Load control device for high-efficiency loads

Patent metadata

Field	Value
Publication number	US-10187944-B2
Application number	US-201615256184-A
Country	US
Kind code	B2
Filing date	Sep 2, 2016
Priority date	Sep 4, 2015
Publication date	Jan 22, 2019
Grant date	Jan 22, 2019

Abstract

A load control device for controlling power delivered from an AC power source to an electrical load may comprise a thyristor, a gate current path, and a control circuit. The control circuit may be configured to control the gate current path to conduct a pulse of gate current through a gate terminal of the thyristor to render the thyristor conductive at a firing time during a half-cycle of the AC power source. The control circuit may operate in a first gate drive mode in which the control circuit renders the gate current path non-conductive after a pulse time period from the firing time. The control circuit may operate in a second gate drive mode in which the control circuit maintains the gate current path conductive after the pulse time period during the half-cycle.

First claim

What is claimed is:

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 comprising a first main terminal, a second main terminal, and a gate terminal, the first and second main terminals configured to conduct current to energize the electrical load, the gate terminal configured to conduct current to render the thyristor conductive;
a gate current path connected to the gate terminal, the gate current path comprising a gate coupling circuit and configured to conduct current through the gate terminal of the thyristor; and
a control circuit electrically coupled to the gate coupling circuit to control the gate current path, the control circuit configured to control the gate current path to conduct a pulse of the current through the gate terminal of the thyristor to render the thyristor conductive at a firing time during a half-cycle of the AC power source, the control circuit further configured to operate in a first gate drive mode and a second gate drive mode,
wherein, in the first gate drive mode, the control circuit renders the gate current path conductive for a pulse time period and renders the gate current path non-conductive after the pulse time period during the half-cycle of the AC power source, and
wherein, in the second gate drive mode, the control circuit maintains the gate current path conductive after the pulse time period to allow at least one other pulse of current to be conducted through the gate terminal of the thyristor after the pulse time period during the half-cycle of the AC power source.

2. The load control device of claim 1 , wherein the control circuit is configured to operate in the first gate drive mode while turning on the electrical load and to operate in the second gate drive mode when in a steady state condition.

3. The load control device of claim 1 , wherein the control circuit is configured to operate in the first gate drive mode over a first plurality of half-cycles of the AC power source and to operate in the second gate drive mode over a second plurality of half-cycles of the AC power source after the first plurality of half-cycles.

4. The load control device of claim 3 , wherein the control circuit is configured to control the pulse time period to a minimum pulse time period during a first one of the first plurality of half cycles, and to increase the pulse time period during a subsequent one of the first plurality of half cycles.

5. The load control device of claim 4 , wherein the control circuit is configured to periodically increase the pulse time period while operating in the first gate drive mode.

6. The load control device of claim 5 , wherein the control circuit is configured to increase the pulse time period in each of the first plurality of half-cycles.

7. The load control device of claim 5 , wherein the control circuit is configured to periodically increase the pulse time period while operating in the first gate drive mode until the pulse time period is equal to a maximum pulse time period.

8. The load control device of claim 7 , wherein, during the second gate drive mode, the control circuit is configured to maintain the gate current path conductive for the maximum pulse time period in each of the second plurality of half-cycles.

9. The load control device of claim 8 , wherein the maximum pulse time period is dependent upon the firing time of the second gate drive mode.

10. The load control device of claim 7 , wherein the number of half cycles over which the control circuit increases the pulse time period from the minimum pulse time period to the maximum pulse time period is dependent upon the firing time of the second gate drive mode.

11. The load control device of claim 3 , wherein the pulse time period is constant while the control circuit is operating in the first gate drive mode.

12. The load control device of claim 1 , wherein the control circuit is configured to operate in the second gate drive mode while turning on the electrical load, detect a fault condition while turning on the electrical load using the second gate drive mode, switch to the first gate drive mode over a first plurality of half-cycles of the AC power source while turning on the electrical load, and operate in the second gate drive mode over a second plurality of half-cycles of the AC power source after the first plurality of half-cycles.

13. The load control device of claim 1 , further comprising:
a first zero-crossing detection circuit configured to generate a first zero-cross signal that provides an indication of a zero-crossing of the AC power source;
wherein the control circuit is configured to control the gate current path to conduct the pulse of current through the gate terminal of the thyristor to render the thyristor conductive at the firing time during the half-cycle of the AC power source based on the first zero-cross signal.

14. The load control device of claim 13 , wherein the control circuit is configured to sample the first zero-cross signal during a zero-cross window and determine if the first zero-cross signal indicated the zero-crossing of the AC power source during the zero-cross window.

15. The load control device of claim 14 , wherein the control circuit is configured to operate in the second gate drive mode while turning on the electrical load and determine that the first zero-cross signal did not indicate the zero-crossing of the AC power source during the zero-cross window while turning on the electrical load using the second gate drive mode, the control circuit configured to subsequently operate in the first gate drive mode while turning on the electrical load.

16. The load control device of claim 13 , wherein the first zero-crossing detection circuit is coupled in parallel with the thyristor.

17. The load control device of claim 16 , further comprising:
a second zero-crossing detection circuit adapted to be coupled in parallel with the AC power source, the second zero-crossing detection circuit configured to generate a second zero-cross signal that provides an indication of a zero-crossing of the AC power source;
wherein the control circuit is configured to determine that the second zero-crossing detection circuit is coupled in parallel with the AC power source and to operate in the first gate drive mode based on the determination while turning on the electrical load and when in a steady state condition.

18. The load control device of claim 1 , wherein the gate current path further comprises a controllable switching circuit configured to be electrically coupled in series between the gate coupling circuit and the gate terminal of the thyristor and to conduct current through the gate terminal of the thyristor, and wherein the control circuit is 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.

19. The load control device of claim 18 , wherein, when operating in the second gate drive mode, the control circuit is configured to render the controllable switching circuit non-conductive before the end of the half-cycle of the AC power source to prevent further pulses of current from being conducted through the gate terminal of the thyristor.

20. The load control device of claim 19 , wherein the thyristor

Assignees

• Lutron Electronics Co

Inventors

• Macadam Russell L
• Parent Joseph T
• Weightman Russell

Classifications

• H05B45/31

  Phase-control circuits · CPC title

• H05B45/3575

  by means of dummy loads or bleeder circuits, e.g. for dimmers · CPC title

• H05B39/044 Primary

  continuously (H05B39/042 takes precedence) · CPC title

• H02M5/2576

  with digital control · CPC title

• H05B45/59

  for reducing or suppressing flicker or glow effects · CPC title