Load control device for high-efficiency loads

• US 9,143,051 B2
• Filed: 11/25/2014
• Issued: 09/22/2015
• Est. Priority Date: 11/25/2009
• Status: Active Grant

• Current Assignee: Lutron Technology Company LLC
• Original Assignee: Lutron Electronics Company Incorporated (Lutron Electronics)
• Inventors: Newman, Robert C. Jr.
• Primary Examiner(s): Le, Tung X
• Application Number:
  US14/552,924
• Publication Number:
  US 20150077006A1
• Time in Patent Office: 301 Days
• Field of Search: 315/194, 315/199, 315/224, 315/291, 315/294, 315/297, 315/307, 315/311, 315/318
• US Class Current: 1/1
• CPC Class Codes: G05F 3/08 wherein the variable is dc
• CPC Class Codes: H02M 7/06 using discharge tubes without control electrode or semiconductor devices without control electrode
• CPC Class Codes: H05B 39/04 Controlling
• CPC Class Codes: H05B 39/048 with reverse phase control
• CPC Class Codes: H05B 45/10 Controlling the intensity of the light
• CPC Class Codes: H05B 47/10 Controlling the light source
• CPC Class Codes: Y02B 20/00 Energy efficient lighting technologies, e.g. halogen lamps or gas discharge lamps

Abstract

A two-wire load control device (such as, a dimmer switch) is operable to control the amount of power delivered from an AC power source to an electrical load (such as, a high-efficiency lighting load) and has substantially no minimum load requirement. The load control device includes a bidirectional semiconductor switch (such as thyristor), which may be operable to remain conductive independent of the magnitude of a load current conducted through the thyristor and to conduct the load current to and from the load during a single half-cycle. The dimmer switch comprises a power supply that conducts a charging current through the load in order to generate a supply voltage. The dimmer switch comprises a control circuit that controls a gate coupling circuit for rendering the thyristor conductive each half-cycle. The control circuit may provide a constant gate drive to the thyristor after the thyristor is rendered conductive each half-cycle.

Claims

1. A load control device for controlling power delivered from an AC power source to an electrical load, the load control device comprising:

a thyristor adapted to be electrically coupled between the AC power source and the electrical load, the thyristor having first and second main terminals through which a load current is conducted to energize the electrical load and a gate terminal through which a gate current is conducted to render the thyristor conductive;

a gate coupling circuit electrically coupled to conduct the gate current through the gate terminal of the thyristor;

a control circuit electrically coupled to control the gate coupling circuit, the control circuit configured to determine a zero-crossing time of a present half-cycle of the AC power source in response to a voltage developed across the thyristor; and

a power supply electrically coupled to conduct a charging current through the electrical load to generate a supply voltage;

wherein the control circuit is configured to control the gate coupling circuit to be conductive to conduct the gate current through the gate terminal of the thyristor to render the thyristor conductive after a first, variable amount of time has elapsed since the zero-crossing time of the present half-cycle, the control circuit configured to maintain the thyristor conductive independent of the magnitude of the load current conducted through the thyristor during the present half-cycle, the control circuit further configured to prevent the gate coupling circuit from conducting the gate current through the gate terminal of the thyristor after a second, fixed amount of time has elapsed since the zero-crossing time of the present half-cycle to allow the thyristor to become non-conductive, the second, fixed amount of time being less than a length of the present half-cycle, the control circuit configured to vary the first, variable amount of time in accordance with a determinate amount of power to be delivered to the electrical load in order to cause the amount of power delivered to the electrical load to be the determinate amount.

2. The load control device of claim 1, wherein the control circuit comprises:

a timing circuit configured to generate a timing signal from the supply voltage, the timing circuit being configured to start to generate the timing signal near the zero-crossing time of the present half-cycle, and to cause the timing signal to increase in magnitude with respect to time; and

a drive circuit arranged to receive the timing signal, the drive circuit being configured to render the thyristor conductive in each half-cycle in response to the timing signal reaching a selected threshold;

wherein the timing circuit is further configured to continue generating the timing signal after the thyristor is rendered conductive in each half-cycle, resulting in the control circuit maintaining the thyristor conductive independent of the magnitude of the load current conducted through the thyristor.

3. The load control device of claim 2, wherein the timing circuit is configured to stop generating the timing signal after the second, fixed amount of time has elapsed since the zero-crossing time of the present half-cycle.

4. The load control device of claim 3, wherein the drive circuit is configured to terminate the drive signal when the timing circuit stops generating the timing signal so as to render the gate coupling circuit non-conductive and prevent the gate terminal of the thyristor from conducting the gate current and thereby allow the thyristor to commutate off.

5. The load control device of claim 3, wherein the timing circuit is configured to increase the magnitude of the timing signal at a constant rate and the length of the first, variable amount of time is not dependent upon the length of the second, fixed amount of time.

6. The load control device of claim 1, wherein the control circuit is configured to generate a drive signal and apply the drive signal to the gate coupling circuit, the control circuit configured to adjust the magnitude of the drive signal to a first magnitude to render the gate coupling circuit conductive after the first, variable amount of time has elapsed since the zero-crossing time, maintain the magnitude of the drive signal at the first magnitude after the gate coupling circuit is rendered conductive, and adjust the magnitude of the drive signal to a second magnitude to prevent the gate coupling circuit from conducting the gate current through the gate terminal of the thyristor after the second, fixed amount of time has elapsed since the zero-crossing time.

7. The load control device of claim 6, wherein a dead time exists between the time at which the control circuit adjusts the drive signal to the second magnitude during a first half-cycle and the time at which the control circuit determines a subsequent zero-crossing time in a second half-cycle immediately following the first half-cycle.

8. The load control device of claim 1, wherein the power supply is configured to generate the supply voltage across a storage capacitor when the thyristor is non-conductive, the gate coupling circuit comprises an opto-coupler having an input photodiode electrically coupled to receive the drive signal from the control circuit and an output photodiode electrically coupled to the gate terminal of the thyristor, the input photodiode configured to conduct a drive current from the storage capacitor of the power supply in order to render the thyristor conductive and maintain the thyristor conductive in response to the gate drive signal.

9. The load control device of claim 1, wherein the thyristor comprises a triac.

10. The load control device of claim 1, wherein the electrical load comprises a high-efficiency lighting load and the load control device is a dimmer switch.

11. The load control device of claim 10, wherein the high-efficiency lighting load is a light-emitting diode light source or a compact fluorescent lamp.

12. The load control device of claim 1, wherein the control circuit comprises a microprocessor powered by the supply voltage.

13. The load control device of claim 1, further comprising:

an RF receiver configured to receive an RF signal;

wherein the control circuit is configured to determine the determinate amount of power to be delivered to the electrical load from the RF signal.

14. The load control device of claim 1, wherein the electrical load is a light-emitting diode light source or a compact fluorescent lamp.

15. The load control device of claim 1, wherein the control circuit is configured to render the gate coupling circuit non-conductive to prevent the gate coupling circuit from conducting the gate current through the gate terminal of the thyristor after the second, fixed amount of time has elapsed since the zero-crossing time of the present half-cycle.

16. The load control device of claim 1, wherein the control circuit is further configured to control the second, fixed amount of time to be approximately equal during each half-cycle of the AC power source.

17. The load control device of claim 1, wherein the control circuit and the gate coupling circuit are arranged in such a way as to enable the thyristor to conduct the load current to the electrical load and to conduct the load current from the electrical load during a single half-cycle of the AC power source.

18. A load control device for controlling power delivered from an AC power source to an electrical load, the load control device comprising:

a thyristor adapted to be electrically coupled between the AC power source and the electrical load, the thyristor having first and second main terminals through which a load current is conducted to energize the electrical load and a gate terminal through which a gate current is conducted to render the thyristor conductive;

a gate coupling circuit electrically coupled to conduct the gate current through the gate terminal of the thyristor;

a control circuit electrically coupled to control the gate coupling circuit, the control circuit configured to control the gate coupling circuit to conduct the gate current through the gate terminal of the thyristor to render the thyristor conductive at a firing time during each half-cycle of the AC power source; and

a power supply electrically coupled to conduct a charging current through the electrical load to generate a supply voltage;

wherein the control circuit is configured to maintain the gate coupling circuit conductive after the firing time, thereby enabling the thyristor both to conduct the load current to the electrical load and to conduct the load current from the electrical load during a single half-cycle of the AC power source.

19. The load control device of claim 18, wherein the control circuit is configured to determine a zero-crossing time of a present half-cycle of the AC power source in response to a voltage developed across the thyristor.

20. The load control device of claim 19, wherein the control circuit is configured to control the gate coupling circuit to be conductive to conduct the gate current through the gate terminal of the thyristor to render the thyristor conductive at the firing time when a variable amount of time has elapsed since the zero-crossing time of the present half-cycle of the AC power source, and to maintain the thyristor conductive independent of the magnitude of the load current conducted through the thyristor between the firing time and a second time during the present half-cycle, the control circuit configured to prevent the gate coupling circuit from conducting the gate current after the second time which occurs when a fixed amount of time has elapsed since the zero-crossing time of the present half-cycle thereby allowing the thyristor to become non-conductive, the fixed amount of time being less than a length of the present half-cycle, the control circuit configured to vary the firing time in accordance with a determinate amount of power to be delivered to the electrical load in order to cause the amount of power delivered to the electrical load to be the determinate amount.

21. The load control device of claim 20, wherein the control circuit comprises:

a timing circuit configured to generate a timing signal from the supply voltage, the timing circuit being configured to start to generate the timing signal near the zero-crossing time of the present half-cycle, and to cause the timing signal to increase in magnitude with respect to time; and

a drive circuit arranged to receive the timing signal, the drive circuit being configured to render the thyristor conductive in each half-cycle in response to the timing signal reaching a selected threshold;

wherein the timing circuit is further configured to continue generating the timing signal after the thyristor is rendered conductive in each half-cycle, resulting in the control circuit maintaining the thyristor conductive independent of the magnitude of the load current conducted through the thyristor, the timing circuit configured to stop generating the timing signal after the second, fixed amount of time has elapsed since the zero-crossing time of the present half-cycle, the drive circuit configured to terminate the drive signal when the timing circuit stops generating the timing signal so as to render the gate coupling circuit non-conductive and prevent the gate terminal of the thyristor from conducting the gate current and thereby allow the thyristor to commutate off.

22. The load control device of claim 18, wherein the control circuit comprises a microprocessor powered by the supply voltage.

23. The load control device of claim 18, further comprising:

an RF receiver powered by the supply voltage and configured to receive an RF signal;

wherein the control circuit is configured to determine the determinate amount of power to be delivered to the electrical load from the RF signal.

24. The load control device of claim 18, wherein the electrical load is a high-efficiency lighting load and the load control device comprises a dimmer switch.

25. The load control device of claim 18, wherein the electrical load is a light-emitting diode light source or a compact fluorescent lamp.

26. The load control device of claim 18, wherein the power supply is configured to conduct the charging current through the electrical load when the thyristor is non-conductive to generate the supply voltage for powering the control circuit.

27. The load control device of claim 18, wherein the thyristor comprises a triac.

28. The load control device of claim 18, wherein the control circuit is configured to generate the drive signal for controlling the gate coupling circuit to maintain the thyristor conductive independent of the magnitude of the load current conducted through the thyristor.

29. The load control device of claim 18, wherein the control circuit is configured to maintain the gate coupling circuit conductive between the firing time and a second time before the end of the half-cycle, thereby enabling the thyristor both to conduct the load current to the electrical load and to conduct the load current from the electrical load between the firing time and the second time during the single half-cycle of the AC power source.

30. The load control device of claim 29, wherein the control circuit is configured to control the gate coupling circuit to be conductive to conduct the gate current through the gate terminal of the thyristor to render the thyristor conductive at the firing time when a variable amount of time has elapsed since the zero-crossing time of the present half-cycle of the AC power source.

31. The load control device of claim 30, wherein the second time occurs when a fixed amount of time has elapsed since the zero-crossing time of the present half-cycle.

32. The load control device of claim 30, wherein the control circuit is configured to prevent the gate coupling circuit from conducting the gate current after the second time to allow the thyristor to become non-conductive.

33. The load control device of claim 18, wherein the control circuit is configured to vary the firing time in accordance with a determinate amount of power to be delivered to the electrical load in order to cause the amount of power delivered to the electrical load to be the determinate amount.