Patent ID: 6744219
Filing Date: 2004-06-01
Classification: H05B,Y02B

Abstract:
An operating circuit for a discharge lamp with preheatable electrodes, comprising:an oscillator circuit comprising at least one switching transistor (T1, T2); a series resonant circuit (C6, C7, L3-A) coupled between the oscillator circuit and the discharge lamp (La), the series resonant circuit comprising a decoupling capacitor (C6), a resonance capacitor (C7), and a resonance inductor (L3-A); and a drive circuit coupled to the at least one switching transistor (T1, T2), the drive circuit comprising: an inductor (L3-B) magnetically coupled to the resonance inductor (L3-A) of the series resonant circuit (C6, C7, L3-A); an independent resonant circuit (L2, C4) coupled between the inductor (L3-B) and the at least one switching transistor (T1, T2) of the oscillator circuit, the independent resonant circuit comprising an independent resonant inductor (L2) and an independent resonant capacitor (C4); a preheating circuit (VS) coupled in series with the independent resonant capacitor (C4), the preheating circuit (VS) having first, second, and third terminals (A, B, C), wherein the first terminal (A) is coupled to a junction between the independent resonant inductor (L2) and the independent resonant capacitor (C4), and the second terminal (B) is coupled to the independent resonant capacitor (C4), the preheating circuit (VS) being operable: (i) during preheating of the preheatable electrodes of the discharge lamp (La), to switch out the independent resonant capacitor (C4); and (ii) after completion of preheating of the preheatable electrodes of the discharge lamp (La), to switch in the independent resonant capacitor (C4) by effectively providing an approximate short circuit between the second and third terminals (B, C).