Starting and operating apparatus for high pressure sodium lamp ballasts

Claim 1

A starting and operating apparatus for connection across an AC source for starting and then operating a high-pressure sodium discharge lamp, said apparatus comprising: (a) input terminals adapted to be connected across said AC source, output terminals adapted to have said sodium discharge lamp connected thereacross, a power factor correction capacitor connected across said input terminals, a ballast inductor winding having a tap intermediate the ends thereof, and said ballast inductor connected in series at its ends between one of said input terminals and one of said output terminals, and the other of said input terminals electrically connected to the other of said output terminals; (b) gate-controlled solid-state switching means connected in series with an energy storage capacitor between one end of said ballast inductor and said ballast inductor tap, resistor means connected between said other input terminal and a point in the line between said series-connected solid-state switching means and said energy storage capacitor, and an additional resistor connecting between gate and cathode of said switching means; and (c) zener diode means, which has a zener voltage greater than the operating voltage for said lamp, connecting across said energy storage capacitor so that the voltage build-up thereacross before said lamp is started is applied across said zener diode means, and said zener diode means also connecting across the gate and anode of said solid-state switching means to gate said switching means when the zener voltage of said zener diode means is exceeded; whereby when said switching means is gated, said energy storage capacitor is discharged through a portion of said ballast inductor to cause the auto-transformer action thereof to apply a lamp starting pulse across said output terminals to start the lamp connected thereacross, and after said lamp is started, the zener voltage of said zener diode means is not exceeded so that the lamp starting portion of said apparatus is rendered inoperative.