US3619716A - High-frequency fluorescent tube lighting circuit and ac driving circuit therefor - Google Patents

Abstract

A sinusoidal voltage source in series with a fluorescent, mercury vapor, sodium vapor device, etc. is pulsed at a given pulse repetition rate with the pulse having a given conduction time. Two or more tubes can sequentially conduct pulses with the current input being a continuous sinusoid. A particular pulsing circuit contains a modified pulse-forming network consisting of one or more stages of a closed series connection of a choke and two capacitors. The chokes of each stage are connected in series. The modified pulse-forming network is used as a frequency converter per se, as DC to AC converter, or specifically is in parallel with a fluorescent tube load.

Description

ali Unite States atent 1 1 3,619,716

[72] Inventors Joel S. Spira [56] References Cited fzf s h ks UNITED STATES PATENTS c 2,936,420 /1960 Tyler 328/27 [21] Appl. No. 843,927 [72} F1 3,037,147 5/1962 Genu1t et al. 315/289 X 1 ed July 23, 1969 P 3,243,711 3/1966 King et a1 323/22 1971 3 320 521 5/1967 S t 1 323 74 [73] Assignee Lutron Electronics Co., Inc. egawae a Emmaus, p FOREIGN PATENTS 793,582 4/1958 Great Britain 315/100T Primary Examiner-Roy Lake Assistant Examiner-E. R. LaRoche Attorney0strolenk, Faber, Gerb & Soffen [54] HIGH-FREQUENCY FLUORESCENT TUBE Z SS AND AC DRIVING CIRCUIT ABSTRACT: A sinusoidal voltage source in series with 21 Claims lsnrawin Fi fluorescent, mercury vapor, sodium vapor device, etc. is g pulsed at a given pulse repetition rate with the pulse having a [52] US. Cl 315/244, given conduction time. Two or more tubes can sequentially 315/105,315/208,315/235,315/242,315/290, conduct pulses with the current input being a continuous 315/D1G.2,315/D1G.5,328/27,328/223 sinusoid. A particular pulsing circuit contains a modified [51] Int. Cl 1105b 41/233, pulse-forming network consisting of one or more stages of a 1105b 41/392 closed series connection of a choke and two capacitors. The Field of Search 315/94, 98, chokes of each stage are connected in Series. The modified pulse-forming network is used as a frequency converter per Se, as DC to AC converter, or specifically is in parallel with a fluorescent tube load.

PATENTEDHUV 9 ISYI 3.619.716

SHEET 3 OF 3 HIGH-FREQUENCY FLUORESCENT TUBE LIGHTING CIRCUIT AND AC DRIVING CIRCUIT THEREFOR This invention relates to AC power supplies, and more particularly relates to AC power supplies for gas discharge tube lighting which eliminates the need for a ballast or other inductances which are normally connected to gas discharge lamps.

A common gas discharge lamp which is operated from a 60 cycle source is commonly provided with a so-called ballast which consists of an inductance (or resistor) connected in series with the lamp. This ballast serves several functions. One function is to limit lamp current which would otherwise increase uncontrollably due to the negative resistance characteristic of the electric discharge in the lamp. Another purpose is to obtain lamp starting and voltage regulation. Thus, a lamp may require a relatively high starting (striking) voltage, but, after the arc is initiated, will have a considerably lower operating voltage. The series ballast will then absorb the difference between line voltage and lamp operating voltage. Note that full line voltage, or greater, is needed to strike the lamp arc to initiate conduction. A third major function of the ballast in certain types of tubes is to provide a transformer of autotransformer which can supply cathode filament voltage, and a voltage surge for initiating arc discharge.

Ballasts using a series resistor are relatively inefficient and are not commonly used. Normally, the ballast takes the form of a series inductance or transformer. Where these ballasts are used in the usual sixty cycle circuit, they are large, heavy, noisy and expensive. Moreover, the need for the ballast must be considered in the design of the lamp fixture. In order to limit the size and expense of ballasts, fluorescent circuits have been operated from high-frequency power sources having frequencies up to a few thousand cycles per second. The use of higher frequencies is also advantageous in the operation of a fluorescent lamp since, at higher frequencies (than 60 cycles) the lamp has greater lumen efficiency, (increased lumens per watt) longer life and easier starting.

When using higher frequencies to drive fluorescent tubes, and having a sixty cycle source available, it is necessary to provide frequency changing apparatus such as mechanical rotating converters or electronic frequency converters. The size and expense of such conversion equipment often offsets the advantages of decreased ballast size and increased lamp efficiency. Moreover, the use of converters frequently requires special wiring mains and branch circuits of limited capacity, and decreases the reliability of the lighting system. Consequently, the use of higher frequency sources for fluorescent lighting has not gained wide commercial acceptance.

In accordance with one aspect of the present invention, a switching means is connected with the 60 cycle source and the fluorescent tube, and operates to turn on and off at a given frequency within the 60 cycle waveform. For example, the switching means may be conductive or ON for 100 microseconds, and nonconductive or OFF for 900 microseconds, whereby a l,000 cycle fundamental is introduced into the 60 cycle wave shape. Obviously, the OFF" times and ON times can be varied in any desired ratio to one another and have various repetition frequencies. As will be later described, the pulsing circuit may drive a delay line pulse-forming network which is in parallel with the tube and which is per se novel for use as a DC to AC converter or frequency changer. The switching means, as used in the novel combination of the invention (with a gas discharge tube) may use conventional switching circuits incorporating controlled rectifiers, transistors, and the like.

The modulation of a low-frequency (frequencies such as 50 or 60 cycles per second, used in lighting circuits) sine wave form at various ON" times and pulse repetition frequencies introduces many desirable effects in a fluorescent lighting circuit. A major advantage is that the conventional ballast can be eliminated. That is, the conduction time is short so that a current-limiting impedance is not needed or can be provided by various simple and small resistors, inductances or capacitors, or combinations thereof. Output regulation may now be provided by varying either pulse repetition frequency or the ON time. Cathode filament voltage may now be extracted from the modulated sine wave by transformers which are small and inexpensive and tuned to the high modulating frequency. Since the tube is driven at the high modulating frequency, it is subject to all the advantages of increased lumen efficiency, longer life and easier starting. Since the ballast can be eliminated, noise, size, weight and cost of the system is substantially decreased. At higher frequencies, noise is eliminated or greatly reduced by virtue of smaller and simpler inductive and capacitive components and also eliminated by operating at a frequency above the audio range. Moreover, the heat generated by the novel system is less than in a conventional ballast system so that the lamps can be operated more efficiently at higher current and light levels.

The novel system of the invention also lends itself to the complementary conduction of two or more lamps, thereby reducing complexity and radio frequency interference. Thus, the low-frequency AC source may conduct a continuous sine wave current. This current is thus sequentially switched between two or more lamps, each sequentially conducting for a given ON time. This arrangement permits a saving in hardware and reduces radio frequency interference since the power input will be a continuous low-frequency sine wave instead of a chopped sine wave.

It is also possible to use a common switching means or modulator for each of a large number of tubes. Thus, a single modulator could serve 10 lamps or more so that the cost of the modulator per lamp becomes very small.

The novel combination of the invention also lends itself to light output regulation and to automatic regulation of light with line voltage change. Thus, light output can be changed by changing the conduction time of the lamp. A potentiometer type adjustment could therefore provide controlled dimming of a fluorescent lamp. It is also possible to maintain constant illumination when input voltage changes by providing a suitable control circuit which varies conduction time inversely with changes in line voltage.

In accordance with an important feature of the invention, the lamp may be connected in parallel with a delay line type network previously adjusted to be used as a pulse-forming network. Such a circuit may be used as frequency converter per se or as a DC to AC converter per se in accordance with an important feature of the invention. This network consists of series-connected chokes with capacitors connected at the junctions of the various chokes. In particular, each section of the delay line consists of at least one inductor and at least one capacitor, connected in a closed series circuit. A single section can be used for the present invention. A network of this type is shown in pages 10 and 11, chapter 6, in the text Principles of Radar, published by McGraw Hill Co., Inc., 1946 (second edition). Circuits of this type are used for forming a square pulse in the driver stage of a radar modulator. In accordance with the invention, a circuit of this type is so adjusted that it will oscillate, whereby the circuit is initially charged for a short charging time from the pulsing circuit and thereafter (during the OFF time of the pulsing circuit, or modulator) provides an oscillating discharge which is connected to any suitable load, such as a fluorescent tube. It will be shown that the wave shape output of this novel modulator, while not completely sinusoidal, is satisfactory for driving gas discharge tubes, and would also be satisfactory for any application which does not require an accurate sinusoidal wave shape. The chokes used in the delay line oscillators may contain one or more windings to provide filament heating windings and the like.

An important feature of the various circuits that can be constructed in accordance with the invention is that there is a significant AC component in the voltage applied to the tube, if not a pure AC voltage. In particular, in a current fed mode, to be described hereinafter, there is a pure AC voltage input to the tube whether the energizing circuit is an AC or DC circuit. This has a significant advantage since most gas discharge lamps are most efiiciently operated when an AC voltage is connected to the lamp. While most gas discharge lamps can be operated from either DC or AC voltage, DC voltage will cause a premature blackening or darkening at one end of certain types of gas discharge lamps, particularly fluorescent lamps. DC operation is also less efficient than AC operation. For example, lamp efficiency for DC operation is about 70 percent of its efiiciency at high-frequency AC operation. DC operation will also cause decreased fluorescent tube life by 10 to 20 percent. Where DC voltage is applied to mercury vapor lamps, there is a loss in life time because of overheating of one electrode. In some sodium vapor lamps, the lamps cannot be operated at all by DC voltage. The main advantage of DC operation is that it does not cause a stroboscopic effect. However, devices operated in accordance with the present invention are operated at sufficiently high frequency to eliminate any strobos'copic problem.

Accordingly, a primary object of this invention is to provide a novel energizing circuit for gas discharge tubes which eliminates the conventional ballast, and operates the tubes at a relatively high frequency.

Another object of this invention is to provide a novel drive circuit for gas discharge tubes which controllably modulates a sine wave at a given pulse repetition frequency and a given conduction time for each pulse.

Still another object of this invention is to operate a plurality of gas discharge tubes from an AC circuit which is switched between the various tubes to establish a given pulse repetition frequency and conduction time for each tube.

Another object of this invention is to provide a novel common energizing circuit for a plurality of gas discharge tubes and for eliminating the ballast of the tubes.

A further object of this invention is to provide a novel, simple and inexpensive frequency converter or DC to AC converter which is formed of a modified pulse-forming network.

These and other objects of this invention will become apparent from the following description when taken in connection with the drawings, in which:

FIG. 1 is a circuit diagram of the combination of modulator and gas discharge tube of the present invention.

FIG. 2 schematically shows two gate controlled switches which could be used in the modulator circuit of FIG. 1.

FIG. 3 shows the output pulse current of the modulator of FIGS. 1 and 2 when the modulator is driven from a sinusoidal voltage source.

FIG. 4 shows the output pulse current of a circuit similar to that of FIG. 1 when the modulator is driven from a DC source.

FIG. 5 illustrates the manner in which a plurality of tubes can share a continuous sine wave current input.

FIG. 6 illustrates the division of current pulses in. the circuit of FIG. 5.

FIG. 7 shows a circuit diagram similar to FIG. 1 which includes line voltage regulation.

FIG. 8 illustrates the use of a delay line network in a circuit using a modulator and gas discharge tube load with the delay line connected in a voltage fed mode.

FIG. 9 is similar to FIG. 8 and shows the delay line connected in a' current fed mode.

FIG. 10 shows the current-time characteristic of FIG. 9 when the load impedance is greater than the network characteristic impedance.

FIG. 11 shows the current-time characteristic of FIG. 9 when load impedance is about equal to the network characteristic impedance.

FIG. 12 shows the current-time characteristic of FIG. 9 when load impedance is about equal to the network characteristic impedance and the pulse-charging time is close to the pulse period.

FIG. 15 is similar to FIG. 14 but uses individual oscillation networks which are modifications of the network shown in FIG. 8.

Referring first to FIG. 1, there is shown a circuit which illustrates the principle of the present invention wherein a voltage source is connected to terminals 20 and 21 and in series with pulse modulator 22, a gas discharge tube 23 and a currentlimiting impedance 24. Tube 23 may be of any desired commercially available variety. It is possible to eliminate this impedance if the conduction time of tube 23 is made sufficiently short. When conduction time is made sufficiently short, ionization does not have time to build up to a high degree. For example, with a small neon tube, a pulse time of less than about 6 microseconds can be used. Therefore, the effective impedance of the lamp is relatively high and the current could not build up to extremely high value, and thus the tube would operate satisfactorily while not burning out due to excessive heating. Where the tube 23 has hot cathode filaments, a filament current supply can be provided by transformer 25 which has filament heater windings 26 and 27. Transformer 25 could have been an autotransformer, and could have been arranged in series with tube 23. A suitable starting circuit (not shown) may be provided if needed for the particular tube selected.

The voltage source connected to terminals 20 and 21 could be a standard low frequency AC source, where low frequency is intended to refer to the usual frequencies used in home lighting and commercial lighting circuits such as 50 or 60 cycles. FIG. 3 shows the sinusoidal voltage wave form of this low-frequency source as dotted line 28.

The modulator 22 is constructed as a pulse modulator, and, accordingly, applies the pulse voltage shown in FIG. 3 to the tube. The pulse repetition frequency is shown to be about 1,000 cycles per second in FIG. 3 and may vary from about 200 cycles per second to any desired upper frequency limit. The modulator, and thus the pulse current may typically have a conduction time of about 100 microseconds and nonconductive time of about 900 microseconds. These times can be varied as desired. It has been found that once the tube 23 has been ignited, it need not be reignited with each successive voltage pulse from modulator 22. That is, the deionizing time of the tube is sufficiently long that the tube is not deionized between successive voltage pulses when the pulse repetition frequency is sufficiently high.

Since the tube 23 is now driven by a relatively high-frequency source, the transformer 25 will be smaller than the equivalent transformer which is designed for low-frequency operation. Moreover, transformer 25 will be appropriately tuned for operation at the relatively high frequency. Similarly, the current-limiting impedance, which could be a reactive type component, will have a smaller size as the frequency of the current conducted thereby is increased. Moreover, since tube 23 is driven at a relatively high frequency, it will have an increased lumen efficiency and longer life. Moreover, by making the modulator in such a manner that pulse length can be controlled, the output of lamp 23 can be controlled or dimmed."

Modulator 22 may be made in any desired manner, for example, as shown in FIG. 2, the modulator 22 may include two back-to-back connected gate-controlled switches 29 and 30 which are conductive so long as a gate signal is applied to their gates 31 and 32, respectively. A suitable pulse timing circuit 33 is then connected to gates 31 and 32 and delivers timed firing pulses to gates 31 and 32.

It has been found possible to apply a DC source to terminals 20 and 21, with modulator 22 generating pulses from the DC source as shown in FIG. 4. Thus, while the DC voltage, shown by dotted lines 34, is below the tube striking voltage, once the tube is fired, the pulse repetition time is less than the deioniz FIG. 13 shows a circuit diagram of a particular circuit '70 ing time of the tubeso that the tube will operate with each sucsimilar to the circuit of FIG. 9.

FIG. 14 shows a circuit using the general concepts of the circuit of FIG. 9 where, however, a plurality of lamps and plurality of oscillation networks for each lamp are used with a common pulse modulator.

herein. Any suitable means could be used to insure proper striking and conduction of all of such parallel connected tubes. Thus considerable economy is achieved in the savings of the ballasts for each lamp, and the cost of the modulator per each lamp of a large number becomes very small. Moreover, the modulator 22 can be combined in the same wall box with the ON-OFF switch 35 so that the designer of the fixture for lamp 23 (or a plurality of such lamps) need not consider the bulk ofa ballast, or the housing for modulator 22, in his fixture design.

In accordance with a further feature of the invention, a plurality of tubes can be arranged to sequentially share current pulses from a continuous sinusoidal current supply. FIG. 5 shows a circuit in which three tubes 40, 41 and 42 (which could be respective groups of tubes) are connected in series with terminals 20 and 21 (as in FIG. 1) which are connected to a suitable low-frequency source. Each of tubes 40, 41 and 42 are then connected in series with respective pulse modulators, shown as back-to-back pairs of gate-controlled switches 43-44, 45-46 and 47-48, respectively. Each of the pairs of switches is provided with a respective pulse timing circuit, such as pulse timing circuits 49, 50 and 51, respectively, which causes the current from terminals 50 and 51 to sequentially switch or commutate from tube 40 to tube 41 to tube 42 and back to tube 40, etc. Thus, a continuous and sinusoidal current is drawn from the source connected to terminals 20 and 21, thereby substantially decreasing radio interference.

This continuous sinusoidal current wave form is shown in FIG. 6. Referring to FIG. 6, the current pulse to tubes 40, 41 and 42 is shown respectively as the cross-hatched pulses (labeled l in which the hatch lines rise from left to right, as the cross-hatched pulses (labeled 2) in which the hatch lines fall from left to right, and as the double-hatched pulses (labeled 3). Clearly, the envelope of the current pulses of FIG. 6 defines a continuous sinusoid.

Note that HGS. 5 and 6 require that the pulse OFF time is twice as long as the pulse ON time since three tubes share the total sinusoid current. Clearly, any desired number of tubes could be used to share the total current with the ratio of ON" to OFF pulse time being suitably adjusted.

The use of a pulse modulator permits many desirable control functions in the lighting circuit. As previously stated, it permits dimming by controlling the length of the conducting pulse in the circuit of FIG. 1. FIG. 7 shows the manner in which the novel concept can be used to offset the effect of varying line voltage. Note that the circuit of FIG. 7 uses the modulator of FIG. 2 in the circuit of FIG. 1 and shows a choke 50 as the current-limiting impedance. Thus in FIG. 7, the terminals 20 and 21 are connected to an AC source which has a varying voltage. This would normally vary the intensity of the output of tube 23. In accordance with the invention, the pulse timing circuit is further provided with a suitable circuit for changing pulse conduction time in response to varying line voltage. Thus, a potential transformer 51 is connected across terminals 20 and 21 and applies a input voltage to the pulse timing circuit. The pulse timing circuit is suitably arranged so that pulse conduction time, or the pulse repetition frequency, is varied inversely with the output voltage of transformer 51. A decrease in line voltage will, therefore, increase the pulse length so that light intensity can be held constant. Similarly, an increase in line voltage will decrease pulse time so that light intensity will be constant. An adjustable resistor 52 can be connected in series with the output of transformer 51 and serve for manual adjustment of output light intensity, or dimming."

FIGS. 8 and 9 illustrate embodiments of the invention in which the pulse modulator is followed by an oscillator-type circuit formed of a modified pulse-forming network with the combination operating to provide a high-frequency current output to one or more fluorescent lamps.

Referring to FIG. 9, there is shown a circuit having input terminals 60 and 61, a modulator 62, an oscillating network 74 and a fluorescent lump 64. Either a low-frequency AC power source or a DC source can be connected to terminals 60 and 61, as previously described in connection with FIG. 1. The modulator 62 may be the same as the modulator 22 of FIGS. 1 and 2, it only being necessary that modulator 62 acts to pulse the voltage connected to terminals 60 and 61. Lamp 64 may be of any desired type.

Network 74 is connected in a current fed mode (a shorted delay line) and consists of two chokes 71 and 72, and capacitor 73 connected as shown. Circuits of this type (with additional stages) are well known as delay line-pulse shaping circuits for radar modulators.

In accordance with the present invention, this type circuit which shall be termed as oscillation network hereinafter, follows the pulse modulator and acts to provide an oscillating output current having a generally sinusoidal characteristic wave shape.

FIGS. 10, 11 and 12 show the current applied to tube 64 from the oscillation network 74 for various designs of the network 74. FIG. 10 shows the system when the impedance of tube 64 is substantially larger (for example, 5 times) than the characteristic impedance of network 74. In FIG. 10, pulses 75 and 76 are the pulses delivered from modulator 62-. These pulses have a period T and a conductive time t. These pulses can be considered to charge network 74 which subsequently oscillates with a period 20 as shown in FIG. 10. Thus, in period T, tube 64 will have six current pulses applied thereto (including pulse 75) with a waveform approximating a sine wave. Note that the closer the pulse time is to 0, the closer the wave shape is to a sinusoid. Therefore, if the pulse repetition frequency of modulator 62 is I,000 p.p.s., the tube 64 will carry a driving current of about 6,000 cycles per second.

As shown in FIG. 10, the circuit has a resonant ring since the load impedance is much greater than the characteristic impedance of network 74. The network can be made nonresonant, as shown in FIGS. 11 and 12, by making the load impedance about equal to the network characteristic impedance. Thus, in FIG. 11, a sinusoid is obtained with the period T of pulses 75 and 76 approximately equal to (20+t). A better or smoother waveform is obtained in FIG. 12 by reducing the period T of pulses 75 and 76 with respect to the oscillation period 20, and by making T=0+t, and t approximately equal to 0.

An important advantage of the circuit of FIG. 9 is that it provides an essentially pure AC input to the tube, even though a DC operating voltage is applied to terminals 60 and 61.

In one particular test that was performed on a circuit of the type shown in FIG. 9, a DC voltage was connected to terminals 60 and 61, which was such that approximately volts AC was measured across the terminals of lamp 64. The DC content of this AC voltage was measured to be less than 0.2 volts. This DC component is believed to be present since the chokes 71 and 72 represent a short circuit to DC current so that the 0.2 volts was an IR drop across the coils. Obviously, this IR drop could be even further reduced by merely using windings for the coils which have a lower resistance.

In the case of the current fed pulse-forming network of FIG. 9, starting may be automatic. When the tube is OFF, its impedance is extremely high (in the order of megohms), and thus the tube impedance is very much greater than the characteristics impedance of the network, regardless of the ratio of load impedance to tube impedance selected in accordance with FIGS. 10, 11 and 12. Thus, the network, during starting, will supply very high voltage pulses to the tube, thereby firing it. It is also possible to wind a few turns on choke 71 or 72 and drive the filaments with these turns to effect completely selfcontained starting and operation for a rapid start lamp.

Another technique for starting may use inductance in the circuit which is adjusted for low Q when the tube is operating. However, when the tube is OFF the inductance has a higher Q and comes out of saturation, therefore generating a high voltage for starting.

FIG. 8 is similar to the circuit of FIG. 9, but operates in a voltage fed mode rather than a current fed mode. Thus, in

FIG. 8 the oscillation network 63 is connected in parallel with tube 64 and consists of chokes 64 and 65 and capacitors 66 and 67. The circuit operates in a similar fashion as previously described in connection with FIGS. l0, l1 and 12.

In the foregoing, the combination of an AC or DC voltage source, a modulator and an oscillation network have been described in connection with a fluorescent lamp load. It should be understood, however, that any type load could have been used, particularly where the load impedance is much greater (for the current fed case) than the network characteristic impedance (as in FIG. Thus, the circuit can operate as a frequency converter per se when the input to terminals 60 and 61 of FIGS. 8 and9 is AC or as a DC to AC converter if DC is applied to terminals 60 and 61. FIG. 13 shows a circuit which was constructed to carry out the current fed mode of operation described in FIG. 9. Referring to FIG. 13, the power source consisted of a 120 volt, 60-cycle source connected to terminals 80 and 81 of a variable transformer 82. The output of variable transformer 82 is variable between 0 to 140 volts and is connected to an isolation transformer 83. The isolation transformer secondary winding is then connected to a full wave rectifier bridge 84 which supplies a DC input voltage to the pulse modulator portion of the circuit.

The pulse modulator was formed of the circuit shown within dotted block 85 and is equivalent to modulator 22 of FIG. 1 or modulator 62 of FIGS. 8 and 9. The modulator 85 has input terminals 86 and 87 which are connected to a suitable pulse timing circuit. Any standard pulse timing circuit could be connected to terminals 86 and 87, and, for experimental purposes, a commercially available pulse generator, manufactured by 'Iektronics Corporation was used as a source of timing pulses.

A resistor 88 (47 ohms) is provided across terminals 86 and 87 to terminate the pulse generator and a resistor 89 (2.2K) connected to the base of transistor 90 (2N4037) and serves as a current limiting and isolating resistor. The collector of transistor 90 is connected to the base of transistor 91 (2N4037. The collector of transistor 91 is in turn connected to the base of power transistor 92 (M1423) through resistor 98 l0 ohms).

Suitable decoupling resistors 93 (33 ohms), 94 (330 ohms), 95 (33 ohms) and 99 1K) are provided along with decoupling capacitors 96 (50 microfarads) and 97 (50 microfarads). Each of resistors 93, 94, 95 and 99 were connected to biasing voltage sources as indicated which were provided by batteries. Clearly, a standard rectifier power supply could be used for this purpose.

The emitter-collector circuit of power transistor 92 is then connected in series with the output of rectifier 84, diode 100 (lN647), and resistor 101 (IOK). Diode 100 protects transistor 92 against voltage reversal and resistor 101 dissipates energy from the oscillating network when the lamp is turned off, as will be described. The lamp was fluorescent lamp 110 which was a 40-watt lamp manufactured by Sylvania type F40CW Life Line." A metal foil starting aid to simulate the fixture 111a, shown in dotted lines, was placed along the tube and connected to one of its electrodes as shown. The cathode filaments of lamp 110 were heated by two 6-volt batteries 112 and l 13, it being obvious that a suitable transformer circuit could be used for this purpose.

The oscillating network was then formed of chokes 120, I21 and 122 and capacitors 123 and 124. Note that the network is connected in the current-fed mode of FIG. 9. Each of chokes I20, 121 and 122 had an inductance of 1.7 millihenrys and each of capacitors I23 and 124 were 0.I7 microfarad, 400 volt capacitors.

The circuit of FIG. 13 operates as follows:

When a positive pulse is applied to terminals 86 and 87, transistor 90, which is biased to normally conduct, is turned off. This turns the transistor 91 on, transistor 91 being biased to be normally off. The conduction of transistor 91 causes transistor 92 to turn on, transistor 91 being normally off. Thus a positive going pulse applied to terminals 86 and 87 turns transistor 92 on for the duration of the input pulse.

When transistor 92 turns on, the output voltage of rectifier 84 appears across resistor 101 and thus across the oscillating network and tube 110. The oscillating network, consisting of chokes 120, 121, 122 and capacitors I23 and 124 is charged for the duration of the pulse across resistor 101, and after the pulse disappears, the circuit oscillates as shown in FIG. 10. Therefore, the tube 110 is driven by the oscillating current shown in FIG. 10, and the tube is driven in a high-frequency mode in accordance with the invention.

It is to be noted that the circuit of FIG. 13 uses a particular modulator which responds only to positive pulses at terminals 86 and 87. Clearly, the circuit could be modified so that both positive and negative pulses could drive the modulator. Moreover, it will be apparent that all biasing voltages could be directly derived from the high-frequency circuit by means of relatively small transformers.

It will also be understood that the lamp 110 could have been replaced by a general load which requires a generally sinusoidal wave shape. By way of example, a winding could be taken from one of chokes 120, I21 and 122 to serve as a highfrequency input to a biasing voltage circuit.

Referring next to FIG. 14, there is illustrated a circuit using the general concepts of the circuit of FIG. 9 where, however, a plurality of gas discharge lamps are operated from the common modulator 62. Thus, in FIG. 14 there is shown three lamps 200, 201 and 202 which may be any desired type of gas discharge lamp, such as fluorescent tube, and each of the tubes 200 to 202 is provided with-a respective oscillator network 203, 204 and 205. The oscillator networks 103, I04 and are each of the current-fed variety as in the case of FIG. 9, and it will be seen that they are each identical to the networks of FIG. 9 if the coil 71 of FIG. 9 is removed. More specifically, it has been found in connection with circuits of the type shown in FIG. 9 that coil 71 can be eliminated. Preferably, however, coil 71 may have an extremely low inductance, for example, I microhenry, as compared to a typical value of millihenrys for. coil 72, where the small inductive impedance of coil 71 preventshigh surge currents from being drawn from modulator 62 directly through capacitor 73 which could damage modulator 62. A small resistance could also perform this current-limiting effect.

In FIG. 14 the pulse-forming networks 203 to 205 consist of chokes 206, 207 and 208, respectively, and capacitors 209, 210 and 211, respectively. Each of the individual circuits are then connected in series with suitable isolating impedances 212, 213 and 214 which essentially decouple the parallel-connected circuits from one another and provides the currentlimiting impedance necessary to limit the magnitude of the pulse current drawn from modulator 62 directly through capacitors 209, 210 or 211. Impedances 212, 213 and 214 may be capacitors.

When using a circuit of the type shown in FIG. 14, it will be apparent that substantial economies are obtained since only a single pulse modulator 62 is needed for a plurality of individual lamps. Note that any number of lamps can be used. Moreover, the size of the components used in oscillating networks 203, 204 and 205 is kept small since they each operate only in connection with a single lamp. This also makes it possible to locate the oscillating networks close to the lamps so that long transmission lines are not needed to convey the highfrequency power from the oscillating network to its particular gas discharge lamp.

FIG. 15 is similar to FIG. 14, but shows a modified version of the oscillating network of FIG. 8 used in connection with the lamps 200, 201 and 202. Thus, in FIG. 15 the oscillating networks consist of the series-connected chokes 220, 221 and 122, respectively, and capacitors 223, 224 and 225, respectively, for the tubes 200, 201 and 202. Each of the oscillating networks of FIG. 15 is essentially identical to the network of FIG. 8 with the choke 65 and capacitor 67 removed. Tests have demonstrated that these components may be eliminated to develop the simpler series oscillating circuit shown in FIG. 15.

Although there has been described a preferred embodiment of this novel invention, many variations and modifications will now be apparent to those skilled in the art. Therefore, this invention is to be limited, not by the specific disclosure herein, but only by the appending claims.

The embodiments of the invention in which an exclusive privilege or property is claimed are defined as follows:

1. A gas discharge lamp energizing circuit comprising, in combination: a voltage source, a pulse modulator means and a gas discharge lamp; said gas discharge lamp having a pair of terminals; said voltage source, pulse modulator means and gas discharge lamp pair of terminals directly connected in series by circuit connection means; said circuit connection means being free of oscillation circuit means; said pulse modulator means being alternately conductive and nonconductive; and an oscillating network connected in parallel with said gas discharge lamp; said oscillating network including at least a first choke and at least a first capacitor connected in parallel with one another.

2. The circuit of claim 1 wherein the period of said oscillating network is substantially independent of the period of said pulse modulator means.

3. The energizing circuit of claim 1 wherein said oscillating network has characteristic impedance substantially less than the impedance of said lamp when said lamp is in conduction.

4. The energizing circuit of claim 1 wherein said oscillating network further includes a second choke and a second capacitor; said second choke connected in series with said first choke and said second capacitor.

5. The energizing circuit of claim 1 wherein said oscillating network further includes a second choke connected in series with both said first choke and said first capacitor.

6. A relatively high frequency AC voltage generator for driving a lighting load from a source of input voltage which has a frequency in the range of from zero cycles per second to a relatively low frequency as compared to said relatively high frequency of said AC voltage generator; said AC voltage generator comprising, in combination: said source of input voltage, a pulse modulator means which is sequentially switched between conduction and nonconduction at a given frequency, a gas discharge type lighting load, and a single oscillating network; said single oscillating network being connected in parallel with said lighting load, said source of input voltage, said pulse modulator means and said single oscillating network being directly connected in a closed series circuit; said single oscillating network being tuned to a single fixed frequency.

7. The AC voltage generator of claim 6 wherein said oscillating network has a charadtei'istic impedance substantially less than the impedance of said gas discharge load when said gas discharge load is in conduction.

8. The AC voltage generator of claim 6 wherein said oscillating network further includes a second choke and a second capacitor; said second choke connected in series with said first choke and said second capacitor.

9. The AC voltage generator of claim 6 wherein said oscillating network further includes a second choke connected in series with both said first choke and said first capacitor.

10. The circuit of claim 6 wherein said oscillating network has a characteristic impedance approximately equal to the impedance of said gas discharge load when said load is in conduction.

11. A gas discharge lamp energizing circuit comprising, in combination, a voltage source, a single pulse modulator means, a plurality of oscillating networks, and a plurality of gas discharge lamps; each of said oscillating networks being connected in circuit relation with a respective one of said gas discharge lamps; said voltage source, pulse modulator means and said circuit of said respective oscillating networks and gas discharge lamps; said voltage source, pulse modulator means and said circuit of said respective oscillating networks and gas discharge lamps being connected in series; said pulse modulator means being altematel conductive and nonconductive thereby to apply voltage pu ses to said oscillating network, and

thereby to energize said gas discharge lamps.

12. The circuit of claim 1 1 wherein said oscillating networks each include a series-connected capacitor and inductor connected in parallel with their said respective gas discharge lamps.

13. The circuit of claim 11 wherein said oscillating networks each include a parallel-connected capacitor and inductor connected in parallel with their said respective gas discharge lamps.

14. A gas discharge lamp energizing circuit comprising, in combination: a voltage source, a single pulse modulator means, a plurality of oscillating network means, a plurality of gas discharge lamps each connected in parallel with a respective one of said plurality of oscillating network means, and a plurality of coupling impedance means respectively connected in series with each of said gas discharge lamps; said plurality of series-connected gas discharge lamps and respective coupling impedance means connected in series with said single pulse modulator means.

15. The circuit of claim 14 wherein each of said plurality of coupling impedance means consists of a capacitor.

* II! i I

Claims (15)

1. A gas discharge lamp energizing circuit comprising, in combination: a voltage source, a pulse modulator means and a gas discharge lamp; said gas discharge lamp having a pair of terminals; said voltage source, pulse modulator means and gas discharge lamp pair of terminals directly connected in series by circuit connection means; said circuit connection means being free of oscillation circuit means; said pulse modulator means being alternately conductive and nonconductive; and an oscillating network connected in parallel with said gas discharge lamp; said oscillating network including at least a first choke and at least a first capacitor connected in parallel with one another.

2. The circuit of claim 1 wherein the period of said oscillating network is substantially independent of the period of said pulse modulator means.

3. The energizing circuit of claim 1 wherein said oscillating network has characteristic impedance substantially less than the impedance of said lamp when said lamp is in conduction.

4. The energizing circuit of claim 1 wherein said oscillating network further includes a second choke and a second capacitor; said second choke connected in series with said first choke and said second capacitor.

5. The energizing circuit of claim 1 wherein said oscillating network further includes a second choke connected in series with both said first choke and said first capacitor.

6. A relatively high frequency AC voltage generator for driving a lighting load from a source of input voltage which has a frequency in the range of from zero cycles per second to a relatively low frequency as compared to said relatively high frequency of said AC voltage generator; said AC voltage generator comprising, in combination: said source of input voltage, a pulse modulator means which is sequentially switched between conduction and nonconduction at a given frequency, a gas discharge type lighting load, and a single oscillating network; said single oscillating network being connected in parallel with said lighting load, said source of input voltage, said pulse modulator means and said single oscillating network being directly connected in a closed series circuit; said single oscillating network being tuned to a single fixed frequency.

7. The AC voltage generator of claim 6 wherein said oscillating network has a characteristic impedance substantially less than the impedance of said gas discharge load when said gas discharge load is in conduction.

8. The AC voltage generator of claim 6 wherein said oscillating network further includes a second choke and a second capacitor; said second choke connected in series with said first choke and said second capacitor.

9. The AC voltage generator of claim 6 wherein said oscillating network further includes a second choke connected in series with both said first choke and said first capacitor.

10. The circuit of claim 6 wherein said oscillating network has a characteristic impedance approximately equal to the impedance of said gas discharge load when said load is in conduction.

11. A gas discharge lamp energizing circuit comprising, in combination, a voltage source, a single pulse modulator means, a plurality of oscillating networks, and a plurality of gas discharge lamps; each of said oscillating networks being connected in circuit relation with a respective one of said gas discharge lamps; said voltage source, pulse modulator means and said circuit of said respective oscillating networks and gas discharge lamps being connected in series; said pulse modulator means being alternately conductive and nonconductive, thereby to apply voltage pulses to said oscillating networks, and thereby to energize said gas discharge lamps.

12. The circuit of claim 11 wherein said oscillating networks each include a series-connected capacitor and inductor connected in parallel with their said respective gas discharge lamps.

13. The circuit of claim 11 wherein said oscillating networks each include a parallel-connected capacitor and inductor connected in parallel with their said respective gas discharge lamps.

14. A gas discharge lamp energizing circuit comprising, in combination: a voltage source, a single pulse modulator means, a plurality of oscillating network means, a plurality of gas discharge lamps each connected in parallel with a respective one of said plurality of oscillating network means, and a plurality of coupling impedance means respectively connected in series with each of said gas discharge lamps; said plurality of series-connected gas discharge lamps and respective coupling impedance means connected in series with said single pulse modulator means.

15. The circuit of claim 14 wherein each of said plurality of coupling impedance means consists of a capacitor.

Images