Nonlinear, discrete time control of power factor correction power converter

1. An apparatus for controlling a power converter operable to receive a cyclically varying input signal, the apparatus comprising:

a discrete-time, on-time generator coupled to the power converter and configured to regulate an output voltage of the power converter; and

a controller configured to compare the output voltage of the power converter against a first predetermined range to:

obtain a comparison result at a zero-crossing of the cyclically varying input signal; and

select one of a plurality of operation levels of the discrete-time, on-time generator in response to the comparison result;

wherein the plurality of operation levels comprises a linear, discrete-time operation level and a nonlinear, discrete-time operation level.

2. The apparatus of claim 1 wherein:

if the output voltage is within the first predetermined range, the linear, discrete-time operation level is selected; and

if the output voltage is outside the first predetermined range, the nonlinear, discrete-time operation level is selected.

3. The apparatus of claim 1 wherein the discrete-time, on-time generator is configured to output a plurality of constant on-time pulses within a half-cycle of the cyclically varying input signal when the controller selects the linear, discrete-time operation level.

4. The apparatus of claim 1 wherein the discrete-time, on-time generator is configured to output at least one adaptive on-time pulse within a half-cycle of the cyclically varying input signal adjacent to the zero-crossing of the cyclically varying input signal when the controller selects the nonlinear, discrete-time operation level.

5. The apparatus of claim 1 wherein the discrete-time, on-time generator is operable to provide a perturbed voltage to the power converter at the zero-crossing during operation at the linear, discrete-time operation level.

6. The apparatus of claim 1 wherein the discrete-time, on-time generator is to provide a perturbed voltage to the power converter within a half-cycle of the zero-crossing during operation at the linear, discrete-time operation level.

7. The apparatus of claim 1 further comprising a periodic interval timer configured to cause the controller to sample the output voltage at the zero crossing of the cyclically varying input signal, wherein the controller is further configured to:

determine a status of a flag;

when the flag is not set, determine whether the output voltage is within the first predetermined range and select the linear, discrete-time operation level when the output voltage is within the first predetermined range; and

stop the linear, discrete-time operation level when the controller detects a second zero crossing of the output voltage.

8. The apparatus of claim 7 wherein the controller is further configured to:

select the nonlinear, discrete-time operation level when the output voltage is not within the first predetermined range;

set the flag; and

stop the nonlinear, discrete-time operation level when the controller detects a third zero crossing of the output voltage.

9. The apparatus of claim 7 wherein the nonlinear, discrete-time operation level is configured to adjust a width of an adaptive on-time pulse of the discrete-time, on-time generator by a first predetermined amount of time in a first half-cycle of the cyclically varying input signal adjacent to the zero-crossing of the cyclically varying input signal.

10. The apparatus of claim 9 wherein the controller is further configured to:

adjust the width of the adaptive on-time pulse of the discrete-time, on-time generator in a second half-cycle immediately following the first half-cycle by a second predetermined amount of time smaller than the first predetermined amount of time; and

reset the flag.

11. The apparatus of claim 1 wherein the controller is further configured to:

sample a second output voltage of the power converter at a set point that is not a zero crossing point of the cyclically varying input signal;

determine whether the sampled second output voltage at the set point is within a second predetermined range greater than the first predetermined range;

when the sampled second output voltage is within the second predetermined range, repeat the step of sampling the second output voltage; and

when the sampled second output voltage is not within the second predetermined range, increase a width of a variable on-time pulse of the discrete-time, on-time generator to a maximum value for a remaining half-cycle of the cyclically varying input signal.

12. The apparatus of claim 1 wherein the linear, discrete-time operation level comprises a critical conduction mode control having constant on-time control signals, and the nonlinear, discrete-time operation level comprises at least one change of input power in a cycle of the cyclically varying input signal.

13. The apparatus of claim 12 wherein the nonlinear, discrete-time operation level returns back to the linear, discrete-time operation level after the at least one change of input power.

14. A method for controlling a power factor of a power converter, the method comprising:

obtaining an output voltage of the power converter at a zero-crossing of a cyclically varying input signal, the output voltage being regulated by an on-time generator;

comparing, by a controller, the output voltage against a first predetermined range to obtain a comparison result; and

selecting, by the controller, one of a plurality of operation levels of the on-time generator in response to the comparison result, the plurality of operation levels comprising a linear, discrete-time operation level and a nonlinear, discrete-time operation level.

15. The method of claim 14 wherein:

comparing the output voltage against the first predetermined range comprises determining whether the output voltage is within the first predetermined range; and

selecting one of the plurality of operation levels comprises:

selecting the linear, discrete-time operation level when the output voltage is within the first predetermined range; and

selecting the nonlinear, discrete-time operation level when the output voltage is not within the first predetermined range.

16. The method of claim 14 wherein the on-time generator is configured to output a plurality of constant on-time pulses within a half-cycle of the cyclically varying input signal when the controller selects the linear, discrete-time operation level and at least one adaptive on-time pulse within a half-cycle of the cyclically varying input signal adjacent to the zero-crossing of the cyclically varying input signal when the controller selects the nonlinear, discrete-time operation level.

17. The method of claim 14 wherein the plurality of operation levels comprises an operation level 1, an operation level 2, and an operation level 3.

18. The method of claim 14 further comprising:

determining a status of a flag:

when the flag is not set, determining whether the output voltage is within the first predetermined range;

selecting the linear, discrete-time operation level when the output voltage is within the first predetermined range; and

stopping the linear, discrete-time operation level when detecting a second zero crossing of the output voltage.

19. The method of claim 14 further comprising:

sampling a second output voltage of the power converter at a set point that is not a zero crossing point of the cyclically varying input signal;

determining whether the sampled second output voltage at the set point is within a second predetermined range greater than the first predetermined range;

when the sampled second output voltage is within the second predetermined range, repeating the step sampling the second output voltage; and

when the sampled second output voltage is not within the second predetermined range, increasing a width of a variable on-time pulse of the on-time generator to a maximum value for a remaining half-cycle of the cyclically varying input signal.

20. The method of claim 14 wherein the on-time generator is configured to generate a plurality of signals having a constant on-time interval and a variable off-time interval.