Electric lamp and discharge devices: systems – With cathode or cathode heater supply circuit – Plural load device systems
Patent
1993-10-14
1994-11-22
Lee, Benny
Electric lamp and discharge devices: systems
With cathode or cathode heater supply circuit
Plural load device systems
358475, 315105, 315307, 315DIG4, 315DIG7, 315156, 315158, 315219, H05B 3702
Patent
active
053672232
ABSTRACT:
A method and apparatus for automatically adjusting the light intensity output of a fluorescent lamp of a document scanner. The fluorescent lamp current level control apparatus comprises preheating circuitry for applying low voltage pulses of alternating polarity across filaments of the lamp, the low voltage pulses sufficient to preheat the filaments but insufficient to cause the lamp to fluoresce; high voltage circuitry for applying high voltage pulses of alternating polarity across the lamp, the high voltage pulses sufficient to cause the lamp to fluoresce; and control circuitry for receiving a first signal (PWM (D)) indicative of a desired level of current in the filaments, sensing a current indicative of the actual level of current in the filaments, and controlling the high voltage circuitry to cause the actual level of current to tend toward the desired level of current.
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Hewlett--Packard Company
Lee Benny
Shingleton Michael B.
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