CA1174267A - Electric flash device - Google Patents

Abstract

Abstract of the Disclosure This invention concerns an electric flash device which comprises a direct current power source circuit, a flash tube circuit including a flash tube, a voltage converter including an oscillator circuit, an oscillator transformer and an oscillation starting circuit, a rectifier circuit for rectifying an alternating current voltage from the voltage converter and a charging circuit including a main storage capacitor for storing electric energy to be supplied to the flash tube, and a triggering circuit for firing the flash tube. The oscillator circuit includes an oscillator switch-ing element which has a high leak resistance, and the oscillation starting circuit includes a switch element for starting the actuation of said voltage converter. In accordance with the electric flash device of the present invention, a power source switch is not required because the oscillation starting switch element is provided in the oscillation starting circuit and because the voltage con-verter automatically becomes deactivated if flash operation is not performed within a predetermined time interval.

Description

~4267 "EIEC~RIC FI~S~ D~VICB"

The present invention relates to a flash light generating apparatus, and more particularly to an electric flash device which generates a ~lash light by energizing a flash tube.
Flash apparatus has become widely used in various kinds of optical apparatus of which the operation requires flash light. Particularly, in the art of photography, arti~icial light is used to illuminate an object to be photographed.
One ~orm o~ arti~icial light which is now widely used is the so-called flash tube.
It is common practice in electric ~lash devices to obtain high intensity illumination for photographic purposes by discharging a chrged capacitor through a gas-~illed ~lash tube. A low voltage D.C. power source is generally employed together with suitable circuitry in order to obtain the rela-tively high D.C. ~oltage which is needed to charge the flash capacitor ~or each ~iring of the ~lash tube. Since an elect-ric ~lash device o~ this type is generally portable, batteries are usually employed as the source o~ low D.C. voltage. High D.C. voltage is obtained ~rom the batteries through the use of a voltage converter. A converter includes a trans~ormer ~or converting low A.C. voltage to high A.C, voltage9 and a rectifier for rectifying the high A.C. voltage, the recti~ied voltage being then applied to the fla~h capacitor in order to charge it.
It can readily be understood that under ordinary cir-cumstances when an electric flash dsvice is being used, a substantial portion o~ the time during which the device is turned on may be ~tandby time; that is~ time which elapses ~' . .

~IL17~7 after power supply has charged the capacitor to a suitable value and before the camera shutter is tripped thereby dis-charging the capacitor through the flash tube, During this time the power supply consumes energy from the batteries with-out producing any useful result. The energy loss may be significant, particularly when the device includes trans-formers, ~s the batteries age their output voltage drops and a longer period of time is required for firing the flash tube, In addition, as the output voltage of the batteries decreases with age, the device becomes incapable of flash-ing the flash tube.
In order to overcome the above disadvantage, the prior art contemplates the use of a timer circuit between the power source and the voltage converter. However, the power circuit itself will consume energy, and the power loss of the timer circuit mitigates against the most effective use of the battery.
It is therefore an object of the invention to provide an electric flash device which overcomes the dis-advantages of the prior art.
In accordance with a particular embodiment of theinvention, there is provided an electric flash device which includes a direct current power source circuit for providing a direct current voltage, a flash tube circuit including a flash tube, a converter circuit for converting said direct current voltage of said direct current power source circuit to an alternating current voltage, a rectifier circuit for rectifying said alternating current voltage to a direct current voltage, a charging circuit for storing an electric charge and for supplying electrical energy to said flash tube, and a trigger pulse generating circuit for triggering the flash tube of the flash tube circuit, The converter ~L~74Z~

circuit includes an oscillating transformer connected to the direct current power source circuit for generating a high alternating current voltage and having a current flowing therein. An oscillator performs an oscillating operation and includes a switch element for switching the current which flows in the oscillating transformer and functions as a high resistance resistor and of which leakage current is negligible when the oscillating operation of the oscil-lator circuit ceases. The switch element includes a control electrode circuit. A switching means is provided in the control electrode circuit of the switch element of the oscillator circuit for actuating the switch element of the oscillator circuit, and means are provided for starting oscillation of the oscillator circuit when the switching means operates.
Certain embodiments of the invention will now ~e described by way of examples and with reference to the accompanying drawings, wherein like parts in each~of the several figures are identified by the same reference character, and wherein~
Figures 1 and 2 are circuit dlagrams of prior art electric flash devices, Figure 3 is a detailed circuit diagram of an electric flash device according to the present invention;
Figure 4 is a detailed circuit diagram of another electric flash device according to the present invention;
Figure 5 shows a modification of the circuit of Figure 4; and Figure 6 is a detailed circuit diagram of further electric -Elash device according to the present invention.

- ~3L7~Z~7 Figure 1 shows an example of a prior art electric flash device. The device shown in Figure 1 comprises a direct current power source circuit A, a voltage converter circuit B for converting direct current voltage from the direct current power source circuit A into alternating current voltage, a rectifier circuit C for rectifying the alternating current voltage, an electric charge storing circuit D for supplying electrical energy to a flash tube, - 3a -~79~2~

a trigger pulse generating circuit E for triggering the flash tube, and a flash tube circuit F including a flash tube, The direct current power source circuit A includes a battery 10 and a power source switch 12 which is connected to the battery 10 in series relationship. The power source switch 10 is a mechanical switch which is manually operated.
The voltage converter circuit B comprises an oscillator cir-cuit, an oscillating time constant circuit having serially connected resistor 14 and capacitor 16, an oscillating trans-former 18 having a primary winding 18a, a secondary winding18b and a third winding 18c, and an oscillation switching element in the form of a PNP type Gerumanium transistor 20 whose internal resistance is extremely low.
The rectifier circuit ~ consists of a diode 22 whose anode electrode is connected to one terminal of the second winding 18b of the oscillating transformer 18. The electric charge storing circuit D includes a main storage capacitor 24, a current-restricting resistor 26 and an indi-cating lamp such as a neon lamp, and is connected as shown.
The trigger pulse generating circuit includes a triggering time constant circuit having a charging resistor 30 and a triggering capacitor 32, and a trigger transformer 36 having a primary winding 36a and a secondary winding 36b. The flash tube circuit F includes a flash tube 38 whose main current c~nducting electrodes 38a and 38b are connected to the main storage capacitor 24 and whose trigger electrode 38c is connected to the secondary winding 36b of the trigger trans-former 36.
In the electric flash device of Figure 1, when the power source switch 12 is c~losed, the voltage converter cir-cuit B activates an oscillating operation, and thereby the ; ::

2~7 high voltage is induced at the secondary winding 18b of the transformer 18. The boosted alternating current voltage is rectified by the rectifier circuit C, and thereafter electric charge is stored on the main storage capacitor 24, When the electric charge stored on the capacitor 24 reaches a predeter-mined value, tube 38 is triggered and the capacitor 24 dis-charges through the flash tube 38.
In this known electric flash device, when the main storage capacitor 24 discharges the electric flash, the vol-tage converter circuit B is adversely affected since part ofthe discharging current flows into the voltage converter cir-cuit through the transistor 20, This can put the transistor 20 in an ON condition when it should be in an OFF condition.
Further when the electric charge in the main storage capacitor discharges the voltage converter circuit B tries to recharge the main storage capacitor 24 in order to prepare for the next flash operation so long as the power source switch 12 is not turned OFF. Accordingly, if the power source switch 12 is left in its conductive condition for a long time interval, the voltage converter circuit B continues an activation so as to maintain the charging of the main storage capacitor 24, and therefore, the current from the battery 10 flows until the - power source switch 12 is opened, During this time the power supply consumes energy from the battery 10 without any useful result, As the battery ages its output voltage drops and a longer period of time is required for the main storage capacitor 24 to be charged to the necessary level for firing the flash tube 38.
Eventually the electric flash device becomes incapable of operating.
One known method of resolving the above described drawbacks, is embodied an electric flash device as shown in 26~

Figure 2 in which a timer circuit T is provided between a power source circuit A and a voltage converter circuit B in order to interrupt the current which flows from the power source circuit A to the voltage converter circuit B, if a flash tube 38 is not fired within a given time period. rrhe timer circuit T, however, includes a semiconductive element such as, for example, a power transistor Q which is serially connected to the power source circuit and the voltage conver-ter circuit B, and, as a result, the actual power input to the voltage converter circuit B is reduced due to the high and specific power loss of the power transistor Q. Accord-ingly, the device of Figure 2 does not make effective use of the battery 10.
rrhe electric flash device shown in Figure 3 com-prises a direct-current power source circuit A, a voltage converter circuit B for converting and boosting the voltage from the direct-current power source circuit A into alter-nating current voltage, a rectifier circuit C for rectifying the voltage from the boosted alternating current voltage, from the voltage converter circuit B, a charging circuit D
for storing electrical energy supplied in the form of dirèct current from the rectifier circuit C and for supplying the electric energy to a flash tube, a trigger signal generating circuit E for triggering the flash tube by applying a trigger-ing signal to a trigger electrode of the flash tube, and a flash tube circuit F which includes a flash tube.
rrhe direct current power source circuit A includes only a battery 10, and does not include a power source switch.
rrhe voltage converter circuit B comprises, substantially, an oscillator circuit OC, an oscillation time constant circuit TC and an oscillation starting circuit OS~ In more detail, 1~74267 the voltage converter circuit B includes a resistor 14 of which one terminal is directly connected to the positive terminal of the battery 10, a capacitor 16 of which one terminal is connected to other terminal of the resistor 14 to form the oscillation time constant circuit TC, an oscil-lator transformer 18, an oscillation switching element in the form of a high performance silicon transistor 40 and an oscillation starting switch in the form of a mechanical slide switch 42. The oscillator transformer 18 consists of a - 6a -~ 74Z~7 primary winding 18a, a secondary winding 18b and a third winding 18e. One terminal of the primary winding 18a is directly connected to the positive terminal of the battery 10, and other terminal of the primary winding 18a is con-neeted to a collector electrode in order to form the oscillator circuit 0C. One terminal of the secondary wind-ing 18b is connected to one terminal of the third winding 18e, and other terminal of the third winding 18e is conneeted to a juneture Jl of the resistor 14 and the eapaeitor 16. The switch 42 is provided and eonnected between a base electrode of the transistor 40 and a juncture J2 of the seeondary winding 18b and the third winding 18e of the oseillating transformer 18 in order to eonstitute the oscillation start-ing circuit OS.
The oscillating transistor 40 is of a high perform-ance NPN type, as is explained hereinabove, and has high internal resistance. Accordingly, the leakage current of the transistor 40 is extremely small and is almost zero in compari-son with that of the Gerumanium transistor. It is, therefore, unnecessary to provide the power source switeh in the power source eireuit A.
The rectifier cireuit C ineludes an eleetric valve in the form of a diode 22 of which the cathode is connected to the other terminal of the secondary winding 18b of the transformer 18, and the diode 22 is provided so as to be reverse direction with respect to the polarity of the battery 10. The eharging circuit D comprises a main storage capacitor 24, a current restricting resistor 26 and an indicating lamp in the form of a neon glow lamp 28 which is connected to the main storage capacitor 24 in parallel by way of the current ;~

Z~7 restricting resistor 26. One terminal of the capacitor 24 is connected to the anode of the diode 22, and other terminal of the capacitor 24 is connected to an emitter electrode of the transistor 40 and to the negative terminal of the battery 10.
The trigger pulse generating circuit E has a charg-ing resistor 30 of which one terminal is connected to the one terminal of the main storage capacitor 24, a triggering capacitor 32 of which one terminal is connected to the other terminal of the charging resistor 30 a trigger transformer 36 having a primary winding 36a and a secondary winding 36b and parallel connected synchronizing switch 34 which is arranged to be switched ON and OFF in synchronizing with a camera shutter and an open flash test button switch 44. The primary winding 36a of the transformer 36 is connected between the triggering capacitor 32 and the switch 34~ The flash tube circuit E comprises a gas-filled flash tube 38. The flash tube 38 is provided with a pair of main current conduct-ing electrodes 38aj 38b and-a trigger electrode 38c which is positioned adjacent but external to the flash tube 38. The trigger electrode 38c is connected to one terminal of the secondary winding 36b of the triggering transformer 36, and one main current conducting electrode 38a is connected to other terminal of the secondary winding 36b.
In operation, the switch 42 is manually actuated between its ON and OFF state. When the switch 42 is in its OFF state, electric charge is stored on the capacitor 16 from the battery 10 through the resistor 14 at the polarity as shown in Figure 3. By turning the switch 42 ON the base electrode of the transistor 40 is biased to ~ - 8 -, .~ i~

cause the transistor 40 to become conductive, because the electric charge of the capacitor 16 discharges through the third winding 18c of the transformer 18, the switch 42, the base electrode and the emitter electrode of the tran- -sistor 40. When the transistor 40 turns on, current flows through the primary winding 18a of the oscillating trans-former 18, the collector-emitter path of the transistor 40 from the battery 10, and, at the same time, the currént flows through the third winding 18c, the switch 42, the base-emitter electrodes of the transistor 40, the battery 10 and the resistor 14, and the electric charge is accumula-ted on the capacitor 16 and thereby the voltage converter-circuit B commences the oscillation and produces high alternating current voltage from the secondary winding 18b.
The high alternating current voltage is rectified by the diode 22 of the rectifier circuit C, to produce a high direct current voltage.
The main storage capacitor 24 is charged by the high D.C. voltage from the rectifier circuit C. When the main storage capacitor 24 is fully charged up to the pre-determined and suitable voltage, the neon glow lamp 28 lights indicating that the device is in readiness for the flash tube 38 to be fired. The flash tube 38 may then be fired by closing of the camera shutter switch 34 or the test button switch 44. It will be readily appreciated that this closing need only be momentary during the actuation of th~ camera shutter.
By closing the switch 34 or 44, the electric charge on the triggering capacitor 32 discharges through the switch 34 or 44 and the primary winding 36a. Then high voltage _ g _ pulse is induced at the secondary winding 36b of the trigger-ing transformer 36. The high voltage thus induced in the secondary winding 36b of the transformer 36 appears at the trigger electrode 38c of the flash tube 38 and ionizes a portion of the gas in the flash tube. The main storage capacitor 24 then discharges across the gas between the main current conducting electrodes, producing a brilliant flash of illumination, After the main storage capacitor 24 has been discharged, the power source circuit A builds up the charge again in preparation for the next flash, According to the device shown in Figure 3, since the high performance transistor 40 is employed in the oscillation starting circuit OS'of the voltage converter circuit B, the loss of the battery energy is prevented even when the switch 42 is left ON state for a long time period. Further, since the current which flows in the base circuit of the transistor 40 is small, voltage drop is eliminated even when a long lea~
wire is to be connected to the switch 42, It is, therefore, appreciated that good characteristics of the voltage converter circuit B are obtained, Furthermore, an advantage obtained is that contacts of the switch 42 need only be of small current carrying capacity because the current which flows in the base electrode of the transistor 40 is about 1/20 of that of the primary current of the oscillator transformer 1~.
Figure 4 is illustrative of other embodiments of the present invention, and the device shown comprises, similar to the device of Figure 3, a power source circuit A, a voltage con-verter circuit ~, a rectifier circuit C, a charging circuit D, a trigger pulse generating circuit E and a flash tube circuit F, The only difference from the device of Figure 3 is that ~.17~'~67 the voltage converter circuit B is actuated and controlled by the application of a voltage from the trigger pulse generating circuit E to an oscillation starting circuit OS, when a flash tube 38 is triggered.
More specifically, in the device of Figure 4, the oscillation starting circuit OS consists of a transistor 40, a first control transistor 46, a second control transistor 48, a biasing capacitor 50, a push-button switch 54 and a control switching element in the form of a silicon controlled semi-conductor element such as, for example, a thyristor 56.
Further, the trigger pulse generating circuit E includes a trigger transformer 36 having a primary winding 36a, a secondary winding 36b and a third winding 36c.
In the oscillation starting circuit OS, an emitter electrode of the first control transistor 46 is connected to a base electrode of the transistor 40, and a collector electrode of the transistor 46 is connected commonly to a third winding 18c of an oscillating transformer 18. An emitter electrode of the second control transistor 48 is connected to a base electrode of the first control transistor 46. Moreover, coupled to the biasing capacitor 50 is a bias-ing resistor 52, and the switch 54 is connected to the biasing capacitor 50 in parallel relationship. The thyristor 56 is also connected to the switch 54 in parallel relationship. In addition, a gate electrode of the thyristor 56 is connected to one terminal of the third winding 36c, and a cathode electrode of the thyristor 56 is connected to other terminal of the third winding of the trigger transformer 36.
In accordance with the electric flash device of Figure 4, when the switch 54 is opened, the capacitors 16 and 1~7~2~7 50 are charged by the current from the battery 10, at the polarity as is shown in the drawing. Accordingly, the second control transistor 48 is OFF state because it is biased to be non-conductive, and thereby the first control transistor 46 and the oscillating transistor 40 are also non-conductive state. In this case, current does not flow in the voltage converter circuit B because the leakage current is extremely small in the transistor 40. Under these conditions, when the switch 54 is closed, electric charge of the biasing capa-citor 50 is fed back to the battery 10 by way of the switch54 and the resistor 52, then the second control transistor 48 is biased toward conductive and turns on. By turning on the transistor 48, the first control transistor 46 becomes con-ductive and thence the transistor 40 also becomes 0~ state for the purpose of the commencement of the oscillation. When the oscillation is performed in the voltage converter circuit B, the biasing capacitor 50 is automatically charged from the battery 10 by way of the resistor 14 and the secondary wind-ing 18b. Since the charging time period of the biasing capacitor 50 is determined by the resistance value of the resistor 52, the duration of the oscillation can be adjusted.
When a voltage across the biasing capacitor 50 reaches a predetermined value, the transistors 46 and 48 are cut off and the transistor 40 is also turned off, and thereby the oscillation is automatically stopped. Under this con-dition, the leakage current is less than several micro-amperes, and a power source switch is unnecessary in the power source circuit A.
In the trigger pulse generating circuit E, when the triggering capacitor 32 discharges through the primary ~i .~,. . .

~7~26~

winding 36a of the triggering transformer 36, a high voltage pulse appears at the secondary winding 36b. The voltage pulse is about 3,000 volts, and this voltage pulse is applied to the trigger electrode 38c of the flash tube 38 in order to fire the flash tube 38. In this case, a voltage of several volts is induced across the third winding 36c. The induced voltage in the third winding 36c is applied to the thyristor 56 in the oscillation starting circuit OS as a gating signal of the thyristor 56, and the thyristor 56 is made conductive.
When the thyristor 56 turns on, the electric charge of the biasing capacitor 50 discharges through the thyristor 56, and the voltage across the capacitor 50 reduces to turn on the transistors 48, 46 and 40. Thence the oscillation of the converter B begins and repeats the operation as described hereinabove.
According to the electric` flash device of Figure 4, the thyristor 56 actuates upon receipt of a firing pulse from the third winding 36c of the transformer 36. In this case, the oscillation starting circuit OS is separated from the trigger pulse generating circuit E in D.C. voltage and current relationship. Mamely, it will be readlly apparent that the performance of the voltage converter circuit B is maintained stabilized because leakage current cannot flow from the trigger pulse generating circuit E to the biasing capacitor 50.
When the main storage capacitor 24 is fully charqed, if the electric flash device is left unused for a long period such as, for example, for half a day or a full day the electric charge on the capacitor 24 and the triggering capacitor 32 gradually decrease, and the thyristor 56 becomes non-conductive because the induced voltage at the third wind-ing 36c is lowered. Under these conditions, the voltage converter circuit can be operated by closing the switch 54.
Figure 5 shows a more effective electric flash device according to the present invention. In the embodi-ment of Figure 5, the device comprises also a power source circuit including a battery, a voltage converter circuit B, a rectifier circuit C, a charging circuit D, a trigger pulse generating circuit E and a flash tube circuit D. Particular-ly, the voltage converter circuit B is greatly improved byproviding a switch for stopping the oscillation and an indicating circuit for indicating an oscillation condition.
As is shown in Figure 5, an oscillation starting circuit OS is provided with an electric valve in the form of a diode 58 of which an anode is connected to a resistor 52 and a cathode electrode is connected to a negative terminal of a battery 10, an oscillation stopping switch 60 which is manually and momentary operated for stopping the activation of the voltage converter circuit B and a push-button switch 62 which is parallel connected to a thyristor 56. Further, an oscillation indicating circuit OI is provided in the output side of a transformer 18. The oscillation indicating circuit consists of an indicating lamp in the form of a neon glow lamp 66 which is connected between both terminals of the secondary winding 18 by way of a current-restricting resistor 64. The neon glow lamp 66 is employed in order to confirm whether the oscillation in the voltage converter circuit B
is normally performed or not.
The operation of the electric flash device, in accordance with Figure 5, will now be explained: When the switch 62 is closed for starting the oscillation, the electric ~ ~742~7 charge discharges through the switch 62, the resistor 52 and the diode 58 from the biasing capacitor 50, and all of the transistors 48, 46 and 40 are biased conductive. When the transistor 40 turns O~, the voltage converter circuit B performs the oscillating operation and at the same time a high A.C. voltage is induced at the secondary winding 18b of the oscillating transormer 18. The induced voltage at the secondary winding 18b causes the electric charge to be stored on the main storage capacitor 24 in the manner as described earlier and causes the neon lamp to glow, and thereby the normal operation may be confirmed.
When the main storage capacitor 24 is charged to the predetermined and desired voltage, the capacitor 24 discharges through the flash tube 38 by activating the trigger pulse generating circuit E. By the activation of the trigger pulse generating circuit E, the thyristor 56 maintains the ON state.
The voltage converter circuit B performs the con-tinuous oscillation as long as the thyristor 56 is maintained conductive. It is, accordingly possible to flash the flash tube 38 continuously. Under the continuous oscillating con-dition, if the switch 60 is closed, the second control transistor 48 becomes non-conductive, since the base electrode is biased negative from the negative electrode of the battery 10. When the transistor 48 is cut off, both of the transistors 46 and 40 are also turned OFF. Accordingly, the oscillation of the voltage converter circuit B is also stopped by closing the switch 60. The diode 58 acts to ensure proper charge storage in the biasing capacitor 50 and to prevent the leakage of current from the biasing capacitor 50, thereby enhancing the performance of the voltage converter 2~

circuit B. In the electric flash device of Figure 5, the operation of the voltage converter circuit B can also be stopped automatically after a given time period which is determined by the resistance value of the resistor 52, because the biasing capacitor 50 is gradually charged to the present voltage value.
Figure 6 illustrates another electric flash device according to the present invention. In accordance with the electric flash device of Figure 6, a transistor 68 is employed instead of a thyristor. Namely, an emitter electrode and a collector electrode of the transistor 68 are respectively connected to a switch 62 so that the transis-tor 68 is connected in parallel to the switch 62 between the emitter electrode and the collector electrode thereof.
Further, a capacitor 70 is connected between a base elec-trode and a juncture of a diode 22 and a main storage capacitor 24 by way of a resistor 72.
According to the device of Figure 6, the transistor 68 is, initially, non-conductive, because the negative voltage has applied to the base electrode of transistor 68, notwith-standing ON and OFF operations of the push-button switch 62.
Oscillation has therefore continued until the biasing capaci-tor becomes charged up to the predetermined voltage. The oscillation of the voltage converter circuit B ceases when the biasing capacitor 50 is charged to the predetermined voltage value. If the flash tube 38 is fired after or immediately before the oscillation is ceased, the electric charge accumulated on the capacitor 70 is discharged through the flash tube 38, thence the induced voltage appears across the capacitor 70 at the polarity as is shown in Figure 6, and thereby the transistor 68 is made conductive. By the con-~742t~7 duction of the transistor 68, the electric charge on the biasing capacitor 50 is discharged by way of the transistor 68 and thereafter and the oscillation is automatically started.
According to the device of Figure 6, the cost of the device is reduced because an inexpensive transistor is used instead of an expensive thyristor, and further, the size of the device is reduced because a triggering trans-former having only two windings may be used.

Claims (12)

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

1. An electric flash device comprising a direct current power source circuit for providing a direct current voltage, a flash tube circuit including a flash tube, a converter circuit for converting said direct current voltage of said direct current power source circuit to an alternating current voltage, a rectifier circuit for rectifying said alternating current voltage, a charging circuit for storing an electric charge and for supplying electrical energy to said flash tube, and a trigger pulse generating circuit for triggering said flash tube of the flash tube circuit, said converter circuit comprising an oscillating transformer connected to said direct current power source circuit for generating a high alternating current voltage and having a current flowing therein, an oscillator circuit for performing an oscillating operation including a switch element for switching said current which flows in said oscillating transformer and functioning as a high resistance resistor and of which leakage current is negligible when the oscillating operation of said oscillator circuit ceases, said switch element including a control electrode circuit, a switching means provided in said control electrode circuit of said switch element of said oscillator circuit for actuat-ing said switch element of said oscillator circuit, and means for starting oscillation of said oscillator circuit when said switching means operates.

2. An electric flash device as claimed in claim 1 wherein said switching means includes a base signal apply-ing means for actuating said oscillator switch element, and a manually operated mechanical switch connecting said base signal applying means to said means for starting oscillation of said oscillator circuit.

3. An electric flash device as claimed in claim 2 wherein said base signal applying means comprises an actuat-ing stabilizing capacitor, and wherein said oscillator transformer has a primary winding arranged for connection across the direct current power source, a secondary winding, and a third winding connected to a resistor element by way of said mechanical switch of said oscillation starting circuit.

4.- An electric flash device as claimed in claim 3 wherein said switch element is a silicon transistor having said high leakage resistance when it is non-conductive, in which a collector electrode is connected to the primary winding of said oscillator transformer and a base electrode is connected to the third winding by way of said manually operated mechanical switch.

5. An electric flash device as claimed in claim 1, and including means for actuating the oscillator circuit of said converter circuit when said trigger pulse generat-ing circuit or said flash tube actuates.

6. An electric flash device as claimed in claim 5 wherein said switching means includes a control switching element for controlling ON and OFF operations of said oscillation switch element of the oscillator circuit and a timer circuit connected to said control switching element.

7. An electric flash device as claimed in claim 6 wherein said means for actuating said oscillator circuit of the converter circuit includes means for resetting said timer circuit by means of a control signal detected when the flash tube is actuated or when a synchronous switch is made on,

8. An electric flash device as claimed in claim 7 wherein said means for actuating the oscillator circuit includes a mechanical switch connected in parallel to said switching means for resetting said timer circuit.

9. An electric flash device as claimed in claim 6 wherein said control switching element comprises means for stopping automatically the oscillating operation of the oscillator circuit after a predetermined time interval when said timer circuit is reset.

10. An electric flash device as claimed in claim 9 further comprising an oscillation indicating circuit including an indication lamp for indicating an oscillating operation of the oscillator circuit during a time interval from commencement to automatic stop of the oscillation of said oscillator circuit.

11. An electric flash device as claimed in claim 5 wherein said means for actuating the oscillator circuit comprises detecting means for obtaining a signal from a third winding of a trigger transformer when said trigger pulse generating circuit activates.

12. An electric flash device as claimed in claim 5 wherein said means for actuating the oscillator circuit comprises means for detecting a voltage change of a capacitor connected to the flash tube circuit.