Reverse charger protection

• US 6,724,593 B1
• Filed: 01/30/2002
• Issued: 04/20/2004
• Est. Priority Date: 01/30/2002
• Status: Active Grant

• Current Assignee: National Semiconductor Corporation (Texas Instruments, Inc.)
• Original Assignee: National Semiconductor Corporation (Texas Instruments, Inc.)
• Inventors: Smith, Gregory J.
• Primary Examiner(s): Patel, Rajnikant B.
• Application Number:
  US10/066,427
• Time in Patent Office: 811 Days
• Field of Search: 361/84, 361/85, 361/93, 361/93.2, 361/82, 320/134, 320/132, 320/136, 320/128, 320/152
• US Class Current: 361/84
• CPC Class Codes: H02J 7/00304 Overcurrent protection
• CPC Class Codes: H02J 7/00308 Overvoltage protection
• CPC Class Codes: H02J 7/00309 Overheat or overtemperature protection
• CPC Class Codes: H02J 7/0034 using reverse polarity correcting or protecting circuits mechanical means of polarity protection H02J7/0045

Abstract

A method and apparatus is provided for protecting voltage regulation circuits and battery cells (“cell”) when a cell is reverse-coupled to a charger. When a charger is reverse-coupled to the cell, parasitic devices in voltage regulation circuits become forward-biased. When the parasitic devices become forward-biased, the parasitic devices may carry a current that is sufficiently large to damage the voltage regulation circuits. A shunt regulator is used to detect the presence of a reverse-coupled charger (“reverse charger”) and to shunt current to a ground potential such that potentially damaging currents are prevented from flowing through the parasitic devices.

Claims

1. An apparatus for protecting a battery charger against a reverse-coupled cell, comprising:

a charge input circuit arranged to provide a charging signal;

a body diode that is located within an over-voltage protection circuit; and

a reverse-voltage protection circuit that is arranged to detect the reverse-coupled cell and to prevent the charging signal from causing the body diode in the over-voltage protection circuit to conduct.

2. The apparatus of claim 1 further comprising a transistor that is arranged to shunt current from the charging signal when the reverse-voltage protection circuit detects the reverse-coupled cell.

3. The apparatus of claim 1 further comprising an amplifier that is arranged to detect when the charging signal exceeds a maximum-allowable reverse-voltage.

4. The apparatus of claim 1 further comprising:

an amplifier that is arranged to detect when the charging signal exceeds a maximum-allowable reverse-voltage; and

a transistor that is arranged to shunt current from the charging signal when the amplifier detects that the charging signal exceeds the maximum-allowable reverse-voltage.

5. The apparatus of claim 1 further comprising a switch circuit that is coupled between the charge input circuit and the reverse-coupled cell.

6. The apparatus of claim 1, wherein the body diode is formed by a drain-to-substrate junction of a transistor that is used by both the over-voltage protection circuit and the reverse-voltage protection circuit.

7. The apparatus of claim 1, wherein the reverse-voltage protection circuit prevents the charging signal from causing a parasitic SCR in the over-voltage protection circuit from latching.

8. The apparatus of claim 1, further comprising an over-voltage protection circuit that is coupled to the charging signal.

9. A method for protecting a charge input circuit from a high current flow that results when a reverse-voltage is applied to the charge input circuit, wherein the reverse-voltage results when a charger is reverse-coupled to a cell, comprising:

comparing a voltage associated with the charging signal to a maximum-allowable reverse-voltage; and

reducing the reverse-voltage of the charging signal when the maximum-allowable reverse-voltage is exceeded.

10. The method of claim 9, wherein reducing the reverse-voltage of the charging signal further comprises shunting current from the charging signal such that the reverse-voltage of the charging signal is reduced.

11. Method of claim 10, wherein shunting current form the charging signal further comprises using a transistor to reduce the reverse-voltage of the charging signal.

12. The method of claim 9, wherein reducing the reverse-voltage of the charging signal further comprises providing a cyclic timing signal for activating and deactivating a current shunt, wherein the cyclic timing signal has a activation duty cycle of greater than 50 percent.

13. The method of claim 9, further comprising selecting a voltage for the maximum-allowable reverse-voltage reference that is based on forward-conduction threshold voltages of parasitic devices that arc present in the charge input circuit.

14. The method of claim 9, further comprising preventing a body diode that is present in the charge input circuit from conducting as a result of reverse-coupling the cell to the charger.

15. The method of claim 9, fiber comprising preventing an SCR that is present in the charge input circuit from latching as a result of reverse-coupling the cell to the charger.

16. The method of claim 9, further comprising preventing a body diode and an SCR that are present in the charge input circuit from conducting as a result of reverse-coupling the cell to the charger.

17. An apparatus for protecting a charge input circuit from a high current flow that results when a reverse-voltage is applied to the charge input circuit, wherein the reverse-voltage results when a charger is reverse-coupled to a cell, comprising:

means for comparing a voltage associated with the charging signal to a maximum-allowable reverse-voltage; and

means for reducing the reverse-voltage of the charging signal when the maximum-allowable reverse-voltage is exceeded.

18. The apparatus of claim 17, wherein the means for reducing the reverse-voltage of the charging signal further comprises means for shunting current from the charging signal such that the reverse-voltage of the charging signal is reduced.

19. The apparatus of claim 18, wherein the means for shunting current from the charging signal further comprises a transistor for reducing the reverse-voltage of the charging signal.

20. The apparatus of claim 17, further comprising means for preventing a body diode that is present in the charge input circuit from conducting as a result of reverse-coupling the cell to the charger.

21. The apparatus of claim 17, further comprising means for preventing an SCR that is present in the charge input circuit from latching as a result of reverse-coupling the cell to the charger.

22. The apparatus of claim 17, further comprising means for preventing a parasitic body diode and a parasitic SCR that are present in the charge input circuit from conducting as a result of reverse-coupling the cell to the charger.