Fluorescent Lamp Stabilizer Harmonics Reduction Method

This invention relates to fluorescent lamp starter systems and more particularly to a method for reducing the harmonics created by rapid start fluorescent lamp stabilizer ballast systems.

Fluorescent lamps are conventionally started by inducing a high voltage generated by a coil in the starting circuit and then stabilizing the illumination by suppressing the abnormally high current developed in the fluorescent tube after the lamp is lit and stabilized. As the consumption of energy became more critical, new techniques were developed to save energy consumed during the start up method which previously was highly energy inefficient compared to the power consumption of the fluorescent lamp once it was lit. These energy saving systems included the low power consumption type of fluorescent lamp stabilizers which incorporated a phase control method to save power. However, in a stabilizer utilizing the phase control method of the prior art, harmonics can develop in the secondary current side of the windings due to a distortion in the current wave form. This distortion can produce a variety of magnetic wave interference effects which could be propagated over substantial distances and can affect various types of electrical components such as communication systems, cellular telephones, and systems that rely on radio frequency transmissions. Furthermore, distortion effects in the current wave form of the primary side of the ballast winding has created problems effecting the power source of the fluorescent light and any other equipment which is connected to it. Another undesirable effect of the wave form distortion is the increased temperature resulting in the stabilizer which is brought about by heat created by the harmonic wave forms. As a result the life of the stabilizer can diminish because of the increased temperature caused by this distortion of the current wave form in the windings. Thus, there remains a need for improved low powered fluorescent lighting methods which avoid the harmonics and distorted wave forms created by previous systems.

The reduction of undesired harmonics and wave form distortion in fluorescent lamp stabilizers is highly desireable since such a method will assist in the prevention of magnetic wave interference deterioration of the insulation of the ballast and increase reliability of the stabilizer due to a lower operating temperature. Additionally, decreased distortion in the primary wave form will diminish the effect that such distortion will have on sensitive electronic systems connected to the same electrical power source. The present invention produces these desirable results and at the same time retains a low power consumption during the fluorescent lamp start up and operation. The present invention features the reduction of harmonics through a reduction in the peak current value while avoiding the distortion of the secondary current of the ballast system. The invention accomplishes this desirable result by increasing the number of turns of the secondary winding of the transformer so as to decrease the secondary current to approximately 40 to 90 percent of the rated lamp current in the rapid start type lamp stabilizer, thereby, almost completely eliminating the peak current value and reducing harmonics without disturbing the secondary current wave form. The invention thus increases the impedance and reduces the secondary current to between 40 and 90 percent of the rated lamp current. At the same time the function of the rapid start system is maintained as the filament voltage is still kept at approximately 3.8 volts to sustain the effective operation of the lamp. By this method, the absolute value of the luminous intensity is lowered somewhat by reducing the secondary current, but the uniform brightness of the lumination is maintained. From the above it may be seen that the present invention provides an improved method of starting fluorescent lights which reduces harmful harmonics and primary wave form distortion while at the same time maintaining adequate luminosity and starting characteristics. Other benefits and advantages of the present invention will be evident to those skilled in the art from the following detailed description, taken in conjunction with the accompanying drawings, which illustrate by way of example, the principles of the invention.

FIG. 1 illustrates the relationship between the harmonic wave peak current value and the rated lamp current ratio for the invention.

FIG. 2 is a circuit diagram of the basic fluorescent lamp stabilizer of the type which may be adapted to use the invention.

FIG. 3 is a plan view illustrating the wiring arrangement of a rapid start type fluorescent lamp stabilizer to which the invention can be applied.

FIG. 4a is an illustration of a typical lamp current wave form generated by prior art stabilizers.

FIG. 4b is an illustration of the lamp current wave form for a stabilizer using the present invention.

FIG. 5a is an illustration of a typical current wave form generated by primary side of the prior art stabilizers.

FIG. 5b is an illustration of the current wave form of the primary side of a stabilizer utilizing the invention.

The present invention obtains the desirable results of reducing harmonics developed in the secondary current side due to the distortion in the current wave form in the primary side of prior art rapid start fluorescent starter system. Thus, the present invention not only gives the benefits of reducing the interference of such starter systems with radio frequency transmissions in the vicinity but also decreases interference with other electronic systems using the same line and reduces the temperature at which the ballast runs due to a reduction in the distortion of the primary current wave form. The present invention provides a novel method which accomplishes this beneficial result by increasing the number of turns of the secondary winding of the transformer so as to decrease the secondary current to approximately 40 to 90 percent of the rated lamp current in the rapid start type fluorescent lamp stabilizer. This reduction in secondary current almost completely eliminates the peak current value and reduces the harmonics produced without disturbing the secondary current wave form.

FIG. 1 illustrates the relationship of the harmonic wave peak current value and the rated lamp current ratio. As this drawing illustrates, the harmonics for the peak current are substantially increased at the ends of the rated lamp current ratio. If the lamp current ratio is reduced from between 40 and 90 percent, the distortion current peak produced is substantially reduced thereby avoiding the problems created by harmonic distortion in both the primary and secondary circuits and the propagation of such distortion in the form of radio frequency interference to the surrounding area.

FIG. 2 is an illustration of the circuit diagram of a typical fluorescent lamp stabilizer to which the present invention may be applied. The particular stabilizer illustrated is a four lamp type utilizing a fluorescent lamp 9. As can be seen in FIG. 2, the transformer 4 includes a magnetic core, a primary winding 1, and a transfer coil 12 directly coupled with the primary winding. A plurality of heating windings 2 are also inductively coupled with the primary winding 1 to supply heating current to the lamp filaments of the fluorescent lamps 9. The circuit includes a capacitor 6 connected at one side of the transfer coil 12 and to one side of the fluorescent lamps to provide a leading current in the secondary circuit side. A pair of terminals are provided for connection to a suitable alternating circuit supply (not shown) which can be, for example, a 110 volt or 120 volt AC supply. When the primary power is switched on the secondary voltage is applied to both ends of the fluorescent lamp 9 and when the electron discharge from the electrode becomes sufficient after the filament becomes heated, discharges occur within the fluorescent lamp 9 between the ungrounded electrode and the ground, normally a metal reflector, which spreads through the entire tube becoming a complete primary discharge. The filament of the fluorescent lamp 9 is constantly heated by the secondary current of the transformer 4. A condenser 10 is used to prevent unwanted noise being propagated from the circuit, although in common usage the lamp current is normally between 415 and 435 miliAmps for the 40 watt rapid start type and 800 miliAmps for the 110 watt rapid start type. The present invention increases the number of turns of the secondary coil winding thereby increasing the impedance and reducing the secondary current to between 40 and 90 percent of the rated lamp current. Thus, the function of the rapid start type is maintained as the filament voltage is kept at 3.8 volts plus or minus 0.4 volts even when the secondary current is reduced.

FIG. 3 illustrates the wiring arrangement of a conventional rapid start type fluorescent lamp stabilizer to which the invention has been applied. The primary coil 1 the secondary coil 2 and the transfer coil 12 with iron core 3 are enclosed in a case 5 additionally with a condenser 6, a thermal protector and lead wires 8.

FIG. 4a illustrates the harmonics existing in the secondary current wave form for the prior art. FIG. 4b illustrates the secondary current wave form in which the peak current is almost non existent as compared to the prior art method. In particular the spike which occurs prior to the peak of the main body of the current wave form is eliminated and the current wave form is made much more symmetrical.

FIG 5a illustrates the primary wave form according to the prior art indicating that distortion exists which can effect other electronic systems hooked to the same primary current source and can generate heat which must be dissipated in the system. Furthermore, the invention has the additional benefit of drastically reducing the power consumption of the system since the primary current value is lowered.

While the use of the invention reduces the absolute value of luminous intensity of the fluorescent light, due to the lowering of the maximum value of the secondary current, uniform brightness of the lumination is still maintained. Furthermore, by utilizing the invention, a lower light flux from an individual lamp is produced thereby reducing the glare and the requirement for high performance defusers in a work area served by fluorescent lamps. Thus, the use of the invention can reduce glare by lowering the cost of glare reduction methods and provide an additional benefit in reduced power utilized by the fluorescent lamp.

Another benefit of the present invention is its available high performance color lamps which has thus far proved unpopular because of the high costs of the lamps. By utilizing the invention with these color lamps a better quality illumination can be obtained by utilizing this more economical method of starting and maintaining the lamps in use. Thus, it may be seen that the present invention provides substantial benefits compared to conventional rapid start fluorescent lamp stabilizers.

The peak current value is reduced thereby reducing harmonics without distorting the secondary current. Distortion in the primary current wave form is also reduced. The radio frequency interference is substantially reduced by use of this method compared to other systems and the power saving is on the order of 35 to 45 percent compared to other systems. The decreased power consumption and improved wave form quality of the primary current also result in lower temperature of the ballast system and a resulting decrease in the cooling required for the stabilizer system. All of these benefits result in increased life spans for the fluorescent lamp and stabilizer as well as the surrounding electronic components and associated systems. While the invention has been described in the context of a four lamp system, it will be evident that it may be applied equally to any fluorescent light system utilizing the rapid starting fluorescent lamp stabilizer system.

While one particular form of the invention has been described, it will be apparent to those skilled in the art that various modifications can be made without departing from the spirit and scope of the invention be limited except as by the appended claims.