Sept. 6, 1960 H. E. SCHULTZ 2,951,971 STARTING CIRCUIT FOR ARC LARP Filed May 2, 1957

Fig.1. 9. 14

7-1 El s fly- /0 Nin a As 7a Y // 2. fe 7a 43/ A3 fice.3 fice.2

(a) /246AE 7/Z//V6 /08CA hy

(2)

(c ) s

E

(a )

s nvent, O. to Ham U E. Sphultz, 77m2A bU 4 His Attorneu. 2,951,971 United States Patent Office Patented Sept. 6, 1960 1. 2 In accordance with the invention, the operating circuit for the discharge lamp comprises a main discharge cur rent regulating loop and an auxiliary starting loop which 2,951,971. induces high voltage pulses in a saturable inductor within the main loop. The auxiliary starting loop comprises a STARTING CIRCUIT FOR ARC LAMP Saturable inductor having a high-permeability core with Harry E. Schultz, Euclid, Ohio, assignor to General a rectangular hysteresis loop characteristic. This inductor Electric Company, a corporation of New York is connected, in series with a coupling winding on the Saturable inductor of the main loop, across a capacitor Filed May 2, 1957, Ser. No. 656,679 10 charged from an alternating voltage source through a 5 Claims. (Cl. 315-174) current limiting impedance. The capacitor discharges through the saturable inductor at the instant when satura tion is reached and its incremental inductance falls sub stantially to zero. A high-current pulse thus occurs This invention relates in general to a circuit for provid 5 through the coupling winding which generates a high volt ing starting pulses of high voltage to an arc lamp in con age pulse in the saturable inductor of the current regulat junction with a pulsed waveform operating circuit. Such ing loop and thereby ionizes the arc lamp. a pulse-generating circuit may be used to effect the initial In a preferred embodiment, both the main discharge ionization of the discharge medium in the lamp, particu current regulating loop and the auxiliary starting loop use larly where the breakdown voltage is of the order of 20 a saturable inductor having a high-permeability core with several times the normal operating voltage of the lamp. substantially rectangular hysteresis loop characteristic. The invention is particularly useful with arc lamps of The circuit of both the main loop and the auxiliary loop the kind frequently referred to as flashtubes, requiring a are similar, there being provided in each loop a T-net high instantaneous loading in order to have a high light work consisting of a current limiting inductor and a ca output. When the instantaneous loading is high, the spec 25 pacitor connected across an alternating voltage source, trum of the radiation produced contains, in addition to In the main loop, the saturable reactor is connected in the usual line spectrum of the inert rare gas filling such series with the arc lamp across the capacitor. In the as Xenon, a continuum of radiation of substantial in auxiliary loop, the saturable reactor is connected, in series tensity whose over-all color is close to that of natural day with the coupling winding on the saturable reactor of the light. In flashtube or stroboscopic applications, the com 30 main loop, across the capacitor. At starting, the auxiliary . mon method of energization of these lamps has been to loop produces high-current pulses through the coupling charge a capacitor to a relatively high voltage, usually winding which induces high-voltage pulses in the saturable several hundred volts, which is then discharged through reactor of the main loop for ionizing the arc lamp. After the flashtube connected across it. The discharge through the lamp has started, the saturable reactor of the main the flashtube is initiated by applying a pulse to a trigger 35 loop provides high-current pulses through the arc lamp ing electrode which may take the form of a capacitive resulting in the desired high instantaneous loading. element disposed along the lamp, for instance a wire. For further objects and advantages and for a detailed spiralled around the flashtube. description of a preferred embodiment of the invention Where continuous pulsed operation of an arc lamp or and its mode of operation, attention is now directed to flashtube is desired, the capacitor discharge method of 40 the following description and accompanying drawing. operation has several limitations. In the first place it is The features of the invention believed to be novel will be basically inefficient by virtue of the losses in the system more particularly pointed out in the appended claims. for charging the capacitor. In the second place, the In the drawing: residual ionization remaining in the lamp limits the rate Fig. 1 illustrates diagrammatically an elongated arc of flashing or the loading below the level at which con 45 lamp or flashtube with an operating circuit therefor em tinuous conduction through the lamp prevents the build bodying the invention. up of charge in the capacitor. Fig. 2 illustrates the rectangular hysteresis loop char In copending application Serial No. 656,595 of Emmett acteristic of the core material of the saturable reactors H. Wiley, filed of even date herewith, entitled "Pulse Cir used in the circuit of Fig. 1. - cuit for Arc Lamp,' and assigned to the same assignee as 50 Fig. 3 shows current and voltage wave forms in the the present invention, there is described and claimed an circuit of Fig. 1. alternating current pulsed operating circuit. This circuit Fig. 4 is a schematic diagram of a modified circuit uses a saturable reactor to provide high-intensity short embodying the invention. duration current pulses for energizing an arc lamp or Referring to the drawing and more particularly to Fig. flashtube with high instantaneous loading and wherein 5 5 1, the circuit illustrated is designed for the operation of the magnetizing current of the reactor is used to maintain an arc lamp or flashtube F consisting of an elongated ionization within the lamp between pulses. For economi tubular quartz envelope a provide with activated thermi cal design, the circuit must provide high-current pulses at onic self-heating electrodes 2 at opposite ends. Each elec a relatively low voltage generally insufficient to start the trode may consist of a tungsten wire helix 3 wound lamp though sufficient to repeat the pulsed discharge at 60 about the inwardly projecting end of the inlead and a cyclic intervals after initial ionization has been produced. thorium sliver disposed alongside. The inleads include It is therefore necessary to provide some means to effect foil portions 4 of molybdenum pinch-sealed through the initial ionization of the lamp for starting purposes. end of the tube. The tube is filled with an inert gas such The object of the invention is to provide a new and as xenon at a pressure below atmospheric pressure. As improved circuit for generating high-voltage starting 65 an example, arc lamp F may consist of a quartz tube 11' pulses to effect the initial ionization of an arc lamp. in over-all length, 4' in diameter, and with a xenon fill A more specific object of the invention is to provide ing at a pressure of 40 mm. of mercury. a circuit combination which will generate high voltage In the illustrated embodiment, both the main discharge and relatively low current pulses for starting a discharge current regulating loop and the auxiliary starting loop ... within an arc lamp, and high current relatively low-volt 70 consist of similar reactive elements forming T-networks. age pulses for energizing the arc lamp with high instan The auxiliary loop is connected across input terminals taneous loading after initial ionization has been effected. T., T adapted to be energized from a 120 volt, 60 cycle 2,951,971 3 4. supply. Closing switch S connects reactor L1 and capaci the same fashion as the auxiliary loop as regards the gen tor C in series across the voltage supply. Li is a Sub eration of the current pulses. However, its current pulses stantially linear reactor and is shown as a winding 6 are used to energize the lamp directly rather than to pro about the central leg of an Elamination 7 provided with vide high voltage pulses for the initial ionization. Capac an air gap at 8 next the end lamination 9 to prevent Satu itor C charges through linear reactor L-3 until the Voltage ration of the core. A saturable reactor L2 is connected across it is sufficient to saturate the core of Saturable across C in series with a coupling winding L5 wound reactor L. At this instant, the inductance of Saturable about the core of a similar saturating reactor L4 of the reactor L4 drops approximately in the ratio of incremen main current regulating loop. tal permeabilities of the core below and above Saturation. In the main loop, closing switch S2 connects reactor 10 This allows the charge across capacitor C. to be dis | 3 and capacitor C in series across input terminals T3, T4 charged in a short high-intensity pulse through the lamp. adapted to be connected to a 280 volt, 60 cycle supply. The discharge current wave form through the lamp is il Reactor L3, like reactor L1, is substantially linear in char lustrated by curve 25 in Fig. 3d. The current pulses acteristics and is shown as a winding 10 on the central occur at times is and t, twice per cycle, that is with a leg of an Elamination 21 provided with the usual air gap time interval of A20 second apart. Times is and ta may at 22 next the end lamination 13. or may not correspond to times t1 and t2, depending upon Saturable reactor L is connected in series with the the adjustment of the circuit elements. lamp F across capacitor C2, being for that purpose con If the voltage-time integral of the charge across capac nected between one side of capacitor C2 and output ter itor C, reaches the saturation level of Saturable reactor minal Ts while the other side of C2 is connected directly 20 L early in the half-cycle of the supply frequency, the to output terminal T6. capacitor may recharge to the saturation level in time to Both saturating reactors L2 and La are wound about generate one of more additional pulses within the half toroidal cores 4 and 5 respectively, consisting of grain cycle, as shown by dotted pulses 22, 22' trailing main oriented silicon steel or nickel-iron strip continuously pulses 22 in Fig. 3b. This may be made use of in the wound in the usual fashion to preserve the grain orienta 25 auxiliary starting circuit to increase the speed with which tion parallel to the direction to magnetization. The mag the lamp is ionized. In the main discharge regulating netic core material is of a high-permeability, high-satura loop, the voltage-time integral of charge across capacitor tion flux density type having a rectangular hysteresis loop C may likewise reach the saturation level of saturable characteristic. Such a characteristic is illustrated in Fig. reactor La more than once during each half-cycle of the 2 showing the flux density B increasing very rapidly with 30 supply voltage. the magnetizing force H up to the saturation levels S The design criteria governing the choice of constants beyond which there is almost no further increase in flux for the various circuit elements and the values selected density. Below saturation, the incremental permeability for a unit actually constructed and found to operate AB under test as previously described are as follows. 35 The size of capacitor C determines the loading or Watt AH input into the lamp, and the voltage applied to terminals is given by the slope of dotted line 16, whereas beyond T, T. must be sufficient to cause the discharge through saturation the incremental permeability is substantially the lamp to take place. If the applied voltage is too that in air and equal to 1. The ratio of incremental low, the discharge will not occur whereas if it is too high, permeabilities below and above saturation may be in the 40 unstable operation with multiple discharges and oscilla range of 10,000 to 1. Grain oriented silicon steel may tions per half-cycle will occur as previously explained. be used for core 5 of L4 and nickel iron having a yet For a loading of 1250 watts into the lamp previously smaller and more rectangular hysteresis loop is prefer described, a voltage supply of 280 volts with a value for ably used for core 14 of L. Nickel iron core material of Cof 42 microfarads is appropriate. Linear inductance this type is sold under the various trade names Deltamax, 45 La must allow the recharging of capacitor C to the Orthonol, and Permeron. operating value so that the voltage-time integral allows In the operation of the auxiliary starting circuit, when the build up of sufficient flux to exceed the saturation switch S1 is closed, capacitor C charges through linear level of saturable reactor La at each half-cycle. The reactor L1 until its voltage is sufficient to saturate satura value selected for L3 is .04 henry and is achieved by ap ble reactor L2. The charging voltage wave form is shown 50 proximately 165 turns on a core cross section 2' x 1%' by curve 25 of Fig. 3a; the charging occurs in a generally measured at the winding leg of E lamination 11. The positive direction from time to to t1, and in a generally saturating reactor L is chosen to saturate once per half negative direction from t to ta. At the voltage level cor cycle at a voltage on the charging cycle above the main responding to t1, saturable reactor La Saturates. At this taining voltage required for arc lamp F. In other words, instant, its incremental permeability may drop by a factor 55 the saturating reactor must have sufficient turns coupled of 10,000 and its inductive reactance falls through the with a cross sectional area achieving saturation on the same ratio. Accordingly, capacitor Ci discharges rapidly charging cycle at or slightly above the striking voltage through the saturable reactor providing the current pulse of the lamp. The saturable reactor used consists of 160 shown by curve 22 at time t in Fig. 3b. This current turns on a toroidal core of grain-oriented silicon steel pulse passes through winding Lis on saturable reactor L. 60 134' x 134' in cross section, 3' inner diameter and 6% ' and the resulting rapid change in flux in the core induces a outer diameter. high-voltage pulse in main winding L4, shown by curve 23 In the auxiliary starting loop, the value capacitor C1 at time t1 in Fig. 3c. A half cycle later at time t, the determines the energy transferred into the main current capacitor discharges in the opposite direction and pro regulating circuit in the form of high-voltage ionizing duces the current pulse shown by curve 22 and the cor 65 pulses. The linear reactor Li is proportioned to allow responding voltage pulse shown by curve 23. The interval capacitor C to charge to the saturating level of saturable from to to t or t to t corresponds to /2 cycle of the inductor L2 at least once per half-cycle. In the unit con supply voltage shown by dotted line curve 24, namely structed, C has a value of 2 microfarads and L1 has an A20 second. The sequence of high voltage pulses applied inductance of approximately .17 henry giving a reactance across the arc lamp causes the xenon filling therein to 70. of approximately 64 ohms at 60 cycles. Saturable in become ionized. ductor. L. must have the necessary volt-ampere capacity Switch S2 of the main current regulating loop may be to transfer sufficient pulse energy from capicitor C, into closed at the same time as switch S1 of the auxiliary start the main loop. to achieve the necessary ionization in lamp ing loop, or at any time thereafter, in order to place the F. In the unit constructed, La consists of 200 turns on a lamp F in normal operation. The main loop operates in 75 toroidal core of high-permeability nickel-iron "Deltamax” 2,951,971 5 6 strip with a rectangular hysteresis loop characteristic, tor connected in series across said input terminals, a 4' x 1' in cross section, 2%' inner diameter and 3%' pair of output terminals adapted for connection to an outer diameter. Coupling winding L5 consists of sufficient arc lamp for pulse energization thereof, a first saturable turns on the core of saturable reactor L4 to obtain inductor connected across said first capacitor in series efficient transfer of energy along with substantial volt with said output terminals, another pair of input ter age multiplication. In the unit constructed, Lis consists of minals adapted to be connected to an alternating cur 5 turns on core 13 of saturable inductor LA; the wind rent source, an auxiliary starting loop including a sec ing ratio as between L4 and L5 is 160 to 5, providing a ond capacitor and a second inductor connected in series voltage multiplication of 32...... across said other input terminals, and a second saturable The circuit which has been described starts the illus O inductor having a high permeability core with a substan trated lamp with pulses of approximately 3,000 volt tially rectangular hysteresis, loop characteristic and a peak amplitude at A20 second time interval repetition, that coupling winding on said first saturable inductor con is at 8,333 microsecond intervals. During normal oper nected in series across said second capacitor to generate ation, the arc lamp operates with a current pulse of high-voltage pulses in said first saturable inductor for approximately 77 amperes peak current and approxi 5 ionizing said lamp at starting. mately 500 microsecond pulse width at 10 percent of 2. An operating circuit for an arc lamp comprising maximum amplitude, the time interval between pulses be a pair of input terminals adapted to be connected to an ing 8,333 microsecond, that is a repetition rate of 120 per alternating current source, a main discharge current reg second. The effective or R.M.S. value of current into ulating loop including a first capacitor and a first cur the lamp is 13.6 amperes at a voltage drop of 117.5 volt 20 rent limiting inductor connected in series across said in and the energy input into the lamp is 1260 watts. The put terminals, a pair of output terminals adapted for measured light output from the lamp is 34,530 lumens in connection to an arc lamp for pulse energization thereof ... dicating an efficiency of 27.4 lumens per watt as regards with a residual current flow for maintaining ionization the lamp and neglecting circuit losses. - therein between pulses, a first saturable inductor having 25 a high permeability core with a substantially rectangular Fig. 4 illustrates schematically a modification of the hysteresis loop characteristic connected across said first present circuit for operation on the ordinary 120 volt, capacitor in series with said output terminals, another 60 cycle A.C. supply generally available. Like refer pair of input terminals adapted to be connected to an ence numerals in this figure denote corresponding parts alternating current source, an auxiliary starting loop in with reference to the circuit of Fig. 1. For ease of ill 30 cluding a second capacitor and a second current limiting lustration all the circuit elements have been symbolically inductor connected in series across said other input ter illustrated. minals, and a second saturable inductor having a high Both the main current regulating loop and the auxil permeability core with a substantially rectangular hys iary starting loop are energized from terminals T1, Ta teresis loop characteristic and a coupling winding on said adapted to be connected to the usual 120 volt, 60 cycle first saturable inductor connected in series across said A.C. supply. The auxiliary starting loop is the same as 35 second capacitor to generate high-voltage pulses in said has been illustrated in Fig. 1 and is energized upon the first saturable inductor for ionizing said lamp at starting. closure of switch Sa through normally closed switch S1. 3. An operating circuit for an arc lamp comprising The main discharge current regulating loop has been a pair of input terminals adapted to be connected to an modified by the provision of an autotransformer 26 40 alternating current source, a main discharge current reg comprising a primary winding 27 and a high-reactance ulating loop including a first capacitor and a substan secondary winding 28 connected in series therewith across tially linear first inductor connected in series across said capacitor C. The primary winding forms the input cir input terminals, a pair of output terminals adapted for -cuit of the transformer whereas the primary and sec connection to an arc lamp for puse energization thereof ondary windings in series form the output circuit. The With a residual current flow for maintaining ionization coutput circuit provides the necessary voltage for operat therein between pulses, a first saturable inductor having ing the lamp and at the same time the leakage reactance - a high permeability core with a substantially rectangular of secondary winding 28 serves the function of reactor hysteresis loop characteristic connected across said first L previously described with respect to Fig. 1. If de capacitor in series with said output terminals, another sired, switch S1 may be a time delay relay which opens pair of input terminals adapted to be connected to an at a predetermined interval of time after energization of alternating current source, an auxiliary starting loop in the circuit in order to disable the auxiliary starting loop cluding a second capacitor and a substantially linear sec after the lamp has started. ond inductor connected in series across said other input If desired one or more peaking stages each including terminals, and a second saturable inductor having a high a charging capacitor and a saturable inductor may be permeability core with a substantially rectangular hys cascaded in either the main current regulating loop, as teresis loop characteristic and a coupling winding on the described in the copending Wiley application, or in the core of said first saturable inductor connected in series auxiliary starting loop, in order to achieve the desired across said second capacitor, said first saturable inductor steepness and intensity of pulse. In such case, the in having a relatively high current ratio relative to said ductors and capacitors intervening between the input ter coupling winding whereby to generate high-voltage pulses minals and the final peaking stage together perform the 60 in said first saturable inductor for ionizing said lamp at current limiting function of the first inductor, that is L. starting and thereafter permit relatively high current and in the auxiliary loop, or L3 in the main regulating loop. low voltage pulse energization thereof by said main reg While the invention has been described in detail by ulating loop. reference to specific constructions embodying its prin 4. An operating circuit for an arc lamp comprising ciples, same are intended as illustrative examples and 65 a main discharge current regulating loop including a not in order to limit the invention thereto. The ap transformer having an input circuit for connection to an pended claims are intended to cover such modifications alternating voltage source and an output circuit includ as will occur to those skilled in the art and coming with ing a high reactance secondary winding, a first capacitor in the true spirit and scope of the invention. connected across said output circuit, a pair of output What I claim as new and desire to secure by Letters 70 Patent of the United States is: terminals adapted for connection to an arc lamp for 1. An operating circuit for an arc lamp comprising pulse energization thereof with a residual current flow a pair of input terminals adapted to be connected to an for maintaining ionization therein between pulses, a first alternating current source, a main discharge current reg saturable inductor having a high permeability core with lating loop including a first capacitor and a first induc 75 a substantially rectangular hysteresis loop characteristic 2,951,971 7 8 connected across said first capacitor in series with said thereof with a residual current flow for maintaining output terminals, another pair of input terminals adapted ionization therein between pulses, another pair of input to be connected to said alternating voltage source, an terminals adapted to be connected to an alternating volt auxiliary starting loop including a second capacitor and age source, an auxiliary starting loep including a second a current limiting inductor connected in series across capacitor and a second current limiting inductor con said other input terminals, and a second saturable induc nected in series across said other input terminals, and a tor having a high permeability core with a substantially second saturable inductor having a high permeability rectangular hysteresis loop characteristic and a coupling core with a substantially rectangular hysteresis loop winding on said first saturable inductor connected in characteristic and a coupling winding on the core of said series across said second capacitor to generate high volt O first saturable inductor connected in series across said age. pulses in said first saturable inductor for ionizing second capacitor, said first saturable inductor having a said lamp at starting. relatively high current ratio relative to said coupling 5. The combination of an arc. lamp comprising an winding whereby to generate high-voltage pulses in said elongated envelope containing an inert gas at a low first saturable inductor for ionizing said lamp at starting pressure and having a pair of self-heating thermionic 5 and thereafter permit relatively high current and low electrodes sealed into opposite ends, with an operating voltage pulse energization thereof by said main regulat circuit comprising input terminals adapted to be con ing loop. nected to an alternating current source, a main discharge current regulating loop including a first capacitor and References Cited in the file of this patent a first current limiting inductor connected in series across 20 UNITED STATES PATENTS said input terminals, a first saturable inductor having a 2,372,857 Setchell ------Apr. 3, 1945 high permeability core with a substantially rectangular 2,462,371 Engle ------Feb. 22, 1949 hysteresis loop characteristic connected across said first 2,683,240 Strange ------July 6, 1954 capacitor in series with said lamp for pulse energization 2,774,917 Passmore ------m---- Dec. 18, 1956