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Zero-voltage switching type electronic ballast for fluorescent lamp

  • US 5,500,792 A
  • Filed: 06/24/1994
  • Issued: 03/19/1996
  • Est. Priority Date: 06/24/1993
  • Status: Expired due to Term
First Claim
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1. A zero-voltage switching type electronic ballast for a fluorescent lamp comprising:

  • a DC power source providing DC power to first and second nodes;

    a first and second capacitor connected in series between said first and second nodes of said DC power source and being connectable therebetween to a first side of said flourescent lamp;

    a first and second switching device having current paths connected in series between said first and second nodes of said DC power source and having a switching device connection node therebetween;

    a third capacitor connected in parallel across said current path of said first switching device;

    a fourth capacitor connected in parallel across said current path of said second switching device;

    a driving transformer having first, second, third and fourth windings, said first winding being connected between a first switching device control line to said first switching device and said switching device connection node, said second winding being connected to said switching device connection node, and said third winding being connected between a second switching device control line to said second switching device and said second node of said DC power source;

    a load resonant circuit connected to said third winding and connectable to a second side of said flourescent lamp; and

    switching control signal generating means connected to said fourth winding of said driving transformer, for comparing a comparison signal of a predetermined high frequency with first and second reference signals, and for interposing a predetermined dead time therebetween, said switching control signal generating means driving said fourth winding so that said first and second windings of said driving transformer alternately control said first and second switching devices, respectively, to switch when a voltage applied across said current paths of said first and second switching devices is zero, said switching control signal generating means comprising;

    sawtooth wave signal generator means connected to said DC power source for generating a comparison signal having a first frequency for a predetermined time, and after said predetermined time, having a second frequency,square wave signal generator means connected to said sawtooth wave signal generator means, for comparing said comparison signal to a reference voltage, and for generating a square wave signal,driving signal generator means connected to said square wave signal generator means, for receiving said square wave signal and for generating a driving signal,driving circuit means connected to said driving signal generator means, for driving said fourth winding of said driving transformer in forward and reverse directions with a dead time interposed therebetween, said dead time guaranteeing a zero-voltage switching of said first and second switching devices,overheating prevention means connected to said sawtooth wave signal generator means, for detecting a temperature of said first and second switching devices, and for shutting down said square wave signal generator means if said detected temperature is above a predetermined temperature, andover-current prevention means connected to said driving signal generator means, for detecting a current regenerated via said fourth winding, and for shutting down said square wave signal generator means if said detected current is above a predetermined value.

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