Switching Power Converter Input Voltage Approximate Zero Crossing Determination

• US 20120286826A1
• Filed: 11/04/2011
• Published: 11/15/2012
• Est. Priority Date: 11/04/2010
• Status: Active Grant

• Current Assignee: Signify Holding B.V. (Signify N.V.)
• Original Assignee: Cirrus Logic Incorporated
• Inventors: King, Eric J., Melanson, John L.
• Granted Patent: US 8,610,365 B2
• Time in Patent Office: Days
• US Class Current: 327/79
• CPC Class Codes: H03K 17/13 Modifications for switching at zero crossing generating an impulse at zero crossing H03K5/1536
• CPC Class Codes: H05B 45/10 Controlling the intensity of the light
• CPC Class Codes: H05B 45/3725 Switched mode power supply [SMPS]
• CPC Class Codes: Y02B 20/30 Semiconductor lamps, e.g. solid state lamps [SSL] light emitting diodes [LED] or organic LED [OLED]

Abstract

In at least one embodiment, the controller senses a leading edge, phase cut AC input voltage value to a switching power converter during a cycle of the AC input voltage. The controller senses the voltage value at a time prior to a zero crossing of the AC input voltage and utilizes the voltage value to determine the approximate zero crossing. In at least one embodiment, by determining an approximate zero crossing of the AC input voltage, the controller is unaffected by any disturbances of the dimmer that could otherwise make detecting the zero crossing problematic. In at least one embodiment, the controller approximates the AC input voltage using a function that estimates a waveform of the AC input voltage and determines the approximate zero crossing of the AC input voltage from the approximation of the AC input voltage.

Claims

1. An apparatus comprising:

a controller having an input to sense a leading edge, phase cut alternating current (AC) input voltage to a switching power converter at least at a first time during a cycle of the AC input voltage, wherein the cycle of the AC input voltage is derived from a cycle of the AC input supply voltage, the first time is prior to an approximate zero crossing of the cycle of the AC input supply voltage, and at least some zero crossings of the AC input supply voltage are not directly observable by the controller, and the controller is configured to;

determine the approximate zero crossing of the AC input supply voltage based on a voltage value of the phase cut AC input voltage sensed at the first time.

2. The apparatus of claim 1 wherein to determine the approximate zero crossing of the AC input supply voltage, the controller is configured to:

approximate the AC input supply voltage using a function that estimates a waveform of the AC input supply voltage and determine the approximate zero crossing of the AC input supply voltage from the approximation of the AC input supply voltage.

3. The apparatus of claim 2 wherein to approximate the AC input supply voltage using a function that estimates a waveform of the AC input supply voltage, the controller is configured to approximate the AC input supply voltage using a polynomial function.

4. The apparatus of claim 2 wherein to approximate the AC input supply voltage using a function that estimates a waveform of the AC input supply voltage, the controller is configured to approximate the AC input supply voltage using a function that generally decreases over time.

5. The apparatus of claim 1 wherein to determine the approximate zero crossing of the AC input supply voltage, the controller is configured to:

synthesize the AC input supply voltage to determine a delay to the approximate zero crossing from the first time.

6. The apparatus of claim 1 wherein the first time occurs at an end of power transfer by the switching power converter to a load.

7. The apparatus of claim 1 wherein to determine the approximate zero crossing of the AC input supply voltage, the controller is configured to:

observe the phase cut AC input voltage during a cycle of the phase cut AC input voltage for during a first time period beginning at or before the leading edge of the AC input supply voltage until when the phase cut AC input voltage disconnects from a switching power converter; and

utilize data associated with the observation of the phase cut AC input voltage from the first time period to determine the approximate zero crossing of the AC input supply voltage.

8. The apparatus of claim 7 wherein the first time period is a period of time during a cycle of the AC input supply voltage when a lamp draws sufficient current so that the phase cut AC voltage tracks the AC input voltage.

9. The apparatus of claim 7 wherein to determine the approximate zero crossing of the AC input supply voltage, the controller is configured to:

iteratively approximate the AC input supply voltage after the first time period until the iterative approximation indicates that the AC input supply voltage equals approximately zero.

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

expose the phase cut AC input voltage to an input voltage node of the controller at the first time while current is drawn through the switching power converter by a load.

11. The apparatus of claim 10 wherein the load comprises a lamp, and the lamp comprises one or more light emitting diodes.

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

hold the rectified phase cut AC input voltage at a constant value until the controller determines the approximate zero crossing of the AC input supply voltage; and

release the phase cut AC input voltage at a time of the approximate zero crossing of the AC input supply voltage as determined by the controller.

13. The apparatus of claim 12 wherein to release the phase cut AC input voltage at a time of the approximate zero crossing of the AC input supply voltage as determined by the controller comprises to release the phase cut AC input voltage when the controller determines the approximate zero crossing of the AC input supply voltage.

14. The apparatus of claim 1 wherein the voltage value of the phase cut AC input voltage sensed at the first time is selected from a group consisting of:

greater than or equal to 50V or greater than or equal to 0.3 times a root mean square value of a peak value of the phase cut AC input voltage.

15. A method comprising:

receiving a sense signal indicating a leading edge, phase cut alternating current (AC) input voltage to a switching power converter, wherein the sense signal is received at least at a first time during a cycle of the AC input voltage, the cycle of the AC input voltage is derived from a cycle of the AC input supply voltage, the first time is prior to an approximate zero crossing of the cycle of the AC input supply voltage, and at least some zero crossings of the AC input supply voltage are not directly observable by a controller of a switching power converter; and

determining the approximate zero crossing of the AC input supply voltage based on a voltage value of the phase cut AC input voltage sensed at the first time.

16. The method of claim 15 wherein determining the approximate zero crossing of the AC input supply voltage further comprises:

estimating a waveform of the AC input supply voltage; and

determining the approximate zero crossing of the AC input supply voltage from the approximation of the AC input supply voltage.

17. The method of claim 16 wherein estimating a waveform of the AC input supply voltage further comprises:

approximating the AC input supply voltage using a function that estimates a waveform of the AC input supply voltage.

18. The method of claim 17 wherein approximating the AC input supply voltage using a function that estimates a waveform of the AC input supply voltage further comprises:

approximating the AC input supply voltage using a polynomial function.

19. The method of claim 17 wherein approximating the AC input supply voltage using a function that estimates a waveform of the AC input supply voltage further comprises:

approximating the AC input supply voltage using a function that generally decreases over time.

20. The method of claim 15 wherein determining the approximate zero crossing of the AC input supply voltage further comprises:

synthesizing the AC input supply voltage to determine a delay to the approximate zero crossing from the first time.

21. The method of claim 15 wherein the first time occurs at an end of power transfer by the switching power converter to a load.

22. The method of claim 15 wherein determining the approximate zero crossing of the AC input supply voltage further comprises:

observing the phase cut AC input voltage during a cycle of the phase cut AC input voltage for during a first time period beginning at or before the leading edge of the AC input supply voltage until when the phase cut AC input voltage disconnects from a switching power converter; and

utilizing data associated with the observation of the phase cut AC input voltage from the first time period to determine the approximate zero crossing of the AC input supply voltage.

23. The method of claim 22 wherein the first time period is a period of time during a cycle of the AC input supply voltage when a lamp draws sufficient current so that the phase cut AC voltage tracks the AC input voltage.

24. The method of claim 22 wherein determining the approximate zero crossing of the AC input supply voltage further comprises:

iteratively approximating the AC input supply voltage after the first time period until the iterative approximation indicates that the AC input supply voltage equals approximately zero.

25. The method of claim 15 further comprising:

exposing the phase cut AC input voltage to an input voltage node of the controller at the first time while current is drawn through the switching power converter by a load.

26. The method of claim 25 wherein the load comprises a lamp, and the lamp comprises one or more light emitting diodes.

27. The method of claim 15 wherein the controller is further configured to:

hold the rectified phase cut AC input voltage at a constant value until the controller determines the approximate zero crossing of the AC input supply voltage; and

release the phase cut AC input voltage at a time of the approximate zero crossing of the AC input supply voltage as determined by the controller.

28. The method of claim 27 wherein releasing the phase cut AC input voltage at a time of the determined approximate zero crossing of the AC input supply voltage further comprises:

releasing the phase cut AC input voltage when the controller determines the approximate zero crossing of the AC input supply voltage.

29. The method of claim 15 wherein the voltage value of the phase cut AC input voltage sensed at the first time is selected from a group consisting of:

greater than or equal to 50V or greater than or equal to 0.3 times a root mean square value of a peak value of the phase cut AC input voltage.

30. A method comprising:

exposing a leading edge, phase cut alternating current (AC) input voltage supplied to a switching power converter for part of a cycle of the AC input voltage, wherein the exposed AC input voltage is used to supply current to a load and the AC input voltage is derived from an AC input supply voltage;

sensing the AC input voltage;

ceasing exposure of the AC input voltage after sensing the AC input voltage; and

determining an approximate zero crossing of the AC input supply voltage based on a value of the sensed AC input voltage.

31. An apparatus comprising:

means for receiving a sense signal indicating a leading edge, phase cut alternating current (AC) input voltage to a switching power converter, wherein the sense signal is received at least at a first time during a cycle of the AC input voltage, the cycle of the AC input voltage is derived from a cycle of the AC input supply voltage, the first time is prior to an approximate zero crossing of the cycle of the AC input supply voltage, and at least some zero crossings of the AC input supply voltage are not directly observable by a controller of a switching power converter; and

means for determining the approximate zero crossing of the AC input supply voltage based on a voltage value of the phase cut AC input voltage sensed at the first time.