Charging system for battery powered devices

• US 5,523,671 A
• Filed: 07/23/1993
• Issued: 06/04/1996
• Est. Priority Date: 02/14/1991
• Status: Expired due to Term

• Current Assignee: Dell USA LP (Dell Technologies Inc.)
• Original Assignee: Dell USA LP (Dell Technologies Inc.)
• Inventors: Stewart, Gregory N.
• Primary Examiner(s): Stephan, Steven L.
• Assistant Examiner(s): Ponomarenko, Nicholas
• Application Number:
  US08/097,339
• Time in Patent Office: 1,047 Days
• Field of Search: 320/21, 320/39
• US Class Current: 320/152
• CPC Class Codes: H02J 7/34 Parallel operation in networks using both storage and other dc sources, e.g. providing buffering H02J7/14 takes precedence

Abstract

A system for controlling the rate and duration of battery charging. A microprocessor is connected in a battery current signal feedback loop and used to control the battery charge cycle. The rate of charge is gradually stepped up at the beginning of the charge cycle until the charging current reaches a defined maximum value, and thereafter maintained between the maximum and a defined minimum value for the duration of the charge cycle. The microcontroller terminates the charge cycle when the battery charging current begins to increase while the rate of charge remains constant, this being an indication that the battery is fully charged. Sensors input signals to the microcontroller to prevent or terminate charging if the battery cells are not within an appropriate temperature range, or if a short circuit or other adverse condition arises.

Claims

1. Apparatus for controlled battery charging in which a battery is connectable to a power source capable of providing charging current at a suitable terminal voltage, the apparatus comprising:

a switch circuit for regulating the charging current of said battery responsive to a variable control signal, said switch circuit connected in series between said battery and said power source;

a circuit connected to said switch circuit for determining said battery charging current and generating a signal proportional thereto;

a control circuit connected to said switch circuit and to said current determining circuit for applying said control signal to said switch circuit, said control circuit comprising logic for;

i). varying said control signal responsive to said current proportional signal, to cause said switch circuit to progressively increase said charging current until said charging current reaches a defined maximum value,

ii). maintaining said control signal until said charging current reaches a defined minimum value, and

iii). varying said control signal to cause said switch circuit to progressively increase said charging current until said charging current reaches said defined maximum value, thereby maintaining said charging current between said maximum value and said minimum value; and

termination logic for terminating said battery charging when said current begins to increase while said control logic is maintaining said selected control signal, as an indication that said battery has reached a fully charged condition.

2. The apparatus of claim 1 further comprising a sensor for measuring the terminal voltage of said battery and for providing a signal representing said battery terminal voltage to said control circuit.

3. The apparatus of claim 2 further comprising control circuit logic for terminating said battery charging responsive to said voltage signal when during said battery charging said voltage begins to decrease, as an indication that said battery is fully charged.

4. The apparatus of claim 2 further comprising control circuit logic for terminating said battery charging responsive to said voltage signal when after said charging current has initially reached said defined maximum value, said battery terminal voltage is lower than a defined threshold value, as an indication that said battery is internally short-circuited.

5. The apparatus of claim 1 further comprising a sensor for measuring the temperature of said battery and for providing a signal representing said battery temperature to said control circuit.

6. The apparatus of claim 5 further comprising control circuit logic for preventing initiation of said battery charging responsive to said battery temperature signal, when said battery temperature is either above or below a defined temperature range.

7. The apparatus of claim 5 further comprising control circuit logic for terminating said charge cycle responsive to said battery temperature signal when said battery temperature exceeds a defined maximum temperature value.

8. Apparatus for controlled battery charging in which a battery is connectable to a power source capable of providing charging current at a suitable terminal voltage, the apparatus comprising:

a switch circuit with a control input for regulating the charging current of said battery, said switch circuit connected in series between said battery and said power source;

a driver circuit for driving said switch circuit control input in response to a pulse width modulated control signal of varying duty ratio applied to said driver circuit;

a circuit connected to said switch circuit for determining said battery charging current and generating a signal proportional thereto;

a control circuit connected to said driver circuit and to said current determining circuit for applying said control signal to said driver circuit, said control circuit comprising logic for varying the duty ratio of said control signal dependent upon said current proportional signal, thereby selecting the value of said charging current applied to said battery by said switching circuit; and

said control circuit further comprising logic to progressively increase said control signal duty ratio to progressively increase said battery charging current until said charging current as determined by said current proportional signal reaches a defined maximum value, thereafter said control signal duty ratio being maintained constant until said charging current as determined by said current proportional signal falls below a defined minimum value, whereupon said control signal duty ratio is again progressively increased, thereby continually asserting said charging current at said maximum value and maintaining said charging current between said minimum and maximum values.

9. The apparatus of claim 8 wherein said control circuit logic terminates said charging current when said current proportional signal begins to increase while said control signal duty cycle is maintained constant, as an indication that said battery has reached a fully charged condition.

10. The apparatus of claim 8 further comprising control circuit logic for periodically averaging values of said charging current as determined by said current proportional signal, comparing said average current value with defined minimum and maximum current values and periodically varying the duty ratio of said control signal to maintain said average current value between said minimum and maximum current values until said battery is fully charged.

11. The apparatus of claim 8 further comprising:

a sensor for measuring the terminal voltage of said battery and for providing a signal representing said battery terminal voltage to said control circuit; and

control circuit logic for terminating said battery charging responsive to said battery voltage signal when during said charging said battery terminal voltage begins to decrease, as an indication that said battery is fully charged.

12. The apparatus of claim 11 further comprising control circuit logic for terminating said battery charging responsive to said battery voltage signal when after said charging current has initially reached said defined maximum value, said battery terminal voltage is lower than a defined threshold value, as an indication that said battery is internally short-circuited.

13. The apparatus of claim 8 further comprising:

a sensor for measuring the temperature of said battery and for providing a signal representing said battery temperature to said control circuit; and

control circuit logic for preventing initiation of said charging cycle responsive to said battery temperature signal, when said battery temperature is outside a defined temperature range.

14. The apparatus of claim 13 further comprising control circuit logic for terminating said battery charging responsive to said battery temperature signal, when said battery temperature exceeds a defined maximum temperature value.

15. A battery-powered electronic device with controlled battery charging, said device including at least one battery connectable to a power source capable of providing charging current at a suitable terminal voltage, the device comprising:

load circuitry connected to said battery;

a switch circuit with a control input for regulating the charging current of said battery, said switch circuit connected in series between said battery and said power source;

a driver circuit for driving said switch circuit control input in response to a pulse width modulated control signal of varying duty ratio applied to said driver circuit;

a circuit connected to said switch circuit for determining said battery charging current and generating a signal proportional thereto;

a control circuit connected to said driver circuit and to said current determining circuit for applying said control signal to said driver circuit;

said control circuit comprising logic for varying or maintaining constant the duty ratio of said control signal dependent upon said current proportional signal, thereby selecting the value of said charging current applied to said battery by said switching circuit; and

said control circuit logic terminating said charging current when said current proportional signal begins to increase while said control signal duty cycle is maintained constant, as an indication that said battery has reached a fully charged condition.

16. The device of claim 15 wherein said control circuit logic progressively increases said control signal duty ratio to progressively increase said battery charging current until said charging current as determined by said current proportional signal reaches a defined maximum value, thereafter said control signal duty ratio being maintained constant until said charging current as determined by said current proportional signal, falls below a defined minimum value, whereupon said control signal duty ratio is again progressively increased to maintain said charging current between said minimum and maximum values until said battery is fully charged.

17. The device of claim 15 wherein said switch circuit comprises a series combination of a resistor, an inductor and a FET switching element.

18. The device of claim 17 wherein said determining circuit comprises an amplifier for amplifying the voltage across said resistor due to said charging current.

19. The device of claim 15 further comprising:

a sensor for measuring the terminal voltage of said battery and for providing a signal representing said battery terminal voltage to said control circuit; and

control circuit logic for terminating said battery charging responsive to said battery voltage signal when after said charging current has initially reached said defined maximum value, said battery terminal voltage is lower than a defined threshold value, as an indication that said battery is internally short-circuited.

20. The device of claim 15 further comprising:

a sensor for measuring the temperature of said battery and for providing a signal representing said battery temperature to said control circuit; and

control circuit logic for preventing said battery charging responsive to said battery temperature signal, when said battery temperature is outside a defined temperature range.

21. A method for controlled battery charging in which a battery is connectable to a power source capable of providing charging current at a suitable terminal voltage, the method comprising:

regulating the charging current of said battery responsive to a variable control signal;

determining said battery charging current and generating a signal proportional thereto;

varying said control signal responsive to said current proportional signal to progressively increase said charging current until said charging current reaches a defined maximum value,

maintaining said control signal until said charging current reaches a defined minimum value,

varying said control signal to progressively increase said charging current until said charging current reaches said defined maximum value; and

terminating said battery charging when said current proportional signal begins to increase while said control signal is being maintained, as an indication that said battery has reached a fully charged condition;

thereby maintaining said charging current between said maximum value and said minimum value until said battery is fully charged.

22. The method of claim 21 further comprising:

measuring the terminal voltage of said battery; and

terminating said battery charging responsive to said voltage signal when during said battery charging said voltage begins to decrease, as an indication that said battery is fully charged.

23. The method of claim 22 further comprising terminating said battery charging responsive to said voltage signal when after said charging current has initially reached said defined maximum value, said battery terminal voltage is lower than a defined threshold value, as an indication that said battery is internally short-circuited.

24. The method of claim 21 further comprising:

measuring the temperature of said battery; and

preventing initiation of said battery charging responsive to said battery temperature signal, when said battery temperature is either above or below a defined temperature range.

25. The method of claim 24 further comprising terminating said charge cycle responsive to said battery temperature signal when said battery temperature exceeds a defined maximum temperature value.