Alternating cathode florescent lamp dimmer

Details Alternating cathode florescent lamp dimmer Alternating cathode florescent lamp dimmer

1989-10-12

1991-06-25

Mis, David

Electric lamp and discharge devices: systems

With cathode or cathode heater supply circuit

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

315 98, 315307, 315DIG4, 315DIG5, H05B 4136, H05B 4138

Patent

active

050270346

ABSTRACT:
An apparatus for use in dimming florescent lamps by alternating cathodes operated with pulsating unidirectional arc currents for a duration that is long relative to the filament thermal time constant, but short in relation to the mercury migration time constant of the florescent lamp. The invention provides apparatus using full bridge switching and full bridge clamping topology in a trigger driver as well as a power driver to prevent low voltage power supply "ride up". The invention further provides means for sensing cathode heater current to detect a failed cathode and to control the phase switching to a good cathode if a cathode failure occurs. The invention further provides apparatus for a balanced-to-group ground lamp drive voltage for improved ignition of the lamp plasma and better lamp luminance uniformity when the lamp is operated dimly. A logarithmic amplifier is provided in a closed loop operation for analog compression and also to provide a logarithmic dimming response. Flash protection is provided in order to eliminate pilot distractions.

REFERENCES:
patent: 4394603 (1983-07-01), Widmayer

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