Abstract: A two level lighting ballast is provided, which includes a self-oscillating inverter circuit and a control circuit. The inverter includes an input; an output to selectively provide current to energize a lamp; a switching circuit operating at a switching frequency; a feedback transformer; and an impedance component. The feedback transformer is connected to the output, and drives the switching circuit based on the lamp current. The impedance component is connected in parallel with the feedback transformer, and is operated by the control circuit. When the control circuit enables the impedance component, the switching circuit operates in a first frequency range, and a first lamp current is provided. When the control circuit disables the impedance component, the switching circuit operates in a second frequency range, and a second lamp current is provided. The first frequency range is lower than the second, and the first lamp current is greater than the second.

Abstract: A ballast that selectively operates multiple lamps is provided. The ballast includes a switching network, capable of operating in a number of switching configurations. The ballast also includes a control circuit, and two lamp control switches. The control circuit is connected to the switching network, and provides respective control signals via respective output terminals as a function of the switching configuration of the switching network. Each lamp control switch is in parallel with its lamp and is connected to a respective output terminal. The first lamp control switch is connected to a ballast power supply, and either provides power to the first lamp or does not, depending on the first control signal. The second lamp control switch is connected to the first lamp control switch and to ground, and either provides power to the second lamp or does not, depending on the second control signal.

Abstract: A ballast that selectively operates multiple lamps is provided. The ballast includes a switching network, capable of operating in a number of switching configurations. The ballast also includes a control circuit, and two lamp control switches. The control circuit is connected to the switching network, and provides respective control signals via respective output terminals as a function of the switching configuration of the switching network. Each lamp control switch is in parallel with its lamp and is connected to a respective output terminal. The first lamp control switch is connected to a ballast power supply, and either provides power to the first lamp or does not, depending on the first control signal. The second lamp control switch is connected to the first lamp control switch and to ground, and either provides power to the second lamp or does not, depending on the second control signal.

Abstract: A two level lighting ballast is provided, which includes a self-oscillating inverter circuit and a control circuit. The inverter includes an input; an output to selectively provide current to energize a lamp; a switching circuit operating at a switching frequency; a feedback transformer; and an impedance component. The feedback transformer is connected to the output, and drives the switching circuit based on the lamp current. The impedance component is connected in parallel with the feedback transformer, and is operated by the control circuit. When the control circuit enables the impedance component, the switching circuit operates in a first frequency range, and a first lamp current is provided. When the control circuit disables the impedance component, the switching circuit operates in a second frequency range, and a second lamp current is provided. The first frequency range is lower than the second, and the first lamp current is greater than the second.

Abstract: An electronic ballast (10) for powering at least one gas discharge lamp (30) includes a current-fed resonant inverter (300) and a load shed circuit (600). Inverter (300) ordinarily powers the lamp at a first level. When a load shed command is sent by the electric utility and received by an associated load shed receiver within the ballast (10), load shed circuit (600) causes the inverter to reduce the lamp power from the first level to a second level. Preferably, load shed circuit (600) includes an isolation circuit (620) and a bidirectional switch (640) that is coupled in parallel with a return ballasting capacitor (388) within inverter (300). In the absence of a load shed command, bidirectional switch (640) effectively shunts return ballasting capacitor (388), which causes the lamp to be powered at the first level. In response to a load shed command, bidirectional switch (640) ceases to shunt return ballasting capacitor (388), thereby causing the lamp power to be reduced to the second level.