Thomas Industries, Inc.

William H Henrich

Thomas E Dean

David M Fischer

Lawrence J Stratton

Herbert E Pietsch

An electronic frequency inverter circuit receives input electrical power at a lower frequency and energizes a load circuit including gaseous discharge lamps in a range of higher frequencies. First and second semiconductors are operated alternatively by a logic circuit in current mode control such that the switches operate at the high frequency range and the frequency of current in the load circuit varies as the magnitude of said source voltage varies. The load circuit has an impedance which varies with frequency such that the peak amplitude of the load current remains substantially constant despite variations in the magnitude of said source voltage to achieve a desirable crest factor for the lamp current. A high current limit circuit rapidly turns off the switches when excessively high current begins to flow through the switches. Low voltage is supplied in port from the high frequency current. Normal operation is ensured during start-up, for reduced line voltage and for a semiconductor chip embodiment.

High frequency ballast for gaseous discharge lamps

In a fluorescent lamp, a 'soft' start-up circuit initially applies a lamp, or inter-electrode, voltage which is limited to a peak voltage that will not start the lamp prior to heating of the lamp cathode to the proper temperature. The lamp cathode is then heated to the proper start-up temperature after which the lamp voltage is increased to a value well in excess of the ignition voltage required for all lamp types and operating characteristics in initiating lamp operation. The increased lamp voltage is applied in a pulsed manner until the lamp is ignited, whereupon the lamp may be operated at normal lamp current and cathode voltages or the lamp filaments may even be turned off with a consequent savings in input power.

Fluorescent lamp circuit with regulation responsive to voltage, current,

A system for controlling the current in a solid state, high frequency ballast energizing a gaseous discharge lamp for providing light dimming therein is disclosed. The ballast includes a thyristor/capacitor inverter bridge for generating the lamp current which is regulated by a commutation circuit synchronized with zero crossings of the thyristor current. Lamp current and voltage level signals are fed back to the commutation circuit for proper lamp current regulation. A dimming signal is added to either the lamp current feedback or voltage feedback signal and this composite signal is provided to the lamp current regulator in varying the bias thereof for selectively controlling light intensity. Dimming may be accomplished either manually by means of a rotatable switch having an output which varies linearly with shaft rotation or automatically by means of an ambient light level sensor to provide a predetermined output light level which may be manually adjusted. A common isolated control line facilitates photosensing control in a multiple ballast/light system with inter-ballast and ground isolation provided by optoisolators. In a preferred embodiment, a user adjustable balanced bridge is responsive to either manual or light level-dependent automatic control inputs for varying the bias of an input amplifier of the lamp current regulator.

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Sparta, TN, United States of America

William H Henrich