US3849703A

US3849703A - Electronic flash apparatus

Info

Publication number: US3849703A
Application number: US00260499A
Authority: US
Inventors: A Shimamura; K Matsuzaki
Original assignee: Shindengen Electric Manufacturing Co Ltd
Current assignee: Shindengen Electric Manufacturing Co Ltd
Priority date: 1971-07-06
Filing date: 1972-06-07
Publication date: 1974-11-19
Anticipated expiration: 1991-11-19

Abstract

An electronic flash apparatus for automatically terminating the flash produced by the flash tube of the device after a condition where a predetermined total quantity of light has been received from the flashed object by a light responsive portion of the device, in which a series connection of a commutating capacitor and an auxiliary switching element is connected in parallel with a series connection of the flash tube and a main switching element, so that the auxiliary switching element is arranged in the same polarity as the main switching element. The commutating capacitor is charged in the reverse voltage to the charged voltage of the main capacitor. The flashing current of the flash tube is terminated by rendering the auxiliary switching element conductive in response to an ignition pulse generated at the above condition, while no commutating current is flowed in the flash tube. Another auxiliary switching element may be inserted in the former series connection so as to form a series connection of a switching element, the commutating capacitor and the auxiliary switching element.

Description

United States Patent [191 Shimamura et al.

[111 3,849,703 Nov. 19, 1974 ELECTRONIC FLASH APPARATUS [75] Inventors: Akira Shimamura, Kawagoe; Kunio Matsuzaki, Hanno, both of Japan [73] Assignee: Shindengen Kogyo Kabushiki Kaisha (a/k/a Shindengen Electric Mfg. Co., Ltd., Tokyo-to, Japan [22] Filed: June 7, 1972 [21] Appl. No.: 260,499

[30] Foreign Application Priority Data July 6, 1971 Japan 46-49284 June 9, 1971 Japan .r 46-47987 July 20, 1971 Japan 46-63478 Aug. 31, 1971 Japan 46-78492 Aug. 31, 1971 Japan 46-78493 Novjl, 1971 Japan 46-101841 Mar. 18, 1972 Japan 47-32431 [52] 11.8. Cl. 315/241 P, 315/151, 315/157, 315/159 [51] Int. Cl. l-l05b 41/40 [58] Field of Search 315/241 P, 151, 156, 157, 315/159, 241 R [56] References Cited UNITED STATES PATENTS 3,683,233 8/1972 Heintze 315/241 P 3,696,268 10/1972 Exner 315/151 3,714,443 1/1973 Ogawa 315/241 P 3,740,610 6/1973 Roncke 315/241 P Primary Examiner-Ronald L. Wibert Assistant Examiner-Richard A. Rosenberger Attorney, Agent, or Firm-Robert E. Burns; Emmanuel J. Lobato; Bruce L. Adams 57 ABSTRACT An electronic flash apparatus for automatically terminating the flash produced by the flash tube of the device after a condition where a predetermined total quantity of light has been received from the flashed object by a light responsive portion of the device, in which a series connection of a commutating capacitor and an auxiliary switching element is connected in parallel with a series connection of the flash tube and a main switching element, so that the auxiliary switching element is arranged in the same polarity as the main switching element. The commutating capacitor is charged in the reverse voltage to the charged voltage of the main capacitor. The flashing current of the flash tube is terminated by rendering the auxiliary switching element conductive in response to an ignition pulse generated at the above condition, while no commutating current is flowed in the flash tube. Another auxiliary switching element may be inserted in the former series connection so as to form a series connection of a switching element, the commutating capacitor and the auxiliary switching element.

13 Claims, 15 Drawing Figures PATENTELNUVIQIBH v 3,849'703 snssn g FIRING- CIR cu/ r PATENTE rsuv 1 91914 3.849.703 SHEEI 20F FIRING CIRCUIT ELECTRONIC FLASH APPARATUS This invention relates to electronic flash apparatus using a flash tube and, more particularly, to electronic flash apparatus with automatic light termination.

Electronic photographic flash devices are known in the art in which the flash produced by the flash tube of the device is automatically terminated after a predetermined total quantity of light has been received from the flashed object by a light responsive portion of the device. A current by-pass type and a current cut-off type have been proposed in the art for the electronic flash devices for the type. In the device of the current bypass type, a by-pass tube having a conductive resistance smaller than the conductive resistance of the flash tube is connected in parallel, so that energy charged in the main capacitor is consumed through the bypass tube when a predetermined total quantity of liqht is projected to the flash object. Since the charged energy is completely discharged, a long time is necessary for charging the main capacitor in the device of the current by-pass type. Accordingly, successive flashes cannot be performed in the device of the current by-pass type, .while power consumption in a battery'used for charging the main capacitor is large. In the device of the current cut-off type, a series connection of the flash tube and a first thyrister is connected in parallel with the main capacitor, while a series connection of a commutating capacitor and a second thyrister is connected in parallel with the first thyrister so as to form a flip-flop circuit. The flashing current of the flash tube is cut off by rendering the second thyrister conductive by use of charged energy of the commutating capacitor after a predetermined total quantity of light has been received from the flashed object. However, a peak current having a peak value twice the normal flashing current is flowed in the flash tube at the commutation time. Since the flash tube is strongly flashed by the peak current, the flashed object is over-flashed in each exposure.

An object of this invention is to provide an electronic flash apparatus capable of performing successive flashes in low power consumption without over or least exposure.

In accordance with the principle of this invention, a first series-connection of a reactor, the flash tube and a main switching element is connected in parallel with a main capacitor which is previously charged by a direct-current source. The flash tube is triggered in response to the conduction of the main switching element. A second series connection of a commutating capacitor and an auxiliary switching element is connected in parallel with a series-connection of the flash tube and the main switching element, so that the auxiliary switching element is arranged in the same polarity as the main switching element. The commutating capacitor is charged in the reverse voltage to the charged voltage of the main capacitor. The flashing current of the flash tube is terminated by rendering the auxiliary switching element conductive in response to an ignition pulse, which is generated after an integrated output of a detected signal from reflected light from a flashed object reaches a predetermined threshold level. In accordance with the above construction, the object of this invention can be attained.

The second series connection may be further composed of another auxiliary switching element.

The principles, construction and operations of this invention will be clearly understood from the following more detailed discussion taken in conjunction with the accompanying drawings, in which the same or equivalent parts are designated by the same reference numerals, and in which:

FIG. 1 is a block diagram illustrating an embodiment of this invention;

FIG. 2 shows time charts explanatory of the operations of the embodiment illustrated in FIG. I;

FIG. 3 is a time-current characteristic explanatory of the operations of the embodiment shown in FIG. 1;

FIGS. 4, 5, 6, 7, 8,7 9, l2, l3, l4 and I5 are block diagrams each illustrating an embodiment of this invention;

FIG. 10 shows time charts explanatory of the operations of the embodiment shown in FIG. 9; and

FIG. '11 shows waveform diagrams explanatory of the embodiment shown in FIG. 9.

With reference to FIG. I, an embodiment of this invention comprises a direct-current source I; a main capacitor 2 previously charged by the direct-current source 1; a first series-connection of a coil 3, a flash tube 4 and a main switching element 5 which connection is connected in parallel with the main capacitor 2; a trigger circuit (6) for triggering the flash tube 4 in response to the conduction of the main switching element 5; a firing circuit 7 for rendering the main switching clement conductive; and commutation means for commutating the main switching element 5 and comprising a second series-connection of a commutating capacitor 11 and an auxiliary switching element 12 which connection is connected in parallel with a seriesconnection of the flash tube 4 and the main switching element. The direct-current source 1 comprises a battery 1-4, an oscillator 1-5 excited by the battery for generating an ac voltage, an power transformer having a primary winding connected to the oscillator for receiving the ac voltage and a secondary winding I-7, and diodes l-ll and l-l2. The secondary winding l-7 has terminals l-8 and I-9 and an intermediate terminal l-10. Respective one terminals of the diodes L1] and l-l2 are connected to the terminals [-8 and I-9. Terminals l-l, l-2 and 'l-3 of the dc source are provided at the intermediate terminal l-l0, and respective other terminals of the diodes l-l l and [-12 respectively. The tenninals l-l and l-2 are connected through a resistor 14 to the main capacitor 2. The terminals l-] and l-3 are connected through a resistor 13 to the commutating capacitor 11. A photosensitve element 10, such as a photo-transistor, detects a signal from reflected light 9 which is reflected from an flashed object in response to flash light of the flash tube 4. The detected signal is integrated in an integrator 8. When the integrated value reaches a predetermined threshold value, the firing circuit 7 generates an ignition pulse P which is applied to the auxiliary switching element 12. The triggering circuit 6 comprises a series connection of a resistor 6-1 and a capacitor 6-2, and a transformer 6-3. The'terminals of the series connection of the triggering circuit 6 are connected to the terminal 1-1 and the output of the coil 3. The primary winding of the transformer 6-3 is connected across a junction between the resistor 6-1 and the capacitor 6-2and a junction between the flash tube 4 and the main switching element 5. A diode I6 is connected in parallel with the flash tube 4 in the reverse polarity to the flowing direction of the flashing current of the flash tube 4. A diode 15 is connected in parallel with the coil 3 in the reverse polarity to the flowing direction of the flashing current.

In operation, the main capacitor 2 is charged by a dc voltage supplied from the terminals 1-1 and 1-2 in a time constant C .R where values C l and R are respectively a capacitance of the main capacitor 2 and a resistance of the resistor 14. The capacitor 11 is charged by a dc voltage supplied from the terminals 1-1 and l-3 through the resistor 13. A trigger pulse P is applied to the control terminal of the main switching element 5 in response to switching-ON of a switch S as shown in FIG. 2 after the charged voltage of the main capacitor 2 exceeds the discharge starting voltage of the flash tube 4. The switch S is provided in the associated camera or the flash device in the usual manner. The main switching element 5 is rendered conductive in response to the trigger P,, so that electric charge in the capacitor 6-2 is discharged through the primary winding of the transformer 6-3 and the main switching element 5. Accordingly, a high pulse is generated at the secondary winding of the transformer 6-3 and starts the flash of the flash tube 4. A flashing current of the flash tube 4 flows through a path: the main capacitor 2, the flash tube 4, the main switching element 5, the coil 3 and the main capacitor 2. The flash tube 4 radiates flash light in response to the flashing current. The flash light is projected to a flashed object and reflected from the flashed object. The reflected light 9 is detected by the photo-sensitive element 10. The detected voltage is integrated in the integrator 8. When the integrated output from the integrator 8 reaches a predetermined threshold value, an ignition pulse P is applied from the firing circuit to the control electrode of the auxiliary switching element 12 for rendering the element 12 conductive. An electronic charge previously charged in the commutating capacitor 1 1 is discharged in a short time through a path: the capacitor 11, the auxiliary switching element 12, the main switching element 5, the flash tube 4 and the capacitor 11. Accordingly, since the anode-cathode path of the main switching element 5 is reversely biased by the terminal voltage of the commutating capacitor 11, the main switching element 5 is turned OFF. At the same time, the electric charge of the commutating capacitor 11 is discharged through a path: the commutating capacitor 11, the auxiliary switching element 12, the coil 3, the main capacitor 2, and the commutating capacitor 11, so that the

capacitors

2 and 11 are charged in the reverse polarities to each other. When the voltage of the capacitor 2 becomes equal to the voltage of the capacitor 11, the discharge current of the commutating capacitor 11 becomes zero while the auxiliary switching element 12 becomes non-conductive. When the main switching element 5 is turned OFF as mentioned before, the flashing current of the flash tube is cut off and the flash light is also terminated. Thereafter, the main capacitor 2 and the commutating capacitor 11 are charged as mentioned above for the next flash.

The diode 15 is employed for absorbing a counter electromotive force of the coil 3 induced at zero conditions of the flashing current and the commutating current to avoid application of a high voltage to the commutating capacitor 11.

As understood from the above, the embodiment shown in FIG. 1 is so designed that the main capacitor 2 and the commutating capacitor 11 are charged by different dc sources (l-l, 1-2) and (l-l, 1-3), and so that the discharge current of the commutating capacitor 1 l is not passed through the flash tube 4. Accordingly. the flash light from the flash tube 4 is suitably terminated as shown in FIG. 3 at the time when an flashed object is flashed by a predetermined quantity of flash light from the flash tube 4. Therefore. the predetermined threshold value can be set over a wide controllable range. Moreover, since the charged voltage of the main capacitor 2 is not discharged until zero for each flash. the power consumption of the battery 1-4 is low and economical and successive flash actions can be also performed.

The diode 16 is employed for readily performing commutation of the main switching element 5.

The dc source 1 may be formed without the intermediate terminal l-10 as shown in FIG. 4, in which the respective one terminals of the rectifiers 1-11 and l-I2 are commonly connected to the output terminal 1-8 of an ac source 1-5 in the reverse polarities to each other. The other terminal of the diode 1-11 and the other output terminal 1-9 of the ac source l-5 are employed for charging the commutating capacitor 11, while the .other terminal of the diode 1-12 and the terminal l-9 of the ac source l-5 are employed for charging the main capacitor 2. In this embodiment, the coil 3 is formed by two parts 3a and 312, so that the series connection of the flash tube 4 and the main switching element 5 is connected through the part 3a of the coil 3 to the main capacitor 2, while a series connection of the diode 16 and the part 3b of the coil 3 is connected in parallel with the flash tube 4. One terminal of the series connection of the commutating capacitor 1] and the auxiliary switching element 12 is connected to a junction between the diode 16 and the part 3b of the coil 3. The part 3b of the coil 3 serves for improvement of the commutation of the main switching element 5.

With reference to FIG. 5, a firing circuit for generating a pulse (P of the embodiment of this invention comprises a resistor 7-11, a capacitor 7-13 a resistor 7-12, a switch 7-14, and a transformer 7-15. The resistor 7-11, the capacitor 7-13 and the resistor 7-12 form a series connection connected in parallel with a series connection of the flash tube 4 and the main switching element 5. The primary winding of the transformer 7-15 is connected, through the switch 7-14, in parallel with the capacitor 7-13. The secondary winding of the transformer is connected across the gate and the cathode of the main switching element 5. The pulse P is obtained from the transformer 7-15 in response to the switching ON of the switch 7-14.

With reference to FIG. 6, an embodiment of this invention further includes constant voltage means connected in parallel with the main switching element 5 and comprising a constant voltage element 19, a votage regulating capacitor 18 and a resistor 17. The capacitor 18 is previously charged through the resistor 17 and the constant voltage element by a terminal voltage of the main switching element 5. A constant voltage is obtained from the constant voltage element 19, such as a zenor diode, by the discharge of the voltage regulating capacitor 18 in response to the conduction of the main switching element. The obtained constant voltage is supplied as the electric may be to pulse means, which includes the photo-sensitive element 10, the integrator 8 and the firing circuit 7. In the embodiment shown in FIG. 6, the integrator 8 comprises an integrating capacitor 8-1, a transistor 8-2, and a variable resistor 8-3. The forementioned predetermined threshold value is determined by the adjustment of the variable resistor 8-3. A switching element 7-16 and a transformer 7-17 form the firing circuit 7 for generating the pulse P when the output of the integrator 8 reaches a predetermined threshold value. The pulse P is applied to the gate of the auxiliary switching element 12.

With reference to FIG. 7,a series connection of a switching element 7-16 and the primary winding of the transformer 7-17 may be connected in parallel with the voltage regulating capacitor 18. The switching element 7-16 isrendered conductive when the adjusted output of the variable resistor 8-3 exceeds the predetermined threshold value determined in accordance with the characteristic of the switching element 7-16. The ignition pulsel is obtained from the secondary winding of v the transformer 7-l7 in response to the conduction of the switching element 7-16 since the charged voltage of the voltage regulating capacitor 18 is discharged through the conductive switching element 7-16 and the transformer 7-17. The voltage regulating capacitor 18 is usually charged at a voltage of 300 volts, which is still maintained at about a voltage of 150 volts after discharge through the above mentioned main switching element 5. Thismaintained voltage 15 and 150 volts is utilized-for generating the ignition pulse P is mentioned above. I

With reference to FIG. 8 illustrating another embodimentof this invention, an auxiliary commutating capacitor 22 is'connected across the gate and cathode of the main switching element 5, while the secondary winding of thetransformer 7-15 is connected, through a diode 7-21, with the anode-cathode path of the main switching element 5. A charged voltage of the capacitor 22 charged by the commutating current from the main commutating capacitor 11 is applied to a junction between the gate and the cathode of the main switching element so as to reversely bias the same junction. This acts to sufficiently shorten the tum-OFF time of the main switching element 5, so that capacity of the main commutating capacitor 11 can be effectively reduced.

With reference to FIG. 9 illustrating another embodiment of this invention, another auxiliary switching element 12a is inserted between the main commutating capacitor 11 and the flash tube 4, so that a series connection of the auxiliary switching element 12a, the commutating capacitor 11 and an auxiliary switching element 12b is connected in parallel with the series connection of the flash tube 4 and the main switching element 5. In this embodiment, the capacitors 2 and l l are charged by the same dc source since the commutating capacitor 11 is charged through

resistors

13a and 13b from outputs of the diode 1-12 and the coil 3. The

switchingelements 12a and 12b are simultaneously controlled as understood from FIGS. 10 and 11. The operations of this embodiment can be readily understood from the above disclosure, details are omitted.

In the aboveembodiments, the main switching element 5 is a silicon controlled rectifier (i.e. a threeterminal unidirectional thyrister, except FIG. 7 employing a silicon symmetrical switch (i.e. a twoterminal bidirectional thyrister). However, a Triac (i.e. a three-terminal bidirectional thyrister) and a fourlayer diode (i.e. a two-terminal unidirectional thyrister) may be employed as the main switching element 5 as shown in FIGS. 13 and 14. Moreover. a silicon symmetrical switch (i.e. a two-terminal bidirectional thyrister), a Triac (i.e. a three-terminal bidirectional thyrister), a four-layer diode (i.e. a two-terminal unidirectional thyrister) may be also employed as each of the

auxiliary switching elements

12a and 12b as shown in FIGS. l2, l3 and 14 in addition to the silicon controlled rectifier (i.e. a three-terminal unidirectional thyrister). A cold cathode discharge tube may be employed as each of the

auxiliary switching elements

12a and 12b as shown in FIG. 15, in which a silicon controlled rectifier is employed as the main switching element 5.

In the embodiment shown in FIG. 14, the four-layer diode 5 is driven by the transformer 7-15 through a parallel connection of a capacitor 7-18 and a diode 7-22, and the four-layer diode 12a is driven by the transformer 7-17 through a parallel connection of a capacitor 7-20 and a diode 7-23, while the four-layer diode 12b is driven by the transformer 7-17 through a parallel connection of a capacitor 7-21 and a diode 7-24.

What we claim is:

1. An electronic flash apparatus using a flash tube, comprising: a flash tube having a triggering electrode; a direct current source, a main capacitor connected to the direct-current source and charged thereby; a coil; a first series circuit connected in parallel with said main capacitor through said coil and comprising the flash tube and a normally nonconducting main switching element; a control switch; a trigger circuit connected to the triggering electrode of the flash tube for triggering the flash tube in response to the conduction ofthe main switching element; a firing circuit connected to said control switch and responsive to the state thereof for rendering the main switching element conductive; a second series circuit connected in parallel with said first series circuit and comprising a first auxiliary switching element, a commutating capacitor and a second auxiliary switching element connected in the order named and wherein the first and second auxiliary switching elements have the same polarity as the main switching element; charging means electrically coupled through the commutating capacitor to said directcurrent source for charging the commutating capacitor to a voltage having a polarity which is the reverse of that of the charged voltage of the main capacitor with respect to the forward current in the first and second auxiliary switching elements; light sensitive means for generating a detection signal responsive to reflected light which is reflected from a flashed object resulting from a light flash from the flash tube; an integrator receptive of said detection signal for integrating same and developing a corresponding output signal; and control means receptive of the output signal of said integrator and connected to the first and second auxiliary switching elements for triggering same when the output signal of the integrator exceeds a predetermined value.

2. An electronic flash apparatus according to claim 1, in which said charging means comprises a first charging resistor connected in parallel with the series connection of the first auxiliary switching element and the commutating capacitor, and a second charging resistor connected in parallel with the series connection of the second auxiliary switching element and the commutating capacitor.

3. An electronic flash apparatus according to claim 1, further including a diode connected in parallel with said flash tube in the reverse polarity to the flowing direction of the flashing current of the flash tube.

4. An electronic flash apparatus according to claim 1, in which said main switching element comprises a three-terminal unidirectional thyrister.

5. An electronic flash apparatus according to claim 1, in which a two-terminal bidirectional thyrister is employed as the main switching element.

6. An electronic flash apparatus according to claim 1, in which a three-terminal bidirectional thyrister is employed as the main switching element.

7. An electronic flash apparatus according to claim 1, in which a two-terminal unidirectional thyrister is employed as the main switching element.

8. An electronic flash apparatus according to claim 7, in which said two-terminal unidirectional thyrister employed as the main switching element is driven by said firing circuit through a parallel connection of a capacitor and a diode.

9. An electronic flash apparatus according to claim 1, in which said first and second auxiliary switching elements each comprise a three-terminal unidirectional thyrister.

10. An electronic flash apparatus according to claim 1, in which a two-terminal bidirectional thyrister is employed as each of the first and second auxiliary switching elements.

11. An electronic flash apparatus according to claim 1, in which a three-terminal bidirectional thyrister is employed as each of the first and second auxiliary switching elements.

12. An electronic flash apparatus according to claim 1, in which a two-terminal unidirectional thyrister is employed as each of the first and second auxiliary switching elements.

13. A light flashing apparatus according to claim 1, in which a cold cathode discharge tube is employed as each of the first and second auxiliary switching elcments.

Claims

1. An electronic flash apparatus using a flash tube, comprising: a flash tube having a triggering electrode; a direct current source, a main capacitor connected to the direct-current source and charged thereby; a coil; a first series circuit connected in parallel with said main capacitor through said coil and comprising the flash tube and a normally nonconducting main switching element; a control switch; a trigger circuit connected to the triggering electrode of the flash tube for triggering the flash tube in response to the conduction of the main switching element; a firing circuit connected to said control switch and responsive to the state thereof for rendering the main switching element conductive; a second series circuit connected in parallel with said first series circuit and comprising a first auxiliary switching element, a commutating capacitor and a second auxiliary switching element connected in the order named and wherein the first and second auxiliary switching elements have the same polarity as the main switching element; charging means electrically coupled through the commutating capacitor to said direct-current source for charging the commutating capacitor to a voltage having a polarity which is the reverse of that of the charged voltage of the main capacitor with respect to the forward current in the first and second auxiliary switching elements; light sensitive means for generating a detection signal responsive to reflected light which is reflected from a flashed object resulting from a light flash from the flash tube; an integrator receptive of said detection signal for integrating same and developing a corresponding output signal; and control means receptive of the output signal of said integrator and connected to the first and second auxiliary switching elements for triggering same when the output signal of the integrator exceeds a predetermined value.

13. A light flashing apparatus according to claim 1, in which a cold cathode discharge tube is employed as each of the first and second auxiliary switching elements.