CA1333920C - System for energizing a fluorescent tube - Google Patents
System for energizing a fluorescent tubeInfo
- Publication number
- CA1333920C CA1333920C CA 541820 CA541820A CA1333920C CA 1333920 C CA1333920 C CA 1333920C CA 541820 CA541820 CA 541820 CA 541820 A CA541820 A CA 541820A CA 1333920 C CA1333920 C CA 1333920C
- Authority
- CA
- Canada
- Prior art keywords
- fluorescent tube
- current
- autotransformer
- direct current
- tube
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Fee Related
Links
Classifications
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
- H05B41/00—Circuit arrangements or apparatus for igniting or operating discharge lamps
- H05B41/14—Circuit arrangements
- H05B41/26—Circuit arrangements in which the lamp is fed by power derived from dc by means of a converter, e.g. by high-voltage dc
- H05B41/28—Circuit arrangements in which the lamp is fed by power derived from dc by means of a converter, e.g. by high-voltage dc using static converters
- H05B41/282—Circuit arrangements in which the lamp is fed by power derived from dc by means of a converter, e.g. by high-voltage dc using static converters with semiconductor devices
- H05B41/2821—Circuit arrangements in which the lamp is fed by power derived from dc by means of a converter, e.g. by high-voltage dc using static converters with semiconductor devices by means of a single-switch converter or a parallel push-pull converter in the final stage
- H05B41/2824—Circuit arrangements in which the lamp is fed by power derived from dc by means of a converter, e.g. by high-voltage dc using static converters with semiconductor devices by means of a single-switch converter or a parallel push-pull converter in the final stage using control circuits for the switching element
Landscapes
- Circuit Arrangements For Discharge Lamps (AREA)
- Discharge-Lamp Control Circuits And Pulse- Feed Circuits (AREA)
Abstract
A fluorescent tube (which may or may not have its heater coils shorted) is energized by a constant current with the direction of the substantially constant current being periodically changed. The magnitude of the constant current may be varied by varying the setting of a control member.
For example, the movable arm of a potentiometer may be varied. The potentiometer may be included in an optically coupled circuit to give isolated control to the constant current when the position of the movable tap is changed. The movement of the movable arm of the potentiometer causes the duration of the output pulse from a pulse width modulator to vary accordingly. During the production of this output pulse, a switch (e.g. a field effect transistor) is closed so that current is able to flow from a rectified alternating voltage to an energy storage member such as a coil. The coil may be connected to the center tap of an autotransformer to introduce stored energy to the autotransformer during the time that the switch is open. The autotransformer is also connected, at positions displaced from the center tap, to switches which become alternately closed at progressive periods of time to change the direction of the flow of the current through the fluorescent tube.
For example, the movable arm of a potentiometer may be varied. The potentiometer may be included in an optically coupled circuit to give isolated control to the constant current when the position of the movable tap is changed. The movement of the movable arm of the potentiometer causes the duration of the output pulse from a pulse width modulator to vary accordingly. During the production of this output pulse, a switch (e.g. a field effect transistor) is closed so that current is able to flow from a rectified alternating voltage to an energy storage member such as a coil. The coil may be connected to the center tap of an autotransformer to introduce stored energy to the autotransformer during the time that the switch is open. The autotransformer is also connected, at positions displaced from the center tap, to switches which become alternately closed at progressive periods of time to change the direction of the flow of the current through the fluorescent tube.
Description
- 2 _ 1 3 33~20 This invention relates to a system for energizing a fluorescent tube. More particularly, the invention relates to a system for energizing a fluorescent tube with a constant current at any set level. The invention is especially adapted to energize the fluorescent tube with the constant current which constant current is switched by a very high speed switch and in a square wave form in alternate, opposite directions to provide an alternating constant current across the fluorescent tube.
Fluorescent tubes have been in existence for decades. During this period, a considerable effort has been devoted, and significant amounts of money have been expended, to perfect such tubes and the systems for energizing the tubes. In spite of such considerable expenditure of effort and money, the systems now in use for energizing the fluorescent tubes are relatively inefficient. The fluorescent tubes also provide a flickering light output and have a relatively limited life. It has also been difficult to provide a controlled amount of light energy in the tubes.
5~ d~sc ~S~r e_ IV This i.. vc.. tion-provides a system which overcomes the above difficulties. It provides a minimal power loss in the fluorescent tubes. It provides a substantially constant illumination in the fluorescent tubes with no light flicker. It provides for the flow of current through the tubes at a constant magnitude, which can be precisely controlled even at low values of current. This provides for a long life of the tubes.
In one embodiment of the invention, a fluorescent tube (which may or may not have its heater coils shorted) is energized by a constant current. However, the direction of the 'C
constant current is periodically changed with a very rapid switching. The magnitude of the constant current may be varied by varying the setting of a control member. For example, the movable arm of a potentiometer may be varied. The potentiometer may be 5 included in an optically coupled circuit to give isolated control to the constant current when the position of the movable tap is changed. The movement of the movable arm of the potentiometer causes the duration of the output current pulse from a pulse width modulator to vary accordingly.
lo During the production of the output current pulse from the pulse width modulator, a switch (e.g. a field effect transistor) is closed so that current is able to flow from a rectified alternating voltage current to an energy storage member such as a coil. The coil may be connected to the center tap of an 15 autotransformer to feed current to the autotransformer when the switch is open and to introduce stored current to the autotransformer during the time that the switch is closed. This provides a constant current to the autotransformer. The autotransformer is also connected, at positions displaced from the 20 center tap, to switches which become alternately closed at very rapid switching speeds to rapidly change the direction of the flow of the constant current through the fluorescent tube, while maintaining a constant current flow across the tube.
Embodiments of the invention will now be described with 25 reference to the accompanying drawings wherein:
- 3a _ 1 3 33~20 Figures la and lb are diagrams, partially in block form, cumulatively indicating a system constituting one embodiment of the invention for producing a flow of a constant current through a fluorescent tube to energize the tube;
13~3~20 Figure 2 is a circuit diagram schematically illustrating additional features of applicant's circuitry for energizing fluorescent tubes in relation to the circuitry for energizing the fluorescent tubes of the prior art;
Figure 3 is a curve illustrating the relationship between voltage and current in circuitry of the prior art for c rn energizing a fluorescent tube and in the circuitry ef this invention; and Figure 4 illustrates waveforms of signals produced at strategic terminals in the circuitry shown in Figures la and lb.
In one embodiment of the invention, a voltage source 10 (Figure la) is adapted to provide an alternating voltage and current from a conventional source such as a wall outlet. The alternating voltage may be in the order of 115 volts. The alternating voltage and current is rectified by a stage 12 and the rectified voltage and current is introduced to a pair of parallel capacitances 14 and 16 to minimize any ripples in the rectified voltage and current.
A switch such as that formed by the source and drain of a field effect transistor 22 is connected between the capacitances 14 and 16 and the junction of a diode 54 and a coil 56. A winding 26 is also connected between the gate and the source of the field effect transistor 22. The winding 26 is magnetically coupled as by a ferrite core to a winding 28 having a center tap 30. The number of turns on the winding 28 may be greater than the number of turns in the winding 26.
~y .
_ 5 _ 1 3 3 3 92 0 The center tap 30 of the winding 28 receives the output signals from a pulse width modulator 34. Signals are introduced to the input terminal of the pulse width modulator 34 from an optical coupler 31 and from a sense resistor 48. The output of the optical coupler 31 is controlled by the positioning of a tap in a potentiometer 52 which is energized from a source such as the battery 32 or an external supply ~pt,`C ~/
D source. The e~tiona~ coupler 31 may be constructed in a manner conventional in the prior art.
The anode of the diode 54 is common with second terminals of the capacitances 14 and 16. The cathode of the diode 54 is connected to one terminal of a coil 56 (Figures la and lb) having a ferrite core. The second terminal of the coil 56 is common with the center tap of an autotransformer 58 (Figure lb) having a ferrite core. A fluorescent tube 60 constructed in a conventional manner is connected between the end terminals of the autotransformer 58. The circuit may or may not have windings 57 connected to heater coils 59 in the fluorescent tube 60. The windings 57 may be magnetically coupled to the winding 58.
Terminals 61 and 62 may be provided in the autotransformer 58 intermediate the center tap and the end terminals of the autotransformer. Switches such as those defined by the source and drain of a field effect transistor 64 and the source and drain of a field effect transistor 66, which switches have a very rapid switching speed, are respectively connected between the intermediate terminals 61 and 62 and a C
- 6 - 1 3 33~2 0 reference potential such as a ground 47. A capacitance 68 and a ~q resistance ~t~ are in series between the center tap of the autotransformer 58 and the reference potential such as the ~onn cct~, ground 47, to which the optical coupler 31 is co.,_~ea.
The gate of the field effect transistor 64 is common with the emitters of a pair of transistors 70 (an NPN) and 72 (a PNP). The collector of the transistor 70 receives a positive voltage from the~ectifier 12. The bases of the transistors 70 and 72 are connected to the output terminal of an inverter 74.
The collector of the transistor 72 receives the reference potential such as the ground 47.
The output of an amplifier 76 is introduced to the input of the inverter 74. The input terminal of the amplifier 76 is common with one terminal of a capacitance 78, the other terminal of which receives the reference potential such as the ground 47. A resistance 80 is connected between the input terminal of the amplifier 76 and the output terminal of the inverter 74.
The output of the inverter 74 is introduced to an amplifier 82, the output of the amplifier in turn being inverted as at 84. The output of the inverter 84 is introduced to the bases of a transistor 86 (an NPN) and a transistor 88 (a PNP).
The collector of the transistor 88 is common with the reference potential such as the ground 47. The emitters of the transistors 86 and 88 are connected to the gate of the field effect transistor 66. The collector of the transistor 86 receives a positive voltage from the rectifier 12.
~` 1333920 The alternating voltage an~current from th~ source 10 is converted into a direct voltag~,ànd current by th~
rectifier 12 and this direct voltage ah~ ~urrent is smdothed by the capacitances 14 and 16 to minimize ripples. This voltage and current is introduced to the drain of the field effect transistor 22. When the field effect transistor 22 is conductive, current flows through the transistor, the coil 56 where the current level is smoothed in the known manner (Figures la and lb), the autotransformer 58 (Figure lb), one of the field e-ffect transistors 64 and 66 and the resistance 48 (Figures la and lb). The output of the pulse width modulator 34 and thus the current through transistor 22 is illustrated at 100 in Figure 4. This current causes current to be stored in the coil 56. The magnitude of the constant current is dependent upon the output from the optical coupler 31. As previously described, the output from optical coupler 31 is controlled by an external setting of the movable arm of the potentiometer S2.
Assume now that the position of the movablé arm in the potentiometer 52 is changed. This causes the output of the optical coupler 31 to change, thereby changing the output of the pulse width modulator 34 in driving the field effect transistor 22. The change in the ouL~uL of the pulse width modulator 34 is illustrated in broken lines at 102 in Figure 4. During the production of the signal 102, a voltage is introduced to the gate of field effect transistor 22 to make the transistor conductive.
When the periodic duration for the flow of current through the transistor 22 changes, the amount of energy stored - 8 - 1 33 392a in the coil 56 also changes. During the period of time that the field effect transistor 22 is not conductive, this energy is discharged through a circuit including the coil 56, the autotransformer 58, one of the field effect transistors 64 and 66, the resistance 48 (Figures la and lb) and the diode 54 (Figures la and lb). Thus, the change in the magnitude of the energy in the coil 56 will cause a corresponding change to be produced in the voltage across the resistance 48. The pulse width modulator 34 senses any difference between the inputs from r) pu,t f'~,r"
line 35 from resistor 48 and ground 47 and the in~--t f~effl-line 37 from optical coupler and source 47.
The circuitry discussed above acts, as a practical matter, as a servo system. When a change is provided in the positioning of the movable arm of the potentiometer 52, a corresponding change is produced in the average value of the current in the resistance 48. In this way, the duration of the periodic pulses 100 from the pulse modulator 34 is adjusted (as indicated at 102) to a level representative of the positioning of the movable arm in the potentiometer 52 and is held to this constant current. This causes the current flowing through the autotransformer 58 to become adjusted to a constant value representative of the positioning of the movable arm of the potentiometer 52.
The direction of the flow of the constant current through the autotransformer 58 is controlled by the circuitry shown in Figure lb. This circuitry includes the amplifier 76, the inverter 74, the resistance 80 and the capacitance 78. This C
- 1333~20 g circuitry acts as a Schmidt trigger in a conventional manner to produce alternately positive and negative pulses at the output ~1 t~ ~ n ~'re, from the inverter 74. The alt~ atcly positive and negative pulses are produced by alternately charging the capacitance 78 to a level for making the amplifier 76 conductive and then discharging the capacitance through the amplifier. The positive pulses from the inverter 74 pass through the transistors 72 and 70, which provide substantially a 1:1 gain in the signals from the inverter and isolate the amplifier 76 and the inverter 74 from the field effect transistor 64. These pulses cause the transistor 64 to become conductive.
When the transistor 64 becomes conductive, the line current flows through a circuit including the autotransformer 58, the transistor 64, through resistor 48. This line current is produced because of the power source 10 and because of the voltage across the coil 56. This line current produces a voltage between the center ~o~ and the intermediate terminal 61 of the autotransformer 58. This creates a stepped up voltage in the transformer circuit across the autotransformer and this stepped up voltage is applied to the fluorescent tube 60. This further produces a flow of current in the transformer circuit toward the left in Figure l(b). The autotransformer functions as a current transformer to produce a current in the transformer circuit and through the tube 60 that is constant in magnitude, except in the very short time interval that the current is switched by transistor 64 and 66. This constant current in the transformer circuit is reduced relative to the current flowing 1333~920 through the transistor 64 because of the stepped-down current produced across the autotransformer 58.
During the time that the inverter 74 produces a low voltage, the inverter 84 produces a high voltage. This voltage is applied through the isolating transistors 88 and 86 (which perform the same functions as the transistors 72 and 70) to the transistor 66 to make the transistor 66 conductive. Current then flows through a circuit including the autotransformer 58 between the center tap and the intermediate terminal 62 of the autotransformer 58, the transistor 66, through resistor 48.
This current is in an opposite direction to that produced in the autotransformer 58 when the transistor 64 is conductive. This current produces in the autotransformer 58 a stepped-up voltage which causes a constant current to flow through the fluorescent tube 60. This current is in a direction opposite to the direction of the current in the fluorescent tube when the transistor 64 is conductive.
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The i.~ io.l described above has certain important advantages. It provides for a flow through the fluorescent tube of a constant current which can be precisely controlled irrespective of slight changes in voltage. Since the current is constant in the set magnitude, the fluorescent tube produces light without any flicker. This follows because the magnitude of the current is not being diminished across the tube, as is the case in prior art alternating current systems. Although the current through the fluorescent tube is constant, the direction C`
- 11- 133392~
of the current through the tube is changed or alternated. This enhances the life of the tube considerably.
The power losses in the fluorescent tube 60 included ~ t~ ~ dc~c~b~
in the EyEtcm of thiE invcntion are relatively low. This results from the fact that the fluorescent tube 60 is energized at a constant level even when the direction of the current flow through the tube is changed periodically. This assures that ions are constantly excited in the tube. The power losses in the fluorescent tube are relatively low for another reason.
This results from the fact that the heater coils 59 at the opposite ends of the tube may be shorted electrically. This is illustrated in Figure 2. This is in contrast to the prior art which passes current through the heater coils 59 to heat the coils. As will be appreciated, such heater current results in a considerable power loss.
Figure 3 illustrates the relationship between the voltage and current in the fluorescent tubes of the prior art.
As will be seen at 112 in Figure 3, a voltage as high as one thousand volts (lOOOv) has to be introduced across the fluorescent tube to excite the tube. When the tubes have been energized, a voltage of the order of one hundred and twenty volts (120v) may be sufficient to maintain the tube energized and to produce progressive amounts of current in the tube.
In the prior art, the current varies from "zero" to several hundred milliamperes at a rate of 120 times per second, once each peak in the positive and negative cycles of the 60 Hertz wave. As a result, the fluorescent tube becomes ~..J
~ i 1333S20 de-energized in each half cycle of the energizing voltage and has to be re-energized in each such half cycle. This requires that a voltage of approximately one thousand (lOOOv) volts is applied to the tube in each half cycle of the alternating voltage. This voltage is obtained from the ballast in the tube. It causes pulsating currents to be produced in the fluorescent tubes of the prior art, as indicated at 120, when a sine wave signal 122 is introduced to the tubes. Such de-energization and re-energization of the tube in each half cycle of the alternating voltage may result in a low efficiency in the tube and provide for a limited life of the tube.
In contrast, the new system is able to operate the fluorescent tube with a constant current with an energy source that will provide the proper current irrespective of the changes in voltage that can be expected in fluorescent - tubes. As previously described, the voltage across fluorescent tubes is generally stable and held by the tube's parameters to around 120 volts. However, even small changes in voltage across the fluorescent tubes can result in large, destructive changes in the current in prior art fluorescent tube systems. The - novel circuit, embodying this invention functions to hold the current constant to that magnitude set by potentiometer 52, and the current magnitude does not change with changes in voltage.
The feed back servo loop circuit, holds the current magnitude to the desired value irrespective of voltage changes in the load.
Also the voltage does-not change in response to current changes, because the voltage is held relatively constant as an inherent - 13 - 13~3920 parameter of the fluorescent tube. The term "constant current"
is used in this disclosure in the context of setting and holding current to a given value over time and that is not subject to changes by load and temperature or input power fluctuations.
This may be seen at 114 in Figure 3. Thus the voltage is held constant with progressive changes in the amplitudes of the current through the tube after the gas in the tube has been ionized initially with a high voltage. Once the fluorescent tube 60 is energized, it remains energized throughout the successive reversal of the input current. This occurs in part because the input alternating voltage or current is converted to a direct current and because the coil 56 stores current to a constant magnitude for introduction to the fluorescent tube 60.
Since the fluorescent tube 60 in the new system remains constantly energized and since the magnitude of the current through the tube remains constant throughout the successive half cycles of the alternating voltage, the fluorescent tube 60 in the new system operates at an optimal efficiency. This insures that the fluorescent tube 60 will have a long life.
Although this invention has been disclosed and illustrate with reference to particular embodiments, the principles involved are susceptible for use in numerous other embodiments which will be apparent to person skilled in the art.
The invention is, therefore, to be limited only as indicated by the scope of the appended claims.
Fluorescent tubes have been in existence for decades. During this period, a considerable effort has been devoted, and significant amounts of money have been expended, to perfect such tubes and the systems for energizing the tubes. In spite of such considerable expenditure of effort and money, the systems now in use for energizing the fluorescent tubes are relatively inefficient. The fluorescent tubes also provide a flickering light output and have a relatively limited life. It has also been difficult to provide a controlled amount of light energy in the tubes.
5~ d~sc ~S~r e_ IV This i.. vc.. tion-provides a system which overcomes the above difficulties. It provides a minimal power loss in the fluorescent tubes. It provides a substantially constant illumination in the fluorescent tubes with no light flicker. It provides for the flow of current through the tubes at a constant magnitude, which can be precisely controlled even at low values of current. This provides for a long life of the tubes.
In one embodiment of the invention, a fluorescent tube (which may or may not have its heater coils shorted) is energized by a constant current. However, the direction of the 'C
constant current is periodically changed with a very rapid switching. The magnitude of the constant current may be varied by varying the setting of a control member. For example, the movable arm of a potentiometer may be varied. The potentiometer may be 5 included in an optically coupled circuit to give isolated control to the constant current when the position of the movable tap is changed. The movement of the movable arm of the potentiometer causes the duration of the output current pulse from a pulse width modulator to vary accordingly.
lo During the production of the output current pulse from the pulse width modulator, a switch (e.g. a field effect transistor) is closed so that current is able to flow from a rectified alternating voltage current to an energy storage member such as a coil. The coil may be connected to the center tap of an 15 autotransformer to feed current to the autotransformer when the switch is open and to introduce stored current to the autotransformer during the time that the switch is closed. This provides a constant current to the autotransformer. The autotransformer is also connected, at positions displaced from the 20 center tap, to switches which become alternately closed at very rapid switching speeds to rapidly change the direction of the flow of the constant current through the fluorescent tube, while maintaining a constant current flow across the tube.
Embodiments of the invention will now be described with 25 reference to the accompanying drawings wherein:
- 3a _ 1 3 33~20 Figures la and lb are diagrams, partially in block form, cumulatively indicating a system constituting one embodiment of the invention for producing a flow of a constant current through a fluorescent tube to energize the tube;
13~3~20 Figure 2 is a circuit diagram schematically illustrating additional features of applicant's circuitry for energizing fluorescent tubes in relation to the circuitry for energizing the fluorescent tubes of the prior art;
Figure 3 is a curve illustrating the relationship between voltage and current in circuitry of the prior art for c rn energizing a fluorescent tube and in the circuitry ef this invention; and Figure 4 illustrates waveforms of signals produced at strategic terminals in the circuitry shown in Figures la and lb.
In one embodiment of the invention, a voltage source 10 (Figure la) is adapted to provide an alternating voltage and current from a conventional source such as a wall outlet. The alternating voltage may be in the order of 115 volts. The alternating voltage and current is rectified by a stage 12 and the rectified voltage and current is introduced to a pair of parallel capacitances 14 and 16 to minimize any ripples in the rectified voltage and current.
A switch such as that formed by the source and drain of a field effect transistor 22 is connected between the capacitances 14 and 16 and the junction of a diode 54 and a coil 56. A winding 26 is also connected between the gate and the source of the field effect transistor 22. The winding 26 is magnetically coupled as by a ferrite core to a winding 28 having a center tap 30. The number of turns on the winding 28 may be greater than the number of turns in the winding 26.
~y .
_ 5 _ 1 3 3 3 92 0 The center tap 30 of the winding 28 receives the output signals from a pulse width modulator 34. Signals are introduced to the input terminal of the pulse width modulator 34 from an optical coupler 31 and from a sense resistor 48. The output of the optical coupler 31 is controlled by the positioning of a tap in a potentiometer 52 which is energized from a source such as the battery 32 or an external supply ~pt,`C ~/
D source. The e~tiona~ coupler 31 may be constructed in a manner conventional in the prior art.
The anode of the diode 54 is common with second terminals of the capacitances 14 and 16. The cathode of the diode 54 is connected to one terminal of a coil 56 (Figures la and lb) having a ferrite core. The second terminal of the coil 56 is common with the center tap of an autotransformer 58 (Figure lb) having a ferrite core. A fluorescent tube 60 constructed in a conventional manner is connected between the end terminals of the autotransformer 58. The circuit may or may not have windings 57 connected to heater coils 59 in the fluorescent tube 60. The windings 57 may be magnetically coupled to the winding 58.
Terminals 61 and 62 may be provided in the autotransformer 58 intermediate the center tap and the end terminals of the autotransformer. Switches such as those defined by the source and drain of a field effect transistor 64 and the source and drain of a field effect transistor 66, which switches have a very rapid switching speed, are respectively connected between the intermediate terminals 61 and 62 and a C
- 6 - 1 3 33~2 0 reference potential such as a ground 47. A capacitance 68 and a ~q resistance ~t~ are in series between the center tap of the autotransformer 58 and the reference potential such as the ~onn cct~, ground 47, to which the optical coupler 31 is co.,_~ea.
The gate of the field effect transistor 64 is common with the emitters of a pair of transistors 70 (an NPN) and 72 (a PNP). The collector of the transistor 70 receives a positive voltage from the~ectifier 12. The bases of the transistors 70 and 72 are connected to the output terminal of an inverter 74.
The collector of the transistor 72 receives the reference potential such as the ground 47.
The output of an amplifier 76 is introduced to the input of the inverter 74. The input terminal of the amplifier 76 is common with one terminal of a capacitance 78, the other terminal of which receives the reference potential such as the ground 47. A resistance 80 is connected between the input terminal of the amplifier 76 and the output terminal of the inverter 74.
The output of the inverter 74 is introduced to an amplifier 82, the output of the amplifier in turn being inverted as at 84. The output of the inverter 84 is introduced to the bases of a transistor 86 (an NPN) and a transistor 88 (a PNP).
The collector of the transistor 88 is common with the reference potential such as the ground 47. The emitters of the transistors 86 and 88 are connected to the gate of the field effect transistor 66. The collector of the transistor 86 receives a positive voltage from the rectifier 12.
~` 1333920 The alternating voltage an~current from th~ source 10 is converted into a direct voltag~,ànd current by th~
rectifier 12 and this direct voltage ah~ ~urrent is smdothed by the capacitances 14 and 16 to minimize ripples. This voltage and current is introduced to the drain of the field effect transistor 22. When the field effect transistor 22 is conductive, current flows through the transistor, the coil 56 where the current level is smoothed in the known manner (Figures la and lb), the autotransformer 58 (Figure lb), one of the field e-ffect transistors 64 and 66 and the resistance 48 (Figures la and lb). The output of the pulse width modulator 34 and thus the current through transistor 22 is illustrated at 100 in Figure 4. This current causes current to be stored in the coil 56. The magnitude of the constant current is dependent upon the output from the optical coupler 31. As previously described, the output from optical coupler 31 is controlled by an external setting of the movable arm of the potentiometer S2.
Assume now that the position of the movablé arm in the potentiometer 52 is changed. This causes the output of the optical coupler 31 to change, thereby changing the output of the pulse width modulator 34 in driving the field effect transistor 22. The change in the ouL~uL of the pulse width modulator 34 is illustrated in broken lines at 102 in Figure 4. During the production of the signal 102, a voltage is introduced to the gate of field effect transistor 22 to make the transistor conductive.
When the periodic duration for the flow of current through the transistor 22 changes, the amount of energy stored - 8 - 1 33 392a in the coil 56 also changes. During the period of time that the field effect transistor 22 is not conductive, this energy is discharged through a circuit including the coil 56, the autotransformer 58, one of the field effect transistors 64 and 66, the resistance 48 (Figures la and lb) and the diode 54 (Figures la and lb). Thus, the change in the magnitude of the energy in the coil 56 will cause a corresponding change to be produced in the voltage across the resistance 48. The pulse width modulator 34 senses any difference between the inputs from r) pu,t f'~,r"
line 35 from resistor 48 and ground 47 and the in~--t f~effl-line 37 from optical coupler and source 47.
The circuitry discussed above acts, as a practical matter, as a servo system. When a change is provided in the positioning of the movable arm of the potentiometer 52, a corresponding change is produced in the average value of the current in the resistance 48. In this way, the duration of the periodic pulses 100 from the pulse modulator 34 is adjusted (as indicated at 102) to a level representative of the positioning of the movable arm in the potentiometer 52 and is held to this constant current. This causes the current flowing through the autotransformer 58 to become adjusted to a constant value representative of the positioning of the movable arm of the potentiometer 52.
The direction of the flow of the constant current through the autotransformer 58 is controlled by the circuitry shown in Figure lb. This circuitry includes the amplifier 76, the inverter 74, the resistance 80 and the capacitance 78. This C
- 1333~20 g circuitry acts as a Schmidt trigger in a conventional manner to produce alternately positive and negative pulses at the output ~1 t~ ~ n ~'re, from the inverter 74. The alt~ atcly positive and negative pulses are produced by alternately charging the capacitance 78 to a level for making the amplifier 76 conductive and then discharging the capacitance through the amplifier. The positive pulses from the inverter 74 pass through the transistors 72 and 70, which provide substantially a 1:1 gain in the signals from the inverter and isolate the amplifier 76 and the inverter 74 from the field effect transistor 64. These pulses cause the transistor 64 to become conductive.
When the transistor 64 becomes conductive, the line current flows through a circuit including the autotransformer 58, the transistor 64, through resistor 48. This line current is produced because of the power source 10 and because of the voltage across the coil 56. This line current produces a voltage between the center ~o~ and the intermediate terminal 61 of the autotransformer 58. This creates a stepped up voltage in the transformer circuit across the autotransformer and this stepped up voltage is applied to the fluorescent tube 60. This further produces a flow of current in the transformer circuit toward the left in Figure l(b). The autotransformer functions as a current transformer to produce a current in the transformer circuit and through the tube 60 that is constant in magnitude, except in the very short time interval that the current is switched by transistor 64 and 66. This constant current in the transformer circuit is reduced relative to the current flowing 1333~920 through the transistor 64 because of the stepped-down current produced across the autotransformer 58.
During the time that the inverter 74 produces a low voltage, the inverter 84 produces a high voltage. This voltage is applied through the isolating transistors 88 and 86 (which perform the same functions as the transistors 72 and 70) to the transistor 66 to make the transistor 66 conductive. Current then flows through a circuit including the autotransformer 58 between the center tap and the intermediate terminal 62 of the autotransformer 58, the transistor 66, through resistor 48.
This current is in an opposite direction to that produced in the autotransformer 58 when the transistor 64 is conductive. This current produces in the autotransformer 58 a stepped-up voltage which causes a constant current to flow through the fluorescent tube 60. This current is in a direction opposite to the direction of the current in the fluorescent tube when the transistor 64 is conductive.
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The i.~ io.l described above has certain important advantages. It provides for a flow through the fluorescent tube of a constant current which can be precisely controlled irrespective of slight changes in voltage. Since the current is constant in the set magnitude, the fluorescent tube produces light without any flicker. This follows because the magnitude of the current is not being diminished across the tube, as is the case in prior art alternating current systems. Although the current through the fluorescent tube is constant, the direction C`
- 11- 133392~
of the current through the tube is changed or alternated. This enhances the life of the tube considerably.
The power losses in the fluorescent tube 60 included ~ t~ ~ dc~c~b~
in the EyEtcm of thiE invcntion are relatively low. This results from the fact that the fluorescent tube 60 is energized at a constant level even when the direction of the current flow through the tube is changed periodically. This assures that ions are constantly excited in the tube. The power losses in the fluorescent tube are relatively low for another reason.
This results from the fact that the heater coils 59 at the opposite ends of the tube may be shorted electrically. This is illustrated in Figure 2. This is in contrast to the prior art which passes current through the heater coils 59 to heat the coils. As will be appreciated, such heater current results in a considerable power loss.
Figure 3 illustrates the relationship between the voltage and current in the fluorescent tubes of the prior art.
As will be seen at 112 in Figure 3, a voltage as high as one thousand volts (lOOOv) has to be introduced across the fluorescent tube to excite the tube. When the tubes have been energized, a voltage of the order of one hundred and twenty volts (120v) may be sufficient to maintain the tube energized and to produce progressive amounts of current in the tube.
In the prior art, the current varies from "zero" to several hundred milliamperes at a rate of 120 times per second, once each peak in the positive and negative cycles of the 60 Hertz wave. As a result, the fluorescent tube becomes ~..J
~ i 1333S20 de-energized in each half cycle of the energizing voltage and has to be re-energized in each such half cycle. This requires that a voltage of approximately one thousand (lOOOv) volts is applied to the tube in each half cycle of the alternating voltage. This voltage is obtained from the ballast in the tube. It causes pulsating currents to be produced in the fluorescent tubes of the prior art, as indicated at 120, when a sine wave signal 122 is introduced to the tubes. Such de-energization and re-energization of the tube in each half cycle of the alternating voltage may result in a low efficiency in the tube and provide for a limited life of the tube.
In contrast, the new system is able to operate the fluorescent tube with a constant current with an energy source that will provide the proper current irrespective of the changes in voltage that can be expected in fluorescent - tubes. As previously described, the voltage across fluorescent tubes is generally stable and held by the tube's parameters to around 120 volts. However, even small changes in voltage across the fluorescent tubes can result in large, destructive changes in the current in prior art fluorescent tube systems. The - novel circuit, embodying this invention functions to hold the current constant to that magnitude set by potentiometer 52, and the current magnitude does not change with changes in voltage.
The feed back servo loop circuit, holds the current magnitude to the desired value irrespective of voltage changes in the load.
Also the voltage does-not change in response to current changes, because the voltage is held relatively constant as an inherent - 13 - 13~3920 parameter of the fluorescent tube. The term "constant current"
is used in this disclosure in the context of setting and holding current to a given value over time and that is not subject to changes by load and temperature or input power fluctuations.
This may be seen at 114 in Figure 3. Thus the voltage is held constant with progressive changes in the amplitudes of the current through the tube after the gas in the tube has been ionized initially with a high voltage. Once the fluorescent tube 60 is energized, it remains energized throughout the successive reversal of the input current. This occurs in part because the input alternating voltage or current is converted to a direct current and because the coil 56 stores current to a constant magnitude for introduction to the fluorescent tube 60.
Since the fluorescent tube 60 in the new system remains constantly energized and since the magnitude of the current through the tube remains constant throughout the successive half cycles of the alternating voltage, the fluorescent tube 60 in the new system operates at an optimal efficiency. This insures that the fluorescent tube 60 will have a long life.
Although this invention has been disclosed and illustrate with reference to particular embodiments, the principles involved are susceptible for use in numerous other embodiments which will be apparent to person skilled in the art.
The invention is, therefore, to be limited only as indicated by the scope of the appended claims.
Claims (6)
1. In a combination for exciting a fluorescent tube to obtain luminescence from the tube, control means having a variable setting, first means responsive to the variable setting of the control means for providing constant direct current in accordance with such variable setting, second means connected to the fluorescent tube and to the first means for energizing the fluorescent tube in accordance with the current flow from the first means, and third means connected to the second means for obtaining the energizing of the fluorescent tube alternately in opposite directions, the fluorescent tube having first and second output terminals, the third means including bistable means having first and second output lines, the bistable means alternately providing outputs on the first and second output lines, the first and second output lines being respectively coupled electrically to the first and second output terminals of the fluorescent tube.
2. In a combination as set forth in claim 1, the second means including an autotransformer having a center tap and taps removed in the autotransformer from the center tap, the removed taps of the autotransformer being connected to the fluorescent tube, the center tap of the autotransformer being connected to the first means.
3. In a combination as set forth in claim 1, the first means including a pulse width modulator means responsive to variations in the setting of the control means for producing direct current pulses having a variable width.
4. In combination for exciting a fluorescent tube to obtain luminescence from the tube, means for providing a constant direct current, control means having a variable setting, first means responsive to the variable setting of the control means for providing a level of constant direct current dependent upon such variable setting, second means responsive to the constant direct current from the first means for energizing the fluorescent tube at a constant direct current magnitude dependent upon the constant direct current from the first means, and third means operatively coupled to the second means for energizing the fluorescent tube at the constant direct current magnitude alternately in opposite directions, the first means including a switch responsive to the variable setting of the control means for becoming closed at a relative percentage of time dependent upon such variable setting and further including current leveling means for leveling current during the period of time that such switch is closed.
5. In a combination as set forth in claim 4, the third means including bistable means having first and second states of operation, the bistable means being operatively coupled to the fluorescent tube to activate the fluorescent tube in a first direction in the first state of operation of the bistable means and to activate the fluorescent tube in a second direction opposite to the first direction in the second state of operation of the fluorescent tube, means for periodically changing the direction of the flow of the constant current through the fluorescent tube.
6. In a combination as set forth in claim 4, the leveling means comprising an inductance.
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US89496886A | 1986-08-08 | 1986-08-08 | |
| US894,968 | 1986-08-08 | ||
| US1022287A | 1987-02-03 | 1987-02-03 | |
| US010,222 | 1987-02-03 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1333920C true CA1333920C (en) | 1995-01-10 |
Family
ID=26680930
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 541820 Expired - Fee Related CA1333920C (en) | 1986-08-08 | 1987-07-10 | System for energizing a fluorescent tube |
Country Status (4)
| Country | Link |
|---|---|
| EP (1) | EP0259603B1 (en) |
| JP (1) | JP3012649B2 (en) |
| CA (1) | CA1333920C (en) |
| DE (1) | DE3786432T2 (en) |
Families Citing this family (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2212995A (en) * | 1987-10-23 | 1989-08-02 | Rockwell International Corp | Fluorescent lamp dimmer |
| US5051665A (en) * | 1990-06-21 | 1991-09-24 | Gte Products Corporation | Fast warm-up ballast for arc discharge lamp |
| US6469454B1 (en) * | 2000-06-27 | 2002-10-22 | Maxim Integrated Products, Inc. | Cold cathode fluorescent lamp controller |
| US8049432B2 (en) * | 2008-09-05 | 2011-11-01 | Lutron Electronics Co., Inc. | Measurement circuit for an electronic ballast |
Family Cites Families (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS5682899U (en) * | 1979-11-30 | 1981-07-04 | ||
| JPS6016080B2 (en) * | 1980-08-20 | 1985-04-23 | ウシオ電機株式会社 | DC discharge lamp lighting device |
| US4373146A (en) * | 1980-10-20 | 1983-02-08 | Gte Products Corporation | Method and circuit for operating discharge lamp |
| FI63148C (en) * | 1981-09-18 | 1983-04-11 | Helvar Oy | ELEKTRONISKT FOERKOPPLINGSDON FOER URLADDNINGSLAMPA |
| JPS58204496A (en) * | 1982-05-21 | 1983-11-29 | 富士電機株式会社 | High frequency discharge lamp firing device |
| JPS5916100U (en) * | 1982-07-21 | 1984-01-31 | 株式会社三社電機製作所 | Power supply device for discharge lamp |
-
1987
- 1987-07-10 CA CA 541820 patent/CA1333920C/en not_active Expired - Fee Related
- 1987-08-04 EP EP19870111263 patent/EP0259603B1/en not_active Expired - Lifetime
- 1987-08-04 DE DE19873786432 patent/DE3786432T2/en not_active Expired - Lifetime
- 1987-08-07 JP JP62196495A patent/JP3012649B2/en not_active Expired - Lifetime
Also Published As
| Publication number | Publication date |
|---|---|
| EP0259603B1 (en) | 1993-07-07 |
| EP0259603A1 (en) | 1988-03-16 |
| DE3786432D1 (en) | 1993-08-12 |
| DE3786432T2 (en) | 1993-10-28 |
| JPS6419698A (en) | 1989-01-23 |
| JP3012649B2 (en) | 2000-02-28 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKLA | Lapsed |