Electric lamp and discharge devices: systems – Pulsating or a.c. supply – Transformer in the supply circuit
Reexamination Certificate
1999-12-16
2001-03-27
Philogene, Haissa (Department: 2821)
Electric lamp and discharge devices: systems
Pulsating or a.c. supply
Transformer in the supply circuit
C315S2090SC, C315S224000
Reexamination Certificate
active
06208086
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a ballast circuit for a low voltage halogen lamp, and more particularly, to such a ballast circuit employing a pair of complementary switches in a pulsating-d.c.-to-a.c. inverter.
BACKGROUND OF THE INVENTION
The typical method of supplying low voltage lamps, halogen in particular, from a high voltage supply (e.g., 120 volt, 60 Hz) is to use conventional half-bridge, high frequency inverters. These use a level shifting scheme to periodically switch on and off the high side switch. One design would be to employ a step-down transformer between the supply voltage and the low voltage lamp. Several disadvantages of this method are that transformers operating at 60 Hz are typically larger and heavier than would be needed at higher frequencies, step-down transformers are relatively expensive, and there is no inherent short circuit protection when employing a step-down transformer.
The present invention provides a ballast circuit for halogen, or other low voltage lamps, that overcomes the foregoing drawbacks.
BRIEF SUMMARY OF THE INVENTION
A ballast circuit is described for supplying high frequency a.c. current to a load circuit incorporating a low voltage halogen or other heated filament lamp and an autotransformer, or separate coupled transformers, and a capacitance. The ballast circuit includes an a.c.—d.c. converter circuit, comprising a full-wave rectifier and capacitance, and a pulsating-d.c.-to-a.c. inverter circuit comprising first and second switches serially connected between a bus conductor and a reference conductor. The switches are connected together at a common node through which the a.c. current flows, and at a control node. Also connected between the control node and the common node is a serially connected circuit including a capacitor and two inductors. The voltage between the control node and the common node is used to determine the conduction state of the associated switches, where the time constant of the serially connected circuit determines the frequency of operation.
Also included are first and second resistors connected serially between the bus conductor and the reference conductor and also connected to the control node. A third resistor is connected between the common node and one of the bus conductor and the reference conductor, to set the initial polarity of the control node with reference to the common node.
REFERENCES:
patent: 4972124 (1990-11-01), Powers
patent: 5623186 (1997-04-01), Archdekin
patent: 5917289 (1999-06-01), Nerone et al.
patent: 5952790 (1999-09-01), Nerone et al.
patent: 5955843 (1999-09-01), Nuckolls et al.
Fay Sharpe Fagan Minnich & McKee LLP
General Electric Company
Lee Wilson
Philogene Haissa
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