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 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 control the gate coupling circuit and the controllable switching 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 being configured to control the gate coupling circuit and the controllable switching circuit to allow the gate terminal of the thyristor to conduct current 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 controllable switching 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.