JPH11164492A - Battery charging circuit and battery charger - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a battery charging circuit and battery charger for lithium ion battery or the like, which is able to restrain variance in detected charging current and conduct proper charging. SOLUTION: This device involves a charging current supply circuit 2, which supplies prescribed current to a battery 3 via a charging current detecting resistor R, and a charging current detection circuit 9. The charging current detection circuit 9 is provided with a voltage follower which receives power supply for the operation with a power source side reference line +Vc connected to the first terminal 6 on the charging current supply circuit 2 side of the resistor R and involves an input terminal to a second terminal 7 on the battery 3 side of the resistor R, and a converting circuit involving a resistor R6 , which receives a current value according to the potential difference between a reference line +Vc and the output of the voltage follower and converts it into a voltage signal the reference of which is a reference line on a ground side.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a storage battery charging circuit and a battery charging device, and more particularly, to a lithium-ion battery capable of suppressing variation in detected charging current for each product and performing proper charging.
The present invention relates to a storage battery charging circuit such as an ion storage battery.

[0002]

2. Description of the Related Art Charging of a lithium-ion secondary storage battery or the like can be performed, for example, by charging the storage battery in a state after discharging, for example, by 3
When charging is performed at a constant current of 00 mA, and then the battery is considerably charged and the charging state advances, the charging mode is switched to a constant voltage charging mode.
When the voltage becomes 0 mA or less, or when the charging voltage becomes a predetermined value or more, it is determined that the charging has been sufficiently performed, and the charging is terminated.

FIG. 2 shows an example of such a conventional battery charging circuit. Reference numeral 8 denotes a battery charger, 1 denotes a control circuit including the microcomputer and the like, 2 denotes a charging current supply circuit that starts or stops a charging operation according to the control signal, and includes a driving circuit 2a and a MOSFET output transistor. 2b. Reference numeral 3 denotes a lithium ion battery (hereinafter referred to as a battery) charged by the charging current from the charging current supply circuit 2 via the detection resistor R, 4 denotes a charging current detection circuit having the detection resistor R, and 5 denotes A / D conversion circuit (A / D). D is the charging current supply circuit 2
Is an overcharge preventing diode provided between the output transistor 2b and the resistor R. As the overall charging operation of this circuit, the control circuit 1 detects that the battery 3 is loaded, and the control circuit 1 sends a charging start signal to the charging current supply circuit 2.
To control the driving circuit 2a,
Is operated to charge the battery 3. In this charging process, the current value of the charging current is detected by the charging current detection circuit 4, the A / D conversion is performed by the A / D 5, and the converted value is transmitted to the control circuit 1. The control circuit 1 compares the current charging current value with a reference value to determine the charging state, and stops the charging current supply circuit 2 when the charging is ended.

Here, the charging current detection circuit 4 is formed by a subtraction circuit that receives a terminal voltage between both ends of the detection resistor R. This subtraction circuit comprises a voltage dividing circuit composed of voltage dividing resistors R1 and R2 having a voltage dividing ratio equal to the (+) input and (-) input of the operational amplifier or the differential amplifier circuit 4a, and a voltage dividing circuit of the voltage dividing resistors R3 and R4. To obtain a voltage difference between the voltages V1 and V2 of the terminals 6 and 7 of the detection resistor R as the output voltage Vo. Note that, of the voltage dividing resistors R3 and R4, the resistor R4 is a feedback resistor of the differential amplifier circuit 4a, and the resistor R3 is a reference resistor. At this time, the differential amplifier circuit 4a is a circuit that performs an inverting operation and a non-inverting operation at the same time, and the detection voltage Vo on the output side is:
It is given by the following equation. Vo = V1 (R3 + R4) R2 / (R1 + R2) R3-V2 (R4
/ R3) Here, if R1 = R2 = R3 = R4, Vo = V1-V2
Becomes However, R1, R2, R3, and R4 are resistors R1, R2
2, R3 and R4.

[0005]

However, when such a charging current detection circuit is used, the detection voltage Vo is changed for each manufactured charging device due to variations in the four resistance values of the resistors R1, R2, R3, and R4. The voltage does not become V1−V2, but varies, and the detection voltages for detecting the completion of charging differ from each other. As a result, the detected charging current value differs depending on the charging device. In this case, the device in which the detection of the charging completion current value varies to the smaller side, the battery charging ends before the completion of charging, and the charged battery uses a battery that is not completely charged, and the usage time is shortened. Be shorter. On the other hand, in a device in which the detection of the charging completion current value varies to a large value, even if the overcharge prevention diode D is provided, the device is slightly overcharged, which affects the battery life. SUMMARY OF THE INVENTION An object of the present invention is to solve such a problem of the prior art, and suppresses the variation of the detected charging current for each product, and enables a proper charging of a storage battery charging circuit such as a lithium ion storage battery and a battery charging device. Is to provide.

[0006]

SUMMARY OF THE INVENTION A battery charging circuit and a charging apparatus according to the present invention for achieving the above object provide a charging current supply for supplying a predetermined current to a storage battery via a resistor for detecting a charging current value. And a detection circuit for detecting the charging current, wherein the detection circuit includes a first circuit on the charging current supply circuit side of the resistor.
The voltage difference between the reference line and the output of the voltage follower, wherein the voltage follower is connected to the power supply side reference line and connected to the power supply side to operate by receiving the power supply and the input terminal is connected to the resistor storage battery side second terminal. And a conversion circuit having a resistor for receiving a current value corresponding to the current value and converting the current value into a voltage signal based on the ground-side reference line.

[0007]

As described above, according to the present invention,
By providing the voltage follower, the same voltage value as that of the second terminal on the downstream side of the detection resistor for detecting the charging current value can be obtained as the output voltage of the voltage follower. Further, the voltage follower is connected to the first terminal on the upstream side of the detection resistor and connected to the power supply side reference line, and operates by receiving power supply therefrom. Therefore, the voltage between the power supply-side reference line and the output terminal of the voltage follower becomes equal to the voltage at both terminals of the detection resistor. Since this equal voltage is converted into a voltage with the ground side as a reference by the conversion circuit, the voltage of the detection resistor can be obtained as a detection voltage substantially as it is or at a predetermined ratio. In addition, the conversion circuit having the resistance in this case usually requires only one or at most about two resistance circuits.
Variations in the detected charging current for each product due to variations in resistance can be suppressed.

[0008]

FIG. 1 is a circuit diagram mainly showing a charging current detecting circuit according to an embodiment to which a battery charging circuit of the present invention is applied. The same components as those in FIG. 2 are denoted by the same reference numerals. Therefore, explanation of it is omitted. The battery charging device 10 of FIG. 1 has a charging current detection circuit 9. Other configurations are the same as those in FIG. The charging current detection circuit 9
It is composed of a differential amplifier 11 and an emitter follower 12,
Further, by completely feeding back the output of the emitter follower 12, a voltage follower is formed as a whole circuit by these. Further, the power supply side reference line + Vc of this voltage follower is connected to the terminal 6 on the upstream side of the detection resistor R, and receives power supply from the charging current supply circuit 2 side.
The reference line for the signal output of the emitter follower 12 is not the ground GND but the power supply side reference line + Vc.

A differential amplifier circuit 11 is a PNP type of a current mirror-connected active load provided between an NPN type differential transistor Q4, Q5 and a power supply side reference line + Vc upstream of the transistor Q4, Q5. Transistor Q
6, Q7, a resistor Ra provided between the common emitter of the transistors Q4 and Q5 and the ground GND. The output is taken out from the connection point between the collectors of the transistors Q7 and Q4 and sent to the base of the transistor Q1 of the emitter follower 12. The capacitor C connecting the collectors of the transistors Q4 and Q5 is a noise canceling capacitor.

In the differential amplifier circuit 11, a transistor Q2 is provided in front of the transistor Q4 as a minute current amplifier circuit, and the base of the transistor Q2 is a terminal of the detection resistor R on the charging side of the battery 3. The collector is connected to the terminal 7, the collector is connected to the power supply side reference line + Vc, and the emitter is connected to the ground G via the resistor Rb.
ND, and this emitter is connected to the transistor Q
Connected to the base of 4. Further, a transistor Q3 is provided before the transistor Q5 so as to be symmetric with the transistor Q2. The base of the transistor Q3 is connected to the output side of the load resistor R5 on the emitter side of the transistor Q2 of the emitter follower, the collector is connected to the power supply side reference line + Vc, and the emitter is connected to the ground GND via the resistor Rc. And the emitter is connected to the base of transistor Q5. In the above description, the resistors Rb and Rb, including the resistor Ra on the ground GND side of the differential amplifier circuit 11
c may each be a constant current source.

As described above, the power supply-side reference line +
Vc is connected to a terminal 6 connected to the output side of the charging current supply circuit 2 of the detection resistor R. Emitter follower 1
Reference numeral 2 denotes an emitter connected to the power supply-side reference line + Vc via a load resistor R5, and a collector connected to the ground GND via a resistor R6. The emitter is connected to the base of the transistor Q3, so that the output on the emitter side is fully fed back to the differential amplifier 11. As a result, the same voltage as the base voltage of the transistor Q2 is generated at the base voltage of the transistor Q3, and the output voltage generated at the load resistor R5 follows the voltage at the terminal 7 of the detection resistor R and becomes equal thereto. In addition, since the power supply side reference line + Vc is connected to the terminal 6, the same voltage as the voltages V1 and V2 of the terminals 6 and 7 of the detection resistor R is obtained at the power supply side reference line + Vc and the emitter side terminal of the resistor R5. Can be. Of course, in this case, power is supplied to the charging current detection circuit 9 in the same manner as the battery 3.
Through the terminal 6 of the charging current detection resistor R.

The terminal voltage of the resistor R5 at which the same voltage as the voltages V1 and V2 is generated is detected by the current flowing through the resistor R5. Therefore, the voltage of the resistor R6 through which this current flows is a voltage corresponding to the difference between the voltages V1 and V2. The terminal voltage of the resistor R6 is a voltage value with the ground GND side as a reference. That is, the emitter follower 12 at this time converts the detection voltage into a voltage value based on the ground GND by the resistor R6 connected to the collector. At this time, the detection voltage is extracted as a voltage value according to the ratio of the resistance values of the resistors R5 and R6. This becomes the output voltage Vo of the charging current detection circuit 9 and is output to the A / D conversion circuit 5. At this time, the variation of the detection voltage is determined by the variation of the two resistance values R5 and R6. In addition, the resistances R5, R6
At the same time, as a result, the variation in the detection voltage can be suppressed to a degree that is slightly added to the variation in the resistance R5, and the variation in the detection current value can be suppressed to substantially the variation in the resistance value of about one. it can.

Since the circuits other than the charging current detection circuit 9 have the same configuration as the respective circuits shown in FIG. 2, the description of the overall operation of the charging detection is omitted. The emitter follower in this embodiment is a circuit that generates a current value according to the potential difference between the output voltage of the voltage follower of the full feedback amplifier and the voltage of the power supply-side reference line. This current value is converted to a voltage value with reference to the ground side by a resistor on the collector side.

As described above, in this embodiment, the output stage of the emitter follower is fully fed back to the input stage side, and a conversion circuit having a load resistance and an all feedback amplifier are simultaneously configured to form a voltage follower and a conversion circuit. However, the present invention is not limited to such a configuration,
Any circuit may be used as long as it has a resistor for converting a current value corresponding to the potential difference between the output of the voltage follower and the power supply-side reference line into a voltage value based on the ground side.

[0015]

As can be understood from the above description, according to the present invention, a voltage follower in which a reference line on the power supply side is connected to the first terminal on the upstream side of the detection resistor is provided. As the output voltage of the follower, the same voltage value as that of the second terminal on the downstream side of the detection resistor of the charging current value is obtained, and further, a voltage equal to the voltage of both terminals of the detection resistor is obtained. Then, since the equal voltage is converted by the conversion circuit into a voltage with respect to the ground side, the voltage of the detection resistor can be obtained as a detection voltage substantially as it is or at a predetermined ratio. In addition, the conversion circuit having the resistance in this case usually requires only one or at most about two resistance circuits.
Variations in the detected charging current for each product due to variations in resistance can be suppressed. As a result, a variation in the detected charging current for each product can be suppressed, and a storage battery charging circuit and a battery charging device such as a titanium-ion storage battery that can ensure proper charging can be realized.

[Brief description of the drawings]

FIG. 1 is a circuit diagram mainly showing a charging current detection circuit of one embodiment to which a battery charging circuit of the present invention is applied.

FIG. 2 is a block diagram of such a conventional battery charging circuit.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Control circuit, 2 ... Charge current supply circuit, 3 ... Storage battery, 4, 9 ... Charge current detection circuit, 5 ... A / D conversion circuit, 6,7 ... Terminal, 8,10 ... Battery charger, 11 ... Difference Dynamic amplifier circuit, 12: emitter follower, Q1 to Q7: transistor.

Claims (4)

[Claims] 1. A charge current supply circuit for supplying a predetermined current to a storage battery via a resistor for detecting a charge current value, and a charge current detection circuit, wherein the detection circuit comprises a charge current supply circuit for the resistor. A voltage follower having a power supply side reference line connected to a first terminal on the power supply side, receiving power supply and operating, and an input terminal connected to a second terminal on the storage battery side of the resistor; and A conversion circuit having a resistor for receiving a current value corresponding to a potential difference from an output of the voltage follower and converting the current value into a voltage signal based on a ground-side reference line. 2. The voltage follower according to claim 1, wherein the voltage follower has a differential amplifier circuit receiving a signal corresponding to a voltage signal from the second terminal at one input, and a reference line on the power supply side receiving an output of the differential amplifier circuit. The output of the emitter follower is fully fed back to the other input of the differential amplifier, and the conversion circuit includes the emitter follower, its collector side, and the ground side reference line. 3. The storage battery charging circuit according to claim 2, wherein the storage battery charging circuit is formed by a resistor that converts the voltage signal and that is provided between the two. 3. A charging current supply circuit for supplying a predetermined current to a storage battery through a resistor for detecting a charging current value, a charging current detection circuit, and a detection voltage signal output from the detection circuit.
An A / D conversion circuit for performing A / D conversion, and a control circuit that receives the digital value A / D converted by the A / D conversion circuit and controls the charging current supply circuit to stop operation. A detection circuit is connected to a first terminal on the charging current supply circuit side of the resistor, a reference line on a power supply side is connected to the power supply, operates and receives an input terminal on a second terminal of the resistor on the storage battery side. And a current follower connected to the voltage follower, and a current value corresponding to a potential difference between the reference line and the output of the voltage follower, and converted into a voltage signal based on a ground-side reference line to generate the detection voltage signal. A battery charger comprising a conversion circuit having resistance. 4. The voltage follower includes: a differential amplifier circuit receiving a signal corresponding to a voltage signal from the second terminal at one input; and a reference line on the power supply side receiving an output of the differential amplifier circuit. The output of the emitter follower is fully fed back to the other input of the differential amplifier, and the conversion circuit includes the emitter follower, its collector side, and the ground side reference line. The battery charging device according to claim 3, wherein the battery charging device is formed by a resistor provided between the first and second terminals for converting the voltage signal.