Electric lamp and discharge devices: systems – Periodic switch in the supply circuit – Silicon controlled rectifier ignition
Reexamination Certificate
2000-06-16
2003-02-11
Wong, Don (Department: 2821)
Electric lamp and discharge devices: systems
Periodic switch in the supply circuit
Silicon controlled rectifier ignition
C315S20000A
Reexamination Certificate
active
06518710
ABSTRACT:
BACKGROUND AND BRIEF DESCRIPTION OF THE INVENTION
The present invention relates to gas discharge light-producing systems and methods and, more particularly, to low-current, non-thermionic (e.g., no heated filament) ballast-free energy-efficient light-producing systems and methods which are more efficient, less expensive, substantially free of RF emissions and which can use conventional industrial, commercial or home gas discharge lamps (fluorescent tubes of various shapes and sizes, high-intensity discharge lamps, sodium vapor lamps, mercury vapor lamps, neon signage tubes).
In most commercial and home-grade fluorescent lighting systems, the heart of the system is the ballast, which is an inductance or transformer device that boosts the incoming voltage to a higher voltage level to start the fluorescent tubes and then, once the fluorescent tubes are lit or ignited (gas ionized or discharged), reduces the voltage to a level for normal continuous lighting.
Moreover, these prior systems often use transformer filament windings to heat the filaments to therefore provide thermionic emission for assisting in the ignition phase. Heated filaments vaporize and form black deposits at the end of each tube and limit tube life. The evaporation of the Tungsten filament invades the mercury Vapor limiting luminosity and tube life. Early ballasted fluorescent lighting systems are shown in
FIGS. 1A and 1B
. In
FIG. 1A
the ballast unit L is in series with filaments F and switch S, and in
FIG. 1B
, glow switch GS which opens after the filaments are heated to initiate a discharge.
Ballast transformers are often the most expensive part of commercial fluorescent lighting systems. There have been numerous past efforts to provide fluorescent lighting systems which do not use ballast transformers.
Electronic ballasts of the type shown in
FIG. 1C
are common in the art and are disclosed in International Rectifier Publication Application Notes AN-995, “Electronic Ballasts Using the Cost-Saving IR2155 Driver”. In this circuit, two power switches Q
1
, Q
2
are connected in a totem pole topology with the tube circuits consisting of an LC series resonant circuit with the lamp across one of the reactances. The switches are power MOSFETS driven to conduct alternately by windings on current transformer T. In this circuit, the primary winding is driven by current to the lamp circuit and operates at the resonant frequency of L and C. A starting pulse is provided by a starting circuit comprised of resistor R
1
and capacitor C
1
and DIAC D
1
connected to one of the gates of one of the power switches. After oscillation is initiated, a high frequency square wave (30-80 kHz) excites the LC resonant circuit. The sinusoidal voltage across the reactance C is magnified by the Q at resonance and develops sufficient amplitude to strike the fluorescent lamp. In this system, the filaments of the lamp are connected in series with the series resonant circuit.
In the case of neon tubes as used in neon signage, conventional art uses high voltage (as a rule of thumb approximately 1000 volts per foot of sign) ballasted driver circuits which are inefficient, noisy, large, emit heat, require heavy high voltage insulation, are not usually dimmable).
The Present Invention
The basic objective of the present invention is to provide improved gas discharge light-producing systems and methods.
Another object of the present invention is to provide a more energy-efficient gas discharge light-producing system and method.
Another object of the invention is to provide a more energy-efficient light-producing system which is low in cost and operates at and low currents.
Another object of the invention is to provide a light-producing system having a square wave voltage in the frequency range of about 75 kHz to about 3.5-4 MHz.
Another objective of this invention is to provide a light-producing system wherein one or more conventional gas discharge tubes is non-thermionically operated and driven by a high-frequency alternating current square wave source.
Another objective of this invention is to provide a gas discharge lighting system wherein multiple gas discharge tubes are electrically connected in series and non-thermionically driven by a square wave voltage.
Another object of the invention is to provide a gas discharge light-producing system in which the light intensity is variable from low-level illumination to high-level illumination and from high-level illumination to low-level illumination.
According to the invention, non-thermionic, ballast-free, fluorescent lighting system comprises at least one gas discharge light-producing lamp or tube and an alternating current square wave power supply. The square wave power supply incorporates a solid state switch means which is operated to generate a substantially square wave alternating current wave at the lamp or tube electrodes such that the voltage supplied to the electrodes reverses polarity more rapidly than the pattern of electron and ion density in the tube can shift so that electrons throughout the length of the device are continually accelerated and will, through several cycles of the applied square wave, create free electrons and ions throughout the tube's volume, in steady state operation and ionize the gas lighting lamp.
According to a preferred embodiment of the present invention, at least one light-producing device with electrodes (which may be conventional filaments or not) immersed in a gaseous discharge medium (such as noble gases, argon, neon, helium or xenon, and mercury vapor and mixtures thereof; however, other gases and gas mixtures can be used) and is non-thermionically (no heater or filament currents) driven with a high-frequency square wave voltage. In the preferred embodiment, the driver circuit includes an inverter circuit using two solid state switching devices which are connected in totem pole fashion across a direct current supply. The gate electrode of each switch transistor is connected in circuit with a primary winding for each switch device and a primary winding of the transformer. A starting circuit to start the oscillator is utilized to provide a positive turn-on pulse to the gate electrode of one of the transistor switches. When one of the transistor switches turns on, its voltage is rapidly switched to ground which starts the circuit in oscillation. In the preferred embodiment, the oscillating frequency is set at about 100 kHz, but the range of successful operation runs from about 75 kHz through about 4 MHz. Since there are no high voltages in the driver circuit, safe operation is assured.
Illumination or luminosity levels or dimming can be achieved by varying the voltage (or energy level) from the direct current supply. In the preferred embodiment, care is taken to assure that there are no spike voltages due to inductive kick and the like. Since the gas discharge lamps or devices are non-thermionically driven, the luminous efficiency is significantly improved. Moreover, at the preferred high frequency of 100 kHz, power supply components can be smaller.
A salient difference between the system of the present invention and traditional fluorescent lamp systems is the marked reduction of heat that accompanies a given light output, which is in turn the reason why their efficiency of conversion of electricity to light is so high. Some of the heat reduction is, of course, recognizable as resulting from the absence of direct heating of the filaments in each end of the tube by applied voltages. Some is also explained in terms of energy transfer in the high-field region which occurs near the momentary cathode. However, fluorescent and neon tubes in the system of the present invention are much cooler throughout their length, including areas that are at great distances from the filaments whose heating could not possibly be explained by conduction, radiation, or diffusive heat transfer through the low-pressure gas filling the tube. (The overall applied voltage is not large enough to suggest that local regions of high field exit in tubes driven by the present inve
Clinger James
Wong Don
Zegeer Jim
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