CIRCUITS AND METHODS FOR MEASURING A CELL VOLTAGE IN A BATTERY

• US 20130214789A1
• Filed: 08/15/2012
• Published: 08/22/2013
• Est. Priority Date: 12/29/2009
• Status: Active Grant

• Current Assignee: O2 Micro International Limited (O2 Micro Incorporated)
• Original Assignee: Guoxing Li, Xiaohu Tang
• Inventors: TANG, Xiaohu, LI, Guoxing
• Granted Patent: US 9,291,680 B2
• Time in Patent Office: Days
• US Class Current: 324/431
• CPC Class Codes: G01R 19/16542 for batteries charge condition monitoring in G01R31/36
• CPC Class Codes: G01R 31/3644 Constructional arrangements
• CPC Class Codes: G01R 31/382 Arrangements for monitoring battery or accumulator variables, e.g. SoC
• CPC Class Codes: G01R 31/3835 involving only voltage measurements
• CPC Class Codes: G01R 31/396 Acquisition or processing of data for testing or for monitoring individual cells or groups of cells within a battery
• CPC Class Codes: H01M 6/5044 Cells or batteries structurally combined with cell condition indicating means

Abstract

A circuit measures a cell voltage of a cell in a battery. The circuit includes a measurement circuit and a current generator. The measurement circuit includes a first terminal coupled to a positive terminal of a cell via a first resistive element and includes a second terminal coupled to a negative terminal of the cell via a second resistive element. The measurement circuit consumes a first current. The current generator generates a first compensation current according to the first current. The first current and the first compensation current flow from the positive terminal through the first resistive element to the first terminal. The measurement circuit calculates the cell voltage according to a first voltage difference between the first and second terminals when the first compensation current is disabled and according to a second voltage difference between the first and second terminals when the first compensation current is enabled.

Claims

1. A circuit for measuring a cell voltage of a cell in a battery, said circuit comprising:

a measurement circuit that comprises a first terminal coupled to a positive terminal of said cell via a first resistive element and comprises a second terminal coupled to a negative terminal of said cell via a second resistive element, wherein said measurement circuit consumes a first current flowing from said positive terminal through said first resistive element to said first terminal and consumes a second current flowing from said negative terminal through said second resistive element to said second terminal; and

a current generator, coupled to said battery, that generates a first compensation current according to said first current, wherein said first compensation current flows from said positive terminal through said first resistive element to said first terminal,

wherein said measurement circuit receives a first voltage difference between said first terminal and said second terminal when said first compensation current is disabled, and receives a second voltage difference between said first terminal and said second terminal when said first compensation current is enabled, and wherein said measurement circuit calculates said cell voltage according to said first voltage difference and said second voltage difference.

2. The circuit of claim 1, wherein a first voltage drop is generated across said first resistive element when said first compensation current is disabled, wherein a second voltage drop is generated across said first resistive element when said first compensation current is enabled, and

wherein said measurement circuit further calculates said cell voltage according to a proportion of said second voltage drop to said first voltage drop.

3. The circuit of claim 1, wherein said first compensation current is proportional to said first current.

4. The circuit of claim 1, wherein said measurement circuit includes a level shifter that provides a first shifted voltage difference indicative of said first voltage difference if said first compensation current is disabled, and provides a second shifted voltage difference indicative of said second voltage difference if said first compensation current is enabled.

5. The circuit of claim 4, wherein said measurement circuit calculates said cell voltage by calculating a third voltage proportional to said first shifted voltage difference, and subtracting said second shifted voltage difference from said third voltage.

6. The circuit of claim 4, wherein said level shifter comprises an amplifier that generates a sense current according to said first current and receives a predetermined reference voltage, and wherein said current generator generates said first compensation current according to said sense current.

7. The circuit of claim 1, wherein said measurement circuit further measures a third voltage difference when said first terminal and said second terminal shorts and said first compensation current is disabled, and measures a fourth voltage difference when said first terminal and said second terminal shorts and said first compensation current is enabled, and wherein said measurement circuit further calculates said cell voltage according to said third and fourth voltage differences.

8. The circuit of claim 1, wherein said current generator further generates a second compensation current according to said second current, wherein said second compensation current flows from said second terminal through said second resistive element to said negative terminal.

9. The circuit of claim 1, wherein said measurement circuit comprises an analog-to-digital converter for converting signals indicative of said first and second voltage differences into digital signals, and wherein said measurement circuit calculates said cell voltage based on said digital signals.

10. A system comprising:

a plurality of cells;

a plurality of resistors coupled to said cells;

a measurement circuit that comprises a first terminal coupled to a positive terminal of a cell of said cells via a first resistor of said resistors and comprises a second terminal coupled to a negative terminal of said cell via a second resistor of said resistors, and that consumes a first current flowing from said positive terminal through said first resistor to said first terminal and consumes a second current flowing from said negative terminal through said second resistor to said second terminal; and

a current generator, coupled to said cells, that generates a first compensation current according to said first current, wherein said first compensation current flows from said positive terminal through said first resistor to said first terminal,

wherein a first voltage drop is generated across said first resistor when said first compensation current is disabled, wherein a second voltage drop is generated across said first resistor when said first compensation current is enabled, and wherein said measurement circuit calculates said cell voltage according to said first voltage drop and said second voltage drop.

11. The system of claim 10, wherein said first compensation current is proportional to said first current.

12. The system of claim 10, wherein said measurement circuit receives a first voltage difference between said cell voltage and said first voltage drop, and receives a second voltage difference between said cell voltage and said second voltage drop, and wherein said measurement circuit calculates said cell voltage according to said first and second voltage differences.

13. The system of claim 12, wherein said measurement circuit includes a level shifter that provides a first shifted voltage difference indicative of said first voltage difference if said first compensation current is disabled, and provides a second shifted voltage difference indicative of said second voltage difference if said first compensation current is enabled.

14. The system of claim 13, wherein said measurement circuit calculates said cell voltage by calculating a third voltage proportional to said first shifted voltage difference, and subtracting said second shifted voltage difference from said third voltage.

15. The system of claim 10, wherein said current generator further generates a second compensation current according to said second current, wherein said second compensation current flows from said second terminal through said second resistive element to said negative terminal.

16. A method for measuring a cell voltage of a cell in a battery, said method comprising:

consuming a first current flowing from a positive terminal of said cell through a first resistive element to a first terminal and consuming a second current flowing from a negative terminal of said cell through a second resistive element to a second terminal;

generating a first compensation current according to said first current, wherein said first compensation current flows from said positive terminal through said first resistive element to said first terminal;

receiving a first voltage difference between said first terminal and said second terminal when said first compensation current is disabled, and receiving a second voltage difference between said first terminal and said second terminal when said first compensation current is enabled; and

calculating said cell voltage according to said first voltage difference and said second voltage difference.

17. The method of claim 16, wherein a first voltage drop across said first resistive element is generated when said first compensation current is disabled, and a second voltage drop across said first resistive element is generated when said first compensation current is enabled, wherein said method further comprises calculating said cell voltage according to a proportion of said second voltage drop to said first voltage drop.

18. The method of claim 17, wherein said first voltage difference indicates a first difference between said cell voltage and said first voltage drop, and wherein said second voltage difference indicates a second difference between said cell voltage and said second voltage drop.

19. The method of claim 16, further comprising:

providing a first shifted voltage difference indicating said first voltage difference and a second shifted voltage difference indicating said second voltage difference.

20. The method of claim 19, further comprising:

calculating a third voltage proportional to said first shifted voltage difference; and

subtracting said second shifted voltage difference from said third voltage.