Load control device for high-efficiency loads

• US 10,541,620 B2
• Filed: 11/12/2018
• Issued: 01/21/2020
• Est. Priority Date: 11/25/2009
• Status: Active Grant

• Current Assignee: Lutron Technology Company LLC
• Original Assignee: Lutron Technology Company LLC
• Inventors: Newman, Jr., Robert C.
• Primary Examiner(s): Laxton, Gary L
• Application Number:
  US16/186,863
• Publication Number:
  US 20190081570A1
• Time in Patent Office: 435 Days
• 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 the amount of 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 load terminal and the gate of the thyristor, and a control circuit coupled to a control input of the gate coupling circuit. The control circuit generates a drive voltage for causing the gate coupling circuit to conduct a gate current to thus 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 the gate current at any time from the firing time through approximately the remainder of the half cycle, where the gate coupling circuit conducts approximately no net average current to render and maintain the thyristor conductive.

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 bidirectional semiconductor switch adapted to be electrically coupled between the AC power source and the electrical load, and configured to conduct a load current to energize the electrical load, the bidirectional semiconductor switch comprises first and second switching transistors coupled in anti-series connection, the bidirectional semiconductor switch having a control input configured to receive at least one drive signal to render the bidirectional semiconductor switch conductive and non-conductive;

a control circuit configured to control the bidirectional semiconductor switch to render the bidirectional semiconductor switch conductive and non-conductive, 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 bidirectional semiconductor switch; 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 magnitude of the drive signal to a first magnitude to render the bidirectional semiconductor switch 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 bidirectional semiconductor switch conductive independent of the magnitude of the load current conducted through the bidirectional semiconductor switch during the present half-cycle, the control circuit further configured to control the magnitude of the 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 zero-crossing time of the present half-cycle, 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 configured to control the magnitude of the drive signal to the first magnitude to render the bidirectional semiconductor switch 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 bidirectional semiconductor switch is rendered conductive in each half-cycle, resulting in the control circuit maintaining the bidirectional semiconductor switch conductive independent of the magnitude of the load current conducted through the bidirectional semiconductor switch.

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 control the magnitude of the drive signal to the second magnitude when the timing circuit stops generating the timing signal to render the bidirectional semiconductor switch non-conductive.

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 first and second switching transistors comprise first and second FETs.

7. The load control device of claim 6, 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.

8. The load control device of claim 1, 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.

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

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

a bidirectional semiconductor switch adapted to be electrically coupled between the AC power source and the electrical load and configured to conduct a load current to energize the electrical load, the bidirectional semiconductor switch comprises first and second switching transistors coupled in anti-series connection, the bidirectional semiconductor switch having a control input configured to receive at least one drive signal for rendering the bidirectional semiconductor switch conductive and non-conductive;

a control circuit configured to control the bidirectional semiconductor switch to render the bidirectional semiconductor switch conductive and non-conductive, the control circuit configured to control the magnitude of the drive signal to a first magnitude to render the bidirectional semiconductor switch 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 drive signal at the first magnitude after the firing time, thereby enabling the bidirectional semiconductor switch 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.

11. The load control device of claim 10, 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 bidirectional semiconductor switch.

12. The load control device of claim 11, wherein the control circuit is configured to control the magnitude of the drive signal to the first magnitude to render the bidirectional semiconductor switch 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 bidirectional semiconductor switch conductive independent of the magnitude of the load current conducted through the bidirectional semiconductor switch between the firing time and a second time during the present half-cycle, the control circuit configured to control the magnitude of the drive signal to a second magnitude to render the bidirectional semiconductor switch non-conductive after the second time which occurs when a fixed amount of time has elapsed since the zero-crossing time of the present half-cycle, 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.

13. The load control device of claim 12, 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 configured control the magnitude of the drive signal to the first magnitude to render the bidirectional semiconductor switch 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 bidirectional semiconductor switch is rendered conductive in each half-cycle, 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 control the magnitude of the drive signal to the second magnitude when the timing circuit stops generating the timing signal to render the bidirectional semiconductor switch non-conductive.

14. The load control device of claim 10, wherein the first and second switching transistors comprise first and second FETs.

15. The load control device of claim 14, 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.

16. The load control device of claim 10, wherein the control circuit is configured to maintain the bidirectional semiconductor switch conductive between the firing time and a second time before the end of the half-cycle, and to control the magnitude of the drive signal to a second magnitude to render the bidirectional semiconductor switch non-conductive after the second time.

17. The load control device of claim 10, 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.

18. The load control device of claim 10, wherein the control circuit is configured to generate the drive signal for controlling the gate coupling circuit to maintain the bidirectional semiconductor switch conductive independent of the magnitude of the load current conducted through the bidirectional semiconductor switch.

19. The load control device of claim 10, wherein the power supply is configured to conduct the charging current through the electrical load when the bidirectional semiconductor switch is non-conductive to generate the supply voltage for powering the control circuit.

20. The load control device of claim 10, wherein the control circuit comprises a microprocessor powered by the supply voltage.