Integrated tuning capacitor network and heat sink for an electrodeless high intensity discharge lamp ballast

Claim 1

A ballast for an electrodeless high intensity discharge lamp of the type having an excitation coil situated about an arc tube for exciting a plasma discharge therein upon application of a radio frequency signal to said excitation coil, said ballast comprising: first and second switching devices connected in series in a half-bridge configuration with a junction therebetween; ballast drive means coupled to said first and second switching devices, said ballast drive means being adapted to be coupled to an RF power supply for alternately driving said first and second switching devices; and resonant circuit means coupled to said first and second switching devices at the junction therebetween, said resonant circuit means comprising said excitation coil, a first capacitor in parallel combination with said excitation coil, and a second capacitor connected in series with said parallel combination, said first and second capacitors each comprising a first and second metal plate with a dielectric material therebetween, said first metal plate being common to said first and second capacitors so as to comprise one of the metal plates of each of said first and second capacitors, and at least a portion of said second metal plate of each of said first and second capacitors overlapping each other so as to minimize any parasitic inductance therebetween; said first and second capacitors together comprising impedance matching means for matching the ballast load impedance to maximize efficiency, the capacitance of said first capacitor being optimized for matching the ballast load resistance, and the capacitance of said second capacitor being optimized for matching the ballast load angle.