Methods, apparatus and articles of manufacture to regulate relay coil switching

1. A method for regulating switching times of a relay having a pair of contacts to selectively and electrically couple an analog alternating current (AC) power source and a load, the method comprising:

forming a digital pulse train representative of an AC signal at the load;

determining a first value corresponding to a representative pulse width of the digital pulse train;

providing a first relay switching signal to the relay at a first time relative to a zero crossing of the AC signal;

selecting a second time for providing a second relay switching signal to the relay based on the first value and a second value representative of the width of a first pulse of the digital pulse train associated with the first relay switching signal at the first time; and

providing the second relay switching signal to the relay at the second time.

2. A method as defined in claim 1 , wherein selecting the second time is based on a comparison on the first and second values.

3. A method as defined in claim 1 , wherein the first value comprises an average pulse width.

4. A method as defined in claim 1 , wherein the first value comprises a running average pulse width.

5. A method as defined in claim 1 , wherein the second time is selected according to a predetermined increment.

6. A method as defined in claim 1 , wherein providing the second relay switching signal to the relay at the second time is to effect a switching of the relay at a desired third time relative to the zero crossing.

7. A method as defined in claim 1 , wherein determining the first value representative of the average pulse width of the digital pulse train comprises:

computing two or more counts of samples between rising and falling edges of respective ones of two or more pulses of the digital pulse train; and

computing the first value as an average of the two or more sample counts.

8. A method as defined in claim 1 , wherein the second time is selected based on an estimated switching time of the relay to effect the width of a second pulse of the digital pulse train to be approximately half the value, and further comprising:

determining a third value representative of the width of the second pulse; and

selecting a third switching time for providing a third relay switching signal to the relay based on a comparison of the first and third values.

9. A method as defined in claim 1 , wherein the first relay switching signal is to electrically connect the power supply and the load.

10. An apparatus comprising:

a relay controllable to selectively and electrically couple an alternating current (AC) power source and a load;

a sensing circuit to form a digital pulse train representative of an AC signal at the load; and

a computing unit configured to regulate switching times of the relay by:

determining a first value representative of an average pulse width of the digital pulse train;

providing a first relay switching signal to the relay at a first time relative to a zero crossing of the AC signal;

determining a second value representative of the width of a first pulse of the digital pulse train associated with the first relay switching signal at the first time;

selecting a second time for providing a second relay switching signal to the relay based on a comparison of the first and second values; and

providing the second relay switching signal to the relay at the second time.

11. An apparatus as defined in claim 10 , wherein the computing unit comprises:

a processor; and

a tangible article of manufacture storing machine-readable instructions that, when executed, cause the processor to determine the value, provide the first relay switching signal, and select the second time; and

the sensing circuit comprises a comparator.

12. An apparatus as defined in claim 10 , wherein the computing unit determines the first value as a running average pulse width.

13. An apparatus as defined in claim 10 , wherein the computing unit selects the second time according to a predetermined increment.

14. An apparatus as defined in claim 10 , wherein the computing unit provides the first relay switching signal to the relay at the first time to effect a switching of the relay at a desired third time relative to the zero crossing.

15. An apparatus as defined in claim 10 , wherein the computing unit determines the first value representative of the average pulse width of the digital pulse train by at least:

computing two or more counts of samples between rising and fallings edges of respective ones of two or more pulses of the digital pulse train; and

computing the first value as an average of the two or more sample counts.

16. An apparatus as defined in claim 10 , wherein the computing unit:

selects the second time based on an estimated switching time of the relay to effect the width of a second pulse of the digital pulse train to be approximately half the value;

determines a third value representative of the width of the second pulse; and

selects a third switching time for providing a third relay switching signal to the relay based on a comparison of the first and third values.

17. An apparatus as defined in claim 10 , wherein the computing unit sends the first relay switching signal to the relay to electrically disconnect the power supply and the load.

18. A non-transitory tangible article of manufacturing storing machine-readable instructions that, when executed, cause a machine to at least:

receive from a circuit a digital pulse train representative of an alternating current (AC) signal at a load selectively and electrically coupled to an AC power source via a relay;

determine a first value representative of an average pulse width of the digital pulse train;

provide a first relay switching signal to the relay at a first time relative to a zero crossing of the AC signal;

select a second time for providing a second relay switching signal to the relay based on a comparison of the first value and a second value representative of the width of a first pulse of the digital pulse train associated with the first relay switching signal at the first time; and

provide the second relay switching signal to the relay at the second time.