Patent ID: 6049177
Filing Date: 2000-04-11
Classification: H05B,Y02B

Abstract:
A ballast circuit for energizing one or more fluorescent lamps connected in series or parallel, said ballast circuit being powered from a line voltage of 120 VAC, 50/60 Hz; said ballast circuit in combination comprising:(a) an input power connector;(b) a protection fuse which is connected to said input power connector;(c) an AC-DC converter circuit which is connected to said input power connector and to said fuse, said AC-DC converter circuit comprising: means for circuit surge protection from high transient input voltage signals, an electromagnetic interference (EMI) filter circuit means which is connected to said means for circuit surge protection, a full-wave bridge rectifier circuit which is connected to said EMI filter circuit means, said rectifier circuit having a ripple waveform DC output, and DC output filter means for smoothing said ripple waveform DC output;said AC-DC converter circuit producing an approximately 165 VDC output voltage at its DC output terminals, commensurate with a 120 VAC input voltage applied to said input power connector;(d) a DC-AC converter circuit which is connected to said DC output terminals to accept a DC line output, said DC-AC converter comprising: a push-pull switching circuit comprising an auto-transformer and a pair of transistors that are connected in push-pull configuration to the primary of said auto-transformer; a frequency-set circuit which sets the resonant frequency of said push-pull transformer circuit, said frequency set circuit comprising a resonant inductor having its input connected to said DC output terminals, and its output connected to the center tap of the primary inductance of said auto-transformer, and a resonant capacitor which is connected in parallel with said primary inductance, said frequency set circuit producing an output frequency of about 90 kHz;two gate-drive windings, said gate-drive windings being energized by said autotransformer, each said winding having an output connection to the gate of one of said transistors for applying drive signals; andan oscillation starting circuit, said starting circuit comprising a zener diode that is supplied from the DC line through a resistor, said zener diode having an output voltage connected to the center tap point of said gate-drive windings, and thence through said windings to the gates of said transistors, providing a starting voltage high enough to turn on a transistor, said starting voltage being counteracted by the drive voltage generated by said auto-transformer through said gate-drive windings once oscillation has started due to transistor switching;(e) an output circuit comprising a multiplicity of capacitors, said capacitors being connected in parallel to the output of said auto-transformer and reflecting back to the primary of said auto-transformer and modifying the output frequency, said capacitors providing current limiting for any loads connected to their output terminals; and(f) ballast output terminals connected to said capacitors in said output circuit, said output terminals being marked for connection to fluorescent lamps;each of said capacitors in said output circuit reacting with said autotransformer output voltage to produce a sine wave voltage and current waveform at about 600 VAC, and about 90 kHz open circuit, and producing a constant current for supplying any number of connected fluorescent lamps.