Abstract: A ballast having a converter for converting input power into DC at a high frequency and a commutator for converting the DC to AC at a low frequency to cause light emission from a gas discharge lamp. The converter also contains a transformer for converting the input AC to a low voltage AC for heating the filaments in the lamp. Current and Voltage sensors associated with the commutator provide feedback to control circuitry which allows power conversion after the filaments heat and the voltage to the lamp to increase to the voltage required to start the lamp even when different starting voltage requirement lamps are used. After the lamp starts, the lamp is soley current mode controlled. By frequency modulation of the commutator, both power and crest factor can be controlled.

Abstract: A ballast for controlling the light emitted by fluorescent lamps (25) is disclosed. DC power derived from either a DC source or a rectified AC source is switched on and off at a high frequency rate by a switch (15) to control the flow of current through the primary winding of the transformer of a flyback converter (27). The switched output is rectified and applied by the flyback converter to the filaments of the fluorescent lamps (25) to be controlled. The rectified, switched output is also applied by a .pi. filter (17) to a commutator circuit (21) that controls the starting of the fluorescent lamps (25). The commutator circuit (21) is switched at a lower frequency rate. The bridge input voltage and current are sensed and fed back to a control circuit (23), which includes a regulating pulse width modulator and a bridge switching circuit. The control circuit (23) also receives a pulse current feedback signal from the switch (15) and an external dimming control signal.