Patent ID: 6316885
Filing Date: 2001-11-13
Classification: H05B

Abstract:
A ballast circuit for at least two serially connected, high pressure gas discharge lamps, the circuit comprising:an electromagnetic ballast arrangement receptive of an input power signal, providing an output ballast voltage for driving said lamps during steady state operation of said lamps, providing an open circuit ballast voltage (OCV) when said lamps are disconnected from said arrangement;an ignitor circuit for producing at least one ignitor pulse of high voltage and high frequency with respect to said open circuit ballast voltage, to initiate lamp starting;a non-shunted lamp of the at least two lamps; andat least one capacitance shunting the at least one remaining lamp providing a sufficiently low impedance to a high frequency ignitor pulse that a substantial portion of said pulse first appears across a non-shunted lamp during lamp starting so as to start said non-shunted lamp and then, when the voltage across said non-shunted lamp falls, to impress a substantial portion of the OCV across said shunted lamp to initiate its starting, wherein the at least one capacitance is selected such that the phase of the ignitor pulse at the at least one remaining lamp is different from the non-shunted lamp such that the voltage peaks across each of said lamps do not add together in real time.