Battery fuel gauge circuit

• US 7,531,989 B2
• Filed: 05/09/2006
• Issued: 05/12/2009
• Est. Priority Date: 11/02/2005
• Status: Active Grant

• Current Assignee: O2 Micro International Limited (O2 Micro Incorporated)
• Original Assignee: O2 Micro International Limited (O2 Micro Incorporated)
• Inventors: Maireanu, Stefan
• Primary Examiner(s): Ullah; Akm E
• Assistant Examiner(s): WILLIAMS, ARUN C
• Application Number:
  US11/430,442
• Publication Number:
  US 20070096697A1
• Time in Patent Office: 1,099 Days
• Field of Search: 320/150, 320/152, 320/132, 320/134, 320/136, 320/153, 324/432, 324/434
• US Class Current: 320/150
• CPC Class Codes: G01R 19/16542 for batteries charge condition monitoring in G01R31/36
• CPC Class Codes: G01R 31/3648 comprising digital calculation means, e.g. for performing an algorithm
• CPC Class Codes: G01R 31/374 with means for correcting the measurement for temperature or ageing
• CPC Class Codes: G01R 31/3842 combining voltage and current measurements

Abstract

The present invention is a battery fuel gauge circuit for measuring the capacity of a battery pack. The battery fuel gauge circuit includes an amplifier circuit, a correction circuit, a plurality of comparators, and a multiplexer. The amplifier circuit can sense a discharge current flowing through a sense resistor and a variable temperature from the battery pack and generate a first and a second voltage signals, which are corrected by the correction circuit and compared with a reference voltage by the plurality of comparators. After correction and comparison, the multiplexer can transmit the compared signals to an external indicating circuit that controls the display of the capacity of the battery pack.

Claims

1. A battery fuel gauge circuit for measuring a capacity of a rechargeable battery pack, the battery pack being capable of generating a battery voltage and a discharge current, the battery pack having a temperature, the battery fuel gauge circuit comprising:

an amplifier circuit capable of sensing the discharge current and the temperature of the battery pack and generating a first and a second voltage signals based upon the discharge current and the temperature;

a correction circuit capable of receiving the first and the second voltage signals and generating a plurality of voltages;

a plurality of comparators capable of receiving a reference voltage based upon the battery voltage, the plurality of comparator comparing the reference voltage with the plurality of voltages from the correction circuit and generating a plurality of digital signals; and

a multiplexer capable of receiving the plurality of digital signals from the plurality of comparators, and controlling an external indicating circuit to indicate the capacity of the battery pack based upon the plurality of digital signals.

2. The battery fuel gauge circuit of claim 1, further comprising a sense resistor coupled to the battery pack, the sense resistor upon which the discharge current flowing through, and the sense resistor having a resistance.

3. The battery fuel gauge circuit of claim 2, wherein the amplifier circuit further comprising:

a first amplifier capable of receiving a voltage across the sense resistor, amplifying the voltage, and generating the first voltage signal, the voltage across the sense resistor being equal to the discharge current multiplied by the resistance of the sense resistor; and

a second amplifier capable of receiving a voltage based upon the temperature of the battery pack, amplifying the voltage and generating the second voltage signal.

4. The battery fuel gauge circuit of claim 1, wherein the correction circuit further comprising:

a first plurality of coefficient generators capable of receiving the first voltage signal from the amplifier circuit and generating a first plurality of products through multiplying the first voltage signal by a first plurality of coefficients;

a second plurality of coefficient generators capable of receiving the second voltage signal from the amplifier circuit and generating a second plurality of products through multiplying the second voltage signal by a second plurality of coefficients;

a third plurality of coefficient generators capable of receiving a reference voltage and generating a third plurality of products through multiplying the reference voltage by a third plurality of coefficients; and

a plurality of adders, each of the plurality of adders being capable of receiving one product from the first plurality of coefficient generators, one product from the second plurality of coefficient generators, and one product from the third plurality of coefficient generators and summing up the three products to generate a voltage.

5. An integrated circuit for measuring a battery capacity, comprising:

a battery pack capable of generating a discharge current and a battery voltage, the battery pack having a temperature;

a resistor upon which the discharge current flowing through;

a charger capable of charging the battery pack through the resistor;

an amplifier circuit capable of sensing the discharge current and the temperature of the battery pack and generating two voltage signals based upon the discharge current and the temperature;

a correction circuit capable of receiving the two voltage signals from the amplifier circuit and generating a plurality of voltages;

a plurality of comparators receiving a reference voltage based upon the battery voltage, the plurality of comparator comparing the reference voltage with the plurality of voltages from the correction circuit and generating a plurality of digital signals; and

a multiplexer, the multiplexer being capable of receiving the plurality of digital signals from the plurality of comparators, and controlling an external indicating circuit representative of the battery fuel gauge of the battery pack based upon the plurality of digital signals.

6. The integrated circuit of claim 5, wherein battery pack including a plurality of battery cells.

7. The integrated circuit of claim 5, wherein the resistor being a sense resistor.

8. The integrated circuit of claim 5, wherein the amplifier circuit further comprising:

a first amplifier capable of receiving a voltage across the resistor, amplifying the voltage, and generating the first voltage signal, the voltage across the resistor being equal to the discharge current multiplied by the resistance of the resistor; and

a second amplifier capable of receiving a voltage based upon the temperature of the battery pack, amplifying the voltage and generating the second voltage signal.

9. The integrated circuit of claim 5, wherein the correction circuit further comprising:

a first plurality of coefficient generators capable of receiving the first voltage signal from the amplifier circuit and generating a first plurality of products through multiplying the first voltage signal by a first plurality of coefficients;

a second plurality of coefficient generators capable of receiving the second voltage signal from the amplifier circuit and generating a second plurality of products through multiplying the second voltage signal by a second plurality of coefficients;

a third plurality of coefficient generators capable of receiving a reference voltage and generating a third plurality of products through multiplying the reference voltage by a third plurality of coefficients; and

a plurality of adders, each of the plurality of adders being capable of receiving one product from the first plurality of coefficient generators, one product from the second plurality of coefficient generators, and one product from the third plurality of coefficient generators and adding up the three products to generate one of the plurality of voltages.

10. A portable computer comprising:

an input device for taking inputs from an user;

a microcontroller for performing operations based on the inputs from the user;

a power supply for supplying power to the portable computer; and

a battery fuel gauge circuit for measuring a remaining capacity of the power supply, the battery fuel gauge circuit including;

a battery pack capable of generating a discharge current and a battery voltage, the battery pack having a temperature;

a resistor upon which the discharge current flowing through;

a charger capable of charging the battery pack through the resistor;

an amplifier circuit capable of sensing the discharge current and the temperature of the battery pack and generating two voltage signals based upon the discharge current and the temperature;

a correction circuit capable of receiving the two voltage signals from the amplifier circuit and generating a plurality of voltages;

a plurality of comparators receiving a reference voltage based upon the battery voltage, the plurality of comparator comparing the reference voltage with the plurality of voltages from the correction circuit and generating a plurality of digital signals; and

a multiplexer, the multiplexer being capable of receiving the plurality of digital signals from the plurality of comparators, and controlling an external indicating circuit representative of the battery fuel gauge of the battery pack based upon the plurality of digital signals.

11. The portable computer of claim 10, wherein battery pack including a plurality of battery cells.

12. The portable computer of claim 10, wherein the resistor being a sense resistor.

13. The portable computer of claim 10, wherein the amplifier circuit further comprising:

a first amplifier capable of receiving a voltage across the resistor, amplifying the voltage, and generating the first voltage signal, the voltage across the resistor being equal to the discharge current multiplied by the resistance of the resistor; and

a second amplifier capable of receiving a voltage based upon the temperature of the battery pack, amplifying the voltage and generating the second voltage signal.

14. The portable computer of claim 10, wherein the correction circuit further comprising:

a first plurality of coefficient generators capable of receiving the first voltage signal from the amplifier circuit and generating a first plurality of products through multiplying the first voltage signal by a first plurality of coefficients;

a second plurality of coefficient generators capable of receiving the second voltage signal from the amplifier circuit and generating a second plurality of products through multiplying the second voltage signal by a second plurality of coefficients;

a third plurality of coefficient generators capable of receiving a reference voltage and generating a third plurality of products through multiplying the reference voltage by a third plurality of coefficients; and

a plurality of adders, each of the plurality of adders being capable of receiving one product from the first plurality of coefficient generators, one product from the second plurality of coefficient generators, and one product from the third plurality of coefficient generators and adding up the three products to generate one of the plurality of voltages.

15. A method for measuring a capacity of a battery pack, comprising the steps of:

a) receiving a battery voltage from the battery pack;

b) generating a sense voltage based upon the battery voltage;

c) generating a temperature voltage indicative of a temperature of the battery pack;

d) receiving the sense voltage and the temperature voltage;

e) generating a plurality of threshold voltages according to the sense voltage and the temperature voltage;

f) comparing the plurality of threshold voltages with a reference voltage, the reference voltage being based upon the battery voltage;

g) generating a plurality of control signals based on results of the comparison; and

h) controlling an external indicating circuit to display the capacity of the battery pack according to the plurality of the control signals.

16. The method of claim 15, wherein the step of b) further comprising:

generating a discharge current based upon the battery voltage; and

converting the discharge current into the sense voltage.

17. The method of claim 15, wherein the step of d) further comprising:

multiplying the sense voltage by a first plurality of coefficients to generate a first plurality of products;

multiplying the voltage based upon the temperature of the battery pack by a second plurality of coefficients to generate a second plurality of products;

multiplying a reference voltage by a third plurality of coefficients to generate a third plurality of products; and

adding up the first plurality of products, the second plurality of products, and the third plurality of products respectively.