A multi-function feedback sense input in an electronic ballast control
indicates a number of lamp faults on the basis of lamp parameters
exceeding specified thresholds. An end of life detection is achieved by
conditioning a lamp feedback with a DC offset to provide a simple
threshold comparison to determine if the lamp exceeds specified
operational boundaries. An open filament, absent lamp or broken cathode
is detected on the same feedback sense by detecting an open circuit in
the lamp filament and driving the sense feedback to a shutdown state in
the event of a filament open circuit. The ballast control includes a
current sense feedback for detecting overcurrent conditions as well as
lamp faults so that the control detects an end of life condition, lamp
absence, broken lamp, open filament, broken cathode, overcurrent,
hardswitching or failure to ignite fault with a minimum number of
feedback sensors. The ballast control provides a number of protections
with a simplified circuit to reduce cost and improve functionality of the
electronic ballast control.