AC/DC power conversion methods and apparatus

1. An AC/DC converter for converting an AC input voltage Vin to a DC output voltage Vout, comprising:

an inductor;

first and second switches that, only during positive half cycles of the AC input voltage when Vin>Vout, alternately configure said inductor between storing energy and supplying current;

third and fourth switches that, only during negative half cycles of the AC input voltage when Vin<−Vout, alternately configure said inductor between storing energy and supplying current; and

a controller configured to control said first, second, third and fourth switches.

2. The AC/DC converter of claim 1 wherein said controller includes a comparison circuit configured to compare the AC input voltage Vin to the DC output voltage Vout.

3. The AC/DC converter of claim 2 wherein said controller further includes a switch control circuit that controls the switching of said first, second, third and fourth switches depending on comparisons of the AC input voltage Vin to the DC output voltage Vout.

4. The AC/DC converter of claim 1 where said controller includes a switch control circuit that controls the switching of said first, second, third and fourth switches depending on the AC input voltage Vin compared to the DC output voltage Vout.

5. The AC/DC converter of claim 1 wherein only during positive half cycles of the AC input voltage when Vin>Vout said controller is configured to switch said first switch on and off at frequency f and duty cycle D, and is configured to switch said second switch on and off at the frequency f and duty cycle ( 1 -D).

6. The AC/DC converter of claim 5 wherein only during negative half cycles of the AC input voltage when Vin<−Vout said controller is configured to switch said third switch on and off at the frequency f and duty cycle D, and is configured to switch said fourth switch on and off at the frequency f and duty cycle ( 1 -D).

7. The AC/DC converter of claim 6 wherein said controller includes a pulse-width modulator configured to modulate D and regulate the DC output voltage Vout.

8. An AC/DC converter for converting an AC input voltage Vin to a DC output voltage Vout, comprising:

an inductor;

a capacitor selectively coupled to said inductor;

a plurality of switches; and

a controller that configures the plurality of switches, inductor and capacitor to operate as a buck converter during times when Vin>Vout, and configures the plurality of switches, inductor and capacitor to operate as an inverting buck converter during times when Vin<−Vout,

wherein said inductor is the only inductor needed by said AC/DC converter to convert said AC input voltage Vin to said DC output voltage Vout.

9. The AC/DC converter of claim 8 wherein said plurality of switches includes first and second switches that serve as buck switches of the buck converter but only during the times when Vin>Vout.

10. The AC/DC converter of claim 9 wherein said plurality of switches further includes third and fourth switches that serve as inverting buck switches of the inverting buck converter but only during the times when Vin<−Vout.

11. The AC/DC converter of claim 8 wherein said plurality of switches includes first, second, third and fourth switches and said controller is configured to:

switch said first and second switches on and off at a common frequency f and at a duty cycle D and duty cycle ( 1 -D), respectively, but only during the times when Vin>Vout; and

switch said third and fourth switches on and off at the common frequency f and at the duty cycle D and duty cycle ( 1 -D), respectively, but only during the times when Vin<−Vout.

12. The AC/DC converter of claim 11 wherein said controller includes a pulse-width modulator configured to regulate the DC output voltage by modulating the duty cycle D of the first and third switches and by modulating the duty cycle ( 1 -D) of the second and fourth switches.

13. A method of converting an AC input voltage Vin to a DC output voltage Vout, comprising:

converting the AC input voltage during positive half cycles to the DC output voltage Vout using a buck converter; and

converting the AC input voltage during negative half cycles to the DC output voltage Vout using an inverting buck converter,

wherein said buck converter and said inverting buck converter share an inductor and said shared inductor is the only inductor needed by said buck converter and said inverting buck converter to convert said AC input voltage Vin to said DC output voltage Vout.

14. The method of claim 13 wherein converting the AC input voltage to the DC output voltage during the positive and negative half cycles are performed by modulating duty cycles of switches of said buck converter and said inverting buck converter.

15. The method of claim 13 wherein converting positive half cycles of the AC input voltage to the DC output voltage Vout using the buck converter comprises:

determining times when Vin>Vout; and

for times it is determined that Vin>Vout, converting the AC input voltage to the DC output voltage Vout.

16. The method of claim 13 wherein converting negative half cycles of the AC input voltage to the DC output voltage Vout using an inverting buck converter comprises:

determining times when Vin<−Vout; and

for times it is determined that Vin<−Vout, converting the AC input voltage to the DC output voltage Vout.

17. The method of claim 13 wherein the buck converter and inverting buck converter comprise a conjoined buck and inverting buck converter circuit that shares said inductor.

18. An AC/DC converter for converting an AC input voltage Vin to a DC output voltage Vout, comprising:

means for determining times when Vin>Vout and times when Vin<−Vout;

first converting means for converting the AC input voltage during positive half cycles to the DC output voltage Vout during times when Vin>Vout; and

second converting means for converting the AC input voltage during negative half cycles to the DC output voltage Vout during times when Vin<−Vout.

19. The AC/DC converter of claim 18 , further comprising means for controlling said first converting means and said second converting means.

20. The AC/DC converter of claim 19 wherein:

said first converting means includes first switching means;

said second converting means includes second switching means; and

said means for controlling is configured to control said first and second switching means to maintain the DC output voltage Vout at a constant level.

21. An AC/DC converter for converting an AC input voltage Vin to a DC output voltage Vout, comprising:

an inductor;

a first plurality of switches configured to alternately couple and decouple said inductor to and from an AC input voltage during positive half cycles of the AC input voltage; and

a second plurality of switches configured to alternately couple and decouple said inductor to and from the AC input voltage during negative half cycles of the AC input voltage,

wherein said inductor and said second plurality of switches are configured as an inverting buck converter during times when Vin<−Vout.

22. An AC/DC converter for converting an AC input voltage Vin to a DC output voltage Vout, comprising:

an inductor;

a first plurality of switches configured to alternately couple and decouple said inductor to and from an AC input voltage during positive half cycles of the AC input voltage; and

a second plurality of switches configured to alternately couple and decouple said inductor to and from the AC input voltage during negative half cycles of the AC input voltage,

wherein all switches of said first and second pluralities of switches are configured to remain off during times when |Vin|<Vout.

23. The AC/DC converter of claim 1 wherein said inductor is the only inductor needed to convert said AC input voltage Vin to said DC output voltage Vout.

24. An AC/DC converter for converting an AC input voltage Vin to a DC output voltage Vout, comprising:

an inductor;

a first plurality of switches configured to alternately couple and decouple said inductor to and from an AC input voltage during positive half cycles of the AC input voltage; and

a second plurality of switches configured to alternately couple and decouple said inductor to and from the AC input voltage during negative half cycles of the AC input voltage,

wherein said inductor is the only inductor needed to convert said AC input voltage Vin to said DC output voltage Vout.