Protective circuit

• US 20070097572A1
• Filed: 10/28/2005
• Published: 05/03/2007
• Est. Priority Date: 10/28/2005
• Status: Abandoned Application

• Current Assignee: Caretta Integrated Circuits
• Original Assignee: Caretta Integrated Circuits
• Inventors: Wu, Bin
• Application Number:
  US11/262,542
• Publication Number:
  US 20070097572A1
• Time in Patent Office: Days
• US Class Current: 361/82
• CPC Class Codes: H02J 7/0031 using battery or load disconnect circuits H02J9/002 takes precedence

Abstract

A protective circuit for a battery includes: (1) an MOS transistor having a first drain/source terminal coupled to one terminal of the battery; (2) a switch selectable to couple the bulk terminal of the MOS transistor to (a) the first drain/source terminal, (b) a second drain/source terminal, or (c) float; and (3) a control circuit which provides control signals for the gate terminal of the MOS transistor and the switch. By allowing the bulk terminal to float during normal operation (i.e., charging or discharging operation), a sensitive, low-power comparator used in the prior art is eliminated, thereby allowing the protective circuit to have a small foot-print. The protective circuit may further include a resistor. The switch connects the bulk terminal of the MOS transistor to the first drain/source terminal through this first resistor, thereby limiting any “rush” current which occurs when the battery circuit switches from discharging to charging, or vice versa, over a very short time period. Consequently, safe operation of the battery circuit is achieved.

Claims

1. A protective circuit for a battery, comprising:

an MOS transistor having a bulk terminal, a gate terminal, a first drain/source terminal and a second drain/source terminal, wherein the first drain/source terminal is coupled to one terminal of the battery;

a switch selectable to couple the bulk terminal of the MOS transistor to (a) the first drain/source terminal, (b) the second drain/source terminal, or (c) float; and

a control circuit which provides control signals for the gate terminal of the MOS transistor and the switch.

2. A protective circuit as in claim 1, further comprising a first resistor, wherein the switch connects the bulk terminal of the MOS transistor to the first drain/source terminal through the first resistor.

3. A protective circuit as in claim 2, further comprising a second resistor, wherein the switch connects the bulk terminal of the MOS transistor to the second drain/source terminal through the second resistor.

4. A protective circuit as in claim 1 wherein, during normal operation, the switch floats the bulk terminal of the MOS transistor.

5. A protective circuit as in claim 1, a load is to be provided between the other terminal of the battery and the second drain/source terminal of the MOS transistor.

6. A protective circuit for a battery, comprising:

an MOS transistor having a bulk terminal, a gate terminal, a first drain/source terminal and a second drain/source terminal, wherein the first drain/source terminal is coupled to one terminal of the battery;

a switch selectable to couple the bulk terminal of the MOS transistor to (a) the first drain/source terminal, (b) the second drain/source terminal;

a first resistor in series with the switch, such that the bulk terminal of the MOS transistor is connected to the first drain/source terminal through the first resistor; and

a control circuit which provides control signals for the gate terminal of the MOS transistor and the switch.

7. A protective circuit as in claim 6, further comprising a second resistor, wherein the switch connects the bulk terminal of the MOS transistor to the second drain/source terminal through the second resistor.

8. A protective circuit as in claim 6, wherein the control circuit comprises a comparator circuit that controls at any given time whether the bulk terminal of the MOS transistor is connected to the first drain/source terminal or the second drain/source terminal.

9. A protective circuit as in claim 6, a load is to be provided between the other terminal of the battery and the second drain/source terminal of the MOS transistor.

10. A method for protecting a battery, comprising:

Connecting a first drain/source terminal of an MOS transistor to one terminal of the battery, wherein the MOS transistor has a bulk terminal, a gate terminal, the first drain/source terminal and a second drain/source terminal;

Providing a switch selectable to couple the bulk terminal of the MOS transistor to (a) the first drain/source terminal, (b) the second drain/source terminal, or (c) float; and

generating control signals for the gate terminal of the MOS transistor and the switch.

11. A method as in claim 10, wherein the switch connects the bulk terminal of the MOS transistor to the first drain/source terminal through a first resistor.

12. A method as in claim 11, wherein the switch connects the bulk terminal of the MOS transistor to the second drain/source terminal through a second resistor.

13. A method as in claim 10 wherein, during normal operation, the switch floats the bulk terminal of the MOS transistor.

14. A method as in claim 10, further comprising providing a load between the other terminal of the battery and the second drain/source terminal of the MOS transistor.

15. A method for protecting a battery, comprising:

Connecting a first drain/source terminal of an MOS transistor to one terminal of the battery, wherein the MOS transistor has a bulk terminal, a gate terminal, the first drain/source terminal and a second drain/source terminal;

Providing a switch selectable to couple the bulk terminal of the MOS transistor through a first resistor to (a) the first drain/source terminal, (b) the second drain/source terminal; and

Providing control signals for the gate terminal of the MOS transistor and the switch.

16. A method as in claim 16, wherein the switch connects the bulk terminal of the MOS transistor to the second drain/source terminal through a second resistor.

17. A method as in claim 16, wherein a comparator circuit controls at any given time whether the bulk terminal of the MOS transistor is connected to the first drain/source terminal or the second drain/source terminal.

18. A method as in claim 16, providing a load between the other terminal of the battery and the second drain/source terminal of the MOS transistor.