Electronic ballast with interface circuitry for multiple dimming inputs

Abstract

A lamp controller includes an interface circuit, or receiver, which receives an input signal and decodes control signals supplied from a transmitting device, such as a power line wall controller, according to at least two of the following communication techniques: phase angle control, step control, and coded control. The receiver tests the input signal and identifies which type of control technique is employed by the wall controller connected to the lamp controller. The receiver then decodes the control command from the input signal. In a disclosed embodiment, the lamp controller is gas discharge lamp dimming ballast having a two wire input for connection to the hot dimmed and neutral leads of the power line controller. The ballast has an improved topology in which a pre-conditioner supplies a substantially constant DC voltage to a ballast stage including an inverter, a resonant tank output and a control circuit. The dim signal output by the receiver is independent of the DC rail voltage and, in combination with the maintenance of a substantially constant DC rail voltage, permits of improved dimming control while providing the ease of installation of a two wire ballast.