04/874098

08/24/1971

11/05/1969

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315/200R

83/337, 315/208, 83/424, 315/241S, 83/408

H03K17/725; H05B41/34; H03K17/72; H05B41/30; H05B37/00

315/200,208,219,241,241P,227,262 320/1

Lake, Roy

Dahl, Lawrence J.

What I claim is

1. In a stroboscopic lamp firing circuit including an AC voltage source and striking means, the combination comprising: initiating means for operating said striking means, said initiating means comprising a switch means connected between said voltage source and said striking means; booster means for raising the voltage from said source means for firing said lamp, said booster means including a capacitor connected between said lamp and said AC source; and a diode connected between the point of connection of said capacitor to said lamp and the junction of said switch means and said source, said diode permitting charging of said capacitor by said voltage source when said switch means is open and blocking current flow from said capacitor through said switch means when said switch means is closed, said initiating means being responsive to the phase of said AC source to operate said striking means at the same point in time that boosted voltage is available at said lamp.

2. A circuit according to claim 1, in which said boosted voltage is a positive voltage and said initiating means is responsive to positive peak, or close to peak values of said AC source.

3. A circuit according to claim 1, in which said boosted voltage is a negative voltage and said initiating means is responsive to negative peak, or close to peak values of said AC source.

4. A circuit for assuring firing of a stroboscopic gas discharge lamp comprising, in combination:

5. A circuit according to claim 5, in which said AC source includes a half-wave doubler circuit, the voltage across said lamp at the time of firing being substantially four times the peak value of AC voltage in said source passed to said half-wave doubler circuit.

6. A circuit for assuring firing of a stroboscopic gas discharge lamp comprising, in combination:

This invention relates to improved stroboscopic lamp firing circuits for greatly increasing the reliability of operation of the lamp and more particularly, to circuits in addition to those shown and described in my copending U.S. Pat. application Ser. No. 828,605 filed May 28, 1969, and entitled STROBOSCOPIC LAMP CIRCUIT.

BACKGROUND OF THE INVENTION

Stroboscopic lighting is well known in the art and has a wide range of uses. Essentially, a stroboscope incorporates a gas discharge lamp capable of emitting an extremely intense flash of light for an extremely short time duration. The firing circuit for the lamp is generally designed such that the lamp can be successively fired at various repetition rates or frequencies or, fired only once at a desired instant in time. In fairly sophisticated stroboscopic lamp circuits, extremely accurate repetition rates can be achieved and the lamp itself is thus useful in timing operations; for example, in monitoring moving machine parts. In simpler versions, a stroboscopic lamp is very useful in photography for taking flash pictures wherein the lamp need only be flashed once at a given instant in time. In still other versions, a relatively simple circuit can be provided for flashing the lamp at a relatively low frequency such as from 1 to 30 times per second and wherein the particular frequency of the flashing is not of primary importance. This type of lamp is useful for psychedelic lighting effects.

The present invention is primarily concerned with the foregoing types of stroboscopic lamps wherein fairly simplified and economical firing circuits may be provided. However, it is to be understood that the invention is applicable to all types of stroboscopic lamps.

Essentially, the firing circuit for such lamps includes a voltage source which may constitute an AC source, or battery powered AC source connected to charge a storage capacitor through a resistance. The lamp is connected across the capacitor and when not operated presents a very high resistance so that the source voltage can readily be stored on the capacitor. The circuit is completed by a striking means which generally takes the form of a high step-up transformer capable of applying a trigger pulse which serves to strike a small arc within the lamp; that is, effect at least a partial ionization of the gas in the lamp. If the voltage across the storage capacitor and thus across the lamp is sufficient to fire the lamp, the gas suddenly becomes highly ionized and the resistance of the lamp becomes very low. As a result, a very high current is drawn through the lamp from the storage capacitor and the desired high intensity flash from the lamp results. Discharge of the power on the storage capacitor through the lamp reduces the voltage from the source across the lamp to a low value so that the lamp extinguishes itself. At this point, the lamp again presents a very high resistance and the storage capacitor can then become recharged through the resistance and the circuit is ready for a subsequent firing. The maximum repetition rate of firing is thus determined in part by the time constant of charging of the storage capacitor since it is essential that the storage capacitor be sufficiently charged before a subsequent firing to provide the necessary voltage to fire the lamp.

One of the major problems in the foregoing types of circuits is the assuring that a sufficient voltage from the voltage source exists across the lamp at the time of striking of the lamp. In the case of portable stroboscopic lighting units wherein batteries are often used for the voltage source, the available voltage for firing the lamp generally decreases over prolonged use simply as a result of degradation of the batteries. Thus reliability of firing of the lamp is impaired. In addition, physical changes take place in the lamp itself such that increased voltages are necessary to fire the same over those necessary when the lamp is first used. Many other factors may also determine whether or not a sufficient voltage is available to fire the lamp.

In order to increase reliability of stroboscopes, the first step has been to assure that a sufficient voltage is available to fire the lamp at the time of striking of the lamp. Assurance of a sufficient voltage has sometimes been accomplished in the past by utilizing a step-up transformer between the voltage source and the lamp itself. However, this involves additional circuit elements and oftentimes will require more expensive type storage capacitors. Even under these circumstances, the storage capacitor itself can be damaged from too much voltage. It would be highly desirable to provide some means for assuring that sufficient voltage is available with present-day circuits employed in the more simplified versions of stroboscopic lighting all to the end that economy can be realized in the manufacture of such stroboscopic systems and yet the desired increased reliability of operation can be assured.

BRIEF DESCRIPTION OF THE PRESENT INVENTION

With the foregoing considerations in mind, it is a primary object of the present invention to provide an improved stroboscopic lamp firing circuit wherein a voltage of higher value than that normally appearing on the storage capacitor is applied to the lamp at the time of striking of the lamp wherein this higher voltage is derived from the normal voltage source already available in the lamp circuit, all to the end that a greatly increased reliability of operation is assured.

Briefly, the foregoing is accomplished by incorporating elements in the lamp circuit in the form of booster means for raising the voltage from the source means for firing the lamp. The result is that a substantially increased voltage is provided across the lamp at the point in time of striking of the lamp to thereby effect complete ionization and sufficiently lower the resistance of the lamp that power from the storage capacitor can be assured of passing through the lamp. In the preferred embodiment of the invention, the booster means takes the form of a single additional capacitor to the circuit and a cooperating diode. The arrangement is such that the capacitor is charged from the voltage source through the diode to a given voltage. One side of the capacitor is connected to the lamp, and the other side is connected to the source in such a manner that a boosted voltage appears on the first side relative to ground when the initiating means is operated to strike the lamp. The diode prevents back flow of current from the boost capacitor through the storage capacitor or the firing circuit so that the boosted voltage is applied across the lamp at the point in time of striking of the lamp. The result is an assurance of complete ionization of the gas in the lamp so that the energy stored in the storage capacitor can readily discharge through the lamp.

The advantages of the foregoing arrangement are numerous. First, by utilizing the booster means, a higher voltage type of lamp can be used with a lower voltage circuit. Further, if the condition of the lamp is such that an increased voltage across it is necessary to fire the same, the lamp can still be fired reliably even though the voltage across the storage capacitor is not sufficient to fire the lamp. Thus the useful life of the lamp can be substantially increased.

Moreover, for a given time constant of recharge of the storage capacitor, a faster flash repetition rate can be achieved since it is not essential that the storage capacitor be completely charged at the time of firing in view of the presence of the boosted voltage. Alternatively, for a given flash repetition rate, a longer time constant of recharge for the capacitor can be used.

Since it is possible to use a lower source voltage, the breakdown voltage rating of the storage capacitor can be lower for a given lamp. Step-up transformers heretofore thought necessary can also be eliminated. In addition, apparatus for sensing the phase of the incoming AC source may have additional advantages, such as striking the lamp on a negative peak and eliminating lamp current in the positive side of the rectifier system.

BRIEF DESCRIPTION OF THE DRAWINGS

A better understanding of the invention will be had by now referring to the accompanying drawings, in which:

FIG. 1 represents a typical simplified prior art type of stroboscopic lamp and firing circuit therefor;

FIG. 2 illustrates the same circuit as FIG. 1 except for the incorporation of the voltage boosting means of the present invention and the use of an SCR as one possible switch means;

FIG. 3 is a qualitative plot of voltage values during a firing of the lamp appearing at one of the lamp terminals useful in explaining the operation of the invention;

FIG. 4 is a modified circuit in accordance with the invention, utilizing negative boost;

FIG. 5 is a further modification of the circuit of FIG. 1; and

FIG. 6 shows still another modification of the circuit of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1, there is illustrated a simplified stroboscopic lighting circuit including an AC source 10, connected across a storage capacitor C by way of leads 11 and 12. A gas discharge lamp 13 which may be of the xenon type also connects across the leads 11 and 12 so that voltage stored on the capacitor C appears across the lamp 13.

A striking circuit enclosed within the dashed outline 14 includes a transformer 15. The primary of the transformer coil 15 connects through tap 16 and condenser CT to a lead 17 arranged to be energized from the voltage source and storage capacitor C through a switch means S when closed to a junction point 18 in the lead 11. A high discharge resistance RT connects between the junction point of the lead 17 and condenser CT and the lead 12. The secondary of the transformer 15 terminates in a coil 20 surrounding the lamp 13. The resistance R, capacitor 21, and diodes 22 and 23 comprise a charging circuit for the storage capacitor C.

The foregoing elements are entirely conventional. The switch means S, while shown as a simple mechanical-type switch, may constitute electrical contacts to be closed as in the case of a photographic strobe lamp circuit or may constitute any type of electronic switch such as a vacuum tube, solid-state element, or other equivalent means for closing the circuit between the junction points 18 and 19.

In the operation of the circuit of FIG. 1, assume that the switch means S is open as shown. Under these conditions, the voltage V1 of the AC source 10 will result in a current flow through the resistance R to charge the capacitors C through the charging circuit elements 21, 22, and 23 which define a one-half wave doubler. The resistance of the lamp 13 when it is not fired, is extremely high so that the peak voltage stored across the capacitor C will correspond substantially to 2v1. This same voltage will also appear across the lamp 13 by way of the leads 11 and 12.

The switch S essentially constitutes an initiating means for the striking circuit 14. When the switch S is closed, the voltage 2v1 (peak) will be applied to the junction point 19 and capacitor CT. Since the voltage across a capacitor cannot change instantaneously, the same 2v1 (peak) volts will energize the primary of the transformer 15 through the tap 16 in the form of a transient or high rate of change voltage as the capacitor CT charges. This changing voltage in the primary will be reflected in an extremely large voltage generated in the secondary of the coil 15 in accord with the step-up ratio of the turns. The high secondary voltage will be applied to the coil 20 and result in the striking of a small arc in the gas in the lamp 13; that is, at least a partial ionization of the gas will occur. At this point, the voltage across the storage capacitor C appears across the lamp 13, and if sufficiently high, will cause an avalanching of the ionization and a discharging of the stored energy through the lamp.

The discharge through the lamp 13 results in a highly intense flash of light. Since the resistance of the lamp 13 is dropped to an extremely low value, the discharge from the storage capacitor C is extremely rapid, and the voltage across the lamp drops to a relatively low value so that the lamp is extinguished.

When the lamp has completed its firing, it will assume its former very high resistance value so that the storage capacitor C will then commence recharging through the resistance R and elements 21, 22, and 23. If the switch S should remain closed, the small striking circuit capacitor CT will also be charged to the voltage value 2v1 (peak) and the lamp cannot be refired until the switch is opened so that the striking circuit capacitor CT can discharge through RT.After the striking circuit capacitor CT has completed its discharge, reclosing of the switch S will result in a subsequent firing of the lamp 13.

The condition of firing of the lamp 13 in the above described operation is that the voltage 2v1 (peak) from the voltage source across the lamp be of a sufficient value to fire the lamp when the striking circuit operates. This "sufficient voltage," as mentioned heretofore, depends on the lamp involved. If the voltage source in the form of a battery powered AC source provides a voltage just sufficient to fire the lamp, it is very possible after prolonged use that the voltage will degrade as a consequence of aging of the battery to a value in which the lamp will not fire. Alternately, and as also described heretofore, repeated use of the lamp can result in the necessity of a higher firing voltage with age of the lamp. Thus, in the circuit of FIG. 1 unless some type of very high initial voltage source is provided, the reliability of firing of the lamp is subject to the foregoing conditions.

Referring now to a first embodiment of the present invention as shown in FIG. 2, assurance of a sufficient voltage across the lamp at the point in time of striking of the lamp is realized by providing an increased peak voltage from the voltage source at the lamp terminal in the lead 11 and initiating striking of the lamp at the proper point in time that the peak voltage is present. Towards this end, the switch S of FIG. 1, is replaced by an SCR 24 in FIG. 2 with its gate lead 25 connecting through variable resistance RT' and lead 26 to the source 10 as at 27. A voltage booster means takes the form of a lead 28 including a small capacitor 29 connected between the lamp terminal at the point 30 and the AC source at a junction point 31 (other points in the AC source could also be used). Cooperating with this small capacitor is a diode 32 connected between the point 30 of connection of the capacitor to the lamp terminal and the junction 18 of the SCR switch means with the storage capacitor C.

With the foregoing additional elements in the circuit, substantially higher than the normally available voltage across the lamp is provided to the lamp if the striking means is energized at the proper phase of the AC source voltage. This phase is sensed by the gate lead 25 of the SCR.

The foregoing is depicted in FIG. 3, wherein the waveform 33 of the voltage at the lamp junction 30 during a firing operation is shown. Thus, when the SCR 24 is closed by voltage from the AC source at the time depicted by the vertical line T1, voltage waveform portion 34 reaches a peak at the lamp terminal 30 as indicated at 35. This voltage is more than sufficient to assure firing of the lamp 13 so that discharge from the storage capacitor will take place through the lamp to the point in time designated by the vertical line T2. At this point, the voltage across the lamp is sufficiently low that the lamp is extinguished. The portion of the curve 36 represents the charging of the storage capacitor C. The time interval between T1 and T2 is greatly exaggerated in FIG. 3 for purposes of clarity. Actually, this time interval represents the duration of the flash of the lamp and in practice could be of the order of milliseconds or microseconds.

FIG. 4 illustrates a slightly modified circuit from that shown in FIG. 2. In this respect, some of the same numerals have been employed to designate corresponding components as in FIG. 2. The circuit of FIG. 4 essentially applies the boosted voltage to the negative side of the lamp terminal rather than the positive side. Towards this end, and referring specifically to FIG. 4, the SCR switch is illustrated at 37 having a trigger gate terminal 38 connected through the variable resistance RT' to a junction 39 between a voltage divider comprising resistances R1 R2. R2.A diode 40 (corresponding to the diode 23 in FIG. 2) cooperates with the diode 22, resistance R, and capacitor 21' to define the half-wave doubler charging circuit for the storage capacitor C. However, the diode 32 of FIG. 2 constituting part of the boost voltage circuit is replaced by a diode 41 in FIG. 4 and the capacitor 29 of FIG. 2 connected into a line 42 connecting from the lower lamp terminal 43 of the lamp 13 and terminating at the junction 27 of the AC source as indicated at 44. The variable resistance RT' connecting to the junction point 39 of the resistance voltage divider defined by R1 and R2 senses the negative phase of the voltage source rather than the positive phase as described in conjunction with FIG. 2. The SCR 37 in turn is arranged to initiate the striking means during negative phase peaks of the voltage from the source 10. With this arrangement, the boosted voltage is boosted in a negative sense so that the voltage across the lamp at the time of striking is again substantially increased.

FIG. 5 illustrates a standard voltage quadrupler for providing a boost voltage except that the added capacitors may be very small compared to the storage capacitor. These capacitors in the quadrupler circuit can be made small since, in the configuration shown, they need not contribute significant illumination to the power of the lamp.

Thus with specific reference to FIG. 5, it will be noted that the circuit is substantially the same as the prior art circuit of FIG. 1 except for the quadrupler components. The additional elements are included in a line 45 in the form of capacitor 46, diode 47, diode 48, and capacitor 49.

FIG. 6 is similar to FIG. 5 except that the two additional diodes and two additional capacitors are connected to the negative lamp terminal and serve to supply negative boosted voltage. Thus, in FIG. 6, a line 50 connects to the negative lamp terminal 51 and includes diodes 52 and 53 along with capacitor 54, the other side of the line 50 terminating at the AC source at 55. The final capacitor is shown at 56 connected in the line 12 to the negative lamp terminal 51. In the circuit of FIG. 6, a positive half-wave doubler cooperates with a negative half-wave doubler to provide in effect a quadrupled boosted voltage across the lamp.

OPERATION

With the foregoing brief description of the circuits in mind, their operation will now be fully described. Starting first with the operation of the circuit of FIG. 2, and with reference to FIG. 3, assume first that the SCR switch means 24 is open (that is, nonconducting). Under these conditions, the storage capacitor C will be charged up to the 2v1 peak voltage through the charging resistance R and the one-half wave doubler elements 21', 22, and 23. This one-half wave doubler is shown merely as a typical circuit. It should be understood that a full-wave rectifier, full-wave doubler, tripler or even quadrupler, could be used. The capacitor 29 can be substantially smaller than the storage capacitor C but the same 2v1 peak voltage will appear across the capacitor 29. The voltage at the lamp terminal 30, however, will now have an AC voltage equal to V1 riding on a DC level equal to 2v1 peak. There is thus applied to the lamp a voltage which varies between 2v1 peak and 4v1 peak depending upon the phase of V1 at any given point in time.

The foregoing quiescent situation is depicted by the initial portion 34 of the curve of FIG. 3 between 0 and the time T1. If the SCR 24 is triggered or closed at the time T1, 4V1 peak voltage will be available at the lamp to start heavy ionization of the gas. The value 4v1 peak is now greater than the value of voltage on the storage capacitor by an amount equal to 2v1 peak. Thus, a boosted voltage has been realized. The capacitor 29 could be connected to other points on the AC source, such as point 27 rather than point 31.

The lamp terminal 30 will thus exhibit a peak voltage as indicated at 35 in FIG. 3, which voltage is substantially twice that of the voltage on the storage capacitor.

Simultaneously, with the closing of the SCR switch, the stored voltage is applied across the striking circuit capacitor CT resulting in the transient current in the primary of the transformer 15 providing an extremely high voltage on the secondary to strike the lamp. It should be noted that the lower lead of the transformer 15 could be connected to the line 11 rather than the line 12 in FIG. 2; that is, at the junction point 18. This connection would reverse the action of CT; that is, whether it charges or discharges during firing. The important feature of the invention is the fact that the boosted voltage appears at the point 30 at the same point in time as the striking of the lamp 13 as a result of the striking circuit being responsive to the proper phase of V1.

The manner in which the foregoing proper phase response is accomplished is as follows. After a discharge has taken place through the lamp 13, capacitors C and CT are charged up as indicated by the portion 36 of the plot in FIG. 3. The point 19 of CT is thus somewhere near the value of 2v1 peak. As the V1 source voltage cycles down from its peak, the potential at the point 27 falls towards a value of -V1 peak. This change in voltage causes point 27 to be negative with respect to the gate terminal 25 of the SCR 24 and the junction point 19. At this point, it should be understood that for the particular one-half wave doubler circuit shown, the point 27 will never be more positive than a value of V1 peak.

Since the junction point 18 can be at a value of 2v1 peak, the junction 19 will assume this 2v1 peak value when the SCR switch 24 closes. Thus, after firing, the junction point 19 will be above the value V1 peak.

As the voltage at the junction point 27 falls towards its negative peak value, it causes a current flow through the resistor RT' from the junction 19. This flow makes the SCR gate terminal 25 negative with respect to its cathode and the reversed biased gate breaks down to permit discharge of capacitor CT. (If it should be desired that the reverse bias gate to cathode junction not be used for this particular function, an external diode can be added across the gate and cathode leads or a blocking diode could be added in series with the gate and another resistor connected to the cathode lead and tied to ground or another suitable point.)

The discharging of capacitor CT through the resistance RT' continues until the AC voltage at the point 27 rises above the voltage at the junction 19 by an amount sufficient to fire the SCR. Such can occur only after one cycle or after a number of cycles as determined by the time constant of the resistor RT and capacitor CT. By making RT' variable, it can thus be used as a flash rate control.

From the foregoing, it will be evident that the positive gate drive to fire the SCR can only occur at a peak or near a peak of the V1 voltage since at any value less than a peak or near a peak, the condenser CT is still discharging through RT and thus through the reversed biased gate.

Several possible alternate connections could be used to accomplish the foregoing phase sensing. However, with the particular connections described and shown in FIG. 2, a minimum number of component parts accomplishes the desired end.

In the event it should be desired to shift the firing point with respect to the incoming AC phase signal, a voltage divider could be used across the AC source and the resistance RT' could be connected at a midposition on this divider. Since the source is AC, the divider could be reactive or resistive.

Referring once again to FIG. 3, with the high peak value of voltage as indicated at 35 appearing across the lamp 13 at the point in time of striking of the lamp, firing of the lamp is assured and the discharge of the high voltage will take place as shown between the lines T1 and T2. When the voltage at the lamp terminal 30 decreases sufficiently below the stored voltage on the capacitor C so that the diode 32 can now conduct, the power or energy stored on the storage capacitor C will all avalanche through the lamp 13 to provide the desired high intensity flash. In this respect, it should be noted that the diode 32 is in a sense functioning as a switch since it permits the boosted voltage to be retained at the lamp terminal 30 at the time of its generation; that is, the capacitor 29 cannot discharge back through the diode 32 and storage capacitor because of the orientation of the diode 32. Thus, it is assured that the increased voltage is available across the lamp at the time of striking. Since the capacitor 29 does not appreciably contribute to lamp illumination, it can be made very small compared to the storage capacitor C.

After the lamp 13 is extinguished; that is, at the time T2 as shown in FIG. 3, and when the SCR switch is open (that is, off), the storage capacitor C will then again be charged as indicated by the curve 36 through the resistance R and half-wave doubler circuit preparatory to a subsequent firing of the lamp. Also, the capacitor 29 will be charged through the diode 32 preparatory to providing the increased voltage all as described when a subsequent firing is to take place.

The circuit of FIG. 4 operates in substantially the same manner as the circuit of FIG. 2 except that the boosted voltage is negative and applied to the lower lamp terminal 43. Also, the SCR switch 37 is caused to be actuated on a negative peak of the source voltage, the gate terminal 38 being returned through the resistance RT' to a voltage divider across the AC source comprising the resistances R1 and R2. The gate for the SCR is connected at the junction 39 of these resistances. The phase sensing is similar to that described for FIG. 2 except that the SCR is energized on negative peaks since the cathode now has an AC potential which can fall faster than the gate potential. This is accomplished by returning the transformer 15 and the SCR anode to the junction of diode 22 and capacitor 21' as shown in FIG. 4 so they will have full AC source voltage applied to them while the SCR gate 38 is returned to point 39 which has less than full AC source voltage applied to it.

With the SCR switch nonconducting, the capacitor 44 will thus charge up to a given voltage peak through the diode 41. When the SCR switch is closed to initiate action of the striking circuit during a negative peak of the source voltage, the negative 2v1 peak voltage will be available at the terminal 43 of the lamp since the negative V1 charge on the capacitor 44 will be added to the negative V1 peak from the source 10. The total boosted voltage across the lamp taking into account the +2v1 peak voltage at the upper terminal will thus be 4v1 peak voltage.

As in the case of the circuit of FIG. 2, many alternate connections are possible in the circuit of FIG. 4 including the additional diodes and reactive components to effect a change in the RT'-CT time constant range, phase shift of the switch closure, and striking energy level. Also, as transformer 15 and capacitor CT are effectively in series, they can be reversed in termination so that transformer 15 connects to the SCR cathode and capacitor CT connects to the SCR anode.

The operation of the circuit of FIG. 5 is precisely the same as that described for the prior art circuit of FIG. 1 except for the provision of a quadrupled peak voltage for the lamp 13. The doubling of the 2v1 peak voltage is accomplished by the additional diodes 47 and 48 and additional capacitors 46 and 49, the lamp terminal for the lamp 13 now connecting to the junction of the diode 48 and capacitor 49. Contrary to conventional prior art circuits however, the additional capacitors 46 and 49 can be extremely small compared to the storage capacitor C since they do not contribute significant illumination to the lamp. This smaller capacity value is at least one-tenth and preferably less than one one-hundredth the capacity of storage capacitor C. The same is true of the boost capacitors 29 and 44 of FIGS. 2 and 4 respectively. These capacitors, although small, provide a significantly increased voltage to the lamp so as to insure initial firing of the lamp. The added diodes act as switches to pass the stored capacitor charge to the lamp after the lamp begins to fire.

The operation of FIG. 6 is similar in effect to FIG. 5 except that the two additional diodes and two additional capacitances 52, 53 and 54, 56 are connected to the negative lamp terminal 51 and supply a negative boost voltage of -2v1. In essence, FIG. 6 thus provides a positive one-half wave doubler in cooperation with a negative one-half wave doubler to provide the total of 4v1 peak across the lamp. The

In the circuits of FIGS. 2, 4, 5, and 6, the term "voltage source" is used herein to designate generally the combination of the AC source 10, charging resistance R, and one-half wave doubler. The term "initiating menas" is used to designate the switch S or the SCRs as described as one form of such switch since the closing of the switch initiates operation of the striking circuit. The term "striking means" is meant to cover the various elements enclosed within the dashed line 14 of FIG. 1 and the corresponding elements in FIG. 2.

From the foregoing, it will be appreciated that the present invention has provided very simple and economical circuits for vastly improving the reliability of stroboscopic lighting circuits.