Battery charging safety circuit

• US 6,734,652 B1
• Filed: 11/13/2002
• Issued: 05/11/2004
• Est. Priority Date: 05/22/2002
• Status: Expired due to Term

• Current Assignee: National Semiconductor Corporation (Texas Instruments, Inc.)
• Original Assignee: National Semiconductor Corporation (Texas Instruments, Inc.)
• Inventors: Smith, Gregory J.
• Primary Examiner(s): Tso, Ed
• Assistant Examiner(s): TIBBITS, PIA FLORENCE
• Application Number:
  US10/293,062
• Time in Patent Office: 545 Days
• Field of Search: 320/163, 320/134, 320/150, 361/18, 361/21, 361/90, 361/91.1, 307/10.7, 307/46, 307/48, 307/112, 307/113, 307/132.E, 307/132.T
• US Class Current: 320/163
• CPC Class Codes: H02J 7/00302 Overcharge protection
• CPC Class Codes: H02J 7/00304 Overcurrent protection
• CPC Class Codes: H02J 7/00306 Overdischarge protection
• CPC Class Codes: H02J 7/00308 Overvoltage protection
• CPC Class Codes: H02J 7/00309 Overheat or overtemperature protection
• CPC Class Codes: H02J 7/00718 in response to charge current gradient
• CPC Class Codes: H02J 7/04 Regulation of charging current or voltage
• CPC Class Codes: H02J 7/06 using discharge tubes or semiconductor devices

Abstract

A safety circuit monitors a charging signal supplied by a charging circuit for charging a battery. Damage to the battery may occur when the voltage at the input terminal of the battery rises above the safe level for the battery. A voltage drop across a coupling circuit is used to generate an activation signal. The activation signal causes a power amplifier to lower the voltage of the charging signal before the charging signal can drive the inductances associated with the battery input terminal and leads to the point where damage to the battery may occur.

Claims

1. A safety circuit for protecting a cell against an over-voltage condition, comprising:

a first transistor having a control terminal that is coupled to a first node, a first noncontrol terminal that is coupled to a terminal that is arranged for coupling to the cell, and a second noncontrol terminal that is coupled to a second node;

a second transistor having a control terminal that is coupled to a third node, a first noncontrol terminal that is coupled to the second node, and a second noncontrol terminal that is coupled to a low power supply;

a third transistor having a control terminal that is coupled to a fourth node, a first noncontrol terminal that is coupled to the second node, a second noncontrol terminal that is coupled to the third node; and

a fourth transistor having a control terminal that is coupled to a fifth node, a first noncontrol terminal that is coupled to the terminal that is arranged for coupling to the cell, and a second noncontrol terminal that is coupled to the third node.

2. The circuit of claim 1, wherein the first node is further arranged to cause the first transistor to conduct in response to detection of a voltage that is suitable for charging the cell.

3. The circuit of claim 1, wherein the second node is further coupled to a charging signal.

4. The circuit of claim 1, wherein the fourth node is further arranged to cause the third transistor to conduct in response to a slew rate of a charging signal for the cell exceeding a maximum expected slew rate of a stable charging circuit.

5. The circuit of claim 1, wherein the fourth node is further coupled to a thermal regulation circuit.

6. The circuit of claim 1, wherein a current source is further coupled between the fourth node and the terminal that is arranged for coupling to a cell.

7. The circuit of claim 1, wherein the fifth node is further coupled to an output of a differential amplifier.

8. The circuit of claim 1, wherein the fifth node is further coupled to a voltage regulation circuit.

9. The circuit of claim 1, wherein the third node is further resistively coupled to the low power supply.

10. The circuit of claim 1, wherein the low power supply is a ground voltage reference.

11. The circuit of claim 1, wherein the first node is further arranged to cause the first transistor to conduct in response to detection of a voltage that is suitable for charging the cell, wherein the fourth node is arranged to cause the third transistor to conduct in response to a slew rate of a charging signal for the cell exceeding a maximum expected slew rate of a stable charging circuit, wherein the fifth node is coupled to a voltage regulation circuit, and wherein the third node is resistively coupled to the low power supply.

12. A method for protecting a cell against an over-voltage condition, comprising:

coupling a control terminal of a first transistor to a first node;

coupling a first noncontrol terminal of the first transistor to a terminal that is arranged for coupling to the cell;

coupling a second noncontrol terminal of the first transistor to a second node;

coupling a control terminal of a second transistor to a third node;

coupling a first noncontrol terminal of the second transistor to the second node;

coupling a second noncontrol terminal of the second transistor to a low power supply;

coupling a control terminal of a third transistor to a fourth node;

coupling a first noncontrol terminal of the third transistor to the second node;

coupling a second noncontrol terminal of the third transistor to the third node;

coupling a control terminal of a fourth transistor to a fifth node;

coupling a first noncontrol terminal of the fourth transistor to the terminal that is arranged for coupling to the cell; and

coupling a second noncontrol terminal of the fourth transistor to the third node.

13. The method of claim 12, further comprising coupling the first node to a signal that causes the first transistor to conduct in response to detection of a voltage that is suitable for charging the cell.

14. The method of claim 12, further comprising coupling the fourth node to a signal that causes the third transistor to conduct in response to a slew rate of a charging signal for the cell exceeding a maximum expected slew rate of a stable charging circuit.

15. The method of claim 12, further comprising coupling the fifth node to a voltage regulation circuit.

16. The method of claim 12, further comprising:

coupling the first node to a signal that causes the first transistor to conduct in response to detection of a voltage that is suitable for charging the cell;

coupling the fourth node to a signal that causes the third transistor to conduct in response to a slew rate of a charging signal for the cell exceeding a maximum expected slew rate of a stable charging circuit;

coupling the fifth node to a voltage regulation circuit; and

resistively coupling the third node to the low power supply.

17. The method of claim 12, further comprising coupling the cell to the terminal that is arranged for coupling to the cell.

18. The method of claim 12, further comprising coupling a charging signal to the second node.