AC-DC switching power converters with frequency variation in response to load changes
View Patent ↗A method of operating a switching power converter having at least one power switch controlled by a drive signal having a switching frequency is disclosed. The method includes monitoring an output power of the switching power converter, determining whether the output power has decreased below a threshold level and, in response to the output power decreasing below the threshold level, changing the switching frequency of the drive signal from a first switching frequency to a second switching frequency when an operating condition of the switching power converter is satisfied. Also disclosed are controllers and switching power converters (including PFC converters).
1. An AC-DC switching power converter comprising:
an input for coupling to a rectified AC voltage;
an output for providing output power to a load;
a power circuit coupled between the input and the output and including at least one power switch; and
a controller configured to:
control the power switch with a drive signal having a switching frequency;
determine whether the output power decreases below a threshold level; and
in response to the output power decreasing below the threshold level, change the switching frequency of the drive signal from a first switching frequency to a second switching frequency when the rectified AC voltage is about zero volts to improve efficiency of the AC-DC switching power converter.
2. The converter of claim 1 wherein the controller is further configured to change the switching frequency of the drive signal only if the output power remains below the threshold level for a minimum time period.
3. The converter of claim 2 wherein the power converter is configured to provide a substantially constant output voltage, and wherein the controller is configured to determine whether the output power decreases below the threshold level by monitoring an output current, and to change the switching frequency in response to the output current decreasing below a current threshold level.
4. The converter of claim 2 wherein the controller is further configured to change the switching frequency from the second switching frequency to the first switching frequency in response to the output power increasing above the threshold level.
5. The converter of claim 2 wherein the controller is configured to change the switching frequency of the drive signal a first time the rectified AC voltage is about zero volts after the minimum time period.
6. The converter of claim 1 wherein the controller is configured to change the switching frequency of the drive signal a first time the rectified AC voltage is about zero volts after the output power decreases below the threshold level.
7. The converter of claim 1 wherein the power converter is configured to provide a substantially constant output voltage, and wherein the controller is configured to determine whether the output power decreases below the threshold level by monitoring an output current, and to change the switching frequency in response to the output current decreasing below a current threshold level.
8. The converter of claim 1 wherein the power converter is an active power factor correction circuit.
9. The converter of claim 1 wherein the power converter is configured to provide a substantially constant output current, and wherein the controller is configured to determine whether the output power decreases below the threshold level by monitoring an output voltage, and to change the switching frequency in response to the output voltage decreasing below a voltage threshold level.
10. The converter of claim 1 wherein the controller is configured to not change the switching frequency during a defined wait period following start-up of the power converter.
11. The converter of claim 1 wherein the first switching frequency and the second switching frequency are set at predetermined values.
12. A method of operating an AC-DC switching power converter having an input for coupling to a rectified AC voltage and at least one power switch controlled by a drive signal having a switching frequency, the method comprising:
monitoring an output power of the switching power converter;
determining whether the output power has decreased below a threshold level; and
in response to the output power decreasing below the threshold level, changing the switching frequency of the drive signal from a first switching frequency to a second switching frequency when the rectified AC voltage is about zero volts to improve efficiency of the AC-DC switching power converter.
13. The method of claim 12 wherein changing includes changing the switching frequency of the drive signal only if the output power remains below the threshold level for a minimum time period.
14. The method of claim 13 wherein changing includes changing the switching frequency of the drive signal a first time the rectified AC voltage is about zero volts after the minimum time period.
15. The method of claim 12 further comprising:
in response to the output power increasing above the threshold level, changing the switching frequency of the drive signal from the second switching frequency to the first switching frequency when the rectified AC voltage is about zero volts.
16. The method of claim 12 wherein the first frequency is greater than the second frequency.
17. The method of claim 12 wherein the first frequency is less than the second frequency.
18. The method of claim 12 wherein the switching power converter is a PFC converter.
19. The method of claim 12 wherein the input of the switching power converter is coupled to an AC utility grid.
20. A controller for a switching power converter, the controller configured to perform the method of claim 12 .
21. The method of claim 12 wherein the switching power converter is configured to provide a substantially constant output voltage, wherein determining includes monitoring an output current, and wherein changing includes changing the switching frequency in response to the output current decreasing below a current threshold level.
22. The method of claim 12 wherein the switching power converter is configured to provide a substantially constant output current, wherein determining includes monitoring an output voltage, and wherein changing includes changing the switching frequency in response to the output voltage decreasing below a voltage threshold level.
23. The method of claim 12 wherein the first switching frequency and the second switching frequency are set at predetermined values.
24. The method of claim 12 wherein changing includes changing the switching frequency of the drive signal a first time the rectified AC voltage is about zero volts after the output power decreases below the threshold level.