GB2074800A

GB2074800A - Flash discharge lamp circuit

Info

Publication number: GB2074800A
Application number: GB8108339A
Authority: GB
Original assignee: Fuji Koeki Corp
Current assignee: Fuji Koeki Corp
Priority date: 1980-03-19
Filing date: 1981-03-17
Publication date: 1981-11-04
Also published as: DE3110589A1; IT8148051A0; IT1142353B; FR2478934A1; NL8101331A; JPS56130730A

Abstract

An electric flash device comprises a d.c. source A, voltage converting means B for converting the direct current source voltage to an alternating current voltage, a rectifier C for rectifying said alternating current voltage and producing a high direct current voltage, electrical energy storing means D including a main storage capacitor 20, trigger signal generating means E, and flash light F supplied from the main capacitor 20. The oscillator circuit of the voltage converter is controlled by oscillation starting means OS and oscillation stopping means ST. The duration of oscillation is controlled by oscillation timing control means, e.g. the time constant circuit 40, 41. <IMAGE>

Description

SPECIFICATION Electric flash device The present invention relates to a flash light generat ing apparatus, and more particularly to an electric flash device which generates a flash light by energiz ing a flash tube.

Flash apparatus has been widely used in various kinds of optical apparatus of which the operation requires flash light. Particularly, in the art of photo graphy, artificial light is used to illuminate an object 'to be photographed, one form of artificial light which is now widely used is the so-called flash tube.

It is common practice to obtain high intensity illumination for photographic purposes by discharg ing a charged capacitor through a gas-filled flash tube. A low voltage D.C. power source is generally employed together with suitable circuitry in order to obtain the relatively high D.C. voltage which is needed to charge the flash capacitor for each firing of the flash tube. Since an electric flash device of this type is generally portable, batteries are usually employed as a source of D. C. voltage. High D.C.

voltage is obtained from a battery through the use of a voltage converter. A converter includes a transfor mer for converting low A.C. voltage to high A.C.

voltage, and a rectifier for rectifying the high A.C.

voltage, the rectified voltage being then applied to the flash capacitor in order to charge it.

It can readily be understood that under ordinary circumstances when an electric flash device is being used, a substantial portion of the time during which the device is turned on may be stand-by time; that is, the time which elapses after the power supply has charged the capacitor to a suitable value and before the camera shutter is tripped, thereby discharging the capacitor through the flash tube. During this time the power supply consumes energy from the batter ies without producing any useful result. The energy loss may be significant, particularly when the device includes transformers. As the battery voltage drops a longer period is required for firing the flash tube, In addition, as the output voltage of the batteries decreases with age, the device becomes incapable of flashing the flash tube.

The primary object of the present invention is the provision of an improved battery operated electric flash device.

More specifically, an object of the present invention is to provide, at least in a preferred embodi ment, a high performance electric flash device which can adjust the duration of oscillation of the oscillator circuit which consumes a small amount of electrical energy by interrupting the current from the battery automatically after a predetermined time interval, and is efficient in use.

According to the present invention there is provided an electric flash device comprising a direct current power source circuit including a battery, a voltage converter circuit, including a switching oscil lator, for converting and boosting a direct current voltage of said direct current power source circuit, a rectifier circuit for rectifying an alternating current from said voltage converter, an electric charge storing circuit including a main storage capacitor which receives direct current from said rectifier circuit, a flash tube for converting electric charge stored in said main storage capacitor to flash light, a trigger signal generating circuit for triggering said flash tube, means for starting an oscillating operation of said oscillator by applying a control signal to a control electrode of a switching element of said oscillator, a timer for controlling the oscillating time of said oscillator, and means responsive to the timer to stop oscillation of the oscillator after a predetermined time interval from the commencement of oscillation of said oscillator, said switching element having high internal resistance and functioning as a high resistance when it is cut-off.

Some embodiments of the invention will now be described by way of example 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: Figure 1 is a detailed circuit diagram of an electric flash device according to the present invention; Figure 2 is a detailed circuit diagram of a modification of the electric flash device of Figure 1; Figure 3 is a detailed circuit diagram of a modification of the electric flash device of Figure 2; Figure 4 is a detailed circuit diagram of another electric flash device according to the present invention; Figure 5 is a detailed circuit diagram of a modification of the electric flash device of Figure 4; Figure 6 is a detailed circuit diagram of a modification of the electric flash device of Figure 5;; Figure 7 is a detailed circuit diagram of a modification of the electric flash device of Figure 6; Figure 8 is a detailed circuit diagram of another electric flash device according to the present invention; Figure 9 is a circuit diagram for illustrating the operation of an effective electric flash device; Figure 10 is another circuit diagram for illustrating the operation of an electric flash device; Figure 11 is a detailed circuit diagram of an electric flash device operating according to Figures 9 and 10; Figure 12 is a detailed circuit diagram of a modification of the electric flash device of Figure 11; Figure 13 is a detailed circuit diagram of a modification of the electric flash device of Figure 12; Figure 14 is a detailed circuit diagram of another electric flash device according to the present invention; and Figure 15 is a detailed circuit diagram of a modification of the electric flash device of Figure 14.

The electric flash device shown in Figure 1 comprises, substantially a direct current power source circuitAwhich includes a battery 10, a voltage converter circuit B for converting and boosting a voltage from the direct current power source circuit A two an alternating voltage, a rectifier C for the conversion of this voltage to a high direct voltage, an electric charge storing circuit D, a trigger signal generating circuit E and a flash light generating circuit F.

The electric flash device of the invention further comprises an oscillation control circuit G for con trolling operation of the voltage converter circuit B, and an indicating circuit H for indicating the oscillating operation of the voltage converter circuit B.

In more detail, the voltage converter circuit B comprises substantially, an oscillator circuit OC, a starting circuit OS for starting the oscillating operation of the oscillator circuit OC, an oscillation stopping circuit ST, and oscillation timing control means for controlling the timing of cessation of the oscillator operation. The oscillator circuit OC of the voltage converter circuit B comprises a transformer 11 having a primary winding 1 1a and a secondary winding 11 b, a switch in the form of an NPN type silicon transistor 12, and capacitor 13 connected between a base electrode and an emitter electrode of the transistor 12.The collector-emitter path of the transistor 12 is directly connected to a positive terminal of the battery by way of the primary winding 1 1a of the transformer 11, and the base electrode of the transistor 12 is connected to the secondary winding 11b of the transformer 11.The starting circuit OS comprises a manually operated mechanical switch 14 connected to the positive terminal of the battery 10, a diode 15 of which an anode is connected to the switch 14, and a diode 17 connected between the base of the transistor 12 and the cathode of the diode 15 by way of resistor 16.

The stopping circuit ST includes a transistor 18 of which the emitter-collector path is connected in parallel with the capacitor 13. The voltage converter circuit B is substantially a transformer-complex blocking oscillator. The oscillating transistor 12 has high internal resistance in its emitter-collector path when it is cut-off. The leakage current of the transistor 12 is extremely small, about 0.1 yA.

Accordingly, it is unnecessary to connect a power switch between the power source A and the voltage converter circuit B. The rectifier circuit C comprises a diode 19 of which the cathode is connected to the secondary winding 1 2b of the transformer 12.

The electric charge storing circuit D includes a main storage capacitor 20 connected between the anode of the diode 19 of the rectifier circuit C, a capacitor 22 connected in parallel with the main storage capacitor 20 by way of a protecting resistor 21 and an indicating lamp in the form of a neon glow lamp 23 connected to the capacitor 22.

The trigger signal generating circuit E has a charging resistor 24 of which one terminal is connected to the one terminal of the main storage capacitor 20, a triggering capacitor 25 of which one terminal is connected to the other terminal of the charging resistor 22, a protecting resistor 26 connected between other terminal of the triggering capacitor 25 and the negative terminal of the battery 10, a triggering transformer 27 having a primary winding 27a and a secondary winding 27b and a parallel connected synchronous switch 28 which is arranged to be switched ON and OFF in synchronism with a camera shutter (not shown in the drawing).

The flash light generating circuit F comprises a gas-filled flash tube 29 provided with a pair of main current conducting current electrodes 27a and 27b and a trigger electrode 27c which is positioned adjacent but external to the flash tube 29. The trigger electrode 27c is connected to a terminal of the secondary winding 27b.

An oscillation control circuit G is provided between a juncture J1 located between the anode electrode of the diode 19 of the rectifier circuit C and the main storage capacitor 20 of the electric charge storing circuit D and the voltage converter circuit B.

The oscillation controlling circuit G comprises switches in the form of transistors 30 and 33, resistors 31 and 34, and a capacitor 32. The oscilla; tion controlling circuit further includes an oscillation controlling capacitor 35 and a resistor 36. The transistor 30 is connected to the battery 10 by way of a parallel circuit of the resistor 31 and the capacitor 32. A collector-emitter path of the transistor 33 is connected in parallel with the switch 14, and a base electrode of the transistor 33 is connected to the emitter electrode of the transistor 30. The capacitor 35 is connected between the base electrode and a juncture J1 of the diode 19 and the main storage capacitor 20, by way of the resistor 36.The circuit H is connected in parallel with the secondary winding 11 b of the oscillating transformer 11 and comprises a series network of a resistor 37, a diode 38 and an indicating lamp in the form of a neon glow lamp 39.

One important feature of the present invention is that the device is provided with an oscillation timing control for controlling the oscillation timing of the voltage converter circuit B, in case the current from the direct current power source is automatically interrupted. The oscillation timing control means includes a timer circuit K provided in the voltage converter circuit B. The circuit K comprises an integrating capacitor 40, a variable resistor 41 which is used in order to adjust the time constant and connected in parallel to the capacitor 40, and a manually operated mechanical switch 42. The oscillation stopping circuit ST includes the resistor 43 and the transistor 18.

The operation of the flash device constructed above will be described as follows.

Stray capacitance in the transformer 11 is sufficlient to start the operation of the oscillator provided that switch 14 is cloed. Thereafter the capacitor 13 restricts the oscillator's output voltage. A feed-back voltage is applied from the secondary side of the oscillating transformer 11 to the base electrode of the transistor 12.

When the switch 14 is in its OFF state, the oscillator circuit OC does not initially activate. When switch 14 is closed, the base electrode of the transistor 12 is biased to cause the transistor 12 to become conductive, because current flows from the battery 10 to that base and to capacitor 13 by way of the switch 14, the diode 15, the resistor 16 and the diode 17. The voltage converter circuit B commences oscillation and produces high alternating voltage at the secondary winding 11 b. The high alternating voltage from the transformer 11 is rectified by the diode 19 of the rectifier circuit C, to produce a high direct voltage.

As each winding of the oscillating transformer 11 is wound such that the base current increases, the transistor 12 becomes conductive by means of positive feed-back from the transformer 11. The collector current almost linearly increases with re spect to time. Eventually the increment of the collector current becomes non-linear, and does not increase any longer. Further, the increment of the collector current of the transistor 12 is also stopped by the saturation of the core of the transformer 11.

Accordingly, the base current of the transistor 12 decreases swiftly. By the decrement of the collector current, the transistor 12 is cut-off.

When the transistor 12 is non-conductive, current flowing through the primary winding 11 a of the oscillating transformer 11 is swiftly interrupted and then the voltage stored on the oscillating capacitor 13 appears at the base electrode of the transistor 12 as a reverse voltage, due to the nature of the primary winding 1 Ia. In this case, the charging current on the capacitor 13 becomes the oscillating current because the transistor 12 is cut-off. Under these conditions, the current which flows in the primary winding 1 a of the oscillating transformer 11 is reversed at a half cycle of the oscillation of the charging current of the capacitor 13, and the voltage appears at the base electrode of the transistor 12.The transistor 12 is, therefore, biased again to be conductive and thereby the oscillating operation of the oscillator circuit OC is started again.

When the oscillation starting switch 14 is momen tary ON, current flows from the battery 10 to the integrating capacitor 40 of the timer circuit K by way of the diode 15 and to the oscillating capacitor 13 by way of the resistor 16 and the diode 17, and a positive potential appears at the base electrode of the transistor 12. The transistor 12 is made conduc tive by the positive potential of the base electrode.

The oscillating operation of the oscillator circuit OC is continued by virtue of the energy stored in the inductance of the transformer 11.

The switch 14 is not always required to be switched OFF immediately after its ON function finishes, but may be a switch which becomes OFF after predetermined time interval such as, for exam ple, three seconds.

The diode 38 of the indicating circuit H rectifies the alternating voltage of the secondary winding 11 b of the oscillating transformer 11. In this case, the average voltage applied to the neon glow lamp 39 is decreased by the rectifying operation of the diode .39, and consumed power is decreased. The feed back current is increased so that the activation time of the transistor 12 becomes long. The oscillation of the circuit OC may be confirmed by the illumination of the neon glow lamp 39 and the inactivation of the oscillator circuit OC may be confirmed when the neon glow lamp 39 does not illuminate.

The current due to the rectifying operation of the rectifier circuit flows in a current loop formed by the secondary winding 11 b of the oscillating transformer 11, the base-emitter path of the oscillating transistor 12, the main storage capacitor 20 and the diode 19, and electric charge is stored on the main storage capacitor 20 at a polarity as shown in Figure 1 and, at the same time, electric charge is accumulated on the oscillation control capacitor 35. Further, electric charge is stored on the trigger capacitor 25 due to the current which flows through a current loop consisting of the secondary winding 11 b, the baseemitter path of the transistor 12, the trigger capacitor 25, the charging resistor 24 and the diode 19.

Next, the OFF operation of the voltage converter circuit B will be described hereinbelow.

When the oscillation starting switch 14 is closed, the electric charge is stored to make the transistor 12 conductive, and thereby the oscillating operation of the oscillator circuit OC is performed in order to charge the main storage capacitor 20. When the oscillation starting switch 14 is reset to be OFF, the electric charge is stored on the integration capacitor 40 of the timer circuit K is discharged through the variable resistor 41. When the voltage of the integration capacitor 40 becomes approximately zero after an interval determined by the time constant of the integration capacitor 40 and the variable resistor 41, the transistor 18 becomes conductive. By the conduction of the transistor 18, the oscillating capacitor is short-circuited and the oscillating transistor is made non-conductive to stop the oscillating operation automatically.In this case, the operating time duration of the oscillator OC can be adjusted by adjusting variable resistor 41. Moreover, the oscillating operation of the oscillator circuit OC can be swiftly stopped by closing manually the switch 42, because the integration capacitor can discharge through switch 42.

When the main storage capacitor 20 of the electric charge storing circuit D is fully charged to the pre-determined value, the neon glow lamp 23 lights, indicating that the device is in readiness for the flash tube 29 to be fired. The flash tube 29 may then be fired by closing the switch 28. It will be readily appreciated that this closing need only be momentary during the actuation of the camera shutter. By the closing of the switch 28 the electric charge on the trigger capacitor 25 is discharged through the switch 28 and the primary winding 27a. A high voltage pulse is induced at the secondary winding 27b of the triggering transformer 27. The high voltage thus induced at the secondary winding 27b of the triggering transformer 27 appears at the trigger electrode 29c of the flash tube 29 and ionizes a portion of the gas in the flash tube 29.The main storage capacitor 20 then discharges across the gas between the main current conducting electrodes 29a and 29b, producing a brilliantflash of illumination.

After the main storage capacitor 20 has been discharged, the terminal voltage of the main storage capacitor 20 becomes low and thereby the electric charge stored on the oscillation control capacitor 35 discharges by way of the base-emitter path of the transistor 30, the resistor 31 and the main storage capacitor 20. By discharging of the oscillation control capacitor 35, a positive potential appears at the base electrode of the transistor 30 and thereby the transistor 30 becomes conductive. By the conduction of the transistor 30, a positive potential appears at the base electrode of the transistor 33 and thereby the transistor 33 becomes conductive. When the transistor 33 becomes conductive, the oscillating operation is started again as in the case of the closing operation of the oscillation starting switch 14.The transistor 12 is turned ON by the positive potential of its base electrode, and then the oscillating operation of the oscillator circuit OC is started again.

The operation of the oscillator circuit OC can be stopped, if desired, positively and swiftly by closing the oscillation stopping switch 42 of the timer circuit K. In more detail, the electric charge stored on the integration capacitor 40 is discharged through the switch 42 when the switch 42 is closed. By the discharge of the electric charge of the capacitor 40, the negative potential is applied to the base electrode of the transistor 18, and the transistor 18 is made conductive.

Additionally, the voltage converter circuit B can be started by closing the switch 14 and can be stopped automatically, without using the timer circuit K. The voltage converter circuit B can not control the time interval of the oscillation when the timer circuit K is not provided in the voltage converter circuit B.

Accordingly, a transistor having a high life is employed as the oscillating transistor 12 in orderto prevent the stopping of the oscillation of the oscillator circuit OC when the base current of the transistor 12 supplied from the transformer 11 is small. In the device of Figure 1, it is, however, necessary to provie the diode 17, the protecting resistor 16, the integration capacitor 40, the variable resistor 41, the resistor 43 and the transistor 18 in the voltage converter circuit B, because the oscillating time duration of the oscillator OC is set by the time constant of integration capacitor 40 and the variable resistor 41.

Further, the electric charge is supplied to the base electrode of the oscillating transistor 12 in order to continue the operation by way of the resistor 16 and the diode 17 when the electric charge is fully stored on the integration capacitor 40; it is unnecessary to provide the resistor 43 and the transistor 18 if a transistor of low life is used for the oscillating transistor 12.

According to the electric flash device of Figure 1, since the high performance transistor 12 is employed in the voltage converter circuit B, loss of the battery energy is slight even when the switch 14 is left ON state for a long time period.

Particularly, the electric flash device of Figure 1 has the advantage that the identified characteristics of the voltage converter circuit B can be obtained by adjusting the resistance value of the variable resistor 41 of the timer circuit K, and the power supply arrangement is applicable to all flash devices.

Another advantage of the device is that the oscillating time duration can be adjustable over the wide range by selecting the resistance value of the variable resistor 41.

Figure 2 shows a modification of the electric flash device of Figure 1. In the device shown in Figure 2, an oscillation controlling circuit G is provided: it comprises a thyristor 44, a diode 45 and a detection winding 46 for detecting activation of the trigger signal generating circuit E. In more detail, the oscillation controlling circuit G comprises the thyristor 44 connected in parallel to the oscillation starting switch 14 of the oscillation starting circuit OS, the diode 45 connected to a gate electrode of the thyristor 44, and the detection winding 46 provided in the triggering transformer 27 and connected to between the gate electrode and a cathode electrode of the thyristor 44 by way of the diode 44.

In operation, the oscillation controlling circuit G is activated by the operation of the trigger signal generating circuit E. When the synchronous switch 28 is closed, the electric charge stored on the trigger capacitor 25 is discharged through the switch 28 and the primary winding 27a of the triggering transformer 27, to produce a trigger signal at the secondary winding 27b and, at the same time, a trigger signal at the control winding 46. The latter trigger signal is supplied to the thyristor 44 as a gating signal, and.

thereby the thyristor 44 is made conductive. By the conduction of the thyristor 44, current is supplied from the battery 10 to charge the capacitor 40 and the oscillating capacitor 13. When the electric charge is stored on the integration capacitor 40 of the timer circuit K, the oscillating transistor 12 is made conductive and thereby the oscillating operation of the oscillator circuit OC is started again, after the flash tube circuit F operates.

Figure 3 is illustrative of a modification of the device of Figure 2. In the device of Figure 3, the voltage converter circuit B is controlled by the actuation of the flash tube circuit F. In the device of Figure 3, the trigger signal for the thyristor 44 is obtained from a transformer 47 which comprises a primary winding 47a connected in series with the flash tube 29 and a secondary winding 47b coupled to the gate and cathode of the thyristor 44.

Figure 4 is illustrative of other embodiment of the present invention, and the electric flash device comprises, similar to the devices of Figures 1 to 3, a direct current power source circuit A including a battery 10, a voltage converter circuit B for converting a direct current voltage of the battery 10 to an alternating current voltage, a rectifier circuit C for rectifying the alternating current voltage from the voltage converter circuit B to a direct current voltage, an electric charge storing circuit D for storing the electrical energy to be supplied to a flash tube. A trigger signal generating circuit E for triggering the load, an oscillation controlling circuit G, said flash device further includes an oscillation timing control means for controlling the oscillation time interval of the voltage converter circuit B.

In more detail, the voltage converter circuit B includes an oscillator circuit OC, an oscillation starting circuit OS and an oscillation stopping circuit ST. The oscillator circuit OC comprises a transformer 11 having a primary winding 11 a directly connected to the battery 10 of the direct current power source circuit A, a secondary winding 11 b, and an oscillating transistor 12. The oscillation starting circuit OS comprises a resistor 52 connected in parallel to the primary winding 1 1a of the transformer 11, an oscillation starting switch in the form of a manually operated switch 14, and an oscillation starting transistor 49 of which a collector-emitter path is connected between the battery 10 and an oscillation capacitor 13 of the oscillator circuit OC by way of a resistor 48. The circuits D, E and F are similar to those in Figure 1.

The oscillation controlling circuit C comprises a transistor 30 of which a collector-emitter path is connected to the battery 10 by way of a resistor 31 and a capacitor 32, and a transistor 33 of which a collector-emitter path is connected in parallel with the oscillation starting switch 14. A base electrode of the transistor 33 is connected to the emitter electrode by way of a resistor 34. An oscillation indicating circuit H comprises a series circuit of a protecting resistor 37 and a neon glow lamp 39 connected the secondary winding 11 b of the transformer 11 and a collector-emitter path of the oscillating transistor 12.

The timer circuit K comprises an integration capacitor 40 connected to the switch 14, a variable resistor 41, a Zener diode 50 and a variable resistor 43a connected between the integration capacitor 40 and a base electrode of the transistor 49.

In operation, when the switch 14 is closed, electric charge is stored on the integration capacitor 40 at a polarity as shown in the drawing. The transistor 49 becomes conductive and electric charge is stored on the oscillating capacitor 13. The oscillating transistor is made conductive, and then the oscillating operation is commenced. By the activation of the voltage converter circuit B, the electric charge is also stored on the main storage capacitor 20 and on the trigger capacitor 25. When the switch 14 of the oscillation starting circuit OS is reset to open, the electric charge stored on the integration capacitor 40 of the timer circuit K discharges through the variable resistor 41 after the predetermined time interval decided by the time constant of the capacitor 40 and the variable resistors 41 and 43a. By discharging of the capacitor 40, the transistor 49 becomes nonconductive.

When the switch 14 is turned ON during a predetermined time interval such as during 0.5 second, a reverse voltage is applied to the capacitor 40 and therefore the Zener diode is connected to the capacitor 40 in order to stabilize the charging voltage of the capacitor 40. Further, the oscillating operation of the oscillator circuit OC can be stopped by closing the switch 51, since the feed-back path to the capacitor 13 is by-passed. When the main storage capacitor 20 of the electric charge storing circuit D is fully charged, the flash tube 29 may be fired by closing the synchronous switch 28.After the main storage capacitor 20 has been discharged, a terminal voltage of the main storage capacitor 20 becomes low and thereby the electric charge of the control capacitor 35 discharges by way of the base-emitter path of the transistor 30, the resistor 31 and the main 'storage capacitor 20. A positive potential appears at the base electrode of the transistor 30 and thereby the transistors 30 and 33 become conductive, and thereafter the operation of the voltage converter circuit B is started again.

In accordance with the flash device of Figure 4, the capacitor 40 is swiftly charged when the switch 14 is ON, and voltage is applied to the base electrode of the transistor 12 of the oscillator circuit OC as long as there is voltage on the capacitor 40.

Figure 5 shows a modification of the flash device of Figure 4. In the flash device of Figure 5, the transformer 11 is provided with a control winding 11 c. The control winding 11 c is connected between the base of the transistor 12 and a positive terminal of the battery 10 by way of a resistor 48 and a collector-emitter path of a transistor 49.

According to the flash device of Figure 5, base current is supplied to the transistor 12 from the battery 10 of a direct current power source circuit A by way of the resistor 48 and the transistor49 and the control winding 1 1c of the transformer 11 to turn the transistor on. When the transistor 12 turns on, current flows through the primary winding 1 1a of the oscillating transformer 11, the collector-emitter path of the transistor 12 from the battery 10, and, at the same time, current flows through the control winding 11 c, the base-emitter path of the transistor 12 to the capacitor 13. The control winding 11 c serves to stabilize the oscillating operation of the oscillator circuit OC.In more detail, when the oscillator circuit OC activates its oscillating operation, the electromagnetic energy of the oscillating transformer 11 is supplied to the base of the transistor 12 from the control winding 11 c as feed-back current.

Figure 6 is illustrative of a further modification of the electric flash device of Figure 4. In the flash device of Figure 6, the oscillation starting circuit of a voltage converter circuit B comprises an oscillation starting switch 14 connected to a positive terminal of the battery 10, a diode 15 of which an anode is connected to the switch 14, a transistor 53, of which a collector-emitter path is connected to the battery 10 by way of a resistor 54, and a transistor 49. The base electrode of the transistor 53 is connected to the cathode of the diode 15, and the base of the transistor 49 is connected to the emitter of the transistor 53. The timer circuit K comprises a parallel connection of an integration capacitor 40, a variable resistor 41, a Zener diode 50 and a resetting switch 42.A diode 56 is connected between a base electrode of the oscillating transistor 12 and the timer circuit K to form the oscillation controlling circuit G.

In the voltage converter circuit B a resistor is connected in parellel with the primary winding, but may be omitted if the hfe of the transistor 12 is appropriate.

In accordance with the electric flash device of Figure 6, the oscillating operation of the voltage converter circuit continues as long as the signal is applied to the base electrode of the transistor 12. In this case, the oscillating operation is liable to cease because energy generated from the oscillating transformer 11 is consumed by the resistor 52, a resistor 37 and a neon glow lamp 39 of an oscillation indicating circuit H and thereby feed-back current to be supplied to the base electrode of the oscillating transistor 12 from the transformer 11 is decreased.

The oscillating transistor 12 has a high teak resistance, and leakage current is about 0.1 uAwhen the transistor 12 is nonconductive state. Accordingly, a power source switch to be connected to a battery 10 in series relationship is not always needed.

By making the switch 14 ON, current flows to the capacitor 40 of the timer circuit K by way of the switch 14 and the diode 15, and electric charge is stored on the capacitor 40 at a polarity as shown. By the charging voltage of the capacitor 40 the transistor 53 is made conductive. When the transistor 53 turns on, positive potential appears at the base electrode of the transistor 49 and thereby the transistor is turned on. When the transistor 49 becomes conductive, the current flows to the oscillating capacitor 13 by way of the resistor 48 and the collector electrode and the emitter electrode of the transistor 49 to charge the capacitor 13. When electric charge is stored on the capacitor, the oscillator circuit OC of the voltage converter circuit B commences the oscillation to charge electric charge on the main storage capacitor 20 and the trigger capacitor 25.

In the commencement of the activation of the voltage converter circuit B, a reverse voltage is applied to the capacitor 40 of the timer circuit K when the switch 14 is made ON at the predetermined time interval such as, for example, 0.5 seconds. The reverse voltage is, however, absorbed by the Zener diode 50, and the charging voltage of the capacitor 40 is made constant. When the switch 14 becomes OFF, the charge of the capacitor 40 is discharged through the variable resistors 41 and 43a, adjustment of which varies the time constant of the discharge. When the charging voltage of the capacitor 40 decreases below the actuating voltage of the transistor 53, the transistors 53,49 and 12 are made nonconductive and thereby the operation of the voltage converter circuit B is stopped.Accordingly, the activation of the voltage converter circuit B is continued during the predetermined time interval after the ON operation of the switch 14. The activation of the voltage converter circuit B can also be stopped immediately by means of the switch 42.

Figure 7 shows a further modification of the electric flash device of Figure 6, which incorporates the thyristor 44 connected as already described with reference to Figure 3.

Figure 8 shows another embodiment of the flash device of the present invention. It includes the circuits A, OC, B, C, D, E, F and H already described with reference to Figure 1.

The oscillation starting circuit OS in this embodiment comprises an oscillation starting switch 14, a diode 57 of which the anode is connected to the switch 14, and a resistor 58. The cathode of the diode 57 is connected to the base of the transistor 12. The oscillation stopping circuit ST comprises a transistor 53 of which a collector-emitter path is connected to the battery 10 by way of a resistor 54 and a transistor 18 of which an emitter-collector path is connected to the oscillating capacitor 13 and a base-emitter path of the transistor 12. The timer circuit K (like that of Figure 6) is connected between the oscillation starting switch 14 and the battery 10 by way of a diode 15.

In this embodiment, when oscillation commences, the integration capacitor 40 is charged such that the charging voltage becomes higher than the battery voltage such as for example, 3 volts, and the charging voltage of the capacitor 40 is maintained to be constant by means of the Zener diode 50. The voltage of the capacitor 40 is applied to the base electrode of the transistor 53, and the transistor 53 becomes conductive. When the transistor 53 becomes conductive, positive potential is applied to the base electrode of the transistor 18 to maintain the transistor 18 OFF state. Under these conditions, the electric charge stored on the integration capacitor 40 discharges through the variable resistors 41 and 43a when the switch 14 is reset to be OFF state.When the charging voltage becomes below the actuation voltage of the transistor 33, the transistor 53 becomes nonconductive and thereby the transistor 18 becomes conductive. The base-emitter path ofthetransis- tor 12 is short-circuited, and the feed-back currentsupplied from the secondary winding 11 b of the transformer 11 to the base electrode of the transistor 12 is by-passed by the transistor 18 and thereby the oscillating transistor 12 is made nonconductive.

In accordance with the electric flash device of Figure 8, once the oscillator circuit OC is activated by closing the switch 14, the feed-back voltage is supplied to the base circuitry of the oscillating transistor 12 from the secondary winding 11 b of the transformer 11 and, therefore, the oscillating operation can be maintained until the transistor 18 becomes conductive.

Figures 9 and 10 show principles of other embodi mentsoftheelectricflash device in accordance with the present invention.

In the device of Figure 9, a primary winding 11 a of an oscillating transformer 11 is connected to a battery 10, and a collector-emitter path of an oscillating transistor 12 is connected to the battery 10 by way of the primary winding 11 a of the transformer 11 and a power source switch SW. A base electrode of the transistor 12 is connected to the battery 10 by way of a resistor 62 and is connected to a secondary winding 11 b of the transformer 11. A Zener diode 60 is connected between the base electrode and an emitter electrode of the transistor 12.

According to the device of Figure 9, the Zener diode 60 is used instead of an oscillating capacitor.

Unlike a capacitor, the Zener diode 60 does not absorb the base voltage of the transistor 12 if that base voltage is below the Zener voltage. Accordingly, a relatively high base voltage can be applied to the transistor 12 and, at the same time, a reverse voltage to the transistor may be prevented by the Zener diode 60. A switching diode can be used instead of the Zener diode 60.

In the device of Figure 10, a manually operated switch 14 is connected between a battery 10 and a base electrode of the transistor 12 by way of a resistor 16. A manual switch 61 is connected in parallel with a Zener diode 60.

According to the device of Figure 10, the tranststor 12 is made conductive by closing the switch 14 and oscillating operation commences. A higher voltage can be applied to the base electrode of the transistor 12 than in device employing an oscillating capacitor.

The device of Figure 10 is convenient to use in a circuit arrangement in which is desired not to stop the oscillating operation.

Figure 11 illustrates another embodiment of the electric flash device of the present invention. The device of Figure 11 employs the arrangements of Figures 9 and 10. It is generally similar, so far as the secondary and load circuits are concerned, to that shown in Figure 1. However, a Zener diode 60 is connected to the secondary winding 11 band is connected between the base and emitter of the transistor 12. The oscillation starting circuit OS comprises the switch 14 connected to the battery 10, a resistor 16 connected to the switch 14 and a diode 17 connected between the resistor 16 and the base electrode of the transistor 12. The oscillation stopping circuit ST comprises a diode 15 connected to the switch 14, and a transistor 18 of which an emitter-collector path is connected to a base-emitter path of the transistor 12.The timer circuit K comprises a series connection of an integration capacitor 40, a variable resistor 41 and a resistor 66, the last two components being in parallel with the switch 42. The oscillation controlling circuit G comprises transistors 63 and 64, and a resistor 65.

In the electric flash device of Figure 11, the oscillator circuit OC does not begin oscillating when the switch 14 is OFF, because a sufficient signal is not applied to the base electrode of the transistor 12.

When the switch 14 is ON, a positive potential appears at the base electrode of the transistor 12, and thereby the transistor 12 becomes conductive to start the oscillating operation. The oscillating transistor 12 is a silicon transistor of which the leakage current is about 0.1 UA, and, therefore, a power source switch is omitted. The electric charge is stored on the integration capacitor 40 at a polarity as shown in the drawing. Both of the transistors 63 and 64 are initially nonconductive. The transistor 18 is also initially nonconductive. In the base circuit of the oscillating transistor 12, a relatively high voltage is maintained by the aid of the Zener diode 60 to maintain the oscillating operation of the oscillator circuit OC.

In the timer circuit K, current flows through the capacitor 40, the variable resistor 41 and the resistor 66. When the charging voltage of the capacitor 40 attains to a given value, both of the transistors 63 and 64 become nonconductive. Negative potential is applied to the base electrode of the transducer 18, and thence the transistor 18 becomes conductive, so that the base-emitter path of transistor 12 is shortcircuited by the transistor 18, the oscillating operation of the oscillator circuit OC being thereby stopped.

Figure 12 illustrates a modification of the electric flash device of Figure 11. In the device shown in Figure 12, the oscillating starting circuit OS of a voltage converter circuit B includes, instead of the resistor 16 and diode 17, a resistor 55 and a diode 67 connected between the base of the transistor 12 and the base of the transistor 18.

According to the electric flash device of Figure 12, actuation of the starting circuit OS and the stopping circuit ST is governed by the actuation of the oscillation starting switch 14. In more detail, the capacitor 40 is discharged, by way of the switch 14, the diode 15, the variable resistor 41 and resistor 66, and then the charging voltage of the capacitor 40 becomes zero. When the voltage of the capacitor 40 becomes zero, both of transistors 63 and 64 become conductive and positive potential appears at a resistor 65. The positive potential of the resistor 65 is applied to both of the base electrodes of the transistors 12 and 18. Under these conditions, the transistor 12 becomes conductive and, at the same time, the transistor 18 becomes nonconductive.

When the transistor 12 turns on, the oscillating operation of the oscillator circuit is commenced and is continued by the aid of the Zener diode 60. When the switch 14 is reset to be OFF, electric charge is fully stored again on the capacitor 40 after a given time interval, and thereby the transistors 63 and 64 become OFF, so that negative potential is applied to the base electrodes of the transistors 12 and 18: the transistor 18 becomes conductive and thereby the transistor 12 is made nonconductive. Accordingly, the transistors 12 and 18 are interlocked.

Figure 13 shows a modification of the electric flash device of Figure 12. It includes means for indicating oscillation in an oscillator circuit OC. The means comprises circuit Lwhich is provided between the voltage converter circuit B and the circuit D. The oscillation indicating circuit L comprises a capacitor 69 connected to the circuit D by way of a resistor 68, a transistor 70 of which an emitter electrode is connected to a battery 10 and an oscillating transformer 11, an indicating lamp in the form of a light emitting diode 74 which is connected to a collector electrode of the transistor 70, and a transistor 75 of which the collector is connected to the diode 74 and of which the emitter is connected to the battery 10.

The base of the transistor 75 is connected to the starting circuit OS and the stopping circuit ST by way of a resistor 76. The parallel connected capacitor 71 and resistor 72 are connected between the emitter electrode and the base electrode of the transistor 70.

The oscillation starting switch 14 has stationary contacts 14a and 14b and a movable contact 14c and the other parts of the device are similar to those of the device of Figure 12.

The transistor 75 of the oscillating indicating circuit L is made conductive when the switch 14 is ON state. When the electric charge is fully stored on the main capacitor 20, electric charge is stored on the capacitor 69 circuit L at the polarity as shown, and thereby the transistor 70 becomes conductive.

When the transistor 70 is ON, current flows from the battery 10 by way of the transistor 70, the resistor 73, the light emitting diode 74 and the transistor 75. The diode 74 lights, indicating that the voltage converter circuit is active and that the main storage capacitor 20 has been fully charged. In this case, the light emitting diode 74 lights for as long as positive potential is applied to the base electrode of the transistor 74, that is, during the predetermined time interval such as three seconds fixed by the time constant of the capacitor 40 and the resistor 77.

Figure 14 is illustrative of another embodiment of the present invention. In this embodiment the oscillation starting circuit OS includes the switch 14, a transistor 49 and a resistor 48, connected as shown.

The oscillation stopping circuit ST includes a diode 56 connected between the base of transistor 12 and the timer circuit K.

In the device of Figure 14, the oscillator circuit OC is designed such that oscillating is stopped when a control signal is not supplied to a control electrode of the switch element and such that the oscillation is stopped after a given time interval. In more detail, the transistor 12 is initially nonconductive and the electric charge is stored on the capacitor 40. When the switch 14 is made ON, the electric charge of the capacitor 40 discharges, and the voltage of the capacitor 40 becomes zero and thereby both of transistors 63 and 64 become conductive. By the conduction of the transistor 64, positive potential appears at the base electrode of the transistor 49; the transistor 49 turns ON and capacitor 13 is charged by the current flowing from the battery 10 by way of the resistor 48 and the transistor 49, and the transistor 12 is made conductive to start the oscillating operation.

The transistor 12 maintains its ON state and the oscillation is continued, even when the flash tube 29 has fired. When the switch 14 is reset OFF, the voltage of the capacitor 40 gradually increases to the predetermined value after some time interval; both of the transistors 63 and 64 become nonconductive, and the transistor 49 is made nonconductive by the application of the negative potential to the base electrode. When the transistor 49 becomes nonconductive, the transistor 12 becomes nonconductive and thereby the oscillation ceases. Although the transistor 63 and 64 becomes nonconductive when the switch 42 is ON, since the voltage of the capacitor 40 becomes about the same as that of the battery 10, the diode 56 is connected between the base electrode of the transistor 12 and the timer circuit K in order to stop completely the oscillating operation of the oscillator circuit OC.

Figure 15 is a modification of the device of Figure 14. In the device of Figure 15, a transistor 80 is connected in parallel with the transistor 12, and a base electrode of the transistor 80 is connected to an emitter of the transistor 64 across a resistor 81. A diode 82 is connected between a resistor 55 and the emitter electrode of the transistor 64. The electric flash device of Figure 15 operates more securely than the device of Figure 14.

In the above described embodiments, a digital timer can be employed instead of the timer circuit which is comprised by the integration capacitor 40 and the associated variable resistor. In this case, a digital timing signal can be produced by a multivibrator circuit or an oscillator which is comprised by a capacitor element and a resistor element, and the switch element 14 of the oscillator circuit OC can be made nonconductive by its short-circuiting after the accummulation of a predetermined digital count.

The oscillation timing control circuit is simplified in construction and is easy to manufacture, since the integration capacitor and the variable resistor is only used in the timer circuit. Since the voltage converter circuit stops the oscillation after the given time interval from the commencement of the operation, undue power loss from the battery can be prevented and a good performance flash device can be obtained by eliminating contact resistance because a mechanical slide switch is not used.

Although NPN type transistors are used in the above embodiments, PN P type transistors can be used instead according mutatis mutandis.

Claims

1. An electric flash device comprising a direct current power source circuit including a battery, a voltage converter circuit, including a switching oscillator, for converting and boosting a direct current voltage of said direct current power source circuit, a rectifier circuit for rectifying an alternating current from said voltage converter, an electric charge storing circuit including a main storage capacitor - which receives direct current from said rectifier circuit, a flash tube for converting electric charge stored in said main storage capacitor to flash light a trigger signal generating circuit for triggering said flash tube, means for starting an oscillating operation of said oscillator by applying a control signal to a control electrode of a switching element of said oscillator, a timer for controlling the oscillating time of said oscillator, and means responsive to the timer to stop oscillation of the oscillator after a predetermined time interval from the commencement of oscillation of said oscillator, said switching element having high internal resistance and functioning as a high resistance when it is cut-off.

2. An electric flash device according to claim 1 further comprising means responsive to operation of the flash tube for causing an oscillating operation of said oscillator to start.

3. An electric flash device as claimed in claim 1 or claim 2, wherein said oscillator is a transformercoupled oscillator of which the coupling transformer has a primary winding connected in series with the battery and a main current path of the switching element, circuit including an integration capacitor connected to a switching element for controlling said oscillation switch element.

4. An electric flash device as claimed in claim 3, further comprising an oscillating capacitor for stabilizing the oscillations of operation of the oscillator circuit and connected to said switching element, the oscillation stopping means comprising a switch for short-circuiting the oscillating capacitor.

5. An electric flash device as claimed in claim 2 or claim 2 taken with claim 3 or claim 4 wherein said means responsive to operation of the flash tube comprises a controlling capacitor connected to the main storage capacitor of said electric charge storing circuit, a second switching element connected to said controlling capacitor, and a switch which activates said oscillator in accordance with the switching of the second switching element.

6. An electric flash device as claimed in claim'2 or claim 2 taken with claim 3 or claim 4 in which the means responsive to operation of the flash tube comprises a thyristor connected between the battery and the said control electrode and a detecting winding provided on a triggering transformer in the trigger signal generating circuit.

7. An electric flash device as claimed in claim 2 or claim 2 taken with claim 3 or claim 4 wherein said means responsive to operation of the flash tube comprises a thyristor connected between the battery and the said control electrode and a transformer coupling including a winding in series with the flash tube.

8. An electric flahs device as claimed in any foregoing claim in which the means for starting the oscillating operation means first switch connected to said control electrode.

9. An electric flash device as claimed in claim 3 or any of claims 4 to 8 wherein said transformer of the oscillator circuit comprises a winding by way of which said first switch is connected to the battery.

10. An electric flash device as claimed in any of 'claims 1 to 7 wherein the means for starting comprises a variable resistor connected to the battery by way of a diode, a first switch of which a control electrode is connected to said variable resistor, and a second switch controlled by the first and connected between the battery and the control electrode of said switching element.

11. An electric flash device as claimed in any foregoing claim wherein timer is connected to the battery by way of the oscillation starting means and includes a parallel connection of a variable resistor an integrating capacitor and a Zener diode.

12. An electric flash device as claimed in claim 1 wherein a switch is connected between said control electrode and said timer.

13. An electric flash device as claimed in claim 1 wherein a diode is connected between said control electrode and said timer.

14. An electric flash device as claimed in claim 1 further comprising a transistor of which a collector emitter path is connected to an oscillation starting switch of the oscillation starting means, and a oscillation controlling capacitor connected between a base electrode of said transistor and the main storage capacitor.

15. An electric flash device as claimed in claim 1 wherein a thyristor is connected in parallel with an oscillation starting switch, and a detecting winding provided on a triggering transformer of said trigger signal generating circuit is connected to a gate electrode of said thyristor by way of a diode.

16. An electric flash device as claimed in any foregoing claim wherein for stopping the oscillation means are provided to short-circuit said switching element when an integration capacitor is charged.

17. An electric flash device as claimed in any foregoing claim, in which the oscillator includes a feedback connection to the control electrode of a transistor constituting the switching element of the oscillator.

18. An electric flash device as claimed in claim 17 wherein an oscillating indicating circuit including a 'diode and an indicating lamp is provided on the output side of said voltage converter.

19. An electric flash device as claimed in claim 1 wherein the oscillator is a transformer-coupled blocking oscillator and for maintaining oscillation thereof a Zener diode is conjointly connected to a secondary winding of the transformer and to the control electrode.

20. An electric flash device as claimed in claim 1 wherein the oscillator is a transformer coupled blocking oscillator and for stopping the oscillation a switch is connected in parallel with said switching element in series with a primary winding of the transformer.

21. An electric flash device as claimed in claim 1 wherein said timer comprises a series connected integration capacitor and variable resistor.

22. An electric flash device as claimed in claim 3 wherein an oscillating capacitor is connected to a secondary winding of said transformer and series circuit, connected in parallel with a series circuit consisting of the secondary winding and the oscillating capacitor, comprises a resistor, an indicating lamp and a diode for preventing reverse current through said indicating lamp.

23. An electric flash device as claimed in claim 1 wherein for stopping the oscillation the potential at the control electrode is fed to the timer.

24. An electric flash device as claimed in claim 1 wherein for stopping the oscillation there is provided a switching device made nonconductive when an oscillation starting switch is closed and made conductive when said starting switch is opened.

25. An electric flash device as claimed in claim 24 wherein said switching device is connected in parallel with said switching element.

26. An electric flash device as claimed in claim 25 wherein an oscillation starting circuit includes a switch arranged to be connected between the battery and the said control electrode of said switching element and to be made conductive when said switching element is made ON.

27. An electric flash device as claimed in claim 1 the timer comprises a digital signal generating circuit.

28. An electric flash device substantially as hereinbefore described with reference to any of Figures 1 to 8 or 10 to 15 of the accompanying drawings.