Ballast apparatus and ballasting method of high intensity discharge lamp

A high intensity discharge lamp ballast apparatus comprising:

• a transformer;
• a plurality of power supplies provided on a primary side of said transformer;
• a plurality of switching elements provided on the primary side of said transformer;
• a control circuit for turning said plurality of switching elements on and off repeatedly to generate, on a secondary side of said transformer, an AC voltage that is higher in voltage and frequency than a primary side voltage of said transformer;
• and
• a voltage multiplier circuit on the secondary side of said transformer, for increasing voltage across a gap switch activating capacitor, connected in parallel with a gap switch, beyond the voltage generated on the secondary side of said transformer.

A high intensity discharge lamp ballasting method comprising:

• producing a desired voltage across a discharge developing capacitor connected in parallel with a DC power supply, on a primary side of a transformer, by charging said discharge developing capacitor;
• charging a gap switch activating capacitor connected to a secondary side of said transformer to a turn-on voltage of a gap switch by repeatedly turning on and off a plurality of switching elements located on the primary side of said transformer;
• generating a breakdown in a high intensity discharge lamp by supplying said high intensity discharge lamp with a counter electromotive force of a pulse voltage generated by turning on said gap switch;
• starting luminous flux after the breakdown by increasing power supplied to said high intensity discharge lamp beyond rated power by applying energy from said discharge developing capacitor to said high intensity discharge lamp, and by controlling a duty factor of waveforms for driving said switching elements;
• and
• maintaining power supplied to said high intensity discharge lamp at the rated power after the start-up of the luminous flux by controlling the duty factor of the waveforms driving said switching elements.