Battery protection device

• US 7,327,544 B2
• Filed: 07/14/2004
• Issued: 02/05/2008
• Est. Priority Date: 12/18/2003
• Status: Expired due to Fees

• Current Assignee: STMicroelectronics Incorporated (STMicroelectronics NV)
• Original Assignee: STMicroelectronics Incorporated (STMicroelectronics NV)
• Inventors: Bishop, William D., McClure, David C.
• Primary Examiner(s): Sherry; Michael
• Assistant Examiner(s): MAI, TIEN HUNG
• Application Number:
  US10/890,964
• Publication Number:
  US 20050134229A1
• Time in Patent Office: 1,301 Days
• Field of Search: 320/134, 361/91.5, 361/93.9
• US Class Current: 361/91.5
• CPC Class Codes: H02J 7/00302 Overcharge protection
• CPC Class Codes: H02J 7/0031 using battery or load disconnect circuits H02J9/002 takes precedence

Abstract

A battery protection structure is described. The structure provides battery overcharging protection while allowing for minimal battery voltage drop during normal battery operation. One resistance element sets voltage drop during normal operation, and the sum of two resistance elements sets the maximum battery charging current which will be allowed. The structure provides protection against single component failures.

Claims

1. A battery protection structure, comprising:

a low voltage drop element coupled to a battery voltage source;

a charging limiting element controlled by a plurality of control signals and being coupled to the low voltage drop element and an output voltage to be supplied to a load;

wherein during a normal operating mode during which the battery voltage source is not supplying power to the load and a primary voltage source is supplying power to the load, the battery charging limiting element and the voltage drop restricting element operate to prevent charging of the battery beyond a predetermined threshold; and

wherein during a backup operating mode the battery voltage source supplies power to the load, and during which the primary voltage source does not supply power to the load, the low voltage drop restricting element may be chosen to reduce voltage drop between the battery voltage source and the load and wherein a voltage drop in the path of the battery during the backup operating mode is set by selecting a resistance value in the low voltage drop element.

2. The battery protection structure of claim 1, wherein a battery charging current is limited by the sum of a first selected resistance value in the low voltage drop element and a second selected resistance value in the charging limiting element.

3. The battery protection structure of claim 1, wherein a single component failure, during normal operation, in the low voltage drop element or the charging limiting element will not result in battery overcharging.

4. The battery protection structure of claim 1, wherein the charging limiting element provides different resistances in the normal and backup operating modes of operation.

5. The battery protection structure of claim 1, wherein the plurality of control inputs to the charging limiting element serves to select between normal operating mode, backup operating mode, and a charging operating mode.

6. The battery protection structure of claim 1, wherein the plurality of control inputs is chosen to allow design of the low voltage drop elements and the charging limiting element such that a single component failure does not result in excessive battery charging.

7. A battery protection structure, comprising:

a first resistor, receiving power from a battery source;

a second resistor, coupled to the battery source;

a first transistor, with drain coupled to the first resistor and the second resistor, and well coupled to the second resistor;

a first diode, with cathode coupled to the first transistor well and anode coupled to the first transistor source;

a second diode, with anode coupled to the first transistor source;

a second transistor, with drain coupled to the first transistor source, well coupled to the second diode cathode and to the second transistor source and to an input power source and to an output and to a load;

a first control signal coupled to the first transistor gate, and

a second control signal coupled to the second transistor gate.

8. The battery protection structure of claim 7, wherein the states of the first control signal and the second control signal function to allow power from the battery source to be applied to the output and the load, through the first resistor.

9. The battery protection structure of claim 7, wherein the states of the first control signal and the second control signal function to allow charging of the battery source from the input power source, through the first resistor and the second resistor.

10. The battery protection structure of claim 7, wherein the value of the first resistor determines the voltage drop from the battery source to the output and load, when the battery source is delivering power to the output and load.

11. The battery protection structure of claim 7, wherein the summed values of the first resistor and the second resistor determine the charging current limit when the battery source is being charged.

12. The battery protection structure of claim 7, wherein no single component failure will result in an overcharging condition of the battery source.

13. A battery protection apparatus, operable to supply battery backup power or to provide backup battery charging, comprising:

means for reducing voltage drop when in backup operation;

means for limiting battery charging current when in battery charging operation; and

means for allowing single component failure without battery overcharging when in normal operation, wherein during normal operation the means for allowing single component failure prevents battery overcharging in response to a single component failure.

14. A battery protection structure capable of protecting a battery source from overcharging in normal operation and capable of providing backup power with low voltage drop, comprising:

a first resistor the value of which determines the voltage drop during backup operation;

a second resistor the value of which, when summed with the first resistor value, determines battery source charging current; and

a plurality of control inputs that allow said structure to have bidirectional resistance characteristics that accommodate normal and backup operations.