General Electric Company

Kurt W Haas

Louis Robert Nerone

David Joseph Kachmarik

Michael M Secen

Gordon Alexander Grigor

Kelvin B Belle

A ballast circuit for a gas discharge lamp comprises a resonant load circuit incorporating the gas discharge lamp and including a resonant inductance and a resonant capacitance. A d.c.-to-a.c. converter circuit induces an a.c. current in the resonant load circuit. The converter circuit comprises first and second switches serially connected between a bus conductor at a d.c. voltage and a reference conductor, and which are connected together at a common node through which the a.c. load current flows. A voltage-breakover (VBO) device is effectively connected between the common node and a second node. A network is provided for setting the voltage of the second node with respect to the common node at less than the breakover voltage of the VBO device when the lamp is operating at steady state. A polarity-determining impedance is connected between the common node and one of the bus conductor and the reference conductor, to set the initial polarity of pulse to be generated upon the firing of the VBO device.

Lamp ballast circuit with simplified starting circuit

A condensed power supply circuit for powering a gas discharge lamp with bi-directional current reduces duty cycle by increasing dead time. The circuit comprises an arrangement for supplying d.c. power from an a.c. voltage, a series half bridge converter, a boost converter, a resistor-capacitor delay circuit associated with a gate to control dead time, and a snubber capacitance for facilitating zero voltage switching to fill the entire dead time. The series half-bridge converter alternately impresses a d.c. bus voltage from a bus conductor across a load circuit first with one polarity and then with an opposite polarity. The series half-bridge converter includes a first switch, a second switch, and a switching control circuit for alternately switching on the first and second switches. The boost converter comprises a boost capacitor, a boost inductor, and means for periodically connecting a load end of the boost inductor through a low impedance path to the ground conductor, thereby charging the boost inductor. The present invention reduces duty cycle via an increase in dead time. The resistor-capacitor delay circuit, associated with a gate, is used to control dead time. The snubber capacitance, which facilitates zero voltage switching to fill the entire dead time range, has a value set by the resistor-capacitor delay circuit.

Reduced bus voltage integrated boost high power factor circuit

A ballast circuit for a gas discharge lamp, of the type having a pair of resistively heated cathodes that are resistively heated both during a cathode pre-heat period prior to lamp turn-on, and during steady state lamp operation, is disclosed. The ballast circuit includes circuitry for providing, on a bus conductor, a d.c. bus voltage with respect to a ground, and a converter, responsive to the d.c. bus voltage, for supplying bidirectional current to a resonant load circuit. The resonant load circuit includes the gas discharge lamp, a resonant capacitor coupled between the lamp cathodes such that its voltage varies with lamp voltage, and a resonant inductor serially coupled to the resonant capacitor and cooperating therewith to set a magnitude, and resonant frequency, of the bidirectional lamp current. Circuitry is provided for powering the resistively heated lamp cathodes, to thereby heat the cathodes. Further included is a circuit for maintaining the lamp voltage during a cathode pre-heat period below a predetermined level so as to prevent lamp turn-on during such period; such circuit includes circuitry for holding a first cathode of the lamp at a substantially constant voltage, and circuitry for clamping a second cathode of the lamp below the predetermined level. Such clamping circuitry includes a positive temperature coefficient (PTC) impedance device coupled to a second cathode of the lamp, and serially connected by a positively poled clamping diode to the bus conductor, and serially connected by a negatively poled clamping diode to the ground.

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Chesterland, OH, United States of America

Kurt W Haas