Load control device fo rhigh-efficiency loads

• US 8,970,128 B2
• Filed: 11/19/2013
• Issued: 03/03/2015
• 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:
  US14/083,968
• Publication Number:
  US 20140077720A1
• Time in Patent Office: 469 Days
• Field of Search: 315/224, 315/194, 315/199, 315/291, 315/294, 315/297, 315/307, 315/311, 315/318
• US Class Current: 315/291
• 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 a thyristor), which may be operable to remain conductive independent of the magnitude of a load current conducted through semiconductor switch and to conduct the load current to and from the load during a single half-cycle. The dimmer switch comprises a control circuit that conducts a control current through the load in order to generate a gate drive signal for rendering the bidirectional semiconductor switch conductive and non-conductive each half-cycle. The control circuit may provide a constant gate drive to the bidirectional semiconductor switch after the bidirectional semiconductor switch is rendered conductive each half-cycle.

Claims

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

a thyristor adapted to be coupled in series electrical connection between the AC power source and the electrical load for conducting a load current from the AC power source to the electrical load, the thyristor having a gate for rendering the thyristor conductive; and

a control circuit generating a gate drive signal for rendering the thyristor conductive at a firing time during each half-cycle of the AC power source, the control circuit comprising a power supply for generating a supply voltage, the power supply adapted to conduct a charging current through the load for generating the supply voltage;

wherein the control circuit is operable to maintain the thyristor conductive after the firing time, such that the thyristor is able to remain conductive independent of the magnitude of the load current conducted through the thyristor and to conduct the load current to and from the electrical load during a single half-cycle of the AC power source.

2. The load control device of claim 1, wherein the supply voltage allows the control circuit to maintain the thyristor conductive after the firing time, so that the thyristor remains conductive independent of the magnitude of the load current conducted through the thyristor.

3. The load control device of claim 2, wherein the control circuit receives a signal representative of a voltage developed across the thyristor, the control circuit operable to determine a half-cycle start time near the beginning of a half-cycle of the AC power source in response to the signal representative of the voltage developed across the thyristor.

4. The load control device of claim 3, wherein the control circuit:

drives the gate drive signal to a first magnitude to render the thyristor conductive after a first variable amount of time has elapsed since the half-cycle start time;

maintains the gate drive signal at the first magnitude after the thyristor is rendered conductive;

drives the gate drive signal to a second magnitude after a second fixed amount of time has elapsed since the half-cycle start time to allow the thyristor to commutate off;

controls the second fixed amount of time to be approximately equal during each half-cycle of the AC power source; and

varies the first variable amount of time in response to a desired amount of power to be delivered to the load to thus control the amount of power delivered to the load to the desired amount.

5. The load control device of claim 4, wherein the control circuit comprises:

a timing circuit for generating a timing signal that increases in magnitude with respect to time, the timing circuit starting to generate the timing signal at the half-cycle start time; and

a drive circuit for receiving the timing voltage and rendering the thyristor conductive each half-cycle in response to the magnitude of the timing signal, so as to control the amount of power delivered to the electrical load to a desired amount;

wherein the timing circuit is operable to continue generating the timing signal after the thyristor is rendered conductive at the firing time each half-cycle, such that the drive circuit continues to render the thyristor conductive and the thyristor remains conductive independent of the magnitude of the load current conducted through the thyristor.

6. The load control device of claim 5, wherein the timing signal increases in magnitude with respect to time at a constant rate, and the timing circuit stops generating the timing signal after the second fixed amount of time has elapsed since the half-cycle start time.

7. The load control device of claim 6, wherein the drive circuit drives the gate drive signal to the first magnitude to render the thyristor conductive when the magnitude of the timing signal exceeds a variable threshold representative of the desired amount of power to be delivered to the load, and drives the gate drive signal to the second magnitude to allow the thyristor to commutate off when the timing circuit stops generating the timing signal.

8. The load control device of claim 6, wherein the first variable amount of time has a length that is not dependent upon the length of the second fixed amount of time that the timing circuit generates the timing signal.

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

10. The load control device of claim 9, further comprising:

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

wherein the microprocessor is coupled to the RF receiver for determining a desired amount of power to be delivered to the load in response to the received RF signal.

11. The load control device of claim 1, wherein the control circuit controls the gate drive signal to allow the control circuit to commutate off before the end of the half-cycle.

12. The load control device of claim 1, wherein the power supply conducts the charging current through the load when the thyristor is non-conductive to generate the supply voltage.

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

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

15. A load control device for controlling the amount of power delivered from an AC power source to an electrical load to a desired amount of power, the load control device comprising:

a bidirectional semiconductor switch adapted to be coupled in series electrical connection between the AC power source and the electrical load for conducting a load current from the AC power source to the electrical load, the bidirectional semiconductor switch having a control input for rendering the bidirectional semiconductor switch conductive and non-conductive; and

a digital control circuit receiving a signal representative of a voltage developed across the bidirectional semiconductor switch, the digital control circuit operable to determine a half-cycle start time near the beginning of a half-cycle of the AC power source in response to the signal representative of the voltage developed across the bidirectional semiconductor switch, the digital control circuit comprising a power supply for generating a supply voltage, the power supply adapted to conduct a charging current through the load for generating the supply voltage;

wherein the digital control circuit is configured to;

generate a gate drive signal that is operatively coupled to the control input of the bidirectional semiconductor switch;

drive the gate drive signal to a first magnitude to render the bidirectional semiconductor switch conductive after a first variable amount of time has elapsed since the half-cycle start time;

maintain the gate drive signal at the first magnitude after the bidirectional semiconductor switch is rendered conductive, such that the bidirectional semiconductor switch remains conductive independent of the magnitude of the load current conducted through the bidirectional semiconductor switch;

drive the gate drive signal to a second magnitude to render the bidirectional semiconductor switch non-conductive after a second fixed amount of time has elapsed since the half-cycle start time;

control the second fixed amount of time to be approximately equal during each half-cycle of the AC power source;

vary the first variable amount of time in response to the desired amount of power to be delivered to the load to thus control the amount of power delivered to the load to the desired amount.

16. The load control device of claim 15, wherein the digital control circuit comprises a digital processing device powered by the supply voltage.

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

an intensity adjustment actuator adapted to be actuated for adjusting the desired amount of power delivered to the load;

wherein the digital processing device is operable to determine the desired amount of power to be delivered to the load in response to the intensity adjustment actuator.

18. The load control device of claim 17, wherein the digital control circuit further comprises raise and lower tactile switches coupled to the digital processing device, and the intensity adjustment actuator comprises a rocker switch for actuating the raise and lower tactile switches for respectively increasing and decreasing the desired amount of power to be delivered to the load.

19. The load control device of claim 17, wherein the intensity adjustment actuator comprises a potentiometer coupled to the digital processing device, and the intensity adjustment actuator comprises a slider knob mechanically coupled to the potentiometer, such that the potentiometer generates a DC voltage representative of the desired amount of power to be delivered to the load.

20. The load control device of claim 16, wherein the power supply conducts the charging current through a storage capacitor and the load when the bidirectional semiconductor switch is non-conductive in order to generate the supply voltage across the storage capacitor.

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

an RF receiver coupled to the digital processing device and operable to receive an RF signal;

wherein the digital processing device is operable to determine the desired amount of power to be delivered to the load in response to the RF signal.

22. The load control device of claim 16, wherein the digital processing device comprises a microprocessor.

23. The load control device of claim 15, wherein the bidirectional semiconductor switch comprises first and second switching transistors coupled in anti-series connection.

24. The load control device of claim 23, wherein the first and second switching transistors comprise first and second FETs.

25. The load control device of claim 24, wherein the control circuit renders both the first and second FETs conductive and non-conductive at the same times each half-cycle to control the amount of power delivered to the load.

26. The load control device of claim 23, wherein the first and second switching transistors comprise first and second IGBTs.

27. The load control device of claim 26, wherein the control circuit renders both the first and second FETs conductive and non-conductive at the same times each half-cycle to control the amount of power delivered to the load.

28. The load control device of claim 15, wherein the bidirectional semiconductor switch comprises a thyristor.