CA1191540A - Line operated fluorescent lamp inverter ballast - Google Patents

Abstract

ABSTRACT
Applicant has provided a ballast circuit for fluorescent lights made up of the combination of (1) a source of electrical energy, (2) a resonant circuit, (3) a switch means for connecting the source of electricity to the resonant circuit, (4) means to connect the resonant circuit to a load, (5) a resonant current monitor controlling the switch means in synchronism with the resonant current so that the switch means switches the resonant current when the resonant current passes through zero.
The resonant current monitor is a current transformer having a primary winding connected in series with the resonant circuit and two secondary winding connected to the bases of the two switching transistors in a two transistor inverter circuit at a polarity that will switch one of the transistors on and the other off at the time current passes through zero. This is the optimum time to switch the transistors since the current flowing through the transistors is passing through zero at that time and therefore the transistors operate at maximum efficiency and there are minimum switching losses and improves the efficiency of the circuit. The circuit will automatically adjust the switching frequency to the changed resonant frequency should the value of the inductor or the capacitor degrade and therefore change, and the switching losses will therefore be maintained at minimum.

Description

REEi~RENCE TO PRIOR ART
The U.S. Patent No. 3,155,875 to C.M. ~Venrich, et al, issued November 3, 1984, discloses a load T~ conneeted in parallel with the series-parallel circuit made up of trallsformer Tl and capflcitor C6~ Tl and C6 like any other inùuctiv~
capacitance circuit could be designed to resonate at some Erequency, using the eamiliar equation f = 1 , however the Wenr;ch circuit would not function as ,~
designed if it was designed to resonate and such design to resonate could only be done in view of Applicant's disclosure viewed in retrospect since Wenrich does not teach resonants but to the contrary teaches a induetor that wiU saturate and provide a surge of current which will trigger the transistors.
The U.S. Patent No~ 3,753,071 to Engel, et al~ issued August 1973, inverter frequency is controlled by the timer made up OI the winding 24a and resistors 26 while Wenrich's circuit operates o~f an inductance which saturates and the capacitor limits the current flow when at the point the circuit saturates so that the inverter switches when the current through the inductance and capacitance is maximum. This is exactly the thing that Applicant is attempting to avoid and is exactly opposite from Applicant's circuit operation.
Both Wenrich and Engel will switch when the inverter has substantial current elowing and not as the current passes through zero. Neither Engel nor Wenrich provide a resonant eurrent monitor for the resonant circuit current Eor controlling the switching means.
U.S. Patent No. 3,753~076, to Zelina9 et al~ issued August l4, 1973, shows an inverter ballast circuit which utilizes the energy stored in a resonant circuit to reduce input current to a value near zero durirlg switching. Patent 4,023,067 shows an inverter eireuit that provides minimum switching losses by use of resonant storage techrliques and a unique feedback system. It attempts to promote zero current switching. The present circuit assures zero current switching.
U.S. Patent No. 4,031,454,to Suzuki, et al, issued June 1977, IJ.S. Patent No. 4,245,177,to Schmitz, issued January 1981, U.S. Patent No. 4,279,011 to Nissen, issued July 1981, and U.S. Patent No. 3,1799901, to Mills, issued April 1965, show the state of the art but are not relevant to the clai ms herein~

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BACKG~OUND OF THE INYENTION

2 General

3 The super;or lumen per watt characteristic of fluorescent lamps has for

4 decades prompted research on ways -~o operate ~hese lamps from a DC supply.
These applications included the transportatioll industry (trains7 transit cars7 buses 6 and airplanes) and the porta~le lighting industry. In these applicat;ons, no AC power 7 is available and therefore the premium cost of these inverter ballasts was justified since the only alternate ligh~ source was ~he incandescent lamps (about 15 lumens 9 per watt). When compared with fluorescent lamps of about 5û lumens per watt and 10 about 10 times the life, the additional inverter ballast cost was justified.
11 It has been demonstrated as early as the early Sû's, that the 1uorescent 12 lamp, when properly operated at frequencies above 15 KHZ, would demonstrate 13 about 1596 improverrlent in the output lumens per watt over 60 HZ operation. This 14 well recognized fact, plus the present impetus on energy saving, has been the driving 15 force behind multi-million dollar research an~ development eforts to apply high 16 frequellcy lighting to commerciPlt industrial and consumer applications. To d~te, 17 there has been limited success in this effort. The season for this record can be 18 understood by studying the complexity of the problem added to the economies of 19 the situation. Many efforts produced costs many times that of the 60 HZ Ballast 20 counterpart with efficiencies, or ballast losses comparable or vvorse than the 60 HZ
2l Ballast. Further, 60 HZ Ballast manufacturing has generally responded with better 22 steel and more copper to improve their efficiency.
23 The Problem 24 The problem of making High Frequency available for general fluoreseent25 lighting can be defined in the following categories:
26 A. Efficiency - must approach 95%. This makes payback an economic 27 reality.
28 B. Cost - The cost of the High Frequency Ballasts must be no more than29 2 or 3 times the cost of the 60 HZ Ballas~.
C. Reliability - The inverter t)allast must match or better the 60 HZ
31 13~ st.
32 D. Life - Typical life must exceed ten years.
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Many of the above problems are intcrdependent. For example, 95%
efficient means extremely small losses and therefore low temperature rise, which generally means h;gh reliability and long li~e. However, generally, cost tends to increase when the above objectives are addressed. We can then sumrnarize our problem statement by saying the -following: We must find a solution, if one exists, that will demonstrate the high efficiency and low loss with primary effort on produetion simplicity and low eosts.
Solution to Problem It has been generally accepted by these inventors sinee their first lighting of a fluorescent lamp with an inverter ballast, in the mid 50's, that resonance plays a dominant factor in ballast efficiency. However, maintaining resonance with component tolerances in produetion and during aging of the ballast appeared to be an impossible problem. In 1970, during work on the Coleman Camping Lantern ballast, the inventors were successful in providing resonant feedback which solved the above problem and produced e~ficiencies approaching 90%. This technology is used extensively in the transit industry and is the basis of U.S. Patent No. 3,753,076, to Zelina, et al, issued August 14, 1973. Following this work, a single transistor resonant feedback ballast was developed which approaehed 95% efficiency. This technology is the bas;s for most of the low voltage camping lantern ballasts made today, for example, U.S. Patent No. 4,023,067 to Zelina7 et al, issued May 107 1977.
The resonant feedback promotes zero current switching of the transistor thereby providing the high efficiency.
The teaching contained herein goes an order of magnitude further in that, instead of promoting zero current switchirlg, it assures it. Eiurther, the start up transient is addressed in such a manner that the switchin~ devices are less stressed during start upO 5till, the above solut;ons have been accomplishecl in such a manner that a cost effeetive solution has been demonstrated. The 25% to 30%
overall energ~y savings with no change in light output can easily justify the higher inverter ballast cost. Retrofitting ~ield ballast should be possible with an approximate one year payback9 depending upon local energy and labor costs.

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The operation of the inverter in synchronism with the resonant current also automatically adjusts the switching frequency to the resonant :frequency should or~

the value of the inductor or capacitor degrade and therefor change. The switching 2 losses will therefole be rnaintained at a minimum.

The solution to the problem diseussecl will be described us;ng Fig. 1 6 through Fig. 4. Before we start~ we should review our Icnowleclge of simple series 7 resonant circuit operation. It should be recalled that in a simple series resonant 8 circuit the voltage across the capacitor will be 180 degrees out oï phase with the 9 inductance and the current flowing will be 90 clegrees out of phase with both the 10 capacitor and inductor voltages ignoring leading and lagging relationships~ With 11 reference to Fig. l ~ one skilled in the art can determine relative relationships of 12 the electrical quantitie~ without experimentatio~. Note also that when current Ir 13 (resonant eurrent) goes through ~ero, the stored energy in condenser 22 (C) is a 14 maximum (1/2 C V2~ and the stored energy in (the reaetance 14 and lB) I. is at 15 zero (1/2 L I2)~
16 II we can inject energy into the tank as Ir goes through zero, l l will 17 switch at zero current and conduet a half sine wave of current into the LC tank 18 circuit- If, as Ir ~oes through zero, we turn ll off and 12 on9 we talce the stored ~9 energy in Condensor 22 and transfer it in reverse polarity to Condensor 22. In this 20 fashion, we ~ontinue to increase stored energy and voltage (the same) in the tank 21 eircuit. If energy is not removed from the resonant tank, voltages (energy) will 22 build to component destruction.
23 Now, we must address ourselves to a better understanding of gas arc 24 lamps (fluorescent lamps). Their general characteristic is such that an are io~ ation 2~ voltage of about 2 to 3 times the operating voltage is requiredO If we eouple the ~6 fluorescent lamp into the tank circuit by a second winding on induetor 17, see Eiig.
27 19 the lamp will ionize and then the voltage will stabilize at the operating arc 28 voltage of the particular lamp used. The tank circuit via transistor ll will aceept 29 exactly the energy each eycle that the lamp rerrloves for operation. Further~ since 30 heating energy is only required for starting, we can see that starting to operate 31 cathode heater watts are about 4 to 17 and up to 9 to l (square oL starting and 32 operating cathode heater voltage)O This is a very desirable charaeteristic since it conserves energy during operation, thus providing the maximum possible lumens per input watt.
~ Furthel, we should consider the fluorescent lamp characteristic. It ls 4 such that the lumen e~fieiency is adversely affected by form factors clrastically 6 different from a sine wave. (Peak to 3~MS r~tio). Because of the sinusoidal operation 6 of the tank circuit we deliver a very acceptable wave shape to the lampD This 7 further improves lumen efficiency over other inverter ballast approaehesu It is an object of the invention to provide an improved combin~tion 11 inverter circuit, resonant cireuit and resonant current monitor for operating the 12 inverterO
13 Ano~her object of the invention is to provide a combination inverter 14 circuit, resonant CircU:it9 resonant eurrent monitor and means to connect the 15 combination to a load and rneans to switeh ~he resonant current in the inverter 16 circuit in synchronism with the resonflnt current as the resonant current passes 1q through zero.
18 Another object is to provide a solid state ballast which is simple in L9 construction, economical to manufacture and simple and et`ficient to use.
~nother object of the invention is to provide an improved solid state 21 ballast.
22 With the above and other objects in view, the present inventon consists 23 of the combination and arrangement of p~rts hereinafter more fully des~ribed, 24 illustrated in the accompanying drawing and more particularly pointecl out in the 25 appencded elaims~ it being understood that changes may be made in the form, si~e, 26 proportions and minor c]etails of construction without departing from the spirit or 27 sacrificing any of the advantages of the invention.

29 GENERAL DESCRIPTION OF THE DR~WINGS
Fig. I is a schematic view of the one embodiment of the invention.
31 Fig. 2 shows a schematic view of one of the transformers.
32 Fig. 3 shows a schematic view of the other trans~ormer.

Fig. 4 is a schematic view of another embodiment of the invention.
2 Fig. 5 shows a schematic view oE another ernbodiment of the invention.
3 Figo 6 is a block diagram oî the inventionO
4 Fig . 7 shows curve of a photograph of an oscilloscope screen showing the current ~hrough the collector of transistor 11 and voltage across transistor 11.
6 Fig. 8 shows a curve like Fig. ~ showing the resonant current and voltage 7 across transistor 11.
Fig. 9 shows a eurve as in Fig. 7 showing the eollector current of 9 trflnsistor 12 and voltage across transistor 12.
~0 Fig. 11) shows a curve like Fig. 7 showing the resonant current and voltage 11 across transistOr 12.

13 DETAILED DESCRIPTION OF THE DRAWINC~
14 The purpose of th;s inYention is to pl ovide an e~ficient inverter ballast circuit for powering a fluorescent lamp from a standard sinusoidal line voltage lB source. The inverter ballast will operate at a high frequency, above the human 17 audible range; which eliminates the problem OI noise, increases the efficiency of 18 lamp operation, and decreases component size and subsequent cost and switches the 1Ç) transistors which control the current in the resonant circuit as the current In the resonant circuit passes through zero and in synchrvnism with the transistors.
21 The Resonant Oscillator 22 The oscillator used to generate a high frequency voltage for driving the 23 fluorescent lamp 55 is a two transistor resonance maintenance circuit eonnected to 24 a series resonant circuit. The entire circuit is made up of five elements; (1) a 2~ I source of eleetricity, ~2) a series resonant circuit designed to resonate at a 26 predetermined frequency, (3) a switehing means connecting the resonant circuit to 27 the source of electricity~ (4) a resonant current rnonitor meansfor actuating the 28 switching rneans, ~nd (5) means for connecting a load to the resonant circuit.
29 I Since it is the current -flowing in the resonant circuit that commands 30 the transistor to switch~ it is axiomatic that the command will be in synchronism 31 with that current and irrespective of the values of the incluctance and capacitance 3~ 8 (within wide frequency limits) the circuit will always operate at resonance. The2 l~ransistors will swits~h in synchronism with that resonant current.
3 The only lirnitation on ~ero switching is not in the circuit itself, but 4 may result from limitations in the ~ransistors thesnselves in ~he form of a delay in transistor switching due to electrical charges stored in the transistor and to a very 6 minor degree limitations in the current trans~orrner. With high quality transistors 7 and high quality current transformers, the transistors would switch exactly at zero 8 irrespective of the values of the inductor and the capacitor within design limits.
9 Applicant's test shown in the sketches reproduced in the drawings and supported by the attached Affidavit~ show that even with commercially available components, the 11 transistors switch at zero insofar as can be determined from ordinary laboratory 12 e~uipment. Applicant has attempted to claim this zero switching as oeeurring "as 13 the resonant eurrenî passes through zero". This is intended to cover variations erom 14 zero that may occur with commercially available components which is indistinguishable in the tes~ Applicant has made.
16 The source Oe electricity may be any suitable source of direct eurrent 17 and it can be 120 volt AC circuit connected to the switching means throu~h a full lS wave rectifier as shown or any other suitable source of direct current.
19 The switching means may be any suitable electronic valve such as a transistor with a control element connected to the resonant eurrent monitor. The21 c~pacitor C22 may have a value of .081 microfarads and the inductance may have 22 a value of 4.7 rnillihenries. The transformer 17 may be a suitable ferrite core 2~ transformer. The transformer 17 has a ferrite core magnetically eonnecting to the 24 primary winding 18 and to the secondary windings 19, 20 and 21. The current transformer has a suitable core which m~ be in the form of a ring on which the 26 windings are wound as shown.
27 When power is applied to the input terminals, 66 and 68 of the full-wave 28 rectifier 27, the input voltage is filtered by the capacitor 21, this DC voltage is 29 applied to the network Nhich includes transistors 11 and 12, eausin~ transistor 11 to turn on. This causes capacitor 22 to start charging through prirnary windin~
31 and primary winding 18. The primary winding 18 Oe the high leakage reactance 32 transformer 17 is rnagnetically coupled to secondary .~indings 197 20 and 2l.
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3~

Secondary winding 20 is used to drive the fluorescent lamp S5 which is of the 2 ionizable gas type lamp.
The transformer l3 i5 a curren~ transformer used to sense current elow ~1 in the resonant loop made up of pr;mary winding 14 and primary winding 1~ andcondensor 22 and to synchronize the switching Oe transistors 11 and 12 with the 6 resonant eurrent. When current is flowing into the terminal 44 (dots on the drawing 7 indicate instant polarity at a given time) current is flowing out of terminal 40 8 because the windings oe transformer 13 are magnetically coupled. This turns 9 transistor 11 on and turns transistor 12 off. When condensor 22 becomes fully10 charged, current flow passes through zero and reverses in the resonant loop. This 11 reversal of current is sensed by the eurrent transformer 13 which turns off transistor 12 11 and turns transistor 12 on. Capacitor 22, through resonant action will transfer 13 its charge to the opposite polarity, again causing current to pass through zero and 14 reverse in the capacitor 22 loop. This second reversal is sensed by transformer 13 15 which turns transistor 11 on and turns transistor 12 off. With commercial tolerance components the swi~ching may occur sligh~ly off the zero current point but with 1~ precise tolerance components the switching will be exactly at zero. The phrase 18 "when passing through zero" is intended to mean switching at essentially ~ero which 19 was, in tests rnade on the eircuits tested by Applicallt, as closely as can be determined 20 from the photographs from which Figs. 7 through 10 were taken.
2~ Transistors 11 and 12 are now maintaining resonance in the capaeitor 22 22 loop. This oscillating current and the subsequent voltage generated by this charging 23 and discharging of capacitor 22 generates a voltage in primary winding 18. This 24 voltage can be either stepped up or down9 to meet the requirements of any size 2~ fluorescent lamp connected to the olltput of secondary winding 20.
26 The resonant frequency of the oscillator is set by the si~e of capacitor 27 22 and the inductance of primary winding 18. The ratio of turns of primary winding 28 18 to secondary winding 20 is utilized to reflect the fluorescent lamp load impedance 29 into the primary circuit In order to dampen the primary circuit.
30 I The Lamp Outpu~
31 i Prior ~o lamp ionization, current is applied to the cathodes of the windings 32 19 and 21 f'or heating purposes. This feature improves lamp life for virtlIally no cost. During this mode the lamp is in a high impedance state, the high irnpedance 2 allows the secondary winding 2() voltage to be high. Because the voltage of winding 3 20 is high~ the ~oltage of winding 19 and the voltage of winding 21 are high enough 4 to generate substantial hea~ing current in the lamp filaments. When the lamp 55 becorlles ionized or turns on, its impedance becormes low. This low impedance S reflected into the resonant loop ~damping) forces the secondary voltage to a low 7 value, which in turn forces the voltage on heaters 56 and 61 to a negligible value 8 because of the turns ratio of windings 19 and 21 to the w;nding 20. The fluorescent 9 lamp 55 is now on with negligible filament heating current flowing.
In the embodiment of the inventiun shown in Figo 4~ an inverter ballast 11 circuit utilizing the basic principles 5et forth in the embodiment of the invention 12 in Fig. 1 is shown.
13 The OSCillatOI' used to generate the high frequency voltage -for driving a 14 fluorescent lamp 55 includes the two transistor resonance maintenance circuit. When 15 power is applied to the input terminals 166 and 168, input voltage is divided by 16 capacitor 133 and capacitor 133~. Seeondary winding 120 on transformer 117 is17 connected to the fluorescent lamp 155. The resonant loop is made up of the primary 18 winding 114 on the current transformer 113 and the primary winding 118 on the19 high leakage reactance transformer 117 and the capacitor 122. The DC voltage is 20 applied to the network which includes transistors 111 and 112 causing transistor 111 21 to turn on. This causes the capacitor 122 tc start charg;ng through the primary 22 windings 114 and 118. Primary winding 118 of the high leakage react~nce tran.sformer 23 117 is magnetically coupled to the secondary winding 120. Secondary winding 120 24 is used to drive ~he fluorescent lamp 155 which is of the ionizable gas lamp type.
2~ The ~ransformer 113 is a current transformer used to sense current flow 26 in the resonant loop and to synchronize the switching of the transistors 111 and 27 112. When current is flowing in the terminal 144 (dots on the drawing indicate 28 instant polarity at a given time), current is flowing out of terminal 140 because 29 the wlndings of transformer 113 are magnetically coupled~ This turns the transistor 30 111 on and turns transistor 112 off. When condensor 122 becomes charged~ current 31 passes through zero and reverses in ths condensor 122 loop. This reve~rsal of current 32 is sensed by the current transformer 113 which turns off transi;,l:or 111 and turns transistor 112 on. Capacitor 122, through resonant actic,n, will transIer its charge 2 to the opposite polarity, agaill causing current to pass through zero and reverse in 3 the capacitor 122 loop. The second reversal is sensed by trans~ormer 113 which 4 turns transistor 111 on and ~urns transistor 112 off. Transistors 111 and 112 are now switching in synchronism with the resonant current as shown by Pig. 8 and ~ig.
6 10 maintaining resonance in capacitor 122 loop. This oscillating current and the 7 subsequent voltage generated by this charging and discharging of eapacitor 122 8 generates Q vol~age in primary winding 118. This voltage can be either stepped up 9 or stepped down to meet the requirements OI any si~e fluorescent lamp connected 10 to the output of secondary winding 120.
11 The resonant frequency of the oscillfltor is set by the size of the capacitor 12 122 and the inductance of primary windings 114 and 118 to reflect the fluorescent 13 lamp load impedanee into the primary circuit in order to dampen the primary eircuit.
1~1 The ~ircuit of the embodiment of Fig. 4 has the beneficial effect described 15 in connection with the other embodiments of the invention.
16 Now, with specific reference to the embodiment of -the invention shown 1~ in Fig. 5, an alternate embodiment of the invention is shown wherein the resonant 18 loop is indicRted at 260 made up oE the prirnary winding 28~ of transformer 282 19 and the secondary winding 220 of transformer 217. Current transformer 213 is connected in series with primary 218 and to the line 241. Secondary winding 215 21 is connected to the base o~ the transistor 211 at 235 and the terminal 243 is 22 connected to the base 236 of the transistor 212. The terrninal 242 is connected to 23 the line 233. The input to this circuit may be considered to be lines 232 and 233.
24 ~ Filter capacitor 221 is connected across the output of a full wave reetif;er as in 25 the other embodiments.
26 The corresponding parts of the embodiment in Fig. 5 have numbers sirnilar 27 to the corresponding parts on the other embodirnents of the invention7 and it will 28 be seen that the oscillator used generate5 a high frequency voltage ~or driving the 29 fluorescent lamp 255. When the power is applied to input terminals 232 and 233 out 30 of the full wave rectiier~ the input voltage is filtered by capacitor 221 and this 31 voltage is applied to the network which includes transistor 211 and 212 causing 32 ~ transistor 211 to turn on. This starts current flowing in the loop which includes primary windings 214 and 218 which induces a voltAge in the winding 220 which in2 turn starts a current elovving in the Loop 260 and condensor 222 starts charging.
3 Transformer 213 is used to sense current Plow in the loop made up of windings 214 ~1 and 218 to synchronize the s~itching of transistors 211 and 2l~. When current is 6 flowing into the winding 214 (r3Ots on ~he drawing indicate instant polarity at a 6 given time), current is flowing out of terminal 240 because the windings of7 transformer 213 ~re magnetically coupled. This turrls transistor 211 on and turns 8 transistor 212 off. When condensor 222 becomes fully charged, current pas~es 9 through zero and reverses in condensor 222 loop9 thus re~ersing the currents in the loop made up of windings 214 and 21~. The reversal of current is sensed by the Ll current transYormer 213 which turns the transistor 211 off and turns transistor 212 12 on. Capacitor 222~ through resonant action will transfer its charge to the opposite 13 polarity again causing current to pass through zero and reverse in the eapac;tor 222 ~4 loop and in the loop made up of windings 214 and 218. The second reversal is sensed by transformer 213 which turns transistor 211 on and turns transistor 212 offO
16 Transistor 211 and 212 are now maintaining resonance in capacitor 222 loop. This 17 oscillating current and subsequent load is generated by this charging and discharging 18 of capacitor 222 generating a voltage in primary winding ~18. This voltage can be 19 either stepped up or stepped down, depending on the requirements of the fluorescent light. The resonant fre~uency is set by capacitor 222 and inductance of primary 21 windings 280 and the leakage inductance of secondary 220. The operation of this 22 circuit will be generally like that in the circuit shown in the other embodiments of 23 the invention; however, the resonant loop 260 is separate from the current monitoring ~4 loop 26 1~
2~ ' ~ig. 4 demonstrates a circuit where substantially equal energy is injected 26 into the circuit during each half cycle. This is accomplished by mear~ of capacitors 27 133 and 133'. A similar effect may be accornplished by substituting a second source 28 of energ~ for capacitor 1331.
29 The circuit described herein is illustrated using a fluorescent lampapplication for example. There are many other examples where generatir~g an 31 unlimited ouput voltage could be utilized. Different types of high voltage lamp ,, applicRtions, ignition systems, and ignitors for rocket engille~ a~e other examples OI
2 the many which are only limited by the imagination of the designeP.
3 With regard to the block diagram shown in Fig. 6~ the numbers on the 4 blocks correspon~ to the numbers shown in the embodiment Oe Fig. I. In F;gure 6, ~i load means 55 is shown connected to a load coupling means 20 which is magnetically 6 coupled to the first magrletic means 18 which in turn is driven by the resonant 7 capacity of means 22. Current monitoring means 14 is connected to the switching means 11 and 12 which in turn are connected to the DC source 27 whicI1 is supplied 9 through the line 25.
The Ioregoing specification sets forth the invention in its preferred, 1]. practical forms but the structure shown is capable of modification within a range 12 o equivalents without departing rom the invention which is to be understood is 13 broadly novel as is commensurate with the appended claims.

2~3 ~1

Claims (13)

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

1. A circuit for driving a load comprising, a resonant circuit, a power supply, an inverter circuit, control means for actuating said inverter, a first transformer having a winding, a second transformer having a primary winding, a first secondary winding and a second secondary winding, said primary winding having a few turns only, a condenser, a first electronic valve having an actuating means, a second electronic valve having an actuating means, said resonant circuit comprising said first transformer winding, said second transformer primary winding and said condenser connected in series with one another and adapted to carry resonant circuit current, said second transformer being a current transformer, said inverter comprising said first electronic valve and said second electronic valve, said first electronic valve being connected to said power supply and to said resonant circuit, said second electronic valve being connected in series with said resonant circuit forming a loop, said first secondary winding of said second transformer being connected to said actuating means on said first electronic valve, said second secondary winding of said second transformer being connected to said actuating means of said second electronic valve, said control means for actuating said inverter consisting of said second transformer, said second transformer first secondary being adapted to actuate said first electronic valve connecting said power supply to said resonant circuit to charge said condenser to a first polarity, said second transformer second secondary winding being adapted to actuate said second electronic valve connecting said resonant circuit into a loop allowing current to flow in said loop to charge said condenser to a second polarity, and means on said circuit for connecting said first transformer winding to a load.

2. The circuit recited in Claim 1 wherein said first transformer winding is a primary winding and said means connecting said circuit to a load comprises a secondary winding on said first transformer.

3. The inverter circuit recited in Claim 1 wherein said first transformer has a second secondary winding and a third secondary winding and said load means comprises a fluorescent lamp connected to said first secondary winding of said first transformer and having a first heater and a second heater, said second secondary transformer winding of said first transformer being connected to said first heater means and said third transformer winding of said first transformer being connected to said second heater means on said fluorescent lamp, said voltage in said secondary windings being adapted to reduce to a substantially low value during the time that the gas in said fluorescent lamp is ionized.

4. The circuit recited in Claim 1 wherein said load is an ionizable gas lamp.

5. The circuit recited in Claim 1 wherein said load is a fluorescent lamp.

6. The circuit recited in Claim 5 wherein said fluorescent lamp has heating elements, said second winding is connected to said heating means.

7. A circuit for driving a load comprising, a resonant circuit, a power supply, an inverter circuit, control means for actuating said inverter, a first transformer having a primary winding and a secondary winding, a second transformer having a primary winding, a first secondary winding and a second secondary winding, a condenser, a first electronic valve having an actuating means, a second electronic valve having an actuating means, said resonant circuit comprising said first transformer winding, said second transformer primary winding and said condenser connected in series with one another and adapted to carry resonant circuit current, said inverter comprising said first electronic valve and said second electronic valve, said first electronic valve being connected to said power supply and to said resonant circuit, said second electronic valve being connected in series with said resonant circuit forming a loop, said first secondary winding of said second transformer being connected to said actuating means on said first electronic valve, said second secondary winding of said second transformer being connected to said actuating means on said second electronic valve, said control means for actuating said inverter consisting of said second transformer, 17a said second transformer first secondary being adapted to actuate said first electronic valve connecting said power supply to said resonant circuit to charge said condenser to a first polarity, said second transformer second secondary winding being adapted to actuate said second electronic valve connecting said resonant circuit into a loop allowing current to flow in said loop to charge said condenser to a second polarity, and means on said circuit for connecting it to a load, said load is a fluorscenlt lamp, said fluorescent lamp has heating elements, said secondary winding of said first transformer being connected to said heating means, said first transformer is a high leakage reactance transformer magnetically coupled to said secondary winding of the first transformer.

8. The circuit recited in Claim 7 wherein said first transformer comprises a magnetic core in the form of a magnetic structure.

9. The circuit recited in Claim 8 wherein said second transformer has a core made of a material having the magnetic properties of ferrite.

10. A circuit for driving a load comprising, a resonant circuit, a power supply, an inverter circuit, control means for actuating said inverter, a first transformer having a winding, a second transformer having a primary winding, a first secondary winding and a second secondary winding, a condenser, a first electronic valve having an actuating means, a second electronic valve having an actuating means, said resonant circuit comprising said first transformer winding, said second transformer primary winding and said condenser connected in series with one another, said inverter comprising said first electronic valve and said second electronic valve, said first electronic valve being connected to said power supply and to said resonant circuit, said second electronic valve being connected in series with said resonant circuit forming a loop, said first secondary winding of said second transformer being connected to said actuating means on said first electronic valve, said second secondary winding of said second transformer being connected to said actuating means of said second electronic valve, said control means for actuating said inverter consisting of said second transformer, said second transformer first secondary being adapted to actuate said first electronic valve connecting said power supply to said resonant circuit to charge said condenser to a first polarity, said second transformer second secondary winding being adapted to actuate said second electronic valve connecting said resonant circuit into a loop allowing current to flow in said loop to charge said condenser to a second polarity, and means on said circuit for connecting it to n load, said second transformer is a current transformer having an annular core made of a material having the properties of ferrite.

11. The circuit recited in Claim 10 wherein said second transformer has a core made of an annular member.

12. The circuit recited in Claim 11 wherein said annular member has an opening there through and said windings wound on said annular member through said opening.

13. A circuit for driving a load comprising, a resonant circuit, a power supply, an inverter circuit, control means for actuating said inverter, a first transformer having a winding, a second transformer having a primary winding, a first secondary winding and a second secondary winding, a condenser, a first electronic valve having an actuating means, a second electronic valve having an actuating means, said resonant circuit comprising said first transformer winding, said second transformer primary winding and said condenser connected in series with one another, said inverter comprising said first electronic valve and said second electronic valve, said first electronic valve being connected to said power supply and to said resonant circuit, said second electronic valve being connected in series with said resonant circuit forming a loop, said first secondary winding of said second transformer being connected to said actuating means on said first electronic valve, said second secondary winding of said second transformer being connected to said actuating means of said second electronic valve, said control means for actuating said inverter consisting of said second transformer, said second transformer first secondary being adapted to actuate said first electronic valve connecting said power supply to said resonant circuit to charge said condenser to a first polarity, said second transformer second secondary winding being adapted to actuate said second electronic valve connecting said resonant circuit into a loop allowing current to flow in said loop to charge said condenser to a second polarity, said second transformer primary has a single turn.