Resonant inverter circuitry for effecting fundamental or harmonic resonance mode starting of a gas discharge lamp

Claim 1

Circuitry for starting and operating a gas discharge lamp, the operation of which is initiated in response to the voltage thereacross exceeding a predetermined value, said circuitry comprising: an excitation signal source including inverter switching means for converting DC voltage to produce a high frequency alternating current excitation signal at a predetermined fundamental frequency for energizing the lamp; reactance means responsive to the excitation signal and connected in circuit with the lamp, said reactance means including inductive means and capacitive means and having an initial natural resonant frequency at starting of the lamp, said initial natural resonant frequency being selected from the group consisting of the fundamental frequency and the second and higher harmonics of said fundamental frequency; sensing means for sensing operation of the lamp; and switching means connected to said sensing means and said reactance means for varying the impedance of one of said inductive means and said capacitive means from a first nonzero value to a second nonzero value in response to the sensing means sensing initiation of the lamp operation, whereby said natural resonant frequency of said reactance means is changed form said initial value to a different value which is also selected from the group consisting of the fundamental frequency and the second and higher harmonics of said fundamental frequency.