Battery cell charging system having voltage threshold and bleeder current generating circuits

• US 6,285,161 B1
• Filed: 09/11/2000
• Issued: 09/04/2001
• Est. Priority Date: 09/11/2000
• Status: Expired due to Term

• Current Assignee: O2 Micro International Limited (O2 Micro Incorporated)
• Original Assignee: O2 Micro International Limited (O2 Micro Incorporated)
• Inventors: Popescu, Serban-Mihai
• Primary Examiner(s): Tso, Edward H.
• Application Number:
  US09/658,747
• Time in Patent Office: 358 Days
• Field of Search: 320/116, 320/117, 320/118, 320/119, 320/162
• US Class Current: 320/118
• CPC Class Codes: H01M 10/44 Methods for charging or discharging circuits for charging H02J7/00
• CPC Class Codes: H02J 7/0016 using shunting, discharge or bypass circuits
• CPC Class Codes: Y02E 60/10 Energy storage using batteries

Abstract

A balanced battery cell charging circuit is provided. The circuit includes a comparator for comparing the voltage of a battery cell to a predetermined threshold voltage. If the cell voltage exceeds the threshold value, a bleeder current is generated. In one preferred embodiment, the bleeder current is subtracted from the charging current. In another embodiment, the bleeder current is multiplied, and the multiplied bleeder current is subtracted from a total charging current supplied to the cell. To control the charger circuit, current feedback is provided by monitoring the bleeder current generated against a maximum bleeder current, and adjusting the charging current accordingly. The topology of the present invention provides active cell balancing between cells of a battery, and low total power dissipation of the circuit.

Claims

1. A battery cell charging circuit, comprising:

a charger circuit supplying a charging current to said battery cell;

a comparator for comparing a battery cell voltage to a predetermined threshold cell voltage, said comparator controlling the generation of a bleeder current based on the amount said battery cell voltage exceeds said predetermined threshold, said bleeder being subtracted from said charging current supplied to said battery cell.

2. A circuit as claimed in claim 1, wherein said comparator comprising a transconductance amplifier comparing said battery cell voltage to a predetermined threshold voltage and controlling the generating said bleeder current as a function of g_m.

3. A circuit as claimed in claim 1, further comprising a second comparator for comparing said bleeder current to a maximum allowable bleeder current value, and generating a feedback signal to said charger circuit to control the value of said charging current.

4. A circuit as claimed in claim 3, further comprising a constant current source generating said maximum allowable bleeder current value.

5. A circuit as claimed in claim 3, further comprising a programmable current source for programmably generating said maximum allowable bleeder current value.

6. A circuit as claimed in claim 1, further comprising a constant voltage source for generating said threshold cell voltage.

7. A circuit as claimed in claim 1, further comprising a programmable voltage source for generating said predetermined threshold cell voltage.

8. A circuit as claimed in claim 1, wherein said battery comprises a lithium ion battery, said charging current is approximately 2 Amps, and said predetermined maximum cell voltage is approximately 4.200 Volts.

9. A circuit as claimed in claim 1, wherein said bleeder current is equal to about 50 μ

A., and said multiple is equal to about 1000.

10. A method for charging a battery, comprising the steps of:

supplying a charging current to a battery cell;

comparing the battery cell voltage to a threshold cell voltage;

generating a bleeder current if said cell voltage exceeds said threshold cell voltage; and

subtracting said bleeder current from said charging current.

11. A method as claimed in claim 10, wherein said step of generating said bleeder current further comprises the step of multiplying said bleeder current by a predetermined constant and subtracting the multiplied bleeder current from said charging current.

12. A method as claimed in claim 10, further comprising the steps of:

comparing said bleeder current to a maximum allowable bleeder current value; and

adjusting the value of said charging current if said bleeder current equals or exceeds said maximum allowable bleeder current value.

13. A method as claimed in claim 12, further comprising the step of:

setting the bleeder current to equal the maximum allowable bleeder current value when said bleeder current equals or exceeds said maximum allowable bleeder current value, and subtracting said maximum allowable bleeder current from said charging current.

14. A battery cell charging circuit, comprising a battery including a plurality of cells;

a charger circuit for supplying a charging current to each said cell;

a first comparator for comparing a battery cell voltage to a predetermined threshold cell voltage, said comparator controlling the generating a bleeder current proportional to the amount said battery cell voltage exceeds said predetermined threshold;

a current mirror for generating said bleeder current and a multiple of said bleeder current, said multiple of said bleeder being subtracted from said charging current supplied to said battery cell; and

a second comparator for comparing said bleeder current to a maximum allowable bleeder current value, and generating a feedback signal to said charger circuit to control the value of said charging current.

15. A circuit as claimed in claim 14, wherein said comparator comprising a transconductance amplifier comparing said battery cell voltage to a predetermined threshold voltage and controlling the generating said bleeder current as a function of g_m.

16. A circuit as claimed in claim 14, further comprising a constant current source generating said maximum allowable bleeder current value.

17. A circuit as claimed in claim 14, further comprising a programmable current source for programmably generating said maximum allowable bleeder current value.

18. A circuit as claimed in claim 14, further comprising a constant voltage source for generating said predetermined threshold cell voltage.

19. A circuit as claimed in claim 14, further comprising a programmable voltage source for generating said predetermined threshold cell voltage.

20. A circuit as claimed in claim 14, wherein said battery comprises a lithium ion battery, said charging current is approximately 2 Amps, and said predetermined maximum cell voltage is approximately 4.200 Volts.

21. A circuit as claimed in claim 14, wherein said bleeder current is equal to about 50 μ

A., and said multiple is equal to about 1000.