Electric lamp and discharge devices: systems – Periodic switch in the supply circuit – Impedance or current regulator in the supply circuit
Reexamination Certificate
1999-12-28
2001-05-15
Vu, David (Department: 2821)
Electric lamp and discharge devices: systems
Periodic switch in the supply circuit
Impedance or current regulator in the supply circuit
C315S250000, C315S256000, C315S307000
Reexamination Certificate
active
06232726
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to a ballast scheme for operating multiple lamps and, more particularly, to a ballast scheme for operating multiple fluorescent lamps having substantially the same current flowing through each lamp.
Conventional ballasts for powering multiple lamps, such as disclosed in U.S. Pat. No. 4,293,799, include a plurality of transformers for isolating the lamps from direct connection to a utility line. The primary windings of the transformers are connected in series. The secondary winding of each transformer is connected to a lamp. Substantially the same current flows through each lamp when the lamps have substantially the same impedance.
Such conventional ballasts, however, often do not sense lamp load conditions so as to achieve/maintain one or more desired lamp parameters. These parameters can include, but are not limited to, the level of illumination, power regulation, preheat, ignition stop/cutoff and/or capacitive mode protection.
It is therefore desirable to provide an improved ballast for operating multiple lamps in which substantially the same level of current flows through each lamp. The improved ballast should include a scheme for sensing lamp load conditions in order to achieve/maintain one or more desired lamp parameters. The scheme should avoid the use of expensive components and minimize the number of components required.
SUMMARY OF THE INVENTION
In accordance with a first aspect of the invention, a ballast for powering more than one lamp includes an inverter having an output; a resonant inductor and a transformer for each lamp. Each transformer has a primary winding and a secondary winding. The primary windings are serially coupled together and to the resonant inductor. The ballast further includes a single sensing element for sensing the flow of current through all lamps and a controller for controlling the switching operation of the inverter in response to the sensed lamp current.
Each of the lamps has substantially the same current flow through serial coupling of the primary windings and resonant inductor to each other. There is no need to provide separate chokes for each lamp in order to balance the current flow among the lamps. The single sensing element senses the flow of current through all lamps. More particularly, the controller in response to the sensed lamp current controls the switching operation of the inverter in order to achieve/maintain one or more desired lamp parameters. Through the use of a single sense element and a single controller, the ballast avoids the need for separate feedpaths for sensing individual lamp conditions and/or the need for separate controllers for controlling the individual lamp conditions. The ballast scheme therefore avoids the use of expensive components (e.g. controllers and chokes) and minimizes the number of components required in order to operate multiple lamps.
It is a feature of this first aspect of the invention that each transformer has a secondary winding connected to a corresponding lamp. The inverter operates at a switching frequency above a resonant frequency, the resonant frequency being based on the impedance of the resonant inductor and each transformer. The single sensing element is preferably connected between a secondary winding of one of the transformers and a reference potential (e.g. ground potential).
In accordance with a second aspect of the invention, a method of operating a ballast for powering more than one lamp includes the steps of supplying an AC signal from an inverter to a resonant inductor and a plurality of transformers; sensing through a single sensing element the flow of current through all lamps; and controlling the switching operation of the inverter in response to the sensed lamp current. The serial combination of the resonant inductor and primary windings of each transformer receive the AC signal. Each transformer is associated with a different lamp.
It is a feature of this second aspect of the invention that the inverter be operated at a switching frequency above a resonant frequency, the resonant frequency being based on the impedance of the resonant inductor and each transformer.
Accordingly, it is an object of the invention to provide an improved ballast for operating multiple lamps in which substantially the same current flows through each lamp.
It is another object of the invention to provide an improved ballast scheme for sensing lamp load conditions in order to achieve/maintain one or more desired lamp parameters.
It is a further object of the invention to provide an improved ballast scheme which avoids the use of expensive components and minimizes the number of components required.
Still other objects and advantages of the invention will, in part, be obvious and will, in part, be apparent from the specification.
The invention accordingly comprises several steps in the relation of one or more such steps with respect to each of the others, and a device embodying features of construction, combination of elements, and arrangements of parts which are adapted to effect such steps, all as exemplified in the following detailed disclosure, and the scope of the invention will be indicated in the claims.
REFERENCES:
patent: 4251752 (1981-02-01), Stolz
patent: 4293799 (1981-10-01), Roberts
patent: 4641061 (1987-02-01), Munson
patent: 4870327 (1989-09-01), Jorgenssen
patent: 5049788 (1991-09-01), Lee
patent: 5068576 (1991-11-01), Hu et al.
patent: 5072090 (1991-12-01), Morita
patent: 5742134 (1998-04-01), Wacyk et al.
patent: 5969483 (1999-10-01), Li et al.
patent: 5998930 (1999-12-01), Upadhyay et al.
Franzblau Bernard
Philips Electronics North America Corporation
Vo Tuyet T.
Vu David
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