JPH1098838A - Charging control circuit for secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce adapter power supply by detecting fluctuation of load from fluctuation of battery voltage, storing and resetting the peak charging voltage of a battery and comparing a detected battery voltage with a stored peak charging voltage thereby preventing the erroneous operation due to fluctuation of the load and realizing a float charging operation. SOLUTION: Battery voltage is detected by a battery voltage detecting circuit 16 and when it is lower than a reference level, a count of a count means 8 is stored in a memory means 4. Upon fluctuation of a load connected with a battery a decision means decides an abrupt fluctuation of the load from the absolute voltage of the battery by controlling the charging current with a predetermined constant current. Memory means 4, 7 store the peak charging voltage of the battery and a reset means 5 resets a stored peak charging voltage. A comparison means 6 compares a detected battery voltage with the stored peak charging voltage. According to the arrangement, two power supply circuits comprising DC stabilized power supplies 1, 2 for charging and the adapter can be reduced to one power supply circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a secondary battery charging control circuit.

[0002]

2. Description of the Related Art In recent years, secondary batteries such as sealed nickel cadmium batteries (hereinafter referred to as "NiCad batteries") and lead sealed batteries have been widely used as power supplies for portable devices such as portable videos 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 voltage of the charging voltage. In addition, in the case of being integrated with a portable device, in many cases, an adapter power supply is combined with a charging power supply in order to enable the operation of the portable device even while the battery is being charged.

Hereinafter, a conventional charge control circuit for detecting a peak voltage of a charge voltage and a circuit including an adapter power supply as described above will be described with reference to the drawings. In FIG. 5, reference numeral 21 denotes a stabilized DC power supply for an adapter;
Is a stabilized DC power supply for charging, 23 is means for detecting an adapter current, 24 is a charging current control circuit, 25 is a comparator,
6 is a resistor, 27 is a diode, 28 is a capacitor, 29
Is a switch for discharging the electric charge of the capacitor 28, 30 is a switch for changing the battery, 31 is a secondary battery to be charged, 32 is an adapter circuit, 33 is a charge control circuit, 34 is a battery pack, and 35 is a portable device.

The operation of the circuit for detecting the peak point of the charge voltage of the battery and the charge control circuit including the adapter circuit will be described below.

When the portable device 35 is operated by the battery pack 34, the changeover switch 30 is turned on to supply power from the secondary battery 31. However, during charging, the changeover switch 30 is turned off, and the portable device 35 is turned off.
Supplies power only from the adapter circuit 32. In charging the secondary battery 31 in this state, after discharging the charge of the capacitor 28 by the discharge switch 29, the discharge switch 29 is opened, and a charging current is supplied from the DC stabilized power supply 22.

The charge of the secondary battery 31 charges a capacitor 28 through a resistor 26 and a diode 27. in this case,
Since the non-inverting input of the comparator 25 is biased higher than the inverting input by the forward voltage of the diode 27,
A high level is output, and the charging current control circuit 24 is activated to perform charging.

[0007] As shown in FIG. 2, the battery voltage during charging continues to increase up to a peak point P, and thereafter decreases. The voltage of the capacitor 28 continues to rise following the battery voltage, reaches the peak point P, and keeps its value. Since the capacitor 28 is charged through the resistor 26 and the diode 27 during the period when the battery voltage is increasing, the diode 27 is biased in the forward direction, and the comparator 25 is also biased higher at the non-inverting input than at the inverting input. The level is output, and the secondary battery 31 is charged by the charging current control circuit 24.

When the charging with the predetermined constant current approaches the end, and the battery voltage starts dropping from the peak point P, the voltage of the capacitor 28 becomes higher than the voltage of the secondary battery 31 and the charge of the capacitor 28 Reverse bias. Accordingly, the inverting input of the comparator 25 is biased higher than the non-inverting input, the output becomes low level, and charging by the charging current control circuit 24 with a predetermined constant current ends. When the adapter current flows due to the operation of the portable device 35 during charging, the current detecting means 2 detects the current.
By 3, the operation of the portable device 35 is detected, and charging with a predetermined constant current is temporarily stopped. Thereafter, when the adapter current stops flowing, control is performed by starting charging with a predetermined constant current again.

[0009]

However, in the charging current control circuit 24 as described above, two stabilized DC power supplies, that is, a stabilized DC power supply 21 for the adapter and a stabilized DC power supply 22 for the charging are required. The changeover switch 30 is also required in the pack 34, and therefore, it is difficult to reduce the size of the charger and the battery pack 34 to the size and weight corresponding to the portable device 35.

SUMMARY OF THE INVENTION The present invention solves such a conventional problem, and does not cause a malfunction due to a change in a load connected to the battery while rapidly charging the battery, and performs floating charging by ─ΔV control. By doing so, the object of the present invention is to eliminate the changeover switch in the adapter power supply and the battery pack and realize a small and lightweight secondary battery charge control circuit.

[0011]

In order to achieve this object, a charge control circuit according to the present invention comprises a means for detecting a battery voltage, a means for storing a battery voltage, and a means for detecting a change in a load connected to the battery. Means for detecting a change in load from a change in battery voltage, means for storing a battery charging peak voltage, means for resetting a stored charging peak voltage, a detected battery voltage and a stored charging peak voltage. And means for comparing

With this configuration, the rechargeable battery charge control circuit of the present invention discriminates between a drop in the battery voltage due to a change in the load connected to the battery and a normal voltage drop during charging with a predetermined constant current. By preventing a malfunction due to a change in load and enabling floating charging, circuits such as an adapter power supply and a changeover switch in a battery pack can be reduced, and the circuit can be significantly reduced.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a charge control circuit for a secondary battery according to an embodiment of the present invention will be described with reference to the drawings. In FIG. 1, 16 is a battery voltage detection circuit for detecting the absolute value of the battery voltage, 15 is a portable device, 14 is a secondary battery,
13 is a capacitor, 12 is means for charging the capacitor with the battery voltage, 11 is a circuit for discharging the capacitor, 1
0 is a reference voltage generating circuit, 9 is a comparator, 8 is a counting means for converting the output voltage of the comparator 9 at a high level into a relative counting time (count value), and 7 is a counting means 8 for the previous time. Means for storing the count value; 6 means for comparing the count value of the count means 8 with the previous count value of the count means 8; 5 means for resetting the minimum count value; 4 means for storing the minimum count value; 3 is a means for comparing the minimum count value with the count value, 2 is a charging current control circuit, and 1 is a stabilized DC power supply.

The operation of the charging current control circuit configured as described above will be described below. First, the discharged secondary battery 14
The portable device 15 is connected as shown in FIG. 1, the charging of the secondary battery 14 is started by the stabilized DC power supply 1, the circuit 11 for discharging the capacitor is turned off and released, and at the same time the counting means 8 is started. In this case, the capacitor 13 is charged by the battery voltage through the means 12 for charging the capacitor. When the voltage of the capacitor 13 becomes higher than the voltage of the reference voltage generating circuit 10, the output of the comparator 9 becomes an inverted output. Here, the counting means 8 stops counting and simultaneously outputs a signal to the capacitor discharging circuit 11 to discharge the capacitor 13. Next, the counting means 8 stored in the storage means 7 by the comparing means 6
Is compared with the current count value of the counting means 8, and if the difference is equal to or smaller than the reference value, the portable device 1
5 is determined to be in a state where the load does not change.
If the current count value counted by is smaller, the value is stored in the storage means 4. When this state is repeated, the battery voltage during charging continues to rise to the peak point P as shown in FIG. 2, and then falls. Correspondingly, the value counted by the counting means 8 becomes minimum at the peak point P of the battery voltage, and thereafter increases. During the period when the battery voltage is rising, the value counted by the counting means 8 is always smaller than the value stored by the storage means 4. When the charging with the predetermined constant current approaches the end and the battery voltage starts dropping from the peak point P, the value stored by the storage means 4 becomes smaller than the value counted by the counting means 8, When the difference is equal to or greater than the set value, the charging current is reduced by the charging current control circuit 2 and the battery voltage is detected by the battery voltage detection circuit 16. The value is stored in the storage means 4, and the charging with the predetermined constant current is restarted. If the value exceeds the reference value, the charging with the predetermined constant current is terminated.

FIG. 4 is a detailed diagram showing this operation according to the state of charge. In the floating charging, the battery voltage drops in two types, that is, at the end of regular charging and when the load on the portable device increases during charging.
Now, when the ─ΔV operation is detected from the normal battery voltage curve at the end of charging of the battery, if the charging current is reduced to the trickle current, the battery voltage is plotted according to the end-of-charging voltage curve of FIG. When the battery voltage exceeds the reference value, the charging with the predetermined constant current is completed. However, when the voltage drop due to the load of the portable device is detected during charging, if the charging current and the trickle current are reduced, the battery voltage becomes the voltage curve during charging shown in FIG. When the charge becomes equal to or less than the reference value, charging with a predetermined constant current is restarted. As a result, malfunction of the portable device 15 at the time of a sudden load change can be eliminated.

FIG. 3 is a flowchart showing this control. In this embodiment, the comparing means 3, 6, the storing means 4, 7, the resetting means 5, the counting means 8, the comparator 9, the reference voltage Each means of the generation circuit 10, the circuit 11 for discharging the capacitor, and the battery voltage detection circuit 16 was realized by a microcomputer.

As described above, according to this embodiment, the counting means for converting the battery voltage into the relative count time (count value), the means for detecting a change in the count value, the minimum count value by the storage means, and the like. A means for comparing the count value by the counting means and a means for detecting the absolute value of the battery voltage are provided, and the battery voltage exceeds the reference value when the count value increases due to a small change, and when the increase amount exceeds a set value. A function of performing floating charging by connecting a load to a portable device or the like by terminating the charging with a predetermined constant current can be provided.

[0018]

As is apparent from the above description of the embodiment, according to the rechargeable battery charging control circuit of the present invention, the means for detecting the battery voltage, the means for storing the battery voltage, and the battery are connected. Means for judging a sudden load change from the absolute voltage of the battery by controlling the charging current at a predetermined constant current when the load fluctuates, a means for storing the charging peak voltage of the battery, By providing a means for resetting and a means for comparing the detected battery voltage with the stored charging peak voltage, it becomes possible to perform floating charging that could not be realized by a conventional circuit, and Two power supply circuits consisting of a stabilized DC power supply for the adapter are used as one power supply circuit, and electronic circuits such as a stabilized DC power supply for the adapter and a changeover switch in the battery pack are reduced. Therefore, compact and lighter charger itself is one that can raise a significant effect on well costs.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a configuration of a secondary battery charge control circuit according to one embodiment of the present invention.

FIG. 2 is a graph showing characteristics of a charging voltage of a secondary battery and a relative count value in a secondary battery charging control circuit according to an embodiment of the present invention;

FIG. 3 is a flowchart illustrating charging control of the secondary battery in the secondary battery charging control circuit according to the embodiment of the present invention;

FIG. 4 (a) is a graph showing a comparison between a normal voltage drop at the end of the charging and FIG. 4 (b) a voltage drop due to an increase in the load of a portable device during charging.

FIG. 5 is a circuit diagram showing a configuration of a conventional charge control circuit.

[Explanation of symbols]

 Reference Signs List 1 DC stabilized power supply 2 Charging current control circuit 3, 6 Comparison means 4, 7 Storage means 5 Reset means 6 Comparison means 8 Counting means 9 Comparator 10 Reference voltage generation circuit 11 Capacitor discharging means 12 Capacitor charging means 13 Capacitor 14 Secondary battery 15 Portable device 16 Battery voltage detection circuit

Claims (1)

[Claims] The present invention controls a charging current at a predetermined constant current by comparing a battery voltage when the battery voltage drops by a set value or more after the battery voltage reaches a stored charging peak voltage with a preset value. A charge control circuit for a secondary battery that determines whether to end charging with the predetermined constant current or to continue charging with the predetermined constant current, comprising: means for detecting a battery voltage; Means for detecting a change in the load from a change in the battery voltage when the load connected to the battery fluctuates; means for storing the charge peak voltage of the battery; and resetting the stored charge peak voltage. Means for comparing the detected battery voltage with the stored charging peak voltage, and controlling the charging current when the battery voltage drops by a set value or more after reaching the stored charging peak voltage. Means for ending the charging with the predetermined constant current or detecting a change in the load connected to the battery, resetting the stored charging peak voltage, and continuing the charging with the predetermined constant current. And a charge control circuit for a secondary battery.