Frequency jitter utilizing a fractional valley switching controller
A method involves determining a target number of valleys of a resonant waveform at a drain node of a main switch of a power converter. The target number of valleys corresponds to a desired off-time of the main switch. A first intermediate valley number of a series of intermediate valley numbers is selected. An average of the series of intermediate valley numbers corresponds to the target number of valleys. A first average off-time of the main switch is controlled, for a duration of a first modulation period, such that the first average off-time corresponds to the first intermediate valley number. Upon expiration of the first modulation period, a second intermediate valley number of the intermediate valley numbers is selected. A second average off-time of the main switch is controlled, for a duration of a second modulation period, such that the second average off-time corresponds to the second intermediate valley number.
1. A method comprising:
determining a target number of valleys of a resonant waveform at a drain node of a main switch of a power converter, the target number of valleys corresponding to a desired off-time of the main switch;
selecting a first intermediate valley number of a plurality of intermediate valley numbers, an average of the plurality of intermediate valley numbers corresponding to the target number of valleys;
controlling, for a duration of a first modulation period, a first average off-time of the main switch such that the first average off-time of the main switch corresponds to the first intermediate valley number;
selecting, upon expiration of the first modulation period, a second intermediate valley number of the plurality of intermediate valley numbers, a difference of the second intermediate valley number and the first intermediate valley number being equal to a fractional valley number offset; and
controlling, for a duration of a second modulation period, a second average off-time of the main switch such that the second average off-time of the main switch corresponds to the second intermediate valley number.
2. The method of claim 1 , wherein controlling the first average off-time of the main switch comprises:
modulating, for the duration of the first modulation period, an off-time of the main switch between a first plurality of off-times, the first plurality of off-times of the main switch having a first average value that corresponds to the first intermediate valley number.
3. The method of claim 2 , wherein controlling the second average off-time of the main switch comprises:
controlling, for the duration of the second modulation period, the off-time of the main switch in accordance with the second intermediate valley number, the second intermediate valley number being an integer.
4. The method of claim 2 , wherein:
each off-time of the first plurality of off-times corresponds to a respective integer valley number of a first plurality of integer valley numbers.
5. The method of claim 4 , wherein:
the first plurality of integer valley numbers comprises a first sequence of one or more first integer valley numbers in series immediately followed by a second sequence of one or more second integer valley numbers in series;
a length of the first sequence is different than a length of the second sequence; and
the one or more first integer valley numbers are not equal to the one or more second integer valley numbers.
6. The method of claim 2 , wherein controlling the second average off-time of the main switch comprises:
modulating, for the duration of the second modulation period, an off-time of the main switch between a second plurality of off-times, the second plurality of off-times of the main switch having a second average value that corresponds to the second intermediate valley number.
7. The method of claim 6 , wherein:
each off-time of the first plurality of off-times corresponds to a respective integer valley number of a first plurality of integer valley numbers; and
each off-time of the second plurality of off-times corresponds to a respective integer valley number of a second plurality of integer valley numbers.
8. The method of claim 7 , further comprising:
generating the first plurality of off-times based on the first intermediate valley number; and
generating the second plurality of off-times based on the second intermediate valley number.
9. The method of claim 1 , further comprising:
selecting, upon expiration of the second modulation period, a third intermediate valley number of the plurality of intermediate valley numbers, a difference of the third intermediate valley number and the second intermediate valley number being equal to the fractional valley number offset.
10. The method of claim 1 , wherein:
the fractional valley number offset is a non-integer number.
11. The method of claim 10 , wherein:
the fractional valley number offset is about 0.5.
12. The method of claim 10 , wherein:
the fractional valley number offset is about 0.25.
13. The method of claim 1 , wherein:
the duration of each of the first and second modulation periods is about 2.5 ms.
14. The method of claim 1 , further comprising:
measuring an off-time of the main switch;
determining a difference between the desired off-time of the main switch and the measured off-time of the main switch; and
generating the target number of valleys based on the determined difference.
15. The method of claim 1 , further comprising:
measuring an off-time of the main switch;
determining a difference between the measured off-time of the main switch and the desired off-time of the main switch;
producing an off-time adjustment signal based on the determined difference between the measured off-time of the main switch and the desired off-time of the main switch; and
generating the target number of valleys based on the off-time adjustment signal.
16. A power converter controller comprising:
a fractional valley controller configured to determine a target number of valleys of a resonant waveform at a drain node of a main switch of a power converter, the target number of valleys corresponding to a desired off-time of the main switch; and
a valley jitter module configured to:
select a first intermediate valley number of a plurality of intermediate valley numbers, an average of the plurality of intermediate valley numbers corresponding to the target number of valleys, the main switch being controlled for a duration of a first modulation period such that a first average off-time of the main switch corresponds to the first intermediate valley number; and
select, upon expiration of the first modulation period, a second intermediate valley number of the plurality of intermediate valley numbers, a difference of the second intermediate valley number and the first intermediate valley number being equal to a fractional valley number offset, the main switch being controlled for the duration of a second modulation period such that a second average off-time of the main switch corresponds to the second intermediate valley number.
17. The power converter of claim 16 , wherein controlling the first average off-time of the main switch comprises:
modulating, for the duration of the first modulation period, an off-time of the main switch between a first plurality of off-times, the first plurality of off-times of the main switch having a first average value that corresponds to the first intermediate valley number.
18. The power converter of claim 17 , wherein controlling the second average off-time of the main switch comprises:
controlling, for the duration of the second modulation period, the off-time of the main switch in accordance with the second intermediate valley number, the second intermediate valley number being an integer.
19. The power converter of claim 17 , wherein:
each off-time of the first plurality of off-times corresponds to a respective integer valley number of a first plurality of integer valley numbers.
20. The power converter of claim 19 , wherein:
the first plurality of integer valley numbers comprises a first sequence of one or more first integer valley numbers in series immediately followed by a second sequence of one or more second integer valley numbers in series;
a length of the first sequence is different than a length of the second sequence; and
the one or more first integer valley numbers are not equal to the one or more second integer valley numbers.
21. The power converter of claim 17 , wherein controlling the second average off-time of the main switch comprises:
modulating, for the duration of the second modulation period, an off-time of the main switch between a second plurality of off-times, the second plurality of off-times of the main switch having a second average value that corresponds to the second intermediate valley number.
22. The power converter of claim 21 , wherein:
each off-time of the first plurality of off-times corresponds to a respective integer valley number of a first plurality of integer valley numbers; and
each off-time of the second plurality of off-times corresponds to a respective integer valley number of a second plurality of integer valley numbers.