Zero-voltage switching type electronic ballast for fluorescent lamp

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,
• temperature-to-time controller means connected to said sawtooth wave signal generator means, for adaptively controlling an initial preheating time in accordance with a variation of ambient temperature, and
• frequency controller means connected to said temperature-to-time controller means, for controlling said comparison signal to be said first frequency for a time set by said temperature-to-time controller means, and for gradually varying said comparison signal to be said second frequency.

A zero-voltage switching type electronic ballast for a fluorescent lamp, comprising:

• a DC power source providing DC power to first and second nodes;
• first and second switching means 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, for providing power to said flourescent lamp in first and second directions, respectively;
• a driving transformer having first, second, third and fourth windings, said first winding being connected between said first switching means and said switching device connection node, said second winding being connected to said switching device connection node, and said third winding being connected between said second switching means and said second node of said DC power source;
• switching control signal generating means connected to said fourth winding of said driving transformer, for driving said fourth winding so that said first and second windings of said driving transformer alternately control said first and second switching means, respectively, to switch when a voltage applied across said current paths of said first and second switching means 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 means,
• overheating prevention means connected to said sawtooth wave signal generator means, for detecting a temperature of said first and second switching means, and for shutting down said square wave signal generator means if said detected temperature is above a predetermined temperature, and
• over-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;
• wherein said flourescent lamp is connectable between said third winding of said driving transformer and said DC power source.

A zero-voltage switching type electronic ballast for a fluorescent lamp comprising:

• a DC power source providing DC power to first and second nodes;
• first and second switching means 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, for providing power to said flourescent lamp in first and second directions, respectively;
• a driving transformer having first, second, third and fourth windings, said first winding being connected between said first switching means and said switching device connection node, said second winding being connected to said switching device connection node, and said third winding being connected between said second switching means and said second node of said DC power source;
• switching control signal generating means connected to said fourth winding of said driving transformer, for driving said fourth winding so that said first and second windings of said driving transformer alternately control said first and second switching means, respectively, to switch when a voltage applied across said current paths of said first and second switching means 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 means,
• temperature-to-time controller means connected to said sawtooth wave signal generator means, for adaptively controlling an initial preheating time in accordance with a variation of ambient temperature, and
• frequency controller means connected to said temperature-to-time controller means, for controlling said comparison signal to be said first frequency for a time set by said temperature-to-time controller means, and for gradually varying said comparison signal to be said second frequency;
• wherein said flourescent lamp is connectable between said third winding of said driving transformer and said DC power source.

A zero-voltage switching type electronic ballast for a fluorescent lamp, comprising:

• a DC power source providing DC power to first and second nodes;
• first and second switching means connected in series between said first and second nodes of said DC power source and having a switching device connection node therebetween, for providing power to said flourescent lamp in first and second directions, respectively;
• switching control signal generator means connected to said first and second switching means, for driving said first and second switching means alternately with a dead time interposed therebetween, and for preventing current from flowing through said first and second switching means during said dead time, said switching control signal generator means comprising:
• transformer means, said transformer means includes first, second, third and fourth windings, said first winding being connected between said first switching means and said switching device connection node, said second winding being connected to said switching device connection node, and said third winding being connected between said second switching means and said second node of said DC power source,
• 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, and
• over-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;
• said flourescent lamp being connectable between said switching device connection node and said DC power source;
• and
• said switching control signal generating means being connected to said fourth winding of said driving transformer.

A zero-voltage switching type electronic ballast for a fluorescent lamp wherein said switching control signal generating means further comprising:

• a DC power source providing DC power to first and second nodes;
• first and second switching means connected in series between said first and second nodes of said DC power source and having a switching device connection node therebetween, for providing power to said flourescent lamp in first and second directions, respectively;
• switching control signal generator means connected to said first and second switching means, for driving said first and second switching means alternately with a dead time interposed therebetween, and for preventing current from flowing through said first and second switching means during said dead time, said switching control signal generator means comprising:
• transformer means, said transformer means includes first, second, third and fourth windings, said first winding being connected between said first switching means and said switching device connection node, said second winding being connected to said switching device connection node, and said third winding being connected between said second switching means and said second node of said DC power source,
• temperature-to-time controller means connected to said sawtooth wave signal generator means, for adaptively controlling an initial preheating time in accordance with a variation of ambient temperature, and
• frequency controller means connected to said temperature-to-time controller means, for controlling said comparison signal to be said first frequency for a time set by said temperature-to-time controller means, and for gradually varying said comparison signal to be said second frequency;
• said flourescent lamp being connectable between said switching device connection node and said DC power source;
• and
• said switching control signal generating means being connected to said fourth winding of said driving transformer.