Method and apparatus for charging and discharging a rechargeable battery

1. A battery protection system for a rechargeable battery, comprising:

a switch module that selectively interrupts battery current from the rechargeable battery to a load based on a control signal;

a battery voltage sensor that senses battery voltage;

a battery temperature sensor that generates a battery temperature signal; and

a control module that generates said control signal based on said battery temperature signal and said battery voltage, wherein said control signal is a pulse-width modulated (PWM) waveform having a period that is set by a first signal and a duty cycle that is set by a second signal that varies based on said battery temperature signal and said first signal and wherein said duty cycle is zero percent when said battery temperature exceeds a first predetermined temperature.

2. The battery protection system of claim 1 wherein said duty cycle is one hundred percent when said battery temperature is less than said first predetermined temperature and said battery voltage is less than a predetermined voltage.

3. The battery protection system of claim 2 wherein said duty cycle is between zero percent and one hundred percent when said battery temperature is less than said first predetermined temperature and said battery voltage is greater than said predetermined voltage.

4. The battery protection system of claim 1 wherein said control module further comprises:

a first oscillator module that generates said first signal having a first period;

a temperature dependent oscillator module that generates said second signal having a second period that varies based on said battery temperature signal; and

a duty cycle generator module that generates said PWM signal from said first signal and said second signal.

5. The battery protection system of claim 4 wherein said temperature dependent oscillator module has at least two ranges of periods, said second period being within one of said at least two ranges of periods.

6. The battery protection system of claim 5 further comprising a temperature controller for selecting which of said at least two period ranges is used by said temperature dependent oscillator.

7. A self-protecting rechargeable power supply comprising the battery protection system of claim 1 and further comprising:

said rechargeable battery; and

a housing containing said rechargeable battery, battery voltage sensor, battery temperature sensor, control module, and switch module.

8. A battery protection circuit comprising:

a switch module that selectively interrupts battery current based on a control signal;

a first oscillator module that generates a first signal having a first period;

a temperature dependent oscillator module that generates a second signal having a second period; and

a duty cycle generator that receives said first signal and said second signal and generates said control signal, wherein said control signal is pulse-width modulated at said first period with a duty cycle established by said second period wherein said temperature dependent oscillator module receives a reset signal that is based on said first signal and generates said second signal based on said reset signal.

9. The battery protection circuit of claim 8 wherein said temperature dependent oscillator is dependent on a battery temperature.

10. The battery protection circuit of claim 8 wherein said duty cycle generator further includes a flip-flop having a set input, a reset input, and an output, said first signal being connected to said set input and said second signal being connected to said reset input, and wherein said output performs the pulse-width modulation of said control signal.

11. The battery protection circuit of claim 8 further comprising a thermostat module, said thermostat module controlling said control signal in accordance with a battery temperature.

12. The battery protection circuit of claim 8 further comprising a comparator module that enables and disables said first signal based on a battery voltage.

13. A self-protecting rechargeable power supply comprising the battery protection system of claim 8 and further comprising:

a rechargeable battery; and

a housing containing said rechargeable battery, said first oscillator, said temperature dependent oscillator, said duty cycle generator, and said switch module.

14. The self-protecting rechargeable power supply of claim 13 further comprising positive and negative electrical terminals for making electrical connections, said positive and negative electrical terminals positioned on an end face of said housing.

15. A method for protecting a rechargeable battery, comprising:

monitoring a battery temperature;

monitoring a battery voltage;

pulse width modulating the current flow from the battery at a period that is set by a first signal and at a duty cycle that is set by a second signal that varies based on said battery temperature and said battery voltage and said first signal; and

setting said duty cycle to turn off the current flow when said battery temperature exceeds a first predetermined temperature.

16. The method of claim 15 further comprising:

setting said duty cycle to completely turn on the current flow when said battery temperature is less than a first predetermined temperature and when said battery voltage is less than a predetermined voltage.

17. The method of claim 16 further comprising:

setting said duty cycle to between zero percent and one hundred percent when said battery temperature is less than said first predetermined temperature and said battery voltage is greater than said predetermined voltage.

18. The method of claim 15 further comprising:

generating said first signal having a first period;

generating said second signal having a second period that varies based on said battery temperature; and

generating said duty cycle based on said first signal and said second signal.

19. The method of claim 15 further comprising:

selecting said second period from at least two ranges of periods.

20. The method of claim 15 further comprising:

providing a housing containing the rechargeable battery.

21. The battery protection system of claim 1 wherein said switch module is in series with the rechargeable battery relative to load terminals of said load.

22. The battery protection system of claim 1 wherein said switch module and the rechargeable battery are in series between power supply terminals that are in communication with load terminals of the load.

23. The battery protection system of claim 1 wherein the rechargeable battery is in series between the switch module and said load.

24. A battery protection circuit comprising:

a switch module that selectively interrupts battery current based on a control signal;

a first oscillator module that generates a first signal having a first period;

a temperature dependent oscillator module that generates a second signal having a second period; and

a duty cycle generator that receives said first signal and said second signal and generates said control signal, wherein said control signal is pulse-width modulated at said first period with a duty cycle established by said second period, wherein said temperature dependent oscillator module generates said second signal based on said first signal.