Importance

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Abstract

A circuit for starting and operating fluorescent lamps from an a-c low frequency power source includes a reactive ballast means connected to ballast the lamps and having a non-linear characteristic for producing a plurality of harmonics of the power source frequency, and a capacitor and a cathode heating transformer connected in series and connected to receive power from said ballast means and resonant in a frequency range encompassing a plurality of said harmonics. This resonant voltage is applied across the lamps to aid the starting of their discharge and thereafter the lamps operate at the a-c power source frequency. The aforesaid resonance frequency range preferably is broad enough to encompass several harmonics of the power source frequency, for example the third through the ninth harmonics (180 to 540 Hz for a source frequency of 80 Hz). Preferably a switch is connected in series with the capacitor and cathode heating transformer for opening the cathode heating circuit when the lamps are operating. This switch may be a bidirectional diode or equivalent voltage sensitive solid state switch, which switches on and off during each half cycle of the lamp starting time period and thus contributes to the harmonic content of the starting voltage waveform.

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First Claim