GB2088157A

GB2088157A - Electric Flash Device

Info

Publication number: GB2088157A
Application number: GB8130862A
Authority: GB
Original assignee: Fuji Koeki Corp
Current assignee: Fuji Koeki Corp
Priority date: 1980-10-15
Filing date: 1981-10-13
Publication date: 1982-06-03
Also published as: FR2492211B3; JPS5767918A; FR2492211A1; NL8104680A; DE3140828A1

Abstract

An electric flash device comprises a voltage converter circuit B for converting a direct current voltage to an alternating current voltage, a rectifier C, storage capacitor 22, a flash tube circuit F and trigger signal generating circuit E for triggering the flash tube. The electric flash device further comprises oscillation stop timing control means I and trigger signal control means J. According to the invention power loss is avoided, by stopping oscillation after a set time, and erroneous operation of the flash tube is avoided by the trigger signal control means. <IMAGE>

Description

SPECIFICATION Electric Flash Device The present invention relates to a flash light generating apparatus, and more particularly to an electric flash device which generating a flash light by triggering a flash tube.

Background of the Invention 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, 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 in electric flash devices to obtain high intensity illumination for photographic purposes by discharging 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 the electric flash device of this type is generally portable, batteries are usually employed as the source of low D.C. voltage. High D.C. voltage is obtained from the batteries through the use of a voltage converter. A converter includes a transformer 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 standby time; that is, time which elapse after 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 batteries without producing any useful result. The energy loss may be significant, particularly when the device includes transformers. As 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 flashing the flash tube.

In thus known electric flash device, when the main storage capacitor discharges the electric flash, the voltage converter circuit is adversely affected since a part of the discharging current flows into the voltage converter circuit through the transistor. Further, when the electric charge in the main storage capacitor discharges, the voltage converter circuit tries to recharge the main storage capacitor in order to prepare for the next flash operation so long as the power source switch is not turned OFF. Accordingly, if the power source switch is left in its conductive condition for a long time interval, the voltage converter circuit continues an activation so as to maintain the charging of the main storage capacitor, and therefore, the current from the battery flows until the power source switch is closed.

During this time the power supply consumes energy from the battery without any useful result.

Eventually the electric flash device becomes incapable of operation.

One method of resolving the above described drawbacks, is embodied an electric flash device in which means for stopping an oscillating operation of an oscillator circuit after a predetermined time interval when the flash tube flashes, so as to prevent the consuming of the battery. In this electric flash device, there are further disadvantages that the electric power is automatically supplied to the device after the power source is made OFF by using a manually operated switch. That is to say, when the power source is automatically made ON, the electric charge is stored on a main storage capacitor, and thereby the flash device performs the flashing operation in synchronizing with a camera shutter, in case that the flash device is set to a camera.

Object of the Invention The primary object of the present invention is the provision of an improved electric flash device which overcomes above drawbacks, namely, an electric flash device in which high performance is obtained and the cost is reduced.

More specifically, an object of the present invention is to provide a high performance electric flash device which consumes a small amount of electrical energy by interrupting forcedly from a battery, and is easy to operate, and is highly efficient in use.

Summary of the Invention These objects and related advantages of the present invention are attained from an improved electric flash device wherein the voltage from a power source of relatively low battery voltage is converted to a relatively high unidirectional output voltage to be supplied to a main storage capacitor. The battery voltage is applied to a transistor oscillator circuit. A suitable bias voltage is applied to a control electrode of the transistor of the oscillator circuit through a switch, to cause the oscillator circuit to oscillate.

The output of the oscillator is rectified and applied as a unidirectional output voltage across the direct current load. The voltage across the load may be applied to a utilization circuit, such as a photoflash lamp, and the like.

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 for converting a direct current voltage from the direct current power source circuit to an alternating current voltage, a charging circuit for storing electric charge and for supplying electrical energy to a flash tube of a flash tube circuit, a trigger signal generating circuit for triggering said flash tube of the flash tube circuit, and timing control means for controlling the operation timing of the voltage converter circuit and trigger signal control circuit for stopping the operation of said trigger signal generating circuit.

Brief Description of the Drawing An embodiment will now be described by way of an example with reference to the accompanying drawing, and wherein: Figure is a detailed circuit diagram of an electric flash device according to the present invention.

Description of the Preferred Embodiment of the Invention An electric flash device shown in Figure comprises 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 alternating current voltage, a rectifier circuit C for rectifying the boosted alternating current voltage from the voltage converter circuit B, a charging circuit D for storing electrical energy supplied in the form of direct-current from the rectifier circuit C and for supplying the electric energy to a load circuit F which includes a flash tube, a trigger signal generating circuit E for triggering the flash tube by applying a trigger signal to a trigger electrode of the flash tube, a load circuit in the form of a flash tube circuit including a flash tube, a signal adjusting circuit G for absorbing the surge voltage and an oscillation control circuit H for making the oscillating operation of the oscillator circuit start.

The electric flash device of the present invention further includes timing control means for controlling the operation timing of said voltage converter circuit B and trigger signal control circuit J for controlling and stopping the operation of said trigger signal generating circuit E.

The power source circuit A includes a battery 1 0. The voltage converter circuit comprises, substantially, an oscillator circuit OC. In more detail, the voltage converter circuit B includes an oscillating transformer 11 having at least two windings such as a primary winding 11 a, and a secondary winding 11 b and a third winding 11 c, an oscillation switching elements in the form of high performance silicon transistors 12 and 13 which are connected in parallel relationship, a resistor 14 for stabilizing the oscillation of the oscillator circuit OC, a capacitor 1 5 for stabilizing the oscillation and a switching control member for controlling the operation of the switching elements in the form of an oscillating transistors 12 and 13.

One terminal of the primary winding 11 a is directly connected to a positive terminal of the battery 10, and other terminal of the primary winding 1 a is connected to collector electrodes of the oscillating transistors 12 and 13 in order to form the oscillator circuit OC. The capacitor 1 5 is connected in parallel with the NPN type transistors 12 and 13. Collector electrodes of control transistors 1 6 and 1 7 are connected to the third winding 11 c of the oscillating transformer 11. The third winding 11 c is connected to the positive terminal of the battery 10 by way of the resistor 14. An emitter electrode of the control transistor 1 6 is connected to a base electrode of the control transistor 1 7.An emitter electrode of the transistor 17 is connected to base electrodes of the transistors 12 and 13.

The voltage converter circuit B is substantially a voltage feedback type oscillator circuit. The oscillating transistors 12 and 13 are of a high performance NPN type, as is explained hereinabove and has high internal resistance when it is cut-off state. Accordingly, the leakage current of the transistors 12 and 13 are extremely small and is almost zero in comparison with that of the Germanium transistor. It is, therefore, unnecessary to provide the power source switch in the power source circuit A. The leakage current are small such as, for example, in the order of 0.1-0.2 ,uA or nearly zero.

The rectifier circuit C includes an electric valve in the form of a diode 21 of which a cathode electrode is connected to other terminal of the secondary winding 11 b of the oscillating transformer 11, and the diode 21 is provided so as to be reverse direction with respect to the polarity of the battery 10. The charging circuit D comprises a main storage capacitor 22, a current restricting resistor 23, and parallel connected an indicating lamp in the form of a neon glow lamp 24 and a capacitor 25. The neon glow lamp 24 and the capacitor 24 are connected to the main storage capacitor 22 in parallel relationship by way of the resistor 23.

The trigger pulse generating circuit E has a charging resistor 26 of which one terminal is connected to the one terminal of the main storage capacitor 22. a trigger capacitor 27 of which one terminal is connected to other terminal of the charging resistor 23, a triggering transformer 28 having a primary winding 28a'and a secondary winding 28b and parallelly connected synchronizing switch 29 which is arranged to be switched ON and OFF in synchronizing with a camera and a test button switch 30. The primary winding 28a of the triggering transformer 28 is connected between the trigger capacitor 27 and the switches 29 and 30. The flash tube circuit F includes a gas-filled flash tube 42. The flash tube 42 is provided with a pair of main current conducting electrodes 42a, 42b and a trigger electrode 42C which is positioned adjacent but external to the flash tube 42. The trigger electrode 42C is connected to one terminal of the secondary winding 28b of the triggering transformer 28, and one main current conducting electrode 42a is connected to other terminal of the secondary winding 28b.

The signal adjusting circuit G comprises a capacitor 1 8 which is connected to the secondary winding 1 8b of the oscillating transformer 11 in parallel, a current restricting resistor 1 9 and an indicating lamp in the form of a neon glow lamp 20 which is connected to the capacitor 1 8 in parallel by way of the current restricting resistor 18.

The oscillation control circuit H comprises a control transistor 34, an oscillation starting capacitor 33 and a resistor 32. A collector-emitter path of the transistor 34 is connected between the collector electrode and the base electrode of the transistor 1 6. One terminal of the oscillation starting capacitor 33 is connected to a base electrode of the transistor 34, and other terminal of the capacitor 33 is connected to a juncture between the diode 21 and the main storage capacitor 22 by way of the charging resistor 32 to form the oscillation control circuit H.

The oscillation timing control circuit I comprises an oscillation start resetting circuit and an oscillation stop timing adjusting circuit. The oscillation stop timing adjusting circuit comprises a first changeover switch 35, a biasing capacitor 36, a resistor 38, a variable resistor 39 and a diode 40. The oscillation start resetting circuit comprises the first changeover switch 35, the resistor 37. The oscillation stop timing adjusting circuit comprises the first changeover switch 35, a timer circuit which includes the first changeover switch 35, the biasing capacitor 36, a resistor 38, the variable resistor 39, and the diode 40.

The changeover switch 35 has a first stationary contact 35a connected to the third winding 11 c, a second stationary contact 35b and a movable contact 35c. The biasing capacitor 36 is connected between the movable contact 35c of the first changeover switch 35 and the base electrode of the transistor 1 6. The resistor 37 is connected between the second stationary contact 35b and the base electrode of the transistor 1 6.

The series connected the resistor 38, the variable resistor 39 and the diode 40 are connected to the between the biasing capacitor 36 and the negative terminal of the battery 10. The trigger signal controlling circuit J includes a second changeover switch 41 which is actuated simultaneously with the first changeover switch 35 and having a first stationary contact 41 a which is connected to the positive terminal of the battery 10, a second stationary contact 41 b which is connected to the charging resistor 26 and the trigger capacitor 27, and a movable contact 41 c which is parallelly connected to the synchronizing switch 28 and the test button switch 30 of the trigger signal generating circuit E and together with the parallelly connected the neon glow lamp 24 and the capacitor 25 of the electric charge storing circuit D.

In operation, the first changeover switch 35 is manually actuated together with and simultaneously with the second changeover switch 41 by its ON and OFF starter. When the first changeover switch 35 is in its OFF state, the oscillator circuit OC does not initially activated its oscillating operation, because the electric charge is not stored on the biasing capacitor 36 and thereby the transistors 1 6 and 1 7 is nonconductive. By turning the changeover switch 35 and 41 ON, the electric charge is stored on the biasing capacitor 36 from the battery 10 of the power source circuit A.By the charging voltage of the biasing capacitor 36, the transistor 1 6 is biased to cause the transistor 1 6 to become conductive, because the voltage is applied such that the potential of the base electrode becomes higher than that of the emitter electrode of the transistor 1 6. By the conduction of the transistor 16, the base electrodes of the transistors 12 and 1 3 are biased to cause the transistors 12 and 13 to become conductive, because the base current is supplied to the transistors 12 and 13 from the battery of the power source circuit A by way of the resistor 14, the third winding 11 c of the oscillating transformer 11 and the transistor 1 7.

When the oscillating transistors 12 and 13 turn on, current flows through the primary winding 11 a of the oscillating transformer 11 from the battery 10 to perform the oscillating operation, and, at the same time, the current flows from the third winding 11 c to the biasing capacitor 36.

When the biasing capacitor 36 are gradually charged at the predetermined voltage, at the polarity as is shown in the drawing, the transistor 1 6 is OFF state because it is biased to be nonconductive, and thereby the transistor 1 7 are also nonconductive state. In this case, current does not flow in the voltage converter circuit B because the leakage current is extremely small in the oscillating transistors 12 and 13.

In this case, the oscillating voltage due to the stray capacity of the windings of the transformer 11 or the capacitor 15 is also employed to make the oscillating transistors 12 and 13 ON and OFF operation. The high alternating current voltage is rectified by the diode 21 of the rectifier circuit C, to produce a high direct current voltage.

As each winding of the oscillating transformer 11 is wound so that the current increases, the transistors 12 and 13 becomes conductive by means of positive feed-back operation of the transformer 11.

The surge absorbing capacitor 18 of the signal adjusting circuit G makes a reverse voltage at the secondary winding 11 b small and compensates a signal by absorbing the surge voltage. The voltage induced on the capacitor 1 8 is applied to the neon glow lamp 20 through the resistor 19, and thereby the neon glow lamp 20 illuminates so that the oscillation of the oscillator circuit OC may be confirmed by the illumination of the neon glow lamp 20. The inactivation of the oscillator circuit OC may also be confirmed when the neon glow lamp 20 does not illuminate.

The main storage capacitor 22 of the electric charge storing circuit D is charged by the high direct-current from the rectifier circuit C at a polarity as shown in the drawing, and, at the same time, the electric charge is also accumulated on the oscillation starting capacitor 33 of the oscillation control circuit H. Further, the electric charge is stored on the trigger capacitor 27.

When the main storage capacitor 22 is fully charged to the predetermined voltage, the neon glow lamp 24 lights continuously by the aid of the electric charge of the capacitor 25 and indicating that the device is in readiness for the flash tube 42 to be fired. The flash tube 42 may then be fired by closing of the camera shutter switch 29. It will be readily appreciated that this closing need only be momentary during the actuation of the camera shutter. By closing the switch 29, the electric charge on the trigger capacitor 27 discharges through the switch 29 and the primary winding 28a. Then high voltage pulse such as, 3000 volts, is induced at the secondary winding 28b of the triggering transformer 28. The high voltage thus induced in the secondary winding 28b appears at the trigger electrode 42c of the flash tube 42 and ionizes a portion of the gas in the flash tube 42.

The main storage capacitor 22 of the charging circuit D then discharges across the gas between the main current conducting electrodes 42a and 42b, producing a brilliant flash of illumination.

After the main storage capacitor 22 becomes low and thereby the electric charge stored on the oscillation starting capacitor 33 is automatically discharged to the battery 10 by way of the baseemitter path of the control transistor 34, the resistor 38, the variable resistor 39, and the diode 40. By discharging of the oscillation starting capacitor 33, the positive potential appears at the base circuitry of the transistors 12 and 13. Under these conditions, the oscillator circuit OC activates its operation or inactivates in some cases. In both cases, the transistors 12 and 13 is made turn ON by the positive potential of its base electrodes, and then the oscillating operation of the oscillator circuit OC is started again.

The operations of the oscillation stop timing circuit I and the trigger signal control circuit J will be described in more detail.

When the first changeover switch 35 of the oscillation stop timing control circuit I is in its OFF state, the charging voltage is zero, and thereby the transistor 1 6 is initially nonconductive. When the transistor 1 6 is in its OFF state, the transistor 1 7 is also nonconductive and, therefore, the oscillating transistor 12 and 13 are initially nonconductive. The activation of the voltage converter circuit B is, therefore, not performed.

When the first changeover switch 35 is made in its ON state, the current is supplied to the biasing capacitor 36 and the charging voltage of the biasing capacitor 36 is increased in some degree, and thereby the transistors 1 6 and 17 are initially made conductive. By the conduction of the transistor 1 7, the switching operations of the oscillating transistors 12 and 1 3 are performed to operate the activation of the voltage converter circuit B. The charging voltage of the capacitor 36 is further increased gradually to a predetermined value decided by a capacitance value in accordance with a time constant value decided by a capacitance value of the capacitor 36 and resistance values of the resistors 14 and 38 and the variable resistor 39 of the timer circuit.When the charging voltage attains to the predetermined value, the transistor 1 6 is made nonconductive after the predetermined time interval, because the potential of the collector electrode of the transistor 1 6 becomes higher than that of the base electrode thereof. When the transistor 1 6 is nonconductive, the transistor 1 7 becomes also conductive, and thereby the oscillating transistors 1 2 and 1 3 become nonconductive to stop the operation of the voltage converter circuit B. In this case, the oscillation stop timing can be adjusted by setting the resistance value of the variable resistor 39.The oscillation stop timing is, generally, preferable to set about 1-3 minutes, since the power source is consumed in case that; the oscillating time interval is relatively long such as 10 minutes and because the power source is interrupted before the full charging of the main storage capacitor 22, in case that the oscillating time interval is too short such as 20 seconds.

When the first changeover switch 35 is made OFF, the electric charge is discharged through the movable contact 35c of the first changeover switch 35, the second stationary contact 35b and the resistor 37 of the oscillation resetting circuit such that the electric charge of the biasing capacitor 36 becomes zero and, at the same time, the negative voltage is applied to the base electrode of the transistor 1 6 from the battery 10 of the power source circuit A by way of the diode 40, the variable resistor 39 and the resistor 38 to make the transistor 1 6 nonconductive state.

When the second changeover switch 41 of the trigger signal control circuit J is in its OFF state, an indicating circuit of the electric charge storing circuit D is interrupted from the battery 10 of the power source circuit A and, therefore, the neon glow lamp 24 does not light Further, when the second changeover switch 41 is in its OFF state, a primary side of the trigger signal generating circuit E is interrupted from the battery 10 and, at the same time, the primary side of the trigger pulse generating circuit E is short-circuited by the movable contact 41 c and the second stationary contact 41 b.Accordingly, the electric charge of the trigger capacitor discharged through the resistor 30 and the movable contact 41 c and the second stationary contact 41 b of the second changeover switch 41, and therefore the flash tube 31 of the flash tube circuit F does not flash even when the synchronous switch is made ON.

In the converter circuit B, the oscillating transistors 12 and 1 3 are parallelly connected to each other, and, therefore, the large amount of current can be flowed than that of employment of only one oscillating transistor. The transistors 1 6 and 1 7 are connected each other as shown, and an input impedance is increased. By the increment of the input impedance, a current interrupting performance is very improved.

Additionally, a PNP type transistors may be employed as oscillating transistors in the above described embodiment in order to perform the same function as that of the electric flash device of the drawing. Further, the power source switch may be used, if it is required in some kinds of the electric flash device.

According to the electric flash device of the present invention, following advantages are obtained.

The electric flash device is convenient to operate, because it is unnecessary for a photographer to operate the operation for next flash of the flash tube, as the oscillator circuit commences the oscillating operation after the flash tube flashes so long as the first changeover switch is in its ON state and even when the current from the power source circuit is interrupted and the oscillator circuit stops oscillating.

Since the oscillation stop timing can be adjusted by means of an oscillation stop timing adjusting circuit, the flash device of the present invention is widely applicable to the various kinds of camera.

The more effective advantages of the present invention is that the power loss can be avoided as well as the erroneous operation of an electric flash device can be prevented, since the operation of a voltage converter circuit is stopped by making a manually operated switch OFF and since a flash tube does not flash even when a synchronizing switch is made its ON state when a manually operated switch is made OFF.

In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results are attained.

Claims

1. An electric flash device comprising a direct current power source circuit including a battery, a voltage converter circuit for converting a direct current voltage from the 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 electric charge and for supplying electrical energy to a flash tube of a flash tube circuit, a trigger signal generating circuit for triggering said flash tube of the flash tube circuit, and timing control means for controlling the operation timing of the voltage converter circuit, said voltage converter circuit includes an oscillator circuit having an oscillating transformer for generating an alternating current voltage and an oscillation switching member for making a current which flows in said oscillating transformer ON and OFF, and said timing control means includes an oscillation stop timing adjusting circuit for adjusting a time interval during said oscillation switching member of said oscillator circuit becomes nonconductive and an oscillation resetting circuit for resetting the operation of said oscillation stop timing adjusting circuit.

2. An electric flash device comprising a direct current power source circuit including a battery, a voltage converter circuit for converting a direct current voltage from the 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 electric charge and for supplying electrical energy to a flash tube of a flash tube circuit, a trigger signal generating circuit for triggering said flash tube of the flash tube cigcuit, timing control means for controlling the operation timing of the voltage converter circuit, and means for stopping the operation of said trigger signal generating circuit, said voltage converter circuit includes an oscillator circuit having an oscillator circuit having an oscillating transformer for generating an alternating current voltage and an oscillation switching member for making a current which flows in said oscillating transformer ON and OFF, and said timing control means includes an oscillation stop timing adjusting circuit for adjusting a time interval during said oscillation switching member of said oscillator circuit becomes nonconductive and an oscillation resetting circuit for resetting the operation of said oscillation stop timing adjusting circuit.

3. An electric flash device as claimed in claim 1 further comprising an oscillation control circuit for controlling an operation of said converter circuit when an electric charge of said charging circuit is decreased.

4. An electric flash device as claimed in claim 1, wherein said voltage converter circuit having a control switching member for controlling of ON and OFF operations of said oscillator circuit of the voltage converter circuit.

5. An electric flash device as claimed in claim 1 further comprising a signal adjusting circuit for adjusting a voltage signal of an alternating voltage generated from the voltage converter circuit.

6. An electric flash device as claimed in claim 2, wherein said means for stopping the operation of said trigger signal generating circuit comprises a second changeover switch which short-circuits a primary side of said trigger signal generating circuit.

clrcult.

7. An electric flash device as claimed in claim 4, wherein said oscillation switching member of the oscillator circuit comprises NPN type silicon transistors having high leakage resistance.

8. An electric flash device as claimed in claim 4, wherein said oscillation switching member of the oscillator circuit comprises PNP type silicon transistors having high leakage resistance.

9. An electric flash device as claimed in claim 4, wherein said control switching member comprises control transistors for controlling ON and OFF operations of said oscillation switching member.

1 0. An electric flash device as claimed in claim 1, wherein said oscillation stop timing adjusting circuit comprises a timer circuit having a first changeover switch which is arranged between said oscillating transformer of the voltage converter circuit, a biasing capacitor connected to said changeover switch and a variable resistor connected between said biasing capacitor and the battery of the power source circuit.

11. An electric flash device as claimed in claim 10, wherein said timer circuit further having a diode connected between said variable resistor and said battery.

12. An electric flash device as claimed in claim 1, wherein said oscillation resetting circuit comprises a first changeover switch connected to the biasing capacitor and a resistor connected in parallel to said biasing capacitor by way of said first changeover switch.

13. An electric flash device as claimed in claim 12, wherein said oscillation resetting circuit further having a diode connected between said resistor and the battery of the power source circuit.

14. An electric flash device as claimed in claim 3, wherein said oscillation control circuit comprises a control transistor operable for making the voltage converter circuit operable and an oscillation starting capacitor for making said control transistor operable when the charging voltage of said charging circuit decreases.

1 5. An electric flash device as claimed in claim 5, wherein said signal adjusting circuit comprises a capacitor connected in parallel to a secondary winding of the oscillating transformer and an indicating lamp connected in parallel to said capacitor.

1 6. An electric flash device substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.