Discharge-lamp operating device using thyristor oscillating circuit

Claim 1

Apparatus comprising a first closed circuit including a power supply, a choke and a discharge lamp connected in series in said closed circuit; anD a second closed circuit including a semiconductor switching element, a capacitor and an inductance element separate from said choke, said switching element and inductance element being connected in series with each other and in parallel with said lamp, said capacitor also being in parallel with said lamp, the lamp being adapted for being ignited and in discharging state having a characteristic tube voltage, said switching element being characterized by a conduction starting voltage which is higher than said tube voltage, said capacitor and inductance element forming a resonant circuit adapted for generating an oscillating voltage which is applied to said lamp, said lamp including electrodes respectively connected between said power supply and capacitor, said power supply charging said capacitor through said electrodes which are thereby heated, said switching element conducting when the capacitor achieves a charge equal to said conduction starting voltage whereupon said oscillating voltage is developed by said resonant circuit, the heating of said electrodes and the developing of said oscillating voltage igniting said discharge lamp, the tube voltage of which prevents the switching element from conducting.