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US 4,375,608 AGranted
Electronic fluorescent lamp ballast
AssigneeBeatrice Foods Co.
InventorThomas P. Kohler
Life of this patent
Estimating the term…
Abstract
An electronic ballast-inverter for multiple fluorescent lamps employs a push-pull inverter and a series resonant circuit for driving the lamps. The inverter operates at the resonant frequency of the series resonant circuit. The current in the resonant circuit is limited, for low load conditions, in response to a sensing voltage which is used to raise the frequency of operation of the inverter to make the load more reactive.
Claims14
An electronic ballast-inverter circuit for fluorescent lamps comprising,
- a transformer having primary and secondary windings, said secondary winding adapted to be connected in series with a fluorescent lamp,
- a capacitor and an inductor connected in series with said secondary winding,
- a source of DC connected to a center tap of said primary winding,
- a transistor connected to one end of said primary winding for selectively drawing current through one-half of said primary winding,
- a feed-back circuit including means for sensing current flowing through said fluorescent lamp for controlling operation of said transistor in response to said current,
- a pair of transistors, one connected to each of said primary windings,
- said feedback circuit including comparator means for comparing the current flowing through the primary of said transformer with the current flowing through the secondary of said transformer, and
- means responsive to said comparison for alternatively causing said pair of transistors to conduct mutually exclusively.
5 more elements
An electronic ballast-inverter circuit for fluorescent lamps comprising,
- a transformer having primary and secondary windings, said secondary windings adapted to be connected in series with a fluorescent lamp,
- a capacitor and an inductor connected in series with said secondary winding,
- a source of DC connected to a center tap of said primary winding,
- a transistor connected to one end of said primary winding for selectively drawing current through one-half of said primary winding,
- a feed-back circuit including means for sensing current flowing through said fluorescent lamp for controlling operation of said transistor in response to said current,
- a filament transformer connected in series with a capacitor across said fluorescent lamp, said filament transformer having a first winding connected to a filament of said lamp,
- said filament transformer having a second winding,
- and means for connecting said second winding in series with a high impedance until said lamp is ignited, and with a low impedance after said lamp is ignited, whereby said filament consumes substantially no power after the ignition of said lamp.
5 more elements
An electronic ballast-inverter circuit for fluorescent lamps comprising,
- a transformer having primary and secondary windings, said secondary winding adapted to be connected in series with a fluorescent lamp,
- a capacitor and an inductor connected in series with said secondary winding,
- a source of DC connected to a center tap of said primary winding,
- a transistor connected to one end of said primary winding for selectively drawing current through one-half of said primary winding,
- a feed-back circuit including means for sensing current flowing through said fluorescent lamp for controlling oepration of said transistor in response to said current,
- said feed-back circuit including timing means for establishing a first maximum level of current flowing through said primary winding during a first interval, and a second higher maximum current level flowing through said primary during a second interval, and
- means for repeating said first and second intervals in sequence until said lamp is ignited.
4 more elements
An electronic ballast-inverter circuit for fluorescent lamps comprising,
- a transformer having primary and secondary windings, said secondary winding adapted to be connected in series with a fluorescent lamp,
- a capacitor and an inductor connected in series with said secondary winding,
- a source of DC connected to a center tap of said primary winding,
- a transistor connected to one end of said primary winding for selectively drawing current through one-half of said primary winding,
- a feed-back circuit including means for sensing current flowing through said fluorescent lamp for controlling operation of said transistor in response to said current,
- said first transformer having a second secondary winding, said feed-back circuit comprising a current transformer connected in series with said secondary winding,
- and means for comparing the phase difference between the signal occurring on said second secondary winding and the secondary winding of said current transformer, and for controlling the operation of said transistor in response thereto.
4 more elements
Dependencies are inferred from the claim text.