Patent ID: 8319451

Claim:
A ballast to power at least one lamp from an alternating current (AC) voltage supply, the ballast comprising: a first switch adapted to selectively connect the ballast to a first high voltage terminal of the AC voltage supply, the first switch having an on state and an off state; a second switch adapted to selectively connect the ballast to a second high voltage terminal of the AC voltage supply, the second switch having an on state and an off state; a lighting system converter circuit to provide voltage suitable to energize the at least one lamp; and a detector circuit, wherein the detector circuit comprises: a first input terminal coupled to the first switch; a second input terminal coupled to the second switch; a first resistor R 1 connected to the first input terminal; a second resistor R 2 connected to the second input terminal; a first output terminal connected to the lighting system converter circuit, wherein the first output terminal provides a supply current to the lighting system converter circuit to power components of the lighting system converter circuit, and wherein the first output terminal is connected to first input terminal via the first resistor R 1 and to the second input terminal via the second resistor R 2 ; a second output terminal connected to the lighting system converter circuit, wherein the second output terminal provides a control signal to the lighting system converter circuit, the control signal indicating one of a plurality voltage levels for providing to the at least one lamp to energize the at least one lamp as a function of the states of the first and second switches, wherein each voltage level corresponds to a different lighting level generated by the at least one lamp; a transistor network to detect a differential voltage between the first input terminal and the second input terminal and to generate a control signal as a function thereof; and a capacitor connected to the transistor network to smooth the control signal from the transistor network to provide a substantially direct current (DC) control signal; wherein the lighting system converter circuit receives the DC control signal via the second output terminal of the detector circuit and provides voltage to the at least one lamp as a function of the DC control signal.