Patent ID: 7977894

Claim:
An electronic ballast for a gas discharge lamp having a filament, comprising: a power converter circuit comprising a pre-heating transformer with a primary winding having first and second ends and a secondary winding for coupling to the filament, a resonant output transformer, a first shunt terminal coupled to the first end of the primary winding, a second shunt terminal coupled to the second end of the primary winding, and an electrical impedance defined between the first and second shunt terminals, wherein the resonant output transformer is operable to provide an output transformer signal to drive the lamp; and a bypass circuit comprising a timing circuit coupled to the resonant output transformer to receive the output transformer signal, the timing circuit having a delay period responsive to the output transformer signal and operable to generate a timing circuit signal after the delay period, the bypass circuit further comprising a shunt circuit coupled to the timing circuit to receive the timing circuit signal and further coupled between the first and second shunt terminals, wherein when the timing circuit signal is present, the shunt circuit reduces the electrical impedance between the first and second shunt terminals.