Electric lamp and discharge devices: systems – With cathode or cathode heater supply circuit – Pulsating or a.c. supply to the cathode or heater circuit
Patent
1993-12-06
1996-01-09
Pascal, Robert J.
Electric lamp and discharge devices: systems
With cathode or cathode heater supply circuit
Pulsating or a.c. supply to the cathode or heater circuit
315104, 315200R, 315209R, 315DIG5, H05B 3904
Patent
active
054831253
ABSTRACT:
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.
REFERENCES:
patent: 4647817 (1987-03-01), Fahnrich et al.
patent: 4782268 (1988-11-01), Fahnrich et al.
patent: 5027033 (1991-06-01), Zuchtriegel
patent: 5122712 (1992-06-01), Hirschmann
Haas Kurt W.
Kachmarik David J.
Nerone Louis R.
Secen Michael M.
Corwin Stanley C.
General Electric Company
Hawranko George E.
Pascal Robert J.
Philogene Haissa
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