Abstract: A circuit containing a ballast for one or more fluorescent lamps. The circuit includes a first inductor in series with a voltage input terminal and a first capacitor to form a series resonant circuit to provide a starting voltage to the lamps. A second, shunt inductors coupled between the first inductor and the capacitor and another input terminal of the circuit to eliminate the high Q of the series resonant circuit and prevent the first inductor from saturating. The inductors are mounted on the legs of an H-shaped core to provide inductive coupling between the inductors and allow a maximum winding area for the first inductor to reduce the series resistance of the lamp current path. The core also allows the shunt inductor to adjust power line power factor independently of lamp power factor. Improvements in system efficiency of up to 15% can be achieved over conventional core/coil type ballasts.

Abstract: A ballast for a fluorescent lamp including a tuned circuit in series with a pair of voltage input terminals to which an input AC voltage is applied. The tuned circuit includes a capacitor in series with an inductor, with the resonant frequency of the tuned circuit being approximately 1/2 the frequency of the input voltage. At start-up, the inductor is very highly reactive to provide a starting voltage which is applied to a fluorescent lamp coupled across the inductor. A positive temperature coefficient resistor is in series with the inductor to limit the current flow therethrough. The inductor forms a part of the primary winding of a transformer having a secondary winding providing the heater voltage for the lamp. A second primary winding of the transformer provides a power factor correction for the tuned circuit.