LOAD CONTROL DEVICE FOR HIGH-EFFICIENCY LOADS

摘要

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 dimmer switch includes a bidirectional semiconductor switch, which is operable to be rendered conductive each half-cycle and to remain conductive independent of the magnitude of a load current conducted through semiconductor switch. 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. The bidirectional semiconductor switch may comprise, for example, a triac or two field-effect transistors coupled in anti-series connection.

主权项

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 having first and second main terminals through which a load current can be conducted to energize the electrical load and a gate terminal through which a gate current can be conducted to render the thyristor conductive; a gate coupling circuit electrically coupled to conduct the gate current through the gate terminal of the thyristor; a control circuit electrically coupled to control the gate coupling circuit, 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 thyristor; 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 gate coupling circuit to be conductive to conduct the gate current through the gate terminal of the thyristor to render the thyristor 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 thyristor conductive independent of the magnitude of the load current conducted through the thyristor during the present half-cycle, the control circuit further configured to prevent the gate coupling circuit from conducting the gate current through the gate terminal of the thyristor after a second, fixed amount of time has elapsed since the zero-crossing time of the present half-cycle to allow the thyristor to become non-conductive, 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.