Circuit for measuring discharging and charging current of a battery providing offset/drift voltage for correcting amplifier output

• US 5,254,951 A
• Filed: 05/27/1992
• Issued: 10/19/1993
• Est. Priority Date: 05/29/1991
• Status: Expired due to Term

• Current Assignee: Fujitsu Limited
• Original Assignee: Fujitsu Limited
• Inventors: Goto, Seiji, Tsunoda, Kazuaki, Murayama, Yukio
• Primary Examiner(s): Strecker, Gerard R.
• Assistant Examiner(s): DO, DIEP N
• Application Number:
  US07/888,785
• Time in Patent Office: 510 Days
• Field of Search: 324/426, 324/429, 324/433, 324/434, 340/636, 320/48
• US Class Current: 324/426
• CPC Class Codes: G01R 31/382 Arrangements for monitoring battery or accumulator variables, e.g. SoC

Abstract

A current measuring circuit for measuring discharging current and charging current of a battery, which is selectively connected to a load and a charger. The current measuring circuit comprises a resistor connected in series with the battery having a sufficiently low resistance value as not to substantially restrain the output current from the battery and a differential amplifier for amplifying a potential difference between both ends of the resistor. By providing a switch for short-circuiting one input terminal and the other input terminal of the differential amplifier, an offset/drift voltage of the differential amplifier can be obtained. This offset/drift voltage is used for correcting the output voltage from the differential amplifier at the time of current measurement and, thereby, the discharging current and charging current of the battery can be measured accurately.

Claims

1. A current measuring circuit for measuring discharging current and charging current of a battery comprising:

a first battery adapted to be selectively connected to a load and a charger;

a resistor connected in series with the first battery having a sufficiently low resistance value as not to substantially restrain an output current from the first battery;

a first differential amplifier, which amplifies a potential difference across the resistor, the first differential amplifier comprising

a first operational amplifier,

a first resistor connected between one end of the resistor and one input terminal of the first operational amplifier,

a second resistor connected between the on input terminal and the output terminal of the first operational amplifier,

a third resistor connected between the other end of the resistor and the other input terminal of the first operational amplifier, and

a fourth resistor connected between the other input terminal of the first operational amplifier and ground, the resistance value of the first resistor being equal to the resistance value of the third resistor and the resistance value of the second resistor being equal to the resistance value of the fourth resistor;

means for short-circuiting the one input terminal and the other input terminal of the first operational amplifier; and

calculating means for calculating difference between a first voltage outputted by the first operational amplifier when the one input terminal and the other input terminal of the first operational amplifier are short-circuited and a second voltage outputted by the first operational amplifier when the one input terminal of the first operational amplifier is connected with the one end of the resistor and the other input terminal of the first operational amplifier is connected with the other end of the resistor .

2. The current measuring circuit according to claim 1, further comprising a second differential amplifier, which amplifies the potential difference across the resistor, the second differential amplifier comprising:

a second operational amplifier;

a seventh resistor connected between the other end of the resistor and one input terminal of the second operational amplifier;

an eighth resistor connected between the one input terminal and the output terminal of the second operational amplifier;

a ninth resistor connected between the one end of the resistor and the other input terminal of the second operational amplifier; and

a tenth resistor connected between the other input terminal of the second operational amplifier and ground, the resistance value of the seventh resistor being equal to the resistance value of the ninth resistor and the resistance value of the eighth resistor being equal to the resistance value of the tenth resistor.

3. The current measuring circuit according to claim 1, further comprising a second battery connected in series with the resistor at the one end of the resistor, wherein the positive power-supply terminal of the first operational amplifier is connected with the positive voltage output terminal of the second battery.

4. The current measuring circuit according to claim 1, further comprising a second battery connected in series with the resistor at the one end of the resistor, wherein the positive power-supply terminals of the first operational amplifier and the second operational amplifier are connected with the positive voltage output terminal of the second battery and the negative power-supply terminals of the first operational amplifier and the second operational amplifier are grounded.

5. The current measuring circuit according to claim 1, wherein the resistance value of the resistor is below 0.1Ω

.

6. A current measuring circuit for measuring discharging current and charging current of a battery comprising:

a first battery adapted to be selectively connected to a load and a charger;

a resistor connected in series with the first battery having a sufficiently low resistance value as not to substantially restrain an output current from the first battery; and

a first differential amplifier, which amplifies a potential difference across the resistor, the first differential amplifier comprising;

a first operational amplifier,

a first resistor connected between one end of the resistor and one input terminal of the first operational amplifier,

a second resistor connected between the one input terminal and the output terminal of the first operational amplifier,

a third resistor connected between the other end of the resistor and the other input terminal of the first operational amplifier,

a fourth resistor connected between the other input terminal of the first operational amplifier and ground, the resistance value of the first resistor being equal to the resistance value of the third resistor and the resistance value of the second resistor being equal to the resistance value of the fourth resistor,

a fifth resistor connected in parallel with the second resistor,

a first switch connected in series with the fifth resistor and in parallel with the second resistor,

a sixth resistor connected in parallel with the fourth resistor, and

a second switch connected in series with the sixth resistor and in parallel with the fourth resistor.

7. A current measuring circuit for measuring discharging current of a battery comprising:

a battery connected to a load;

a resistor connected in series with the battery having a sufficiently low resistance value as not to substantially restrain output current from the battery;

a differential amplifier, which amplifies a potential difference across the resistor, the differential amplifier comprising;

an operational amplifier,

a first resistor connected between one end of the resistor and one input terminal of the first operational amplifier,

a second resistor connected between the one input terminal and the output terminal of the operational amplifier,

a third resistor connected between the other end of the resistor and the other input terminal of the operational amplifier, and

a fourth resistor connected between the other input terminal of the operational amplifier and ground, the resistance value of the first resistor being equal to the resistance value of the third resistor and the resistance value of the second resistor being equal to the resistance value of the fourth resistor;

means for short-circuiting the one input terminal and the other input terminal of the operational amplifier; and

calculating means for calculating differential between a first voltage outputted by the operational amplifier when the one input terminal and the other input terminal of the operational amplifier are short-circuited and a second voltage outputted by the operational amplifier when the one input terminal of the operational amplifier is connected with the one end of said resistor and the other input terminal of the operational amplifier is connected with the other end of the resistor.

8. A current measuring circuit for measuring discharging current of a battery comprising:

a battery connected to a load;

a resistor connected in series with the battery having a sufficiently low resistance value as not to substantially restrain output current from the battery; and

a differential amplifier, which amplifies a pontential difference across the resistor, the differential amplifier comprising;

an operational amplifier,

a first resistor connected between one end of the resistor and one input terminal of the operational amplifier,

a second resitor connected between the one input terminal and the output terminal of the operational amplifier,

a third resistor connected between the other end of the resistor and the other input terminal of the operational amplifier,

a fourth resistor connected between the other input terminal of the operational amplifier and ground, the resistance value of the first resistor being equal to the resistance value of the third resistor and the resistance value of the second resistor being equal to the resistance value of the fourth resistor,

a fifth resistor connected in parallel with the second resistor,

a first switch connected in series with the fifth resistor and in parallel with the second resistor,

a sixth resistor connected in parallel with the fourth resistor, and

a second switch connected in series with the sixth resistor and in parallel with the fourth resistor.

9. A current measuring circuit for measuring discharging current and charging current of a battery, comprising:

a first battery adapted to be selectively connected to a load and a charge, wherein the first battery supplies an output current when connected to the load and receives current when connected to the charger;

a resistor connected in series with the first battery having a sufficiently low resistance value so that the output current from the first battery is not substantially restrained;

a differential amplifier, which amplifies a potential difference across the resistor, the differential amplifier comprising;

an operational amplifier having a first input terminal, a second input terminal and an output terminal,

a first resistor connected between one end of the resistor and the first input terminal of the operational amplifier,

a second resistor connected between the first input terminal and the output terminal of the operational amplifier,

a third resistor connected between other end of the resistor and the second input terminal of the operational amplifier, the third resistor having a resistance value equal to resistance value of the first resistor,

a fourth resistor connected between the second input terminal of the operational amplifier and ground, the fourth resistor having a resistance value equal to the resistance value of the second resistor,

a fifth resistor connected in parallel with the second resistor,

a first switch connected in series with the fifth resistor and in parallel with the second resistor,

a sixth resistor connected in parallel with the fourth resistor, and

a second switch connected in series with the sixth resistor and in parallel with the fourth resistor;

means for controlling the first and second switches to increase or decrease the amplification factor of the differential amplifier;

means for short-circuiting the first input terminal and the second input terminal of the operational amplifier, and

calculating means for calculating difference between a first voltage outputted by the operational amplifier when the first input terminal and the second input terminal of the operational amplifier are not short circuited and a second voltage outputted by the operational amplifier when the first input terminal of the operational amplifier is connected with the one end of the resistor and the second input terminal of the operational amplifier is connected with the other end of the resistor.

10. The current measuring circuit according to claim 9, further comprising a second battery connected in series with the resistor at the one end of the resistor, wherein the positive power-supply terminal of the first operational amplifier is connected with the positive voltage output terminal of the second battery and the negative power-supply terminal of the first operational amplifier is grounded.

11. The current measuring circuit according to claim 9, wherein the resistance value of the resistor is below 0.1Ω

.

12. A current measuring circuit for measuring discharging current and charging current of a battery comprising:

a first battery adapted to be selectively connected to a load and a charger, wherein the first battery supplies an output current when connected to the load and receives current when connected to the charger;

a resistor connected in series with the first battery having a sufficiently low resistance value so that the output current of the first battery is not substantially restrained;

a first differential amplifier, which amplifies a potential difference across the resistor, the first differential amplifier comprising;

a first operational amplifier having a first terminal,

a second terminal and an output terminal,

a first resistor connected between one end of the resistor and the first input terminal of the first operational amplifier,

a second resistor connected between the first input terminal and the output terminal of the first operational amplifier,

a third resistor connected between the other end of the resistor and the second input terminal of the first operational amplifier, the third resistor having a resistance value equal to resistance value of the first transistor,

a fourth resistor connected between the second input terminal of the first operational amplifier and ground, the fourth resistor having a resistance value equal to the resistance value of the second resistor,

a fifth resistor connected in parallel with the second resistor,

a first switch connected in series with the fifth resistor and in parallel with the second resistor,

a sixth resistor connected in parallel with the fourth resistor, and

a second switch connected in series with the sixth resistor and in parallel with the fourth resistor;

a second operational amplifier, which amplifies the potential difference across the resistor, the second differential amplifier comprising;

a second operational amplifier,

a seventh resistor connected between the other end of the resistor and one input terminal of the second operational amplifier,

an eighth resistor connected between the one input terminal and output terminal of the second operational amplifier,

a ninth resistor connected between the one end of the resistor and the other input terminal of the second operational amplifier, a ninth resistor having a resistance value equal to resistance value of the seventh resistor,

a tenth resistor connected between the other input terminal of the second operational amplifier and ground, the tenth resistor having a resistance value equal to resistance value of the eighth resistor,

an eleventh resistor connected in parallel with the eighth resistor,

a third switch connected in series with the eleventh resistor and in parallel with the eleventh resistor,

a twelfth resistor connected in parallel with the tenth resistor, and

a fourth switch connected in series with the twelfth resistor and in parallel with the tenth resistor;

means for short-circuiting the first input terminal and the second input terminal of the first operational amplifier, and for short-circuiting the one input terminal and the other input terminal of the second operation amplifier;

means for controlling the first and second switches to decrease or increase amplification factor of the first differential amplifier and for controlling the third and fourth switches to increase or decrease the amplification factor of the second differential amplifier;

calculating means for calculating difference between a first voltage outputted by the first operational amplifier when the first input terminal and the second input terminal of the first operational amplifier are short-circuited and a second voltage outputted from the first operational amplifier when the first input terminal of the first operational amplifier is connected with the one end of the resistor and the second input terminal of the first operational amplifier is connected with the other end of the resistor; and

calculating means for calculating difference between a third voltage outputted by the second operational amplifier when the one input terminal and the other input terminal of the second operational amplifier are short-circuited and a fourth voltage outputted from the second operational amplifier when the other input terminal of the second operational amplifier is connected with the one end of the resistor and the one input terminal of the second operational amplifier is connected with the other end of the resistor.

13. The current measuring circuit according to claim 12, further comprising a second battery connected in series with the resistor at the one end of the resistor, wherein the positive power-supply terminals of the first operational amplifier and the second operational amplifier are connected with the positive voltage output terminal of the second battery and the negative power-supply terminals of the first operational amplifier and the second operational amplifier are grounded.

14. The current measuring circuit according to claim 12, wherein the resistance value of the resistor is below 0.1 Ω

.