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Variable Intensity Control of Fluorescent Lamp

IP.com Disclosure Number: IPCOM000051044D
Original Publication Date: 1982-Aug-01
Included in the Prior Art Database: 2005-Feb-10
Document File: 2 page(s) / 31K

Publishing Venue

IBM

Related People

Chacon, CC: AUTHOR [+2]

Abstract

Fluorescent lamp 10 in the above circuit has its intensity controlled by regulating the AC current through the lamp. This current is controlled by varying the circuit operating frequency or by modulating transistor 12 on-time (duty cycle). The lamp 10 is AC controlled. In one direction, current through the lamp 10 is supplied by DC supply 13, and stabilized by the combination of inductor 11 and capacitor 14. In the other direction, current is supplied by capacitor 14. The 3.6 VAC source 15 supplies power to the lamp electrodes.

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Variable Intensity Control of Fluorescent Lamp

Fluorescent lamp 10 in the above circuit has its intensity controlled by regulating the AC current through the lamp. This current is controlled by varying the circuit operating frequency or by modulating transistor 12 on-time (duty cycle). The lamp 10 is AC controlled. In one direction, current through the lamp 10 is supplied by DC supply 13, and stabilized by the combination of inductor 11 and capacitor 14. In the other direction, current is supplied by capacitor 14. The
3.6 VAC source 15 supplies power to the lamp electrodes.

During start-up, ignition of the lamp 10 is accomplished by the resultant induced voltage across inductor 11 (as the transistor is turned-off). 0nce ignition is detected by the feedback element (photo-diode 18), the circuit begins its run-mode. During run-mode: a) When transistor 12 turns off, the current I flows through inductor 11, lamp 10, and capacitor 14. Capacitor

14 will then charge to an average operating voltage. b) When transistor 12 turns on, the voltage across capacitor 14 supplies current in the reverse direction through the lamp

to ground via transistor 12.

Light output from the lamp is proportional to the RMS current through the lamp. This RMS current is controlled by the feedback signal of photodiode 18. Intensity control circuitry 16 determines transistor 12 'on' and 'off' time duration. Two possible methods of regulation can be implemented with the intensity control circuitry...