JPH08168186A - Battery charger - Google Patents

Abstract

PURPOSE: To reduce the size while suppressing generation of heat by feeding a transistor for protecting against the overvoltage of an input power supply with a drive current from a reference power supply through a resistor for correcting the input offset of an amplifier thereby reducing power consumption of the circuit. CONSTITUTION: A control line 24 of a microcomputer 20 is pulled High and a second transistor 14 is turned ON to feed a resistor 13 with a current. Consequently, the input offset of an amplifier 12 is canceled and a first driver 6 is driven to charge a battery 18. When the battery 18 is not charged, the control line 24 from the microcomputer 20 is pulled Low and the second transistor 14 is turned OFF thus preventing consumption of drive current in the first transistor 6. When the microcomputer 20 detects an overvoltage at an input power supply terminal 1, a control line 32 is pulled Low to prevent the battery 18 from being charged abnormally.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a battery charger that charges a battery accurately, without waste and safely.

[0002]

2. Description of the Related Art In recent years, small personal computers, home video cameras and the like have become smaller and are becoming popular because they can be carried anywhere by using a battery as a power source.

In the future, the number of battery-operated devices will increase,
Rechargeable batteries, which are economically and resource-saving, have come to be used.

However, a rechargeable battery is required to have an optimal charging function for the battery charger in order to prolong the life of the rechargeable battery and to fully charge the battery and bring out its battery capacity. Its function is as follows.

A. Can be fully charged in a short time. b. A sufficient amount of discharge can be taken out.

C. Can be fully charged over a wide range of temperatures. d. Can be safely charged.

An example of a conventional battery charger will be described below with reference to the drawings. FIG. 2 is a circuit diagram of a conventional battery charger.

Power is supplied from the input power terminals 1 and 2, and the resistors 3, 11, 5, 4, 25 and the transistor 6,
The transistor 7 passes through the transistor 6 and the overvoltage detection circuit 40 composed of
By controlling ON / OFF at 0, a charging current is supplied to the battery 18 via the charging terminal 16. Then, the circuit is grounded via the charging terminal 17, and the current detection resistor 15
Through to the input power supply terminal 2. For the current required to charge the battery, the terminal voltage of the current detection resistor 15 is amplified by the amplifier 1
A amplified by 2 and built in the microcomputer 20
It is input to the / D converter 19 and judged by the data value. The result is transferred to the transistor 7 via the control line 22.
Control.

Specifically, the voltage divided by the resistors 3 and 11 from the input power supply terminals 1 and 2 and the reference power source 10 supplied to the microcomputer 20 are compared by the transistor 9, and the divided settings are made by the resistors 3 and 11. Voltage is reference power 10+
When the voltage becomes higher than Vbe of the transistor 9, the transistor 9 becomes conductive and the voltage drop across the resistors 4 and 5 causes the transistor 8 to become conductive. The voltage of Vbe of the transistor 6 is set to 0V, so that the output of the transistor 6 is turned off and overvoltage protection is performed. However, since the overvoltage detection circuit operates, the charging current to the battery disappears, the input power supply returns to a normal voltage, and charging is restarted again.

In a steady state, the transistor 6 is driven by the current of the resistor 25 attached to the base of the transistor 6, and a sufficient charging current flows.

Next, a transistor 7 is connected to the output of the transistor 6, and the base of the transistor 7 is turned on / off by a microcomputer, or the charging current is changed by a current control circuit by a D / A converter and the terminal 16 is connected.
A charging current is supplied to the battery 18 via the. The charging terminal 17 is used as the circuit ground, and the current detection resistor 15 is connected to the input power supply terminal 2. The current required to charge the battery 18 is obtained by amplifying the terminal voltage of the current detection resistor 15 by the amplifier 12, inputting it to the A / D converter 19 incorporated in the microcomputer 20, and judging by the data value thereof. The result controls transistor 7 via control line 22 as described above.

However, when the terminal voltage of the current detection resistor 15 is amplified by the amplifier 12, the input offset of the amplifier 12 cannot be ignored. Therefore, in order to cancel the input offset, the output of the transistor 6 is switched by the transistor 14 via the resistor 13 and a current is supplied to the current detection resistor 15 in advance.

Therefore, FIG. 3 will be described with reference to the graph of the relationship between the output current (IL) and the A / D output data. First, when the load is not connected (IL = 0), the current I flowing through the current detection resistor 15 is I = Io, and FIG.
Assuming that point A is on the horizontal axis (load current: IL) of A, A output from the A / D converter 19 through the amplifier 12 of FIG.
The / D output data is "DATA1" on the vertical axis in FIG.
This "DATA1" can include the offset variation (MAX, TYP, MIN value) of the amplifier 12 and the current Io flowing through the microcomputer 20 and the transistor 7. Next, the battery 18 is connected as a load, and the charging current for charging the battery 18 is 1000 mA.
Then, the output data of the A / D converter 19 is "DAT.
A3 ". This is uniquely determined by determining the values of the amplification factors of the current detection resistor 15 and the amplifier 12 so that the difference between" DATA1 "and" DATA3 "is obtained when the charging current is 1000 mA.

The fully charged battery 18 is 100 m in order to fully charge the battery and to supplement self-discharge.
It is necessary to flow the charging current as much as A. However, the terminal voltage Vr of the current detection resistor 15 at that time becomes 5 mV when the resistance value of the current detection resistor 15 is 0.05Ω, and the amplifier 1
When amplifying with the No. 2 amplifier, the variations of the input offset of the amplifier are equal or more and cannot be ignored. Therefore, in FIG. 3, the value of the load current of 100 mA is output as the difference of “DATA1” in the output data “DATA2” of the A / D converter 19. As a result, the input offset of the operational amplifier is canceled with the conventional volume, and the logical operation unit (hereinafter referred to as ALU) in the microcomputer 20 changes the output data of the A / D converter 19 to "DAT".
The input offset of the operational amplifier can be canceled by subtracting A1 ″.

However, in the above circuit configuration, the reference power source 10
A large amount of current is required in addition to the current for charging the battery 18, such as the drive current of the transistor 6, the drive current of the transistor 6 and the current for correcting the input offset of the amplifier 12.

[0016]

As described above, in order to charge the battery 18 with high accuracy, the reference power source 10 is conventionally used.
A large amount of current is required for the drive current of the transistor 6, the drive current of the transistor 6 and the current for correcting the input offset of the amplifier 12. As a result, the circuit generates a lot of heat and consumes power,
Further, it was difficult to reduce the size. Further, there is a problem of malfunction due to overvoltage detection of the input power source.

[0017]

SUMMARY OF THE INVENTION A battery charger of the present invention uses a DC power supply device as an input power supply, and an overvoltage detection circuit and an overvoltage detection circuit for comparing a voltage obtained by dividing the voltage of the input power supply with a resistor and a reference power supply. A circuit that controls the first transistor connected to the input power supply by the output of the circuit;
The second transistor, which is controlled by the microcomputer from the base of the first transistor through the resistor, is connected to the negative terminal of the battery and is connected to the charging current detection resistor for the battery, and the other end of the charging current detection resistor is input. Connected to the negative side of the power source, connected to the output of the first transistor and the third transistor controlled by the microcomputer, connected to the positive terminal of the battery to the output of the third transistor, It has means for inputting to the microcomputer the data obtained by amplifying the voltage and converting it by the A / D converter, and controlling it.

Further, the voltage divided by the resistor from the input power source of the battery charger is converted by the A / D converter, the microcomputer determines the overvoltage, and the voltage divided by the resistor from the input power source and the reference power source are used. A fifth transistor of an overvoltage detection circuit in which a voltage is compared by a fourth transistor, a fifth transistor is driven by the output of the fourth transistor, and the base and emitter of the first transistor are short-circuited by the fifth transistor. A battery charger configured so that the microcomputer is controlled by the microcomputer.

[0019]

With the above structure, the present invention reduces the circuit power consumption and heat generation by performing the drive current of the transistor for protecting the overvoltage of the input power source by the reference power source and the resistor for correcting the input offset of the amplifier. The size can be reduced, and when the battery is not charged, no current is passed through the resistor that corrects the input offset, so that the current consumption can be further reduced. Further, it is possible to eliminate malfunction due to overvoltage detection of the input power supply.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a circuit diagram of a battery charger according to an embodiment of the present invention. In the figure, the configuration of the basic circuit is the same as that shown in FIG. 2, and the characteristic drive circuit section will be described here.

In the reference numeral 41, the voltage divided by the resistors 3 and 11 from the input power supply terminals 1 and 2 and the reference power source 10 supplied to the microcomputer 20 are compared by the fourth transistor 9 and the voltage is divided and set by the resistors 3 and 11. When the voltage becomes higher than the reference power supply 10 + Vbe of the fourth transistor 9, the fourth transistor 9 becomes conductive, the voltage drop of the resistors 4 and 5 makes the fifth transistor 8 conductive, and the voltage of Vbe of the first transistor 6 becomes Vbe. Is 0 V, the output of the first transistor 6 is turned off, and the overvoltage detection circuit performs overvoltage protection.

In the steady state, the first transistor 6
The first transistor 6 is driven by the current of the reference power source 10 attached to the base of the.

Next, 7 is a third transistor connected to the output of the first transistor 6, and the base of the third transistor 7 is controlled to be turned on / off by a microcomputer or a current by a D / A converter is used. The charging current is changed by the control circuit and the battery 18 is supplied through the terminal 16.
Supply the charging current to.

The charging terminal 17 is used as the circuit ground, and the current detection resistor 15 is connected to the input power supply terminal 2. The current required for charging the battery 18 is obtained by amplifying the terminal voltage of the current detection resistor 15 by the amplifier 12 and then the A / D converter 19 built in the microcomputer 20.
Input the data into and judge by the data value. Based on the result, the third line is transmitted via the control line 22 as described above.
Of the transistor 7 of FIG.

However, when the terminal voltage of the current detection resistor 15 is amplified by the amplifier 12, the input offset of the amplifier 12 cannot be ignored. Therefore, in order to cancel the input offset, the second transistor 14 is switched from the base of the first transistor 6 through the resistor 13 and a current is supplied to the current detection resistor 15 in advance. That is, the control line 24 of the microcomputer 20 is set to a high level to turn on the second transistor 14 to cause a current to flow through the resistor 13 to cancel the input offset of the amplifier 12 in the same manner as in the conventional example, and the first transistor Since the current flows as the base current of 6, the first transistor 6 can be sufficiently driven to allow the current for charging the battery 18 to flow. When the battery 18 is not charged, the drive current of the first transistor 6 is not consumed if the control line 24 from the microcomputer 20 is set to low level and the second transistor 14 is turned off.

Next, the voltage divided from the input power supply terminal 1 of the battery charger by the resistors 3, 4, 11 and 30 is converted by the A / D converter 19 via the detection line 31, and the overvoltage is generated by the microcomputer 20. Detect and judge. When the microcomputer 20 determines the overvoltage from the input power supply terminal 1, the control line 32 is set to the low level to cause a current to flow through the resistors 4 and 5, driving the fifth transistor 8 and driving the first transistor 6. By shorting the base and the emitter, the first transistor 6
This prevents an abnormal charge from occurring in the circuit and the battery 18 thereafter due to no output to the collector.

By storing the state of the overvoltage from the input power supply terminal 1 even once, the microcomputer 20 can protect the charge even if the voltage from the input power supply terminal 1 returns to normal. . as a result,
There is no charging current and the input power supply returns to normal voltage.
It is possible to eliminate the malfunction of repeating the charging operation again and, if the input power source becomes abnormal, repeating the input overvoltage detection.

As described above, in the above embodiment, (1) the overvoltage detection circuit 41 for comparing the voltage of the DC input power supply divided by the resistors 3 and 11 with the reference power supply 10, and the overvoltage detection circuit 41. And a circuit for controlling the first transistor 6 connected to the input power source by the output of the second transistor 14 and the second transistor 14 connected from the base of the first transistor 6 through the resistor 13 to the negative terminal of the battery. Since the microcomputer 20 is connected to the base of the second transistor 14 and is controlled, it is possible to prevent unnecessary drive current consumption in the first transistor 6 when the battery is not charged. Further, (2) the fifth transistor 8 is obtained by dividing the voltage of the DC input power source with the resistors 3, 11, and 30 and converting the voltage with the A / D converter 19, and determining and storing the overvoltage by the microcomputer 20. The storage of the computer 20 can prevent the overvoltage from being charged without repeating the overvoltage charging by short-circuiting the base and emitter of the first transistor 6 by driving. However, it is not necessary to configure it as one circuit as in the above embodiment, and only the configuration of (1) or (2) above may be selected at the time of use. It goes without saying that it belongs to the category of the invention.

[0030]

As described above, according to the present invention, an overvoltage detection circuit for comparing a voltage obtained by dividing the voltage of a DC input power supply by a resistor with a reference power supply, and an output of the overvoltage detection circuit are connected to an input power supply. A circuit for controlling the first transistor, and a microcomputer for controlling the second transistor by connecting the second transistor to the negative terminal of the battery through a resistor from the base of the first transistor and by connecting the second transistor to the base of the second transistor. With the battery charger configured as described above, it is possible to prevent unnecessary drive current consumption in the first transistor when the battery is not charged, and
A voltage obtained by dividing the voltage of the DC input power source with a resistor is converted by an A / D converter, an overvoltage is determined and stored by a microcomputer, and another transistor inserted between the base and the emitter of the first transistor is added to the above. In the case of driving the microcomputer to short-circuit the base and the emitter of the first transistor, the overvoltage charge can be prevented by the memory of the computer 20 without repeating the overvoltage charge, and the unnecessary current It is also possible to prevent consumption.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a battery charger according to an embodiment of the present invention.

[Fig. 2] Circuit diagram of a conventional battery charger

FIG. 3 is a graph showing the relationship between conventional output current (IL) and A / D output data.

[Explanation of symbols]

 1, 2 Input power supply terminal 3, 4, 5, 11, 13 Resistor 6 First transistor 7 Third transistor 8 Fifth transistor 9 Fourth transistor 10 Reference power supply 12 Amplifier 14 Second transistor 15 Current detection resistor 16, 17 Charging terminal 18 Battery 19 A / D converter 20 Microcomputer 21 Microcomputer power supply 22, 24 Control line 23 Amplifier

Claims (2)

[Claims] 1. An overvoltage detection circuit for comparing at least a voltage obtained by dividing the voltage of a direct current input power supply by a resistor with a reference power supply; and a first voltage connected between the input power supply and one battery terminal by the output of the overvoltage detection circuit. A circuit for controlling the first transistor, and a second transistor connected from the base of the first transistor through a resistor to the other terminal of the battery and connected to the base of the second transistor. A battery charger composed of a microcomputer that controls the transistor. 2. A transistor connected between at least a DC input power source and one battery terminal, an A / D converter for converting a voltage obtained by dividing the voltage of the DC input power source by a resistor, and the A / D converter A battery charger composed of a microcomputer for judging and storing an overvoltage based on data, and another transistor having a base and an emitter connected between the base and the emitter of the transistor driven by the microcomputer.