Electronic dimmable ballast for high intensity discharge lamp

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 switch stage driving the HID lamp;
• 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;
• said electronic ballast control circuit having a feedback input comprising a signal related to the power dissipated by said HID lamp for maintaining said power at a desired level, the desired level being set by a dimming control input to said electronic ballast control circuit;
• and a timing circuit for providing a pulsed timing signal to said electronic ballast control circuit during HID lamp ignition, whereby the pulsed timing signal repeatedly shuts down said electronic ballast control circuit to thereby provide pulses of the driving signal of the electronic ballast control circuit in synchronism with the pulsed timing signal.

A dimmable electronic ballast for an HID lamp comprising:

• a rectifier stage for rectifying an AC input and providing a rectified DC output;
• a boost stage 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 switch stage driving the HID lamp, said electronic ballast control circuit including a feedback input to sense a voltage across 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 voltage across said HID lamp, the zero crossing being proportional to a phase angle of the voltage across 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.