Magnetek, Inc.

Ben A Beer

Bryce L Hesterman

A family of programmed start parallel-resonant electronic ballast circuits operate in a first mode during a preheat interval following application of power to the ballast, and then afterwards operate in a second mode. The ballast circuits can be based on any of the several forms of current-fed parallel-resonant inverters, all of which have a dc choke inductor. A first embodiment operates such that, during the first mode, the parallel-resonant inverter is inhibited, while an auxiliary transistor develops a trapezoidal voltage waveform across the dc choke inductor. Filament preheating is provided by windings coupled to the dc choke inductor. The ballast output voltage is essentially zero so that no destructive glow current is produced. During the second mode, the auxiliary transistor is inhibited, and the parallel-resonant inverter produces a sinusoidal output voltage. The rms magnitude of the filament heating voltage is reduced by about fifty percent as the waveshape changes from the trapezoidal shape to a form similar to that of a full-wave rectified sine-wave in which the dc component has been removed. In an alternative embodiment, the waveforms of the first embodiment are produced without using an auxiliary transistor. During the first mode, all of the switching transistors of the parallel-resonant inverter are operated in unison. During the second mode, they are switched in the normal out-of-phase manner.

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Ossian, IN, United States of America

Ben A Beer