Thermally limited battery protection and charging circuit

• US 6,771,051 B2
• Filed: 06/29/2002
• Issued: 08/03/2004
• Est. Priority Date: 06/29/2002
• Status: Active Grant

• Current Assignee: Motorola Solutions, Inc.
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Herrmann, John E., Geren, Michael D., Demuro, David M., Boyer, Roger L., Oglesbee, John W.
• Primary Examiner(s): Tibbits, Pia
• Application Number:
  US10/185,095
• Publication Number:
  US 20040095097A1
• Time in Patent Office: 766 Days
• Field of Search: 320/150, 320/153, 323/266, 323/273, 323/274, 323/279, 323/282, 323/284, 323/285, 361/18, 361/90, 361/93.8, 361/103, 327/524, 340/3.1, 340/3.9
• US Class Current: 320/150
• CPC Class Codes: H02J 7/00304 Overcurrent protection
• CPC Class Codes: H02J 7/00309 Overheat or overtemperature protection

Abstract

This invention includes a thermally stable, low-cost charging circuit for rechargeable batteries. The circuit includes a thermal control circuit that employs a temperature dependent component such as a thermistor or positive temperature coefficient device. The temperature dependent device is thermally coupled to a charging pass element, which is typically a power transistor. When the transistor enters a danger zone, which is a region of operation characterized by elevated power dissipation in the pass element, the thermal control circuit is actuated to regulate the pass element in a constant power mode until the circuit exits the danger zone.

Claims

1. A charging circuit, the circuit comprising:

a. an interface for coupling to a power source;

b. an interface for coupling to a rechargeable battery cell;

c. at least one pass element having a control terminal, the at least one element coupled serially between the interface for coupling to a power source and the interface for coupling to a rechargeable battery cell;

d. a maximum current limiting circuit coupled serially between the interface for coupling to a power source and the interface for coupling to a rechargeable battery cell;

e. a control circuit coupled to the control terminal of the at least one pass element; and

f. a thermal control circuit, wherein the thermal control circuit is thermally coupled to the pass element and electrically coupled to the control circuit.

2. The circuit of claim 1, further comprising a voltage termination circuit coupled to the control circuit.

3. The circuit of claim 2, further comprising a protection circuit coupled in parallel across the interface for coupling to a rechargeable battery cell.

4. The circuit of claim 3, wherein the thermal control circuit is electrically coupled to the pass element.

5. The circuit of claim 2, wherein the thermal control circuit comprises:

a. a positive temperature coefficient device disposed in close physical proximity to the at least one pass element; and

b. a means of altering current in the thermal control circuit, wherein the means of altering the current is responsive to changes in temperature of the positive temperature coefficient device.

6. The circuit of claim 5, wherein the means of altering current in the thermal control circuit alters current in the control circuit, thereby altering the impedance of the at least one pass element.

7. The circuit of claim 6, wherein the control circuit comprises a bipolar junction transistor having an emitter, further wherein the means for altering current in the thermal control circuit is coupled to the emitter.

8. The circuit of claim 2, wherein the thermal control circuit comprises:

a. a thermistor disposed in close physical proximity to the at least one pass element; and

b. at least one comparator coupled to the thermistor, the at least one comparator capable of generating at least one control signal, the at least one control signal corresponding to a predetermined temperature of the thermistor;

wherein the control circuit alters the impedance of the at least one pass element in response to the at least one control signal.

9. The circuit of claim 8, further comprising at least one reference voltage and at least one hysteresis means, wherein the at least one reference voltage corresponds to a predetermined temperature threshold of the at least one pass element.

10. The circuit of claim 9, comprising:

a. at least a first comparator coupled to the thermistor;

b. at least a second comparator coupled to the thermistor;

c. at least a first reference voltage coupled to the at least a first comparator;

d. at least a second reference voltage coupled to the at least a second comparator;

e. at least a first hysteresis means coupled to the at least a first comparator; and

f. at least a second hysteresis means coupled to the at least a second comparator;

wherein the at least a first hysteresis means establishes a first temperature threshold and a second temperature threshold, and the at least a second hysteresis means establishes a third temperature threshold and a fourth temperature threshold.

11. The circuit of claim 10, wherein:

a. the first temperature threshold is less than the second temperature threshold;

b. the second temperature threshold is less than the third temperature threshold; and

c. the fourth temperature threshold is greater than the third temperature threshold.

12. The circuit of claim 11, wherein:

a. the first temperature threshold is between 50°

C. and 75°

C.;

b. the second level is between 75°

C. and 100°

C.;

c. the third level is between 85°

C. and 115°

C.; and

d. the fourth level is between 85°

C. and 130°

C.

13. The circuit of claim 12, wherein:

a. the first temperature threshold is 75°

C.;

b. the second temperature threshold is 85°

C.

c. the third temperature threshold is 100°

C.; and

d. the fourth temperature threshold is 110°

C.