|Publication number||US3919593 A|
|Publication date||Nov 11, 1975|
|Filing date||Aug 23, 1973|
|Priority date||Aug 28, 1972|
|Publication number||US 3919593 A, US 3919593A, US-A-3919593, US3919593 A, US3919593A|
|Original Assignee||Canon Kk|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (10), Referenced by (5), Classifications (8)|
|External Links: USPTO, USPTO Assignment, Espacenet|
United States Patent 1191 Nakamura Nov. 11, 1975 [5'41 FLASH SAFETY DEVICE IN A FLASH 3.751.714 8/1973 Cooper 315/241 P APPARATUS 3.764.849 10/1973 Ohta 315/241 P 3.777.212 12/1973 Mashimo 315/241 P Inventor: en am ra, Urawa, Japan 3.778.672 12/1973 P61611616. 315/241 P 1. 3,814,985 6/1974 Pecher et a1. 315/241 P  Asslgnee' g Kabushlk' Tokyo 3.819.983 6/1974 Bjork 315/241 P apan  Filed: Aug. 23, 1973 Primary Eraminer-Stanley D. Miller, Jr. pp No: 390,711 Attorney. Agent. or F1rnzToren, McGeady and Stanger  Foreign Application Priority Data 57 ABSTRACT I Aug. 28. 1972 Japan 47-100203[U] A In the disclosed flash System a flash voltage detector operates a switch which enables a flash triggering cir-  :18. C1. 315/241 P; 354/145 i only after the flash voltage reaches a Predetep l lt. C1. H951) 41/14 mined value In a preferred embodiment the Switch 1 held of Search 3 15/ 1' 241 354/145 includes a unidirectional element in series opposition to the triggering current flow. When the flash voltage  References is sufficiently high the switch passes forward current UNITED STATES PATENTS through the unidirectional element thereby decreasing 3.593.061 7/1971 Takahata et a1. 315/241 the voltage drop thereacross and permits a triggering 3.690.237 9/1972 Fuwa 354/145 current. 3.714.872 2/1973 Mashimo 315/241 P 3.723.810 Mashimo 315/241 P 6 Clam, 1 Drawmg Flgure BOOSTER 3 4 CIRCUITI\ g US. Patent Nv. 11,1975 I 3,919,593
BOOSTER 3 4 CIR u POWER SOURCE FLASH SAFETY DEVICE IN A FLASH APPARATUS BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flash safety device of a flash apparatus. I
2. Description of the Prior Art In known flash apparatuses, such as stroboscopic flash apparatuses, flashing is accomplished by boosting the low voltage of the battery to a higher voltage and then applying the electric charge to light a Xenon flash tube. The required flash intensity can be obtained only after the capacitor is suitably charged. Conventionally, a neon tube is used to indicate that the main capacitor has been charged to place it in readiness for flashing the tube. Unfortunately, this requires the photographer to divert his attention to the neon tube when he is taking continuous flash pictures. This is somewhat inconvenient and sometimes troublesome.
SUMMARY OF THE PRESENT INVENTION An object of the present invention is to provide a safety circuit for a flash apparatus in which a conducting element such as diode, etc. is connected to a flashing voltage detection circuit of the flash apparatus to automatically prevent flashing of the flash apparatus when the apparatus does not have prescribed flashing BRIEF DESCRIPTION OF THE DRAWINGS The sole drawing is an arrangement drawing of a safety circuit of the flash circuit apparatus according to the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS The sole drawing is an electric circuit connection diagram to show an example of a safety circuit of the flash apparatus according to the present invention.
In the sole drawing 1 shows a low voltage actuation power source such as battery, etc., 2 is a main switch of a flash apparatus, 3 is a conventionally known booster circuit, 4 is a rectifier diode, 5 is a flashing main capacitor, 6, 7 are bleeder resistors for detecting capacitor terminal voltage, 8 is a neon tube, 9 is a Xenon tube, 10 is a current limiting resistance, 11 is a trigger capacitor, 12 is a trigger transformer, 13 is a triggering thyristor, I4, 15 are resistances, 16, 19 are switching transistors, and l7, 18 are emitter, collector resistances of the transistor 16. Member 20 is an FET, and 21 is a resistance connected in parallel with a temperature compensation diode 22. Component 23 is an adjusting resistance, 24 is a switching transistor, and 25 is a diode as an one way conducting element. Reference character 25A identifies a circuit within a camera, wherein 26 is an exposure meter circuit battery, 27 is a synchronizing switch, 28 is a variable resistance which is varied depending on distance to an object, 29 is an exposure meter, and CdS shows a light receiving element to sense light from an object.
In the above arrangement, when the main switch 2 is turned ON, the voltage as elevated by the booster circuit is impressed upon the main capacitor 5 so that charging is started. Until the terminal voltage of the main capacitor 5 reaches a prescribed level, the bleeder voltage between the bleeder resistances 6, 7 will not become large, because it is in proportion to said terminal voltage. As a result the neon tube 8 will not be lighted, therefore the transistor 16 remains OFF and so does the transistor 19.
As a result of the above, both FET20 and the transistor 24 are retained in OFF state, therefore voltage will not be impressed on the transistor 24. In this state when the synchronizing switch '27 is closed, since the diode 25 is connected in a reverse direction in a circuit of the trigger starting circuit battery 26 synchronizing switch 27 resistance 14 SCR13 diode 25 battery 26, starting current will not flow to the SCR13 and the Xenon tube 9 is not lighted. When the terminal voltage of the capacitor 5 is elevated to a prescribed value or higher, the neon tube 8 is lighted and the tran sistors l6, 19 are turned ON. As a result current from the power source 1 flows to the drain of the FET 20 and the collector of the transistor 24. The diode 25 conducts the collector current of the transistor 24. The collector current of the transistor 24 is almost proportional to the terminal voltageof the capacitor 5. Thus the voltage across'the diode 25 will correspond to the voltage of the capacitor 5 logarithmically with the compression characteristics of the diode 25. This voltage will be impressed upon to the circuit 25A in the camera.
The exposure meter 29 is positioned based on the resistance value of the distance resistance 28 and the sum of the voltage across the diode 25 and the voltage of the battery 26, indicating the aperture value by its pointer position. Therefore, the diaphragm aperture of a camera is adjusted based on this indication. Thus the aperture value for flash auto-photographing can be set based on the distance to an object, and the terminal voltage of the capacitor 5 which voltage corresponds to the amount of light to be emitted by the flash. Next, when the synchronizing switch 27 is closed along with shutter release, the sum of the voltage across the diode 25 and the voltage of the battery 26 will be impressed on the gate of the SCR13 through the resistance 14, the SCR13 is made to conduct and the Xenon tube 9 is ignited.
As has been explained above in the present invention the flash triggering is prevented until the flash apparatus is placed in flashable state by such one way conducting element as diode 25, etc. to prevent unnecessary loss of energy at the power sourc'e by inadequate flashing, thus it is very useful in practical application. As the one way conducting element, beside the above mentioned diode naturally such elements as having one way conducting function by continuance of its terminals for example SCR transistor, etc. can be used.
What is claimed is:
l. A flash apparatus comprising:
an electric power supply means,
a main capacitor coupled with said supply means to be charged thereby,
a flash tube coupled to said main capacitor,
a trigger circuit coupled to said flash tube and capable of igniting said flash tube when the trigger circuit is enabled and a synchronizing signal applied to the circuit, said circuit including a capacitor for accumulating triggering energy, said capacitor being supplied with triggering energy, said trigger circuit including means for applying the energy to the flash tube when the circuit is enabled and the synchronizing signal applied,
a voltage detecting means coupled to said main capacitor for detecting the voltage across said main capacitor so as to emit an output therefrom corresponding to the voltage across said main capacitor,
a switching means connected between the output of said voltage detecting means and said trigger circuit andswitchable to an ON state when the output a of said voltage detecting means reaches a predetermined value so as to enable said trigger circuit.
2.'A flash apparatus according to claim 1, wherein said voltage detecting means contains a bleeder circuit coupled across the flash tube, said bleeder circuit being composed of a plurality of resistances and having an output terminal, the output terminal of said bleeder circuit being coupled to said switching means.
3. A flash apparatus as in claim 1, wherein said switching means includes a constant voltage element connected-to the trigger circuit so as to produce a constant voltage in the trigger circuit when the switching means is ON.
4. A flash apparatus comprising: i
an electric power supply means, a main capacitor connected with said supply means for charging 'thereby,
a flash tube coupled to said main capacitor,
a trigger circuit coupled to said flash tube and capable of igniting said flash tube when the trigger circuit is enabled and a synchronizing signal applied ,tojthe circuit, said circuit including a trigger capacfitor for accumulating triggering energy, means connecting said capacitor to the supply means for supplying triggering energy thereto, said trigger circuit including means connected with said flash tube and to said triggercapacitor for applying the triggering energy when said circuit is enabled and actuated so as to light said flash tube, v :a voltage detecting means connected with said main capacitor for detecting the terminal voltage of said main capacitor so as to produce an output therea from corresponding to the terminal voltage of said main capacitor,
-a switching means connected with said voltage detecting means and switchable to an ON state when the output of said voltage detecting means reaches a predetermined value, a constant current circuit, said circuit being connected in said switching means and generating a constant current when said switching means is turned to the ON state,
a unidirectionally conducting element, said element being connected with said constant current circuit in the forward direction and being turned to an ON state when the constant current circuit generates constant current so as to generate a constant voltage,
a synchronizing switch means coupled to said triggering circuit for producing the synchronizing signal,
a trigger starting means in said trigger circuit for forming a path of trigger starting current to cause said trigger starting current to flow therethrough when said synchronizing switch means is turned to the ON state so as to actuate said trigger circuit, said starting means connecting said unidirectional element within the path of said trigger starting current to vary said trigger starting current, said starting means causing said trigger starting current to flow through said path in order to actuate said trigger circuit when said unidirectional element and said synchronizing switch means respectively are turned to the ON state.
5. A flash circuit, comprising a gas discharge lamp, a main capacitor coupled across the lamp, a capacitor charging circuit coupled across the capacitor, a threshold voltage detector coupled across the capacitor and including a threshold voltage responsive switch whose state is changeable in response to the capacitor voltage reaching a predetermined value, a actuable trigger circuit coupled to the lamp and forming a trigger path, a unidirectional element in the trigger path, characterized in that said unidirectional element is directed to oppose trigger current flow and is connected to said detector to receive forward current from the switch as the switch is switched when the main capacitor exceeds the switchs threshold level.
6. An apparatus as in claim 5, further characterized in that the switch produces a forward current in the unidirectional element corresponding to the capacitor voltage, and means in the trigger circuit responsive to said current to apply the current as an indication capacitor voltage. I
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|Citing Patent||Filing date||Publication date||Applicant||Title|
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|US4464609 *||Nov 14, 1983||Aug 7, 1984||Canon Kabushiki Kaisha||Flash lighting unit for a camera|
|EP0035224A1 *||Feb 25, 1981||Sep 9, 1981||Olympus Optical Co., Ltd.||Electronic flash apparatus|
|U.S. Classification||315/241.00P, 396/180|
|International Classification||H05B41/32, H05B41/30, G03B15/05, G03B7/16|