Abstract: An electronic ballast having particular application for driving small diameter fluorescent tubes or lamps (such as the T2, T4 and T5 sizes). The electronic ballast has a shutdown circuit by which to remove power to the oscillator when the tube or lamp is close to the end of its useful life or when an abnormal condition occurs such that a rise in operating voltage is detected. The shutdown circuit detects the rise in the operating voltage of the tube or lamp and energizes a relay through the conduction path of a photoresponsive transistor that is rendered conducting by a light emitting diode. The relay directs power away from the oscillator and towards the control electrode of the photoresponsive transistor to hold the phototransistor on and thereby disable the ballast. The ballast also includes a power factor controller to provide a high power factor and a more efficient operation.