Patent ID: RE40843

Claim:
A dimmable electronic ballast for an HID lamp comprising: a rectifier stage for rectifying an AC input and providing a rectified DC output; a power factor correction stage for modifying a power factor of said AC input and for providing an increased voltage DC output from said rectified DC output; an electronic ballast control circuit for providing a driving signal comprising a pulse train for controlling a switching operation of an output voltage stage driving the HID lamp, said electronic ballast control circuit including a feedback input to sense a current related to a current flow through said HID lamp and a dimming control input to set a desired power level, said electronic ballast control circuit being configured to maintain an actual power of said HID lamp at the desired power level in accordance with a zero crossing of the current related to the current flow through said HID lamp, the zero crossing being proportional to a phase angle of the current flow through said HID lamp; and said output switch stage comprising at least one electronic switching element coupled to said increased voltage DC output for providing a pulsed power signal to the HID lamp to power the lamp.