US3912968A

US3912968A - Flash tube discharge-producing circuit

Info

Publication number: US3912968A
Application number: US385251A
Authority: US
Inventors: Zenzo Nakamura
Original assignee: Canon Inc
Current assignee: Canon Inc
Priority date: 1972-08-07
Filing date: 1973-08-03
Publication date: 1975-10-14
Anticipated expiration: 1992-10-14
Also published as: JPS4937630A

Abstract

A flash tube discharge-promoting circuit comprising an auxiliary capacitor and a thyristor is incorporated in a flash producing circuit so that, upon the advent of a trigger impulse to the trigger electrode of a discharge flash tube, an instantaneous potential of the charge previously stored in the auxiliary capacitor is added in the negative direction to the negative potential of the charge stored in the flash capacitor to produce a flash impulse. The use of an auxiliary capacitor is essential to achieving the superior operating characteristics of the flash discharge-producing circuit to which this invention relates, because it permits the circuit to be designed with a relatively low voltage power source.

Description

United States Patent Nakamura Oct. 14, 1975 FLASH TUBE DISCHARGE-PRODUCING CIRCUIT Inventor: Zenzo Nakamura, Urawa, Japan Canon Kabushiki Kaisha, Tokyo, Japan Filed: Aug. 3, 1973 Appl. No.: 385,251

Assignee:

Foreign Application Priority Data Aug. 7, 1972 Japan 47-78978 US. Cl. 315/241 P; 315/241 R; 315/227 Int. Cl. H0513 37/00 Field of Search 315/241 P, 2 41 R, 227,

| References Cited UNITED STATES PATENTS FOREIGN PATENTS OR APPLICATIONS 1,264,426 2/ 1972 United Kingdom 315/241 P Primary ExaminerMichael J. Lynch Assistant ExaminerB. P. Davis Attorney, Agent, or FirmToren, McGeady and Stanger [57] ABSTRACT A flash tube discharge-promoting circuit comprising an auxiliary capacitor and a thyristor is incorporated in a flash producing circuit so that, upon the advent of a trigger impulse to the trigger electrode of a discharge flash tube, an instantaneous potential of the charge previously stored in the auxiliary capacitor is added in the negative direction to the negative potential of the charge stored in the flash capacitor to produce a flash impulse. The use of an auxiliary capacitor is essential to achieving the superior operating characteristics of the flash discharge-producing circuit to which this invention relates, because it permits the circuit to be designed with a relatively low voltage power source.

7 Claims, 5 Drawing Figures U11 Patant Oct. 14, 1975 Sheet1of2 3,912,968

US. Patent Oct. 14, 1975 Sheet 2 of 2 F l G 3 ll F I G 4 203 i Ulzos 210 F 2. l H 20:T g H 211 1 FLASH TUBE DISCHARGEPRODUCING CIRCUIT This invention relates to a flash-producing electrical circuit for use in a flash lighting device, and more particularly to a flash tube discharge promoting circuit capable of applying a flash impulse to a discharge flash tube from a low voltage power source.

Gaseous-discharge flash tubes adapted for use in speed light devices are characterized by having a minimum starting voltage dependent on the gas pressure, arc length and so forth. In as much as the voltage applied between the principal electrodes of the flash tube is lower than the minimum starting voltage, the discharge cannot be initiated no matter how high the potential of the trigger impulse is. Therefore, the speed light device requires an electric power source capable of charging the flash capacitor with a voltage higher than the minimum starting voltage, being designed with such a high voltage source under considerations of battery consumption and safety of an operator in using the lighting device.

Xenon flash tubes which are usually employed as a flash lighting source, however, cannot be energized to produce a sufficient energy of flash light unless a voltage on the order of of at least 300 volts is applied. This may offer a serious limitation to the use of such xenon tubes in many applications. When the voltage applied to the xenon tube is increased to as high as, or higher than 300 volts, the flash-producing circuit of the xenon tube must be shielded from the outside, or otherwise it is apt to entail a danger of electric shock.

In order to control the quantity of flash energy to a great degree, a flash lighting device of the conventional type in which the quantity of flash energy is varied by varying the voltage applied to the xenon tube must be provided with a flash-producing circuit so designed as to be capable of varying the voltage applied to the xenon tube over a wide range. However, as the voltage applied on the xenon tube increases, the probability of occurrence of electric shocks increases, making it impossible to employ an electric power source of so high voltage as to satisfy the above requirement. Therefore, if a flash-producing circuit which permits the xenon tube to be energized from a power source of a voltage low enough to avoid the danger can be designed, it would be desirable. But such a low voltage is not sufficient in itself to effect a discharge through the xenon tube, so that it has been impossible to vary the quantity of light energy over a wide range.

An object of the present invention is to provide a flash lighting device which has overcome the abovementioned drawbacks.

Another object of the present invention is to provide a flash-producing circuit including a discharge promoting circuit portion capable, upon advent of a trigger impulse on the flash tube, of performing a function of adding the voltage stored in an auxiliary capacitor incorporated therein to the voltage of a charged main capacitor incorporated in another circuit portion, so arranged that the discharge is effected by the use of a low voltage power source.

FIG. 1 is a schematic diagram, partly in block diagram form, illustrating one embodiment of the electrical circuit including a discharge promoting circuit portion of the flash lighting device according to the present invention.

FIGS. 2, 3 and 4 are schematic diagrams illustrating other embodiments of the electrical circuit including a discharge promoting circuit portion with their respective modifications according to the present invention.

FIG. 5 are curves illustrating certain operating principles common in all the embodiments shown in FIGS. 1 4.

In FIG. 1, reference numeral 1 indicates a battery of low voltage associated with a battery switch 2. An electric power supply that is indicated at 3 is constructed as comprising a direct booster circuit such as, for example, a transistor oscillation circuit, providing for a boosted voltage ranging from to 200 volts. Connected to the power supply 3 are a main capacitor or condenser 4 having a large capacity, a discharge flash tube 5 such as a xenon tube, a diode 6 connected in the discharge current circuit of the flash tube 5, and a resistor 8 and a condenser 9 connected with each other in series circuit. An axiliary capacitor 7 is connected between the anode of the diode 6 and the contact of the resistor 8 and condenser 9. A trigger circuit of the flash tube 5 comprises a resistor 10, a booster transformer 11, a trigger condenser 12 and a thyristor 13. There are further provided with a diode 14 and a trigger switch 15 corresponding to the synchronous contact of a camera.

Consideration will next be given to the operation of the circuit of the present invention. When the battery switch 2 is turned on, the main capacitor 4 is charged with a high direct voltage boosted by a direct booster circuit from the battery 1. At the same time, the auxiliary capacitor 7 is charged in a circuit composed of the resistor 8 and diode 6, while the condenser 12 is charged through the resistor 10 and transformer 1 1. In the state wherein the charging of the main capacitor 4 has advanced sufficiently, when the trigger switch is closed, the charge stored in the condenser 9 is delivered through a switch 15 and diode 14 to cause an electric impulse to generate at the terminal of the diode l4, thereupon the thyristor 13 is made conducting. Therefore, the charge stored in the trigger condenser 12 is allowed to flow through the primary winding of the transformer 11, inducing a trigger impulse in its step-up secondary winding, which is then applied between the trigger electrode and principalelectrode of the flash tube 5. In synchronism with this, an instantaneous negative potential of the charge stored in the auxiliary capacitor 7 is added through switch 15 and diode 14 to the negative terminal of the main capacitor 4, so that a high voltage effected by the addition of the potentials of the main capacitor 4 and the auxiliary capacitor 7 is applied between the both principal electrodes of the flash tube 5. Therefore, even if the main capacitor is charged with a voltage lower than the minimum starting voltage characteristic-of the flash tube 5, the discharge of the flash tube 5 can be initiated inasmuch as the sum of the potentials exceeds the value. In other words, even if the voltage with which the main capacitor 4 is charged is not sufficiently high to effect the discharge, the voltage between the electrodes of the flash tube is increased by the potential drop due to the charge stored in the auxiliary capacitor 7 at the time of the advent of the trigger impulse, so that the discharge is initiated without fail. After the initiation of the discharge, the quantity of the flash energy is controlled depending upon the charge stored in the main capacitor 4. Therefore, it is possible to vary the quantity of the flash energy emitted from the flash tube over a wide range in accordance with the quantity of the charge previously stored on the main capacitor 4. Another advantage of the decrease in the voltage of the charged main capacitor 4 is that the power supply 3 comprising a booster circuit need not generate so high output voltage, as a result of which the possibility of electrical shock is very largely precluded.

FIG. 2 is a circuit diagram illustrating another embodiment of the present invention which is adapted for use with the so-called automatic flash control speed light device" for automatically terminating the discharge of the flash tube when a desired predetermined amount of flash energy has been produced in order to effect proper exposure of a photographic film and the like objects. In figure, the elements corresponding to those shown in FIG. I are similarly numbered. The automatic flash control circuit portion comprises a thyristor 17 corresponding to the diode 6 shown in FIG. 1, resistors 18 and 22 constituting a charging circuit of condenser 20, along with diodes l9 and 23, and a thyristor 21 which is made operative by the control pulse from a control terminal 24. The operation of this circuity shown may be considered as the combination of the operation of the circuity shown in FIG. 1 with the operation of the flash control circuit portion capable of con trolling the duration of flashes in order that a desired guide number results. -When a control pulse is introduced from outside to thecontrol input terminal 24, the thyristor 21 is turned on, so that the voltage stored in the condenser is inversely applied across the thyristor 17 to make it non-conducting, thereupon the discharge current path of the flash tube is cut off to terminate the dischargeThe operations of the other circuit portions are similar to those shown in FIG. 1.

FIG. 3 shows another modification of the circuity adapted for use in the flash discharge producing device according to the present invention, wherein the elements corresponding to these shown in FIGS. 1 and 2 are indicated at the same numerals with addition of one hundred. Unlike the foregoing circuity, one of the terminals of the capacitor 107 is connected both to the trigger switch 115 and to the primary winding of the trigger transformer 111.

In this construction, upon. closure of the battery switch 102 which permits the main capacitor 104 to be charged completely after a certain duration of time, a charging current flows through resistors 108 and 110 into an auxiliary capacitor 107 and is simultaneously stored therein. On the other hand, condenser 112 is charged through resistor 110 and a transformer 111. When the trigger switch 115 is closed, a gate signal from an automatic flash control circuit not shown makes the thyristor 121 conducting, while the charge of the auxiliary capacitor 107 is delivered to earth so that the potential of that terminal of the auxiliary capacitor 107 which is connected to the flash tube 105 is decreased with the result of an increase in the voltage between the electrodes of the flash tube. Simultaneously the trigger condenser 1 12 is shunted so that the.

charge stored therein is applied on the trigger electrode of the flash tube in the form of a trigger impulse,

being discharged 'through the flash tube 105. After the discharge is started, the charge on the auxiliary capacitor 107 leakes away, but once the flash tube 105 is energized, a decrease of the voltage across the flash tube clue to the leaking does not cause the energization of the flash tube to terminate. Next, when a trigger signal from an automatic flash control circuit not shown is applied to the thyristor 121, the thyristor 121 is made non-conducting to cut off the discharge current of the flash tube, thereupon the discharge of the flash tube is terminated. According to the above-mentioned circuit, one of the condensers used in the foregoing circuit is omitted, nevertheless the simplified circuit has an effect similar to that shown in the foregoing circuit.

FIG. 4 illustrates a third embodiment of the circuit for use in the flash discharge-producing device, in which the trigger condenser takes part as an auxiliary capacitor. In the figure, the elements corresponding to those shown in FIGS. 1 and 2 are indicated at the same numerals with addition of two hundreds to clarify the correspondences.

In FIG. 4, when the trigger switch is closed, a gate signal from an automatic flash control circuit not shown makes the thyristor 221 conducting, and simultaneously the charge stored in capacitor 207 is delivered over a circuit that can be traced from capacitor 207 through transformer 211, switch 215 and resistor 208 to the capacitor 207 to cause the cathode potential of the flash tube to drop and simultaneously apply a trigger impulse on the trigger electrode, thereupon the flash tube is energized and the energization continues so long as the charge of the main capacitor continues to make the thyristor 221 conducting. This procedure of operation is the same as that shown in the embodiments so far described.

The feature of the present invention common in all the above-mentioned embodiments consists in that the charging of the main capacitor takes place along with the charging of an auxiliary capacitor, and when the flash tube is about tobe energized, the voltage of the charge on the auxiliary capacitor is inversely applied, so that the voltage applied between the principal electrodes of a flash tube is increased. This operating principle is illustrated in FIG. 5.

In FIG. 5, curve V shows the variation with time of the voltage applied to the flash tube, and curve 1 shows the variation of the current with time. At the time of the trigger voltage is applied to the trigger electrode of the flash tube, and simultaneously the voltage V, of the charged main capacitor is applied to the anode of the flash tube, while the voltage V of the charged auxiliary capacitor is inversely applied on the cathode, so that the sum of the both voltages or V V is applied between the anode and cathod of the flash discharge tube to initiate the discharge. After the initiation of the discharge, the production of the flash light proceeds based on the voltage characteristic V or the discharge current characteristic independent on the discharge characteristics of the main capacitor. Therefore, even if the voltage of the charge on the main capacitor is low, the discharge is effected without fail.

As will be seen from the foregoing description, the discharge promoting circuit portion of the invention performs a function of adding the potential of the auxiliary capacitor to the potential of the main capacitor when the flash tube is triggered, whereby the addition of the both potentials exceeds the potential necessary for starting the discharge of the flash tube. Accordingly, the flash tube may be of conventional structure, and in addition the construction of the flash-producing circuit is simplified. The combination of these two advantages makes it possible to construct a speed light device with high efficiency, thus carrying the present invention into large effect.

What is claimed is:

1. A flash discharge-producing device comprising: a flash lighting power source means, a flash tube for producing a quantity of light energy, a main capacitor con nected to said power source for storing electric energy to be translated into light energy in said flash tube, a one-directionally conducting means arranged in the current supply path between the main capacitor and the flash tube, an auxiliary capacitor, one terminal of which is connected to the contact between the flash tube and the one-directionally conducting means, the other being connected to said power source means to store electric energy to be translated to light energy within the flash tube at an initial period of emission of said flash tube, a flash tube trigger circuit for applying a trigger voltage to the flash tube in order to initiate the flash discharge thereof, being associated with a trigger switch arranged in the charge-delivering path of said auxiliary capacitor.

2. A flash discharge-producing device according to claim 1, wherein said trigger circuit is further provided with a trigger capacitor to which said power source means is connected to charge it, and the chargedelivering path of said trigger capacitor is provided with said trigger switch and a trigger transformer arranged therein.

3. A flash discharge producing device according to claim 1, wherein said one-directionally conducting means is a thyristor having a gate to which a nonconducting signal may be applied.

4. A flash discharge-producing device according to claim 1, wherein said trigger circuit is provided with; a trigger transformer having a primary winding and secondary winding, the primary winding being connected to said trigger switch, and the secondary winding being connected to said trigger switch, and the secondary winding being connected to the trigger electrode of the flash tube, and resistor means connected in parallel to said one-directionally conducting means, through which the primary winding of the trigger transformer forms a closed loop along 'with the trigger switch.

5. A flash discharge device according to claim 3 wherein said trigger circuit is provided with; a subsidiary condenser connected both to the power source and to the other terminal of the auxiliary capacitor, and a subsidiary condenser short circuit having said trigger switch and resistor means incorporated therein, said resistor means being connected to the gate of said thyristor.

6. A flash discharge-producing device according to claim 5, wherein said trigger circuit is further provided with a thyristor, a trigger condenser, and a trigger transformer of which the primary winding forms a closed circuit along with said thyristor and having a secondary winding connected to the trigger electrode of the flash tube; and said thyristor has a gate connected to said resistor means.

7. An electric flash device according to claim 1 wherein said auxiliary capacitor further comprise circuit means for coupling the electrical energy stored in said auxiliary capacitor to said main capacitor through said flash tube.

Claims

1. A flash discharge-producing device comprising: a flash lighting power source means, a flash tube for producing a quantity of light energy, a main capacitor connected to said power source for storing electric energy to be transLated into light energy in said flash tube, a one-directionally conducting means arranged in the current supply path between the main capacitor and the flash tube, an auxiliary capacitor, one terminal of which is connected to the contact between the flash tube and the one-directionally conducting means, the other being connected to said power source means to store electric energy to be translated to light energy within the flash tube at an initial period of emission of said flash tube, a flash tube trigger circuit for applying a trigger voltage to the flash tube in order to initiate the flash discharge thereof, being associated with a trigger switch arranged in the charge-delivering path of said auxiliary capacitor.

2. A flash discharge-producing device according to claim 1, wherein said trigger circuit is further provided with a trigger capacitor to which said power source means is connected to charge it, and the charge-delivering path of said trigger capacitor is provided with said trigger switch and a trigger transformer arranged therein.

3. A flash discharge producing device according to claim 1, wherein said one-directionally conducting means is a thyristor having a gate to which a non-conducting signal may be applied.

4. A flash discharge-producing device according to claim 1, wherein said trigger circuit is provided with; a trigger transformer having a primary winding and secondary winding, the primary winding being connected to said trigger switch, and the secondary winding being connected to said trigger switch, and the secondary winding being connected to the trigger electrode of the flash tube, and resistor means connected in parallel to said one-directionally conducting means, through which the primary winding of the trigger transformer forms a closed loop along with the trigger switch.