Load control device for high-efficiency loads

• US 9,343,997 B2
• Filed: 12/23/2014
• Issued: 05/17/2016
• 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., Salvestrini, Chris J., Harte, Matthew V.
• Primary Examiner(s): Laxton, Gary L
• Application Number:
  US14/581,115
• Publication Number:
  US 20150108913A1
• Time in Patent Office: 511 Days
• Field of Search: 323/217, 323/235, 323/237, 323/239, 323/241, 323/300, 323/319, 323/320, 323/322, 323/324, 323/325, 323/905
• US Class Current: 1/1
• CPC Class Codes: H02M 7/06 using discharge tubes without control electrode or semiconductor devices without control electrode
• CPC Class Codes: H02M 7/155 using semiconductor devices only
• CPC Class Codes: H02M 7/217 using semiconductor devices only
• CPC Class Codes: H05B 39/04 Controlling
• CPC Class Codes: H05B 39/044 continuously H05B39/042 takes precedence
• CPC Class Codes: H05B 39/048 with reverse phase control
• CPC Class Codes: H05B 41/3924 by phase control, e.g. using a triac H05B41/3922 takes precedence
• CPC Class Codes: H05B 45/10 Controlling the intensity of the light
• CPC Class Codes: H05B 45/14 using electrical feedback from LEDs or from LED modules
• CPC Class Codes: H05B 45/315 Reverse phase-control circuits
• CPC Class Codes: H05B 45/37 Converter circuits
• CPC Class Codes: H05B 47/10 Controlling the light source
• CPC Class Codes: H05B 47/19 via wireless transmission
• CPC Class Codes: Y02B 20/00 Energy efficient lighting technologies, e.g. halogen lamps or gas discharge lamps
• CPC Class Codes: Y02B 20/30 Semiconductor lamps, e.g. solid state lamps [SSL] light emitting diodes [LED] or organic LED [OLED]
• CPC Class Codes: Y10S 323/905 Lamp dimmer structure

Abstract

A two-wire load control device (such as, a dimmer switch) for controlling power delivered from an AC power source to an electrical load (such as, a high-efficiency lighting load) includes a thyristor coupled between the source and the load, a gate coupling circuit coupled between a first main terminal and a gate terminal of the thyristor, and a control circuit. The control circuit is configured to control the gate coupling circuit to conduct a pulse of current through the gate terminal to render the thyristor conductive at a firing time during a half cycle of the AC power source, and to allow the gate coupling circuit to conduct at least one other pulse of current after the firing time during the half cycle. The load control device is further arranged to conduct current through the electrical load if the thyristor becomes non-conductive and remains non-conductive during the 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 current can be conducted to energize the electrical load and a gate terminal through which current can be conducted to render the thyristor conductive between the first and second main terminals;

a gate coupling circuit electrically coupled to the first main terminal of the thyristor and arranged to conduct current through the gate terminal of the thyristor;

a controllable switching circuit electrically coupled in series between the gate coupling circuit and the gate terminal of the thyristor and configured to conduct current through the gate terminal of the thyristor; and

a control circuit configured to render the controllable switching circuit conductive and to control the gate coupling circuit to conduct a pulse of current through the gate terminal of the thyristor at a firing time during a present half-cycle of the AC power source to render the thyristor conductive, the control circuit being configured to control the gate coupling circuit to allow the gate coupling circuit to conduct at least one other pulse of current through the gate terminal of the thyristor after the firing time during the present half-cycle, the control circuit being further configured to render the controllable switching circuit non-conductive before the end of the present half-cycle to prevent any further pulses of current from being thereafter conducted through the gate terminal of the thyristor during the present half-cycle.

2. The load control device of claim 1, wherein the thyristor is able to commutate off after the control circuit renders the controllable switching circuit non-conductive, the control circuit being further configured to maintain the controllable switching circuit non-conductive until at least the beginning of the next half-cycle of the AC power source, thereby assuring that the thyristor remains non-conductive for the remainder of the present half-cycle after the thyristor commutates off.

3. The load control device of claim 2, wherein the control circuit is configured to control the gate coupling circuit to provide a path for current to be conducted through the electrical load after the controllable switching circuit is rendered non-conductive during the present half-cycle.

4. The load control device of claim 3, wherein the gate coupling circuit comprises two MOS-gated transistors electrically coupled in anti-series connection between the first main terminal of the thyristor and the controllable switching circuit.

5. The load control device of claim 4, wherein the control circuit is configured to generate two drive signals and to apply the drive signals to respective ones of the MOS-gated transistors to independently control the MOS-gated transistors.

6. The load control device of claim 5, wherein the control circuit is configured to render both of the MOS-gated transistors conductive at the firing time.

7. The load control device of claim 6, wherein the control circuit is configured to render a first one of the MOS-gated transistors non-conductive prior to the end of the present half-cycle, and to render a second one of the MOS-gated transistors non-conductive after the end of the present half-cycle.

8. The load control device of claim 7, wherein the configuration of the control circuit is such that the first one of the MOS-gated transistors blocks current at the beginning of the next half-cycle, and the second one of the MOS-gated transistors conducts current the until the end of the present half-cycle.

9. The load control device of claim 6, wherein the gate coupling circuit comprises two control inputs for receiving the respective drive signals from the control circuit, the gate coupling circuit being configured to conduct through each of the control inputs an amount of current appropriate to charge an input capacitance of a gate terminal of the respective MOS-gated transistor when the MOS-gated transistors are rendered conductive at the firing time.

10. The load control device of claim 4, wherein the control circuit is configured to generate a single drive signal for controlling the gate coupling circuit, the gate coupling circuit comprising a control input for receiving the drive signal from the control circuit.

11. The load control device of claim 10, wherein the gate coupling circuit is configured to conduct through the control input an average current of less than one microamp to maintain the gate coupling circuit conductive between the firing time and the end of the present half-cycle.

12. The load control device of claim 10, wherein the gate coupling circuit is configured to conduct through the control input an amount of current appropriate to charge input capacitances of gate terminals of the MOS-gated transistors when the MOS-gated transistors are rendered conductive at the firing time.

13. The load control device of claim 4, wherein the MOS-gated transistors comprise MOSFETs or IGBTs.

14. The load control device of claim 4, wherein the thyristor comprises a triac.

15. The load control device of claim 1, wherein the control circuit comprises a microprocessor.

16. The load control device of claim 15, wherein the gate coupling circuit comprises two MOS-gated transistors electrically coupled in anti-series connection between the first main terminal and the controllable switching circuit, the control circuit comprising a power supply configured to generate a DC supply voltage to power the microprocessor so that the control circuit is able to render the MOS-gated transistors of the gate coupling circuit conductive.

17. The load control device of claim 16, wherein the power supply is arranged to conduct current through the electrical load in order to generate the DC supply voltage.

18. The load control device of claim 16, further comprising:

a ground terminal adapted to be coupled to earth ground, the ground terminal being coupled such that the power supply is able to conduct current through the ground terminal in order to generate the DC supply voltage.

19. The load control device of claim 16, wherein the microprocessor is configured to generate at least one drive signal and to apply the at least one drive signal to the gate coupling circuit to render the gate coupling circuit conductive and non-conductive, the microprocessor being configured to drive the magnitude of the drive signal above a gate threshold voltage of the MOS-gated transistors to allow the gate coupling circuit to conduct a pulse of current through the gate terminal of the thyristor to render the thyristor conductive, the microprocessor being further configured to maintain the magnitude of the drive signal above the gate threshold voltage from the firing time through substantially the remainder of the present half-cycle to allow the gate coupling circuit to conduct the at least one other pulse of current between the firing time and the end of the present half-cycle.

20. The load control device of claim 1, wherein the control circuit is further configured to control the gate coupling circuit to allow the gate coupling circuit to conduct the at least one other pulse of current between the firing time and a second time that occurs after the firing time and before the end of the present half-cycle, the control circuit being further configured to render the controllable switching circuit non-conductive at the second time in order to prevent the gate coupling circuit from conducting any further pulses of current to thereby allow the thyristor to become non-conductive.

21. The load control device of claim 20, wherein the second time occurs near the end of the present half-cycle.

22. The load control device of claim 20, wherein the gate coupling circuit is arranged to conduct current through the electrical load when the thyristor becomes non-conductive after the second time.

23. 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 current can be conducted to energize the electrical load and a gate terminal through which current can be conducted to render the thyristor conductive between the first and second main terminals;

a gate coupling circuit arranged to conduct current through the gate terminal of the thyristor; and

a control circuit configured to control the gate coupling circuit to conduct a pulse of current through the gate terminal of the thyristor at a firing time during a present half-cycle of the AC power source to render the thyristor conductive, the control circuit being configured to control the gate coupling circuit to allow the gate coupling circuit to conduct at least one other pulse of current through the gate terminal of the thyristor between the firing time and a second time that occurs before the end of the present half-cycle, the control circuit being further configured to prevent the gate coupling circuit from conducting pulses of current through the gate terminal of the thyristor between the second time and the end of the present half-cycle to allow the thyristor to become non-conductive and remain non-conductive until the end of the present half-cycle;

wherein the load control device is further arranged to conduct current through the electrical load if the thyristor becomes non-conductive and remains non-conductive during the present half-cycle.

24. The load control device of claim 23, wherein the control circuit is configured to control the gate coupling circuit to conduct current through the electrical load if the thyristor becomes non-conductive and remains conductive during the present half-cycle.

25. The load control device of claim 24, further comprising:

a controllable switching circuit electrically coupled in series between the gate coupling circuit and the gate terminal of the thyristor and configured to conduct the current through the gate terminal of the thyristor;

wherein the gate coupling circuit is coupled between the first main terminal of the thyristor and the controllable switching circuit, the control circuit being configured to render the controllable switching circuit conductive and to control the gate coupling circuit to conduct the pulse of current through the gate terminal of the thyristor at the firing time to render the thyristor conductive, the control circuit being further configured to render the controllable switching circuit non-conductive at the second time to prevent the gate coupling circuit from conducting pulses of current through the gate terminal of the thyristor between the second time and the end of the present half-cycle.

26. The load control device of claim 24, wherein the gate coupling circuit comprises two MOS-gated transistors electrically coupled in anti-series connection between the first main terminal and the gate terminal of thyristor.

27. The load control device of claim 24, wherein the gate coupling circuit is electrically coupled between the first main terminal of the thyristor and the controllable switching circuit, the load control device further comprising:

a resistor coupled between the gate coupling circuit and the second main terminal of the thyristor, whereby a path is provided for current to flow through the electrical load after the thyristor becomes non-conductive during the present half-cycle.

28. The load control device of claim 24, wherein the control circuit and the gate coupling circuit are further arranged in such a way as to enable current to be conducted through the first and second main terminals of the thyristor during the present half-cycle even after the magnitude of the current conducted through the first and second main terminals of the thyristor drops below a rated holding current of the thyristor.

29. The load control device of claim 23, wherein the second time is sufficiently ahead of the end of the present half-cycle to prevent the thyristor from becoming conductive at the beginning of the next half-cycle.

30. A load control device for controlling 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 current can be conducted to energize the electrical load and a gate terminal through which current can be conducted to render the thyristor conductive between the first and second main terminals, the thyristor characterized by a rated holding current;

a gate coupling circuit arranged to conduct current through the gate terminal of the thyristor; and

a control circuit configured to control the gate coupling circuit to conduct a pulse of current through the gate terminal of the thyristor at a firing time during a present half-cycle of the AC power source to render the thyristor conductive, the control circuit being configured to control the gate coupling circuit to allow the gate coupling circuit to conduct at least one other pulse of current after the firing time during the present half-cycle;

wherein the control circuit is configured to control the gate coupling circuit to conduct current through the electrical load when the magnitude of current conducted through the first and second main terminals of the thyristor falls below the rated holding current of the thyristor.

31. The load control device of claim 30, further comprising:

a controllable switching circuit electrically coupled in series between the gate coupling circuit and the gate terminal of the thyristor and configured to conduct current through the gate terminal of the thyristor;

wherein the gate coupling circuit is coupled between the first main terminal of the thyristor and the controllable switching circuit, the control circuit being configured to render the controllable switching circuit conductive and to control the gate coupling circuit to conduct the pulse of current through the gate terminal of the thyristor at the firing time to render the thyristor conductive, the control circuit being further configured to render the controllable switching circuit non-conductive before the end of the present half-cycle to prevent the gate coupling circuit from thereafter conducting pulses of current through the gate terminal of the thyristor.

32. The load control device of claim 31, wherein the thyristor is able to commutate off after the control circuit renders the controllable switching circuit non-conductive, the control circuit being further configured to maintain the controllable switching circuit non-conductive until at least the beginning of the next half-cycle of the AC power source, thereby assuring that the thyristor remains non-conductive for the remainder of the present half-cycle after the thyristor commutates off.

33. The load control device of claim 32, wherein the control circuit is configured to control the gate coupling circuit to provide a path for current to be conducted through the electrical load after the controllable switching circuit is rendered non-conductive during the present half-cycle.

34. The load control device of claim 31, wherein the gate coupling circuit comprises two MOS-gated transistors electrically coupled in anti-series connection between the first main terminal of the thyristor and the controllable switching circuit.

35. The load control device of claim 31, wherein the gate coupling circuit is electrically coupled between the first main terminal of the thyristor and the controllable switching circuit, the load control device further comprising:

a resistor coupled between the gate coupling circuit and the second main terminal of the thyristor, whereby a path is provided for current to flow through the electrical load after the thyristor becomes non-conductive during the present half-cycle.