Control of a power factor corrected switching power supply

1. A method of controlling a switching power supply comprising:

sampling a plurality of values of an output voltage of the power supply during a previous half cycle of an input voltage, and calculating an average output voltage;

sampling a plurality of values of an output current of the power supply during the previous half cycle of the input voltage, and calculating an average output current;

calculating the power provided by the power supply over the previous half cycle using the average output voltage and average output current; and

adjusting duty cycle of a switching signal applied to a boost circuit in a subsequent half cycle of the input voltage using, in part, the calculated power provided to a load during the previous half cycle of the input voltage.

2. The method as defined in claim 1 further comprising sampling using a digital signal processor.

3. The method as defined in claim 2 wherein calculating further comprises:

calculating the average value of the output voltage using the digital signal processor;

calculating the average value of the output current using the digital signal processor; and

calculating the power provided using the digital signal processor.

4. The method as defined in claim 1 wherein sampling further comprises aligning the sampling with the boost circuit switching signals.

5. The method as defined in claim 4 further comprising sampling proximate in time to the end of a discharge phase of the boost circuit.

6. The method as defined in claim 1 further comprising adjusting the boost circuit switching signals based, in part, on an output voltage error term.

7. The method as defined in claim 6 further comprising adjusting the boost circuit switching signals at substantially each zero crossing of the input voltage.

8. The method as defined in claim 1 further comprising operating the power supply in a discontinuous current mode.

9. The method as defined in claim 8 further comprising adjusting the boost circuit switching signals at substantially each zero crossing of the input voltage.

10. A switching power supply comprising:

a rectifying bridge coupled to an alternating current input power source, wherein the rectifying bridge produces a rectified input voltage;

a boost circuit coupled to the rectifying bridge, the boost circuit converts the rectified input voltage to an output voltage;

a digital signal processor coupled to the rectified input voltage, the output voltage, and a signal indicative of output current, and wherein the digital signal processor produces a boost control signal coupled to the boost circuit; and

wherein the digital signal processor calculates power delivered to a load coupled to the power supply using the output voltage and output current over a previous half cycle of the Input power source, and wherein the digital signal processor adjusts a duty cycle of the boost control signal applied to the plurality of boost circuits during a subsequent half cycle using the calculated power delivered during the previous half cycle.

11. The switching power supply as defined in claim 10 further comprising:

a plurality of boost circuits: and

wherein the digital signal processor selectively utilizes the plurality of boost circuits based on an amount of power required by the load.

12. The switching power supply as defined in claim 11 wherein the digital signal processor ceases using one of the plurality of boost circuits as the amount of power required by the load diminishes, and further wherein the digital signal processor adjusts the phase of the remaining boost control signals.

13. The switching power supply as defined in claim 10 wherein the digital signal processor adjusts the duty cycle of the boost signals based, in part, on a difference between the output voltage and an output voltage set point, and wherein the digital signal processor adjusts the duty cycle at approximately twice a frequency of the input power source.

14. The switching power supply as defined in claim 10 wherein the digital signal processor synchronizes sampling with the boost control signals.

15. The switching power supply as defined in claim 14 wherein the digital signal processor samples during a discharge cycle.

16. A method comprising:

determining a direct current output voltage error of a boost circuit of a switching power supply by:

obtaining a plurality of samples of the direct current output voltage over a previous half cycle of an alternating current input power source;

calculating an average direct current output voltage using the plurality of samples of the direct current output voltage; and

calculating the direct current output voltage error using the average direct current output voltage and an output voltage set point;

applying, at approximately twice the frequency of the alternating current input power source, a correction to switching signals applied to the boost circuit of the switching power supply based on the direct current output voltage error.

17. The method as defined in claim 16 further comprising:

obtaining a plurality of samples of a signal representing output current over the previous half cycle;

calculating an amount of power delivered during the previous half cycle using the average direct current output voltage and the plurality of samples of the signal representing output current; and

applying an additional correction to the switching signals applied to the boost circuit of the switching power supply in a subsequent half cycle using the calculated power delivered in the previous half cycle.

18. A switching power supply comprising:

a means for rectifying an alternating current input source to produce a direct current signal;

a means for boosting the direct current signal to an output voltage coupled to the means for rectifying;

a means for producing a boost control signal coupled to the means for boosting; and

wherein the means for producing a boost control signal calculates a power delivered to a load coupled to the power supply using the output voltage and an output current over a previous half cycle of the input source, and wherein the means for producing a boost control signal adjusts a duty cycle of a boost control signal applied to the means for boosting during a subsequent half cycle using the calculated power delivered during the previous half cycle of the input power source.

19. The switching power supply as defined in claim 18 further comprising:

a plurality of means for boosting; and

wherein the means for producing a plurality of boost control signals selectively utilizes the plurality of means for boosting based on an amount of power required by the load.

20. The switching power supply as defined in claim 19 wherein the means for producing a plurality of boost control signals ceases using one of the plurality of means for boosting as the amount of power required by the load diminishes, and further adjusts the phase of the remaining boost control signals.

21. The switching power supply as defined in claim 18 wherein the means for producing a plurality of boost control signals adjusts the duty cycle of the boost signals based, in part, on a difference between the output voltage and an output voltage set point, and wherein the means for producing a plurality of boost control signals makes the adjustment at approximately twice a frequency of the input power source.

22. The switching power supply as defined in claim 18 wherein the means for producing a plurality of boost control signals synchronizes sampling with the boost control signals.

23. The switching power supply as defined in claim 22 wherein the means for producing a plurality of boost control signals samples during a discharge cycle of the boost inductor.