Symmetry control circuit for pre-heating in electronic ballasts

Details Symmetry control circuit for pre-heating in electronic ballasts Symmetry control circuit for pre-heating in electronic ballasts

1997-08-07

1999-09-28

Shingleton, Michael B

Electric lamp and discharge devices: systems

With cathode or cathode heater supply circuit

Pulsating or a.c. supply to the cathode or heater circuit

315224, 315291, 315DIG7, H05B 3702

Patent

active

059594080

ABSTRACT:
A symmetry control circuit for a ballast driving a gas discharge lamp. The circuit controls the pre-heat time of a gas discharge lamp with heatable filaments by holding off the full striking voltage until the lamp has had sufficient time to pre-heat. The circuit is designed to work with electronic ballasts and especially electronic ballasts without boost power factor correction to properly pre-heat the lamp. A control circuit reduces the duty cycle in an inverter transistor, thereby keeping the voltage across the lamp low while allowing filament heating to occur. The control circuit is disabled after a time interval of about 500 ms, allowing the transistor duty cycle to increase to 50 percent, the lamp voltage to rise, and the properly pre-heated lamp to ignite.

REFERENCES:
patent: 4647817 (1987-03-01), Fahnrich et al.
patent: 4935669 (1990-06-01), Nilssen
patent: 4983887 (1991-01-01), Nilssen
patent: 5023488 (1991-06-01), Gunning
patent: 5028818 (1991-07-01), Go Ang et al.
patent: 5245253 (1993-09-01), Quazi
patent: 5430404 (1995-07-01), Campbell et al.
patent: 5583402 (1996-12-01), Moisin et al.
patent: 5650925 (1997-07-01), Hesterman
Magnetek SPA Italy Ballast 6028 Schematic by David Martini Feb. 16, 1994.

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