Lamp ballast system

Abstract

A ballast circuit for a fluorescent lamp includes a magnetic choke coupled between the lamp and a power supply and an electronic starter circuit coupled across said lamp. The magnetic choke includes an inductor and a capacitor to limit the supply of current to the lamp. The capacitor provides power factor correction and limits current supply without dissipating power in the form of heat. The electronic starter circuit includes a triac coupled across the lamp that is triggered by a diac coupled to the power supply input through a capacitor. When a sufficient charge builds up on the capacitor, the diac is triggered and, in turn, the triac is triggered to provide current through the electrodes of the lamp to thereby preheat the electrodes. Almost as instantly as the triac is triggered, the diac is caused to stop triggering the triac and therefore, the triac becomes non-conducting and is removed from the cirucit. Upon removal of the triac, the sudden stop of current flow causes the magnetic choke inductor to produce a voltage spike across the lamp electrodes to thereby cause an arc to extend between the electrodes. Selective dimming of the lamp is achieved by proper selection of the capacitor coupled to the magnetic choke.