-described configuration, the voltage drop ΔV from the voltage peak point p of the battery voltage in FIG. 2 varies due to the characteristics of the circuit that detects changes in ambient temperature and completion of charging. It has a drawback that the battery is charged or the charging is restarted.

These causes will be described with reference to FIG. First, there is the temperature characteristic of the forward voltage of the diode 24. This is because the peak detection means of the battery is detected by switching from the forward bias of the diode 24 to the reverse pope bias,
The value of the drop voltage ΔV also varies due to the variation in the forward voltage of the diode 24. Secondly, there is a leakage current of the diode 24 and the capacitor 25. This is because after detecting the peak voltage of the battery 27, the diode 24 is reverse biased and the comparator
The output of 23 is set to low level, but if it is left for a long time after that, the voltage of the capacitor 25 will drop due to the leakage current of the diode 24 and its own. It is to set the output of 23 to the high level again to bring it into the charging state again. In particular, the above phenomenon occurs most often when charging a small-capacity battery, because the charging time limit is determined according to the battery with the largest capacity when using batteries with different capacities with a single charger. ing.

In view of the above-mentioned drawbacks, the present invention is a battery that is a charging end detection means.
The present invention provides a charge control circuit having means for accurately detecting a voltage drop ΔV from a voltage peak point p of 27.

Means for Solving the Problems In order to achieve this object, the charge control circuit of the present invention outputs a low level when the capacitor voltage becomes higher than a reference voltage by charging the capacitor with a battery voltage. A comparator, a means for counting the time until the comparator is inverted, a storage means for storing the minimum count value, and a comparison means for comparing the count value with the stored value.
And a means for controlling the charging current to complete the charging when the count value exceeds the stored value by the set value or more.

Function With this configuration, the current battery voltage is calculated relatively by means of charging the capacitor according to the battery voltage and counting the time until the capacitor is charged, and continuously increases from the minimum count value. When the battery is charged, it is not necessary to store the peak value of the battery voltage in the capacitor as in the conventional charging circuit, and the end of charging can be detected accurately without being affected by the performance of electronic components or the surrounding environment. It has the function to do.

Embodiment One embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows a charging control circuit equipped with a circuit for detecting the completion of charging by calculating the charging voltage of the battery from the count time as a circuit for detecting the completion of charging and detecting the peak of the charging voltage of the battery. The structure is shown. In FIG. 1, reference numeral 11 is a secondary battery charged by a charging circuit. Reference numeral 8 is a means for charging the capacitor 9 with the voltage of the battery 11, and 9 is a capacitor charged with the voltage of the battery 11. Reference numeral 10 is a reset circuit for resetting the capacitor 9. Reference numeral 7 is a reference voltage generation circuit connected to the non-inverting input of the comparator 6. Reference numeral 6 is a comparator for comparing the reference voltage generated by the reference voltage generating circuit 7 with the voltage of the capacitor 9. Reference numeral 5 is a counting means for counting the time from the start of charging the capacitor 9 to the output of the inverted output of the comparator 6. Reference numeral 4 is a storage means for storing the minimum value of the count values counted by the counting means 5, and 3 is a comparison between the minimum count value stored by the storage means 4 and the current count value by the counting means 5. It is a comparison means. Reference numeral 2 is a means for controlling the charging current and completing charging when the comparison means 3 determines that the count value by the counting means 5 has increased more than the set minimum value stored by the storage means, and 1 is A DC stabilized power supply for charging the battery 11.

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

First, connect the discharged secondary battery 11 as shown in FIG.
The charging of the battery 11 is started by the stabilized DC power supply 1, and the reset circuit 10 is turned off and released at the same time as the counting means 5
To start counting. In this case, the capacitor 9
Is charged by means of a battery voltage for charging it, and when the voltage of this 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 5 stops counting and at the same time outputs a signal to the reset circuit 10 to discharge the capacitor 9. Next, the comparison unit 3 compares the count value stored in the storage unit 4 with the current count value, and if the value counted by the counting unit is smaller, the value is stored in the storage unit 4. When the battery 11 is repeatedly charged in this manner, the battery voltage during charging continues to rise to the peak value as shown in FIG. 2, and then drops. Corresponding to this, the value counted by the counting means 5 is the battery
It reaches a minimum at 11 peaks and then increases. While the battery voltage is rising, the value counted by the counting means 5 is always smaller than the value stored by the storage means 4, and the battery 11 is continuously charged by the charging current control means. When the battery voltage is nearing completion and the battery voltage starts to drop below the peak point p, the value stored by the storage means 4 becomes smaller than the value counted by the counting means, and this value increases above the set value. The comparison means 3 recognizes that, and the charging current control means terminates the charging. FIG. 3 shows this control by a flow chart. In this embodiment, each of the means 2, 3, 4, 5 in FIG. 1 is realized by a microcomputer.

As described above, according to the present embodiment, the means for converting the battery voltage into the count time relatively, the means for comparing the minimum count value by the storage means, and the means for comparing the count value by the count means are provided, and the count value is continuous. By terminating the charging when the battery voltage has increased, it is not necessary to hold the peak value of the battery voltage with the diode and capacitor for a long time as before, and it is possible to accurately detect the termination of charging without depending on the component performance. Can be carried out satisfactorily, and it is possible to have a function of preventing the charging from re-entering.

EFFECTS OF THE INVENTION As described above, the present invention stores the means for counting the time until the capacitors connected to both ends of the secondary battery are charged by the voltage of the secondary battery itself to be charged, and the minimum count value. By comparing the means, the minimum count value and the current count value, and by continuously increasing the count value,
By including the means for controlling the charging current, it is possible to accurately detect the end of charging without depending on the surrounding environment and circuit performance, and to have the function of preventing the charging from re-entering after the end of charging. It is possible.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of a secondary battery charge control circuit of the present invention, FIG. 2 is a characteristic diagram of the charging voltage of the secondary battery, and a characteristic diagram showing the relative count value in the present invention. FIG. 4 is a flow chart for explaining the secondary battery charge control of the present invention, and FIG. 4 is a circuit diagram showing a conventional charge control circuit. 1 ... DC stabilized power supply, 2 ... Charging current control circuit, 3 ...
... comparing means, 4 ... count value storing means, 5 ... counting means, 6 ... comparator, 7 ... reference voltage generating circuit, 8 ...
... Means for charging the capacitor 9 by battery voltage, 9 ...
… Capacitor, 10… Reset circuit, 11… Secondary battery.

Claims (1)

[Claims] 1. A capacitor connected to both ends of a secondary battery and charged according to the battery voltage, a reset circuit for the capacitor, a comparator having the capacitor voltage as an input, and a reference voltage serving as a reference for comparison. A generation circuit; counting means for measuring the time connected to the output of the comparator; storage means for storing the minimum value of the count value of the counting means; comparison means for comparing the count value with the stored value; Secondary battery charge control, comprising: a means for controlling a charging current by an output signal when the count value continuously increases in comparison with the stored value by a comparing means to complete charging. circuit.