Electric lamp and discharge devices: systems – Discharge device and/or rectifier in the supply circuit – Flashers
Reexamination Certificate
2000-02-28
2001-11-13
Vu, David (Department: 2821)
Electric lamp and discharge devices: systems
Discharge device and/or rectifier in the supply circuit
Flashers
C315S158000, C315S159000, C315S307000
Reexamination Certificate
active
06316880
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to flashlights and more particularly to a constant or variable brightness flashlight which maintains the flashlight light flux until the batteries reach the final end of lifepoint.
BACKGROUND OF THE INVENTION
The flashlight, a small portable device consisting of a small incandescent bulb, a battery and a normally open switch contained in a small plastic or metal casing, has been known to society for many years. Improvements have been made in the construction and operation, for example, the carbon-zinc cell has been almost completely replaced by the alkaline cell while the incandescent bulb has been improved by using xenon as a filling gas and by other similar changes.
However, there remain two fundamental shortcomings of the present day flashlight. One is due to the characteristics of the tungsten filament lamp or bulb which physically approximates to a black body radiator. Such a black body radiates light proportional to the fourth power of the filament temperature. This means that when the batteries are fresh, there is an adequate flux of light, but as batteries age, the light becomes rapidly weaker and more reddish due to the lower operating temperature of the filament. Although alkaline batteries have much flatter voltage versus time discharge characteristics than the earlier carbon-zinc version, increasing internal resistance during discharge still results in steadily decreasing terminal potential and hence light output over the operating life.
A second shortcoming is the inability to reduce the light output at will to either conserve battery life or to avoid an excessive light which decreases dark adaptation. This latter problem afflicts pilots flying at night who need to use a flashlight for finding maps and other objects in the cockpit, nursing staff or security guards conducting night inspections, and other similar users. As of today, this is alleviated by fitting red filters over the flashlight lens, but this reduces visual intensity without any compensating increases of battery life. Also there is not control of the intensity of the red filtered light, if adequate with a new battery it rapidly becomes insufficient as the battery ages.
SUMMARY OF THE INVENTION
An object of this invention is to provide a novel flashlight which is operable for maintaining the light flux at a selectively set and stabilized brightness until the batteries reach the final end of the lifepoint. The operating circuitry for the flashlight includes a commercially available semiconductor boost/buck converter which controls charging and discharging of an inductor, the latter supplying electrical energy to the lamp. “Boost” and “buck” are used in the conventional electronic sense, meaning respectively, step up and step down. Bucking would involve using a higher voltage battery than the flashlight bulb and then using the converter to reduce the voltage applied to the bulb. Servo control of the energy to the lamp is achieved by feedback from a photosensor. In the novel flashlight the brightness of the emitted light does not depend on either the reduction of terminal voltage or increase in internal resistance of the flashlight during their discharge. This therefore maintains the usefulness of the instrument as a light source until all the energy has been extracted from the batteries.
Another object of this invention is to provide a novel flashlight in which the stabilization point of light output by feedback from a photosensor can be readily adjusted downwardly to provide less light without the waste of energy in an optical absorber placed over the lamp. The stabilization point may also be adjusted upwardly to obtain a high flux of light with commensurate reduction in lamp and battery lifetime. Therefore, without significant loss of efficiency, the brightness of the emitted light can be reduced as needed thus prolonging the hours of light obtainable from a set of batteries or can be increased in an emergency mode to provide brilliant light for a short period.
A further object of this invention is to provide a novel flashlight having a low voltage source of electrical current (batteries) but arranged and constructed to operate a much higher voltage and more efficient lamp.
Another object of this invention is to provide a novel flashlight having primary on-off switch which is operable to turn on logic signal to the energy controller, the operation of the latter being insensitive to switch contact resistance.
REFERENCES:
patent: 5418433 (1995-05-01), Nilssen
Bains Herman H.
Vu David
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