Load control device for high-efficiency loads

A load control device for controlling power delivered from an alternating-current (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 between the first main terminal and the gate terminal of the thyristor to conduct current through the gate terminal of the thyristor;
• a controllable switching circuit electrically coupled in parallel with the first and second main terminals of the thyristor;
• and
• a control circuit configured to control the gate coupling circuit to conduct current through the gate terminal of the thyristor to render the thyristor conductive at a firing time during a present half-cycle of the AC power source, the control circuit configured to control the gate coupling circuit to allow the gate coupling circuit to conduct current through the gate terminal of the thyristor again at a first time between the firing time and a second time that occurs after the firing time and before the end of the present half-cycle;
• wherein the control circuit is configured to render the gate coupling circuit non-conductive between approximately the second time and the end of the present half-cycle to prevent current from being thereafter conducted through the gate terminal of the thyristor during the present half-cycle, the control circuit being further configured to render the controllable switching circuit conductive to conduct current through the electrical load between approximately the second time and the end of the present half-cycle.