Powerfactor correcting flyback arrangement having a resonant capacitor

Abstract

A preferred embodiment of the present invention provides a ballast circuit, comprising three sections: an input power section that receives a line AC signal as an input and provides a DC signal as an output; a pre-regulator section that conditions the DC signal; and a lamp driver section that drives a gas discharge lamp load. The pre-regulator section includes a transformer with an input winding, an output winding, and a current sense winding. The input winding receives the DC signal provided by the input power section. The output winding is connected in a flyback configuration with a flyback blocking diode, a bulk storage capacitor, and an output terminal for the conditioned DC signal. The current sense winding generates a signal proportional to the level of the transformer current. The transformer current is controlled by a flyback switch. A resonant capacitor is connected between the flyback switch input and ground, the resonant capacitor and the transformer forming a resonant circuit. A controller actuates the flyback switch, receiving as an input the current level signal and generating as an output a pulse voltage to the gate terminal of the flyback switch. The controller actuates the flyback switch at a predetermined time after the current level signal indicates zero transformer current, coinciding with the timing of the resonant circuit such that the switching means turns on when there is zero voltage across it.