Charging circuit with two levels of safety

• US 20050168193A1
• Filed: 05/03/2003
• Published: 08/04/2005
• Est. Priority Date: 05/03/2003
• Status: Active Grant

• Current Assignee: Motorola Solutions, Inc.
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Xiong, Seng P., Ramsden, Martin H., Riley, Marc B.
• Granted Patent: US 6,998,818 B2
• Time in Patent Office: Days
• US Class Current: 320/134
• CPC Class Codes: H02J 7/00302 Overcharge protection
• CPC Class Codes: H02J 7/00308 Overvoltage protection

Abstract

A battery charging circuit having two levels of safety protection is provided. The circuit is said to have “two levels” of safety because if any one component fails (either as a short circuit or as an open circuit) the remainder of the charging circuit ensures that a rechargeable battery coupled to the circuit will not be overcharged. The circuit includes both hardware and firmware protection components, with a microprocessor providing the firmware protection. Overvoltage protection, voltage regulation and current regulation are provided, along with a microprocessor capable of sensing a plurality of voltages across the circuit. The overvoltage protection, voltage regulator and current regulator each include safety actuation points. In parallel, the microprocessor may isolate a rechargeable battery from the cell if voltage and current minimums and maximums are exceeded. The microprocessor further is able to isolate the battery from the circuit if the power dissipation in the voltage regulator, the current regulator or the overall charging circuit is exceeded, provided the microprocessor has decremented current to a minimum level.

Claims

1. A battery charging circuit, comprising:

a. input terminals for receiving an input voltage and an input current;

b. an overvoltage protection circuit;

c. a voltage regulation circuit having an output voltage;

d. a current regulation circuit;

e. a means for sensing current flowing through the charging circuit;

f. battery terminals for coupling to a rechargeable battery cell; and

g. a microprocessor having a plurality of inputs and outputs;

wherein a first input is coupled to one of the input terminals;

further wherein a second input is coupled to the voltage regulation circuit;

further wherein a third input is coupled to the battery terminals;

further wherein a fourth input is coupled to the means for sensing current;

further wherein the microprocessor is capable of actuating a voltage regulation circuit control signal to cause the voltage regulation circuit to enter a high impedance state; and

further wherein the microprocessor is capable of actuating a current regulation circuit control signal to cause the current regulation circuit to enter a high impedance state.

2. The circuit of claim 1, wherein a first output of the microprocessor is a variable output, further wherein the variable output is coupled to the current regulation circuit, further wherein the microprocessor is capable of altering the amount of current flowing through the current regulator by altering the variable output.

3. The circuit of claim 2, wherein the microprocessor decrements the current by a predetermined decrement amount when a predetermined event occurs, wherein the predetermined event is selected from the group consisting of:

a. the voltage across the input terminals falling below a predetermined minimum input voltage;

b. the voltage across the input terminals falling below the output voltage of the voltage regulation circuit;

c. the voltage across the input terminals exceeds a predetermined maximum input voltage;

d. power dissipation across the current regulation circuit exceeding a predetermined maximum current regulation power threshold;

e. power dissipation across the voltage regulation circuit exceeding a predetermined maximum voltage regulation power threshold; and

f. power dissipation across the charging circuit exceeding a predetermined maximum power dissipation threshold.

4. The circuit of claim 2, wherein the first output comprises a pulse width modulator.

5. The charging circuit of claim 1, wherein when a voltage across the input terminals exceeds a predetermined maximum input threshold, the overvoltage protection circuit actuates, thereby causing a circuit selected from the group consisting of the current regulation circuit and the voltage regulation circuit to enter a high impedance state.

6. The charging circuit of claim 1, wherein the circuit further comprises a memory with firmware stored therein.

7. The charging circuit of claim 6, wherein the firmware comprises a firmware sense voltage, wherein the firmware sense voltage is less than the predetermined maximum input threshold.

8. The charging circuit of claim 6, wherein when a voltage across the input terminals exceeds the firmware sense voltage for a predetermined time, the microprocessor causes a circuit selected from the group consisting of the current regulation circuit and the voltage regulation circuit to enter a high impedance state.

9. The circuit of claim 1, wherein when power is removed from a circuit selected from the group consisting of the voltage regulation circuit and the current regulation circuit, the selected circuit enters a high impedance state.

10. The circuit of claim 1, wherein the overvoltage protection circuit comprises a zener diode and a serial transistor, wherein when the zener diode enters a reverse breakdown mode, the serial transistor enters a high impedance state.

11. The circuit of claim 1, wherein the microprocessor causes a circuit selected from the group consisting of the current regulation circuit and the voltage regulation circuit to enter a high impedance state when a predetermined event occurs, wherein the predetermined event is selected from the group consisting of:

a. a voltage across the input terminals exceeding a predetermined maximum input voltage for a first predetermined time;

b. the voltage across the input terminals falling below a predetermined minimum input voltage for a second predetermined time;

c. the voltage across the input terminals falling below the output voltage of the voltage regulation circuit for a third predetermined time;

d. the output voltage of the voltage regulation circuit exceeding a predetermined maximum regulated voltage for a fourth predetermined time;

e. the output voltage of the voltage regulation circuit falling below a predetermined minimum regulated voltage for a fifth predetermined time;

f. a current flowing through the charging circuit exceeding a predetermined maximum current for a sixth predetermined time;

g. power dissipation across the current regulation circuit exceeding a predetermined maximum current regulation power threshold;

h. power dissipation across the voltage regulation circuit exceeding a predetermined maximum voltage regulation power threshold; and

i. power dissipation across the charging circuit exceeding a predetermined maximum power dissipation threshold.

12. A battery charging circuit, comprising:

a. input terminals for receiving an input voltage and an input current;

b. an overvoltage protection circuit;

c. a voltage regulation circuit having an output voltage;

d. a current regulation circuit;

e. a means for sensing current flowing through the charging circuit;

f. battery terminals for coupling to a rechargeable battery cell; and

g. a microprocessor having a plurality of inputs and outputs;

wherein by way of the plurality of inputs, the microprocessor is capable of sensing;

1. an input voltage across the input terminals;

2. the output voltage of the voltage regulation circuit;

3. a voltage across the voltage regulation circuit;

4. a voltage across the current regulation circuit;

5. a voltage across the means for sensing current; and

6. a voltage across the battery terminals.

13. The circuit of claim 12, wherein the means for sensing current comprises a resistor.

14. The circuit of claim 13, wherein the microprocessor calculates a circuit current by dividing the voltage across the means for sensing current by an impedance value of the resistor.

15. The circuit of claim 14, wherein the microprocessor calculates the power dissipation across the voltage regulation circuit by multiplying the voltage across the voltage regulation circuit by the circuit current.

16. The circuit of claim 15, wherein when the power dissipation across the voltage regulation circuit exceeds a predetermined maximum voltage regulation power threshold, the microprocessor actuates a first output coupled to the current regulation circuit, causing the circuit current to decrement by a predetermined amount.

17. The circuit of claim 16, wherein when the power dissipation across the voltage regulation circuit exceeds the maximum voltage regulation power threshold, and the circuit current has been decremented to a predetermined minimum circuit current, the microprocessor causes a circuit selected from the group consisting of the current regulation circuit and the voltage regulation circuit to enter a high impedance state.

18. The circuit of claim 14, wherein the microprocessor calculates the power dissipation across the current regulation circuit by multiplying the voltage across the current regulation circuit by the circuit current.

19. The circuit of claim 18, wherein when the power dissipation across the current regulation circuit exceeds a predetermined maximum current regulation power threshold, the microprocessor actuates a first output coupled to the current regulation circuit, causing the circuit current to decrement by a predetermined amount.

20. The circuit of claim 19, wherein when the power dissipation across the current regulation circuit exceeds the maximum current regulation power threshold, and the circuit current has been decremented to a predetermined minimum circuit current, the microprocessor causes a circuit selected from the group consisting of the current regulation circuit and the voltage regulation circuit to enter a high impedance state.