Pulse charging circuit and method

• US 6,707,272 B1
• Filed: 11/22/2002
• Issued: 03/16/2004
• Est. Priority Date: 11/22/2002
• Status: Active Grant

• Current Assignee: Google Technology Holdings LLC (Alphabet Inc.)
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Thandiwe, Iilonga
• Primary Examiner(s): Tso, Edward H
• Application Number:
  US10/302,479
• Time in Patent Office: 480 Days
• Field of Search: 320/125, 320/128, 320/137, 320/139, 320/141, 320/160
• US Class Current: 320/141
• CPC Class Codes: H01M 10/44 Methods for charging or discharging circuits for charging H02J7/00
• CPC Class Codes: H02J 7/00711 with introduction of pulses during the charging process
• CPC Class Codes: Y02E 60/10 Energy storage using batteries

Abstract

A circuit and method are disclosed for pulse charging a battery. In this method, the duration of the charging interval of the pulse is governed by the time required to reach an upper threshold voltage. The duration of the non-charging interval is a function of the ionic relaxation of the battery. One preferred embodiment includes a method in which the charging interval is initiated at a voltage that corresponds to the current state of charge of the cell. For example, when the upper threshold is reached, charging is suspended. A microprocessor then determines the state of charge by way of a fuel gauge. If a cell is 70% charged, for instance, an on voltage corresponding to this state of charge is selected. When the cell reaches the on voltage, the charging interval is again initiated. Other alternatives to this method include sensing a slope to determine when ionic relaxation has occurred, and a mathematical approximation of the method.

Claims

1. A method for charging a rechargeable cell, the method comprising the steps of:

a. monitoring stored energy in at least one rechargeable cell;

b. monitoring a voltage across the at least one rechargeable cell;

c. applying a charging current to the at least one rechargeable cell;

d. decoupling the charging current from the a least one rechargeable cell when the voltage across the at least one rechargeable cell reaches a predetermined maximum;

e. determining the amount of stored energy in the at least one rechargeable cell;

f. selecting a criterion based upon the amount of energy stored in the at least one rechargeable cell;

g. waiting until the criterion is met; and

h. coupling the charging current to the at least one rechargeable cell.

2. The method of claim 1, wherein the criterion corresponds to the amount of energy stored in the at least one rechargeable cell.

3. The method of claim 2, wherein the criterion comprises a voltage threshold.

4. The method of claim 3, wherein:

a. when the at least one cell is 60% charged, the voltage threshold is between 88 and 98 percent of the predetermined maximum;

b. when the at least one cell is 70% charged, the voltage threshold is between 92 and 98 percent of the predetermined maximum;

c. when the at least one cell is 80% charged, the voltage threshold is between 94 and 98 percent of the predetermined maximum; and

d. when the at least one cell is 90% charged, the voltage threshold is between 96 and 98 percent of the predetermined maximum.

5. The method of claim 4, wherein charging is terminated when energy stored in the at least one rechargeable cell reaches a predetermined percentage of full capacity.

6. The method of claim 2, wherein the criterion comprises a change in voltage across the at least one rechargeable cell per unit time.

7. The method of claim 6, wherein the change in voltage across the at least one rechargeable cell per unit time is between 2 and 20 millivolts per minute.

8. The method of claim 7, wherein charging is terminated when an event occurs, wherein the event is selected from the group consisting of a pulse charge frequency exceeding a predetermined threshold, energy stored in the at least one rechargeable cell reaching a predetermined percentage of full capacity, a pulse charge on time falling below a predetermined threshold, and expiration of a timer.

9. The method of claim 2, wherein the criterion comprises a change in the change in voltage across the at least one rechargeable cell per unit time.

10. The method of claim 3, 6 or 9, further comprising the step of providing a circuit comprising:

a. a fuel gauge comprising a microprocessor core and a memory; and

b. at least one transistor.

11. A method for charging a rechargeable cell, the method comprising the steps of:

a. monitoring a voltage across the at least one rechargeable cell;

b. applying a charging current to the at least one rechargeable cell;

c. measuring the time that the charging current is applied to the at least one rechargeable cell;

d. decoupling the charging current from the a least one rechargeable cell when the voltage across the at least one rechargeable cell reaches a predetermined maximum;

e. dividing a constant by the time that the charging current is applied to the at least one rechargeable cell to determine a wait time;

f. waiting for the wait time; and

g. coupling the charging current to the at least one rechargeable cell.

12. The circuit of claim 11, wherein the constant is between 200 and 300.

13. The method of claim 12, wherein charging is terminated when an event occurs, wherein the event is selected from the group consisting a pulse charge off-time exceeding a predetermined threshold, energy stored in the at least one rechargeable cell reaching a predetermined percentage of full capacity, a pulse charge on time falling below a predetermined threshold, and expiration of a timer.