GB2133644A - Photographic flash apparatus - Google Patents

Abstract

Photographic flash apparatus including a main discharge capacitor 9 and means for dissipating the charge thereon when non-flash photography is required, further includes blocking means for stopping the charge dissipation when the capacitor voltage has dropped below a predetermined level, whereby energy is saved and less time is required to recharge capacitor 9 when flash photography is next required. When a switch is moved to a non-operative position 2a, capacitor 9 and a trigger capacitor 10 are discharged via a neon lamp 20 until the capacitor voltage falls below the operating voltage of lamp 20. The lamp 20 is a lower voltage type than a neon lamp 16 used to trigger on an LED 18 for indicating that capacitor 9 has charged to a required level. A zener diode (22), (Figures 3, 6) may be used instead of lamp 20. Other embodiments (Figures 8, 10) have a zener (74) to stop a DC-DC converter when the main capacitor (59) voltage has reached the required level, a neon (66) or a flickering LED (68) being used to indicate the latter. In further embodiments the discharge circuit is permanently connected across the main capacitor (Figures 9, 12). <IMAGE>

Description

SPECIFICATION Photographic Flash Apparatus The present invention relates to photographic flash apparatus.

In known flash apparatuses, electric energy stored in the main discharge capacitor is uselessly discharged when the flashlight discharger device is transferred to its non-operative state after said main discharge capacitor has been charged to a sufficient level to be ready for light emission. Broadly, the present invention enables one to reduce or avoid such waste by means of an arrangement such that the main discharge capacitor may hold electric energy already stored therein even when the flash apparatus has been transferred to its non-operative state.

Other features and advantages will be apparent from the foilowing description in detail.

Photographic flash devices are usually so arranged that, upon closure of a source switch, respective capacitors are charged in preparation for light emission,which occurs in response to operation of a shutter release of an associated camera.

However, when the source switch is opened to perform normal photography, without flash, the photography is nevertheless often accompanied by unexpected flash emission, resulting in over-exposure, so far as preparation for light emission has already been completed.

To avoid such inconvenience, many of the recently available flash devices are so arranged that, upon opening of the source switch, the electric charge stored in a trigger capacitor is discharged. Thus the trigger circuit cannot trigger any flash emission once the source switch has been opened.

According to the present invention there is provided a photographic flash apparatus including a main discharge capacitor; means for charging said capacitor; indicating means capable of indicating when the capacitor has been charged to a level at leat as high as a predetermined level; means for transferring the apparatus to a non-operative state; charge releasing means operable to release charge stored in said capacitor when the apparatus is transferred to its non-operative state; and blocking means arranged to block further release of the stored charge from said capacitor in response to a drop of the charging voltageto a level below the predetermined level, said blocking being removable by recharging the capacitor so that said indicating means is reset.

The invention will now be explained in greater detail with reference to the accompanying drawings in which: Figure 1 is a circuit diagram illustrating a prior art flash apparatus; Figures 2 to 6 are circuit diagrams illustrating embodiments of flash apparatus according to the present invention, each including a trigger circuit adapted to be disabled when light emission is suspended; Figure 7 is a circuit diagram illustrating another prior art appratus; Figures 8 to 11 are circuit diagrams illustrating embodiments of the present invention which include charge indicating lamps adapted to be turned off when light emission is suspended; and Figures 12 to 14 are circuit diagrams illustrating embodiments of the present invention which include means for generating signals indicative of readiness for light emission.

Figure 1 illustrates by way of example the circuit arrangement incorporated in one prior art flash device including a discharging circuit for the trigger capacitor. In Figure 1, reference numeral 1 designates a source battery and reference numeral 2 designates a source switch provided with terminals 2a,2b. A transducer comprises a DC-DC converter 3 and a transistor 4. There are also a starter resistor 5 for said converter and a capacitor 6 for operational stability. A smoothing circuit includes a capacitor 7 and a diode 8. There is a main discharge capacitor 9, and a trigger capacitor 10 is connected in parallel to it so that said trigger capacitor is charged though charging resistors 11,12. A trigger transformer 13 serves to apply excitation voltage to a flashlight discharge tube 14. A trigger switch 15 is arranged to close when the camera shutter is operated.These members 10,11,12,13 and 15 form together a trigger circuit. A neon tube lamp 16 is connected between a node P of said charging resistors 11,12 and the base of a switching transistor 17. A light emitting diode 18 is connected to the emitter of said transistor 17. These members 16,17 and 18 form together an indicating circuit for determination ofthe charged state, wherein the light emitting diode 18 is caused to emit light when the main discharge capacitor 9 has been charged to a predetermined level. It should be understood that said light emitting diode 18 is placed at a location which permits its light to be visible externally of the discharger device. There is an electrical connection 19 extending from the node P of the charging resistors 11,12 to the terminal 2a ofthe source switch 2, forming a part of the discharging circuit for the trigger capacitor 10.

Inthisembodimentof priorart,the source switch 2 is normally at its terminal 2a. When this switch 2 is turned onto the terminal 2b, the DC-DC converter starts its oscillation and thereby the main discharge capacitor 9 and the trigger capacitor 10 are charged.

When the main discharge capacitor 9 has been charged to a predetermined level, for example, 270 V, the neon tube lamp 16 is turned conductive, turning the transistor 17 ON, and the light emitting diode 18 is thereby lit. The light emission of this diode 18 tells the user that a desired light emission is now available.

In this 'ready' state, closure of the trigger switch 15 causes in the well known manner the flash discharge tube 14 to emit light. Thereafter, the main discharge capacitor 9 and the trigger capacitor 10 are charged again, so long as the source switch 2 remains on the terminal 2b.

When the source switch 2 is brought back to its terminal 2a after the main discharge capacitor 9 has been charged to the predetermined or higher level and thereby light emission has been prepared for, the trigger capacitor 10 is discharged and the flashlight discharge tube 14 is blocked against further light emission.

Namely, when the source switch 2 is brought back to its terminal 2a, the trigger capacitor 10, the source switch 2, the node P and the charging resistor 12 form together the discharging circuit through which the trigger capacitor 10 is discharged. Once the trigger capacitor 10 has been discharged, the flashlight discharge tube 14 cannot be supplied with excitation voltage and therefore cannot emit light even if the trigger switch 15 is closed.

The embodiment of prior art as illustrated in Figure 1 is certainly advantageous in that the source switch 2 may be brought back to its initial terminal to reliably block the disharge tube against further light emission.

However, such an embodiment is disadvantageous in that the main discharge capacitor 9 is also discharged when the source switch 2 is returned to its initial position. Namely, return ofthe source switch 2 from its terminal 2b to its terminal 2a establishes a closed circuit consisting of the main disharge capacitor 9, the source switch 2, the anode P and the charging resistor 11 through which the main discharge capacitor 9 is fully discharged. Certainly, discharging of the main discharge capacitor 9 occurs moreslowlythan discharging ofthetriggercapacitor 10, since the value of the charging resistor 11 is set substantially higherthan that of the charging resistor 12.Nevertheless, such discharging of the main discharge capacitor 9 means that the electric energy stored in this capacitor 9 is uselessly consumed and this capacitor 9 must be charged again from its no charge state for the next flash. This results in a substantially longer time required for recharging of the main discharge capacitor 9.

The present invention proposes an improved arrangement such that the above-mentioned useless discharge or consumption of the electric energy stored in the main discharge capacitor 9 conventionally occurring through the discharging circuit for the trigger circuit 10 established upon reset of the source switch 2 may be reduced.

In a first embodiment ofthe invention illustrated in Figure 2, a neon tube lamp 20 and a current limiting resistor 21 are in series in the connection 19. The rest of the arrangement is identical to that illustrated in Figure 1.

It should be noted here that the neon tube lamp 20 is adapted to be turned on to emit light at a voltage lower than that at which the neon tube lamp 16 is turned on. For example, the neon tube lamp 20 is turned on at 100 V while the neon tube lamp 16 is turned on at 270 V.

In this manner, return of the source switch 2 from its terminal 2bto its terminal 2a atthe state of readiness for light emission during which the neon tube lamp 16 remains turned on and therefore the light emitting diode 18 also remains turned on reliably causes the neon tube lamp 20 to be turned on and thus conductive, so that the trigger capacitor 10 is discharged through the discharging circuit formed by the source switch 2, the neon tube lamp 20, the cur rentlimiting resistor21,theanodeP and the charging resistor 12.

Meanwhile, the main discharge capacitor 9 is also discharged through the closed circuit consisting of the source switch 2, the neon tube lamp 20, the anode P and the charging resistor 11. However, the neon tube lamp 20 is turned to its non-conductive state as the charging voltage across the main discharge capacitors drops, as a result ofthe above-mentioned discharging, to a level lower than a predetermined value, for example, 100 V. In consequence, said discharging circuit is opened and the main discharge capacitor 9 ceases to be discharged.

In conclusion, the main discharge capacitor 9 is certainly discharged after the source switch 2 has been brought back to its initial position but such discharging is interrupted by the neon tube lamp 20 being turned non-conductive. The trigger capacitor 10 is discharged more quickly than said main discharge capacitor 9; this discharging also is stopped by said neon tube lamp 20 being turned nonconductive. Thus the trigger capacitor 10 is maintained at a voltage, for example, of approximately 100 V. Accordingly, no light emission occurs even upon closure ofthetriggerswitch 15 in such a state and the main discharge capacitor 9 is maintained art a voltage level near to the predetermined value, for example, approximately 100 V.

The embodiment of Figure 3 is distinguished from the embodiment of Figure 2 in that the neon tube lamp 20 used in the latter is replaced by a Zener diode 22 which is a constant voltage element adapted to be activated at a voltage lowerthan the voltage at which the neon tube lamp 16 is turned on, for example, approximately 100 V, so as to achieve the same effect as that of said neon tube lamp 20.

The embodiment of Figure 4 is different from the embodiment of Figure 2 in that the trigger switch 15 employed in the latter is replaced by a SCR 23 and this trigger switch 15 is inserted between the gate of said SCR 23 and the emitter ofthetransistor 17 included in the indicating circuit. In this embodiment, use of the SCR 23 results in inversion of the polarity of the source battery 1 of which the negative electrode is connected, as shown, to a negative potential circuit section 24 of the light emitting circuit. Furthermore, the diode 8 and the light emitting diode 18 are inverted while the transistor 4 is of PNP type and the transistor 17 is of NPN type.

With this embodiment, if it is at the state of readiness for light emission when the source switch 2 is brought backto its terminal 2a, the transistor 17 in the indicating circuit remains turned ON, so that the charging resistor 12,the anode P, the current limiting resistor 21, the neon tube lamp 20 and the source switch 2 together form the discharging circuit for the trigger capacitor 10 while the charging resistor 11,the anode P, the current limiting resistor 21, the neon tube lamp 20 and the source switch 2 together form the closed circuit associated with the main discharge capaitor 9.

The charging voltage of the main discharge capacitor 9 thereby drops until the neon tube lamp 16 is turned non-conductive and the transistor 17 is also turned OFF, i.e. the light emitting diode 18 is turned off, when said discharging circuit and closed circuit are interrupted by said transistor 17.

In other words, the neon tube lamp 16 is immediately turned non-conductive when the charging voltage of the main discharge capacitor 9 drops to a voltage lower than the light maintaining voltage, and the transistor 17 is turned off before the trigger capacitor 10 is sufficiently discharged. Considerable charge remains stored in the trigger capacitor 10 but the transistor 17 has already been turned off, so that its emitter potential has already disappeared and, therefore, the SCR 23 is neverturned conductive even if the trigger switch 15 is closed. Thus, although both the main discharge capacitor 9 and the trigger capacitor 10 remain charged to certain levels, closure ofthe trigger switch 15 causes no light emission from the flashlight discharge tube 14, since the SCR 23 is kept non-conductive.

It should be understood thatthe neon tube lamp 20 may be replaced by a Zener diode also in the embodiment of Figure 4.

The embodiment of Figure 5 is identical to the embodiment of Figure 2 exceptthatthere is provided an operating switch 25 of normally open type associated with the discharging circuit in addition to the source switch 2.

With this embodiment, it is possible to achieve the same effect as with the previously mentioned embodiments ofthe present invention by closing said operating switch 25 in suspending flash photographing. Said operating switch 25 may be operatively associated with the source switch 2 that the operating switch is closed when the source switch 2 is opened or may be arranged so that the operating switch 25 is closed independently of the source switch 2.

The embodiment of Figure 6 is identical to the embodiment of Figure 3 except that the neon tube lamp 16 is interposed between the negative potential side of the main discharge capacitor Sand the base of the transistor 17 in the indicating circuit. Also such arrangement permits the same effect as achieved by the previous embodiments to be achieved.

A further type of embodiment will now be considered with reference to circuit arrangements such as those illustrated in Figures 7 to 11.

Many of the charge indicating means used in the flashlight discharger devices of prior art comprise indicating elements such as neon tube lamps or light emitting diodes each adapted to light in responseto a predetermined level of charging voltage, for example, 270 V when the main discharge capacitor has been charged to said predetermined level.

However, such charge indicating means of prior art are commonly disadvantageous in that they remain turned on when the main discharge capacitor has been charged to the predetermined or higher level and, therefore, the lighted indication of the charged state is maintained even after the source switch has been opened to suspend the flashlight photograph ing. The fact that the charge indicating means remains turned on even after flash photography has been suspended is troublesome for the user since, for example, he may be misled into thinkingthatthe flash apparatus will operate when the camera is used. This is particularly confusing with a camera having the charge indicating lamp in its viewfinder or having a built-in flash device.

It is preferred, accordingly, to have charge indicating means adapted to be turned off as soon as the flash is suspended.

Figure 7 shows another circuit arrangement of known type in which the charge indicating means is turned off when the flashlight photographing is given up. It includes a source battery 51, and a source switch 52 provided with terminals 52a,52b. An oscillatory transducer 53 and an oscillatory transistor 54 form a DC-DC converter. A starting resistor 55 is associated with said converter, and a capacitor 56 serves to stabilise its operation. Capacitor 57 and diode 58 form a smoothing circuit. The main discharge capacitor 59 is arranged to be charged by said DC-DC converter.

A charging resistor 60, a trigger capacitor 61, a triggertransducer62 and atriggerswitch 63 together form a trigger circuit adapted to apply excitation voltage to a flashlight discharge tube 64.

A protecting resistor 65 and a neon tube lamp 66 are connected in series to form a voltage detector adapted to be turned conductive when the main discharge capacitor 69 has been charged to a predetermined level.

Reference numeral 67 designates another protecting resistor 68 a light emitting diode serving as a charge indicating lamp and 69 a transistor adapted to be turned on upon application with a base voltage from said voltage detector, a serial circuit section consisting of these members together with said detector forming the charge indicating circuit. It should be understood thatthe light emitting diode 68 should be placed so that its light can be visually recognised externally of the flashlight discharger device.

A circuit section 70 connecting the terminal 52a of the source switch 52 and an anode Q of said protecting resistor 65 and neon tube lamp 66 forms a discharging circuit for the main discharge capacitor 59.

In such circuit arrangement of prior art, when the source switch 52 is thrown into the terminal 52a, the DC-DC converter initiates oscillation to charge the main discharge capacitor 59 and the trigger capacitor 61. When the main discharge capacitor 59 has been charged to a predetermined level, for example, approximately 270 V as said charging progresses, the neon tube lamp 66 is turned on. Thereby the transis tor69 is turned on and the light emitting diode 68 is lit, indicating that a desired light emission is ready.

Upon closure of the trigger switch 63 under this charged state, the flashlight discharge tube 64 emits light in the well known manner.

If it is desired to suspend the flashlight emission in the state in which the light emitting diode 68 has already been turned on and thus the light emission is ready, the source switch 52 may be brought back to the terminal 52a.

As a result of such manipulation, the main discharge capacitor 59 which has been charged to the predetermined or higher level is now discharged through the source switch 52, the circuit section 70 and the protecting resistor 65.

The neon tube lamp 66 is turned non-conductive when the main discharge capacitor 59 has been discharged to a level lower than its discharge maintaining voltage, so that the transistor 69 is turned off and the light emitting diode 68 is also turned off.

In such a manner it is certainly possible with said circuit arrangement of prior art to put off the light emitting diode 68 serving as the charge indicating lamp by bringing the source switch 52 back to the terminal 52a when it is desired to suspend the flashlight emission.

However, such circuit arrangement of prior art is disadvantageous in that the suspension of flashlight emission causes the main discharge capacitor 59 to be fully discharged.

In consequence, to photograph with flash after such suspension, the main discharge capacitor 59 must be charged again from the initial level. Furthermore, each time that a flash is suspended, electric energy which has been stored in the main discharge capacitor must be uselessly consumed.

Moreover, the source switch 52 is always brought back to the terminal 52a when the flashlight discharger device is not used, leaving the main discharge capacitor 59 in uncharged state, so that the electrical characteristics of this capacitor 59 inevitably deteriorate.

Figures 8 to 11 illustrate embodiments of the present invention. It should be noted here that the circuit elements common to those in the circuit arrangement of prior art are designated in these Figures by the same reference numerals as in Figure 7.

Figure 8 shows an embodiment in which a protect ing resistor71 and a neon tube lamp 72 are connected in series to a circuit section 70 through which the main discharge capacitor 59 is discharged.

In this particular embodiment, the neon tube lamp 66 is used as the charge indicating lamp placed so as to be visuaily recognised externally of the flash discharger device. The other neon tube lamp 72 is adapted to be turned on at a voltage lower than the voltage at which said neon tube lamp 66 is turned on.

For example, the lamp 72 may be turned on at 250 V while the lamp 66 is turned on at 270 V.

In Figure 8, a capacitor 73, a Zener diode 74, a protecting resistor 75 and a diode 76togetherform an oscillation stop circuit adapted to stop further oscilla- tion ofthe DC-DC converterwhen the main discharge capacitor 59 has been charged to a predetermined level.

The embodiment thus constructed functions in a manner as will be described below.

When the source switch 52 is thrown to theterminal 52b and thereby starts the DC-DC converter to oscil late, the main discharge capacitor 59 begins to be charged in the same manner as in the circuit arrangement of prior art as shown in Figure7 until the capacitor 59 is charged to a predetermined value, when the neon tube lamp 66 is turned on and indi cates a readiness for light emission.

When the main discharge capacitor 59 has been charged to the predetermined or higher level, the oscillation stop circuit includingthe Zenerdiode 74 is activated to stop further oscillation of the DC-DC converter.

Upon closure of the trigger switch 63 from this charged state, the flash discharge tube 64 emits light in the well known manner.

When it is desired to suspend the flash emission after the neon tube lamp 66 has already been turned on and the readiness for light emission has been indicated, the source switch 52 may be brought back to the terminal 52a. By such manipulation of the source switch, the charge stored in the main discharge capacitor 59 is applied to the neon lamp 72 which is then turned on and, in consequence, the main discharge capacitor 59 is discharged through the switch 52, the neon lamp 72, the protecting resistor 71 and the other protecting resistor 65.

The charging voltage of the main discharge capacitor 59 drops as this discharge progresses and, when the main discharge capacitor 59 has been discharged to a level lowerthan the discharge maintaining voltageforthe neon lamp 66, said lamp is turned off. When the main discharge capacitor 59 has been further discharged to a level lowerthan the discharge maintaining voltage forthe neon lamp 72, this lamp is turned off, interrupting the discharging circuit including the circuit section 70, so that the main discharge capacitor 59 ceases to be discharged.

Thus it is possible for this embodiment to turn off the neon lamp 66 serving as the charge indicating lamp with cosiderable electric charges remaining stored in the main discharge capacitor 59.

The particular arrangement of this embodiment that the flashlight emission can be suspended with considerable electric charges remaining stored in the main discharge capacitor 59 otherwise would be inconvenient in that a normal photographing made immediately after such suspension of the flashlight photographing might be accompanied by unexpected flashlight emission upon closure of the trigger switch 63. This inconvenience can be avoided by providing suitable means to preventthetriggerswitch 63 from being closed in suspension of the flashlight emission.

Figure 9 shows another embodiment in which the neon tube lamp 72 of the embodiment illustrated by Figure 8 is replaced by a Zener diode 77 having a constant voltage characteristic lower than the discharge maintaining voltage for the neon tube lamp 66. This embodiment functions in the same manner as the embodiment of Figure 8.

Figure 10 shows further another embodiment in which the protecting resistor 71, the neon tube lamp 72, and a switch 78 of normally opened type are serially connected to the circuit section 70 of the well known circuit arrangement as illustrated by Figure 7.

In this embodiment, the source switch 52 is realised as the single circuit switch and the oscillation stop circuit is formed by a constant voltage element 74 and a protecting resistor 75.

When the source switch 52 is closed with a switch 78 being opened, the main discharge capacitor 59 and the trigger capacitor 61 are charged. The neon tube lamp 66 is turned on when the main discharge capacitor 59 has been charged to a predetermined level, and thereby the transistor 69 is turned on, so that the light emitting diode 68 is turned on, indicating a readiness for light emission.

In this embodiment, the charge indication is given by repeated flickering of the light emitting diode 68.

More specifically, the neon lamp 66 and the light emitting diode 68 are turned on and simultaneously the Zener diode 74 is turned conductive when the main discharge capacitor 59 has been charged to the predetermined level. Charges stored in the main discharge capacitor 59 are released through the emitter-base path of the oscillatory transistor 54, the Zener diode 74 and the protecting resistor 75, resulting in that the oscillatory transistor 54 is kept in OFFstate and the DC-DC converter ceases to oscillate. The charging voltage of the main discharge capacitor 59 drops as such discharging progresses, and such voltage drop causes the neon tube lamp 66 to be turned non-conductive and causes the light emitting diode 68 also to be turned off.The Zener diode 74 is turned non-conductive as the main discharge capacitor 59 is discharged, so the DC-DC converter initiates again oscillation to charge the main discharge capacitor 59 again to the predetermined level at which the neon tube lamp 66 and the light emitting diode 68 are turned on (lit) again.

Thus, the flickering indication by the light emitting diode 68 is obtained as the main discharge capacitor 59 is repeatedly charged and discharged.

When it is desired to suspend flash emission, the switch 78 may be closed. If the main discharge capacitor 59 is already charged to the predetermined level, the charge is discharged through the associated discharging circuit including the neon tube lamp 72 and thus the charging voltage of said capacitor 59 drops. As a result, the neon tube lamp 66 is turned non-conductive and the light emitting diode 68 is turned off. Immediately thereafter the neon tube lamp 72 also is turned non-conductive and the main discharge capacitor 59 ceases to be discharged.

Figure 11 shows still anotherembodiment in which a transistor of PNP type is employed as the oscillatory transistor 54 and the trigger circuit includes an SCR 79 adapted to be turned conductive upon closure ofthe trigger switch 63. In this embodiment, the trigger switch 63 provided on the gate of the said SCR 79 is connected to an anode R ofthe light emitting diode 68 and the transistor 69 so thatthe flashlight emission is initiated only upon closure of the trigger switch 63 with the light emitting diode 63 having been turned on.Accordingly, considerable electric charge remains stored in the main discharge capacitor 59 even after suspension of the flashlight emission but the manipulation for suspension of the flashlight emission causes the light emitting diode 68 to be turned off, so that no voltage signal appears at the anode Rand light emission is not initiated even when the trigger switch 63 is closed afterthe flash emission has been given up. In this embodiment, the source battery 51 and the diodes 58,74 and 76 are connected so that their polarities are inverted, since the oscillatory transistor 54 is of PNP type. However, this embodiment is identical to the previously mentioned embodiments so far as the rest of the arrangement and the function are concerned.

It will be understood from the aforegoing description that the present invention enables the charge indicating lamp to be put off substantially upon suspension of the flash emission when it is desired to suspend the emission. The main discharge capacitor can be maintained at a voltage level slightly lower than the predetermined level to achieve said readiness for light emission even after the emission has been suspended. Thus subsequent recharging to permit flash photography may be rapidly achieved, and the main discharge capacitor may be protected against deterioration of its electrical characteristics by keeping it adequately charged during non-use.

Figures 12 to 14 illustrate still other embodiments of the present invention.

Many recent flash devices are arranged to be electrically connected not only through the synchro signal circuit but also through other signal circuits to the camera. For example, there have already been proposed (a) a signal circuit by which a signal supplied from the flash device is used to unlock the camera shutter and to actuate a charge indicating lamp in the viewfinder; and (b) a signal circuit by which signals representing factors such as a diaphragm value and a film sensitivity supplied from the camera are used to set the flash device to a given condition of light emission.

Such signals supplied from the flash device to the camera are generally adapted to be supplied at a moment when the device has been prepared for light emission, i.e. when the main discharge capacitor has been charged to a predetermined level so that the respective signal generators are responsive to a voltage higher than said predetermined level to which the main discharge capacitor has been charged to be started.These signal generators comprise, for example, the charge indicating circuit including the neon lamp connected in parallel to the main discharge capacitor so that said indicating circuit generates signals when said lamp is turned on orthe Zener diode adapted t9 be turned conductive and thereby to generate signals when a potentiometer connected in parallel to the main discharge capacitor indicates a voltage higher than a predetermined value.

However, these signal generators of prior art are disadvantageous in that electric current flows through them always or so long as the main discharge capacitor is at a voltage level higher than the predetermined value. This can represent a serious drain on the battery.

Figure 12 shows a flash discharger circuit provided with a generator of a signal indicating the readiness for light emission. There are a source battery 101, a source switch 102, a transducer 103 and a transistor 104 which together form a DC-DC converter, with a starting resistor 105 and a stabilising capacitor 106. A capacitor 107 and a diode 108 form a smoothing circuit. A main discharge capacitor 109 is of well known type. Atrigger capacitor 110 is adapted to be charged through a charging resistor 111. Atriggertransformer 112 serves to apply excitation voltage to a flashlight discharge tube 113. An SCR 114 is adapted to be turned conductive upon closure of a trigger switch 115. The components 110-1 l5togetherform atrigger circuit.

A neon tube 116, a resistor 117 and a capacitor 118 form a serial circuit section, said neon tube 116 forming, together with a capacitor 119 connected in parallel thereto, a flickering circuit. Respective elements forming said flickering circuit are so adjusted that this flickering circuit initiates flickering when said main discharge capacitor 109 has been charged to a predetermined level, and said flickering circuit serves as a detector for the charging voltage of said main discharge capacitor.

Atransistor 120 is of high input impedance, and is arranged to be activated when the charging voltage of said capacitor 118 is applied across the baseemitter path thereof. This capacitor 118 and transistor 120 form a kind of holding circuit.

A switching transistor 121 is adapted to be turned on upon application of a control signal when said transistor 120 of said holding circuit is turned conductive, and this transistor 121 forms together with a light emitting diode 122 connected to the collector thereof a charge indicating circuit. The charge indicating circuit is connected, as illustrated, so as to be energised from the source battery 101.

A terminal 123 of the collector junction S of the transistor 121 forming said charge indicating circuit functions as a signal terminal to transmit a signal indicating a readiness for light emission to the camera. Although said trigger switch 115 is shown as connected between said junction S and the gate of said SCR 114, this is not critical and the switch 115 may be connected to any one of the signal generators of known type.

Reference numeral 124 designates a gate resistor, 125,126 and 127 protecting resistors, and 128 a bias resistor.

The circuit functions as follows.

Upon closure of the source switch 102, the DC-DC converter initiates its oscillation to charge the main discharge capacitor 109, the trigger capacitor 110 and the capacitor 119 for flickering.

The flickering circuit consisting of the neon tube 116 and the capacitor 119 is not activated during a preparatory period for light emission before the main discharge capacitor 109 has been charged to the predetermined level, so that there is no electric charge in the capacitor 118, the transistor 120 is in nonconductive state and the transistor 121 remains turned off. Accordingly, the light emitting diode 122 also remains turned off during this preparatory period.

When the main discharge capacitor 109 has been charged to the predetermined level, for example, approximately 270 V as charging progresses, said flickering circuit serving as the charge detector initiates flickering and thereby the capacitor 118 begins to be charged. As a result, the transistor 120 is turned conductive and thereby the transistor 121 is turned on, so the light emitting diode 122 is now turned on with energisation from the source battery 101 and indicates a readiness for light emission.

With the light emitting diode 122 being turned on, there appears on the junction S a constant voltage which is, in turn, transmitted through the terminal 123 to the camera as the signal indicating the readiness for light emission. Then, said constant voltage apearing on the junction S is applied, upon closure of the trigger switch 115, to the gate ofthe SCR 114 which is then turned conductive and thereby the flashlight discharge tube 113 is triggered to emit light in the well known manner.

The main discharge capacitor 109 is substantially discharged as the flashlight discharge tube 113 emits light and, as a result, the flickering circuit serving as the charge detector ceases its flickering. The capacitor 118 is rapidly discharged through the base-emitter of the transistor 120, causing both transistors 120 and 121 to be turned off, and now the light emitting diode 122 is turned off.

With the source switch 102 remaining closed, the flickering circuit initiates flickering in the same manner as in the above-mentioned case when the main discharge capacitor 109 has been charged to the predetermined level, so the light emitting diode 122 is turned on and the signal indicating readiness for light emission appears on the junction S.

When the source switch 102 is opened in the state ready for light emission in which the main discharge capacitor 109 has already been charged to a level higher than the predetermined level, the flickering circuit for charge detection continues flickering until the main discharge capacitor 109 is discharged to a level lowerthan the predetermined level, whereupon said flickering ceases. The light emitting diode 122 is turned off upon opening of the source switch 102 independently of said flickering generated by the flickering circuit, and the signal indicating readiness for light emission also disappears from the junction S.After the flickering circuit for charge detection has ceased its flickering, discharging of the main discharge capacitor 109 is substantially suppressed and, even when the source switch 102 remains opened, the main discharge capacitor 109 as well as the trigger capacitor 110 maintains a considerably high charging voltage stored therein. However, the transistor 121 included in the charge indicating circuit has been turned off and no voltage appears on the junction S, so that the SCR 114 is not turned conductive and the flash dischargetube 113 is notturned on even if the trigger switch 115 is closed in such as state.

Accordingly, also in the case that the source switch 102 is opened to suspend the flash and immediately thereafter normal photography occurs, no unnecessary light emission occurs.

The embodiment of Figure 13 is identical to the embodiment as illustrated by Figure 12 except that the serial circuit section (116,117,118) shown in Figure 12 is modified herein.

This embodiment includes a transistor 130 adapted to receive at the base the signal from the flickering circuit through a protecting resistor 129. Through said transistor 130, the capacitor 118 is charged from the source switch 101. In this manner, the transistor 130 is repeatedly turned on and off as the flickering circuit including the neon tube 116 and the capacitor 119 provides flicker signals. The capacitor 118 is correspondingly charged and functions in the same manner as in the embodiment of Figure 12. Figure 14 shows an embodiment identical to the embodiment of Figure 13 except that the emitter of the transistor 121 included in the charge indicating circuit is con netted not through the source switch 102 but directly to the source battery 101.

In this embodiment, light emission is achieved upon closure of the trigger switch 115 even when the source switch 102 is opened, so long as the flickering circuit for charge detection continues to provide flicker signals, since the light emitting diode 122 remains alight so far as said flickering circuit supplies flicker signals. Therefore, this embodiment can be effectively incorporated into a flash device having a source switch 102 adapted to be automatically opened.

As will be understood from the aforegoing description, a flash discharge circuit provided with a generator for a signal indicating readiness for light emission and embodying the present invention may be arranged so that the charging voltage of the main discharge capacitor is detected by the flickering circuit including the neon tube and the capacitor and the load member such as the light emitting diode is energised from the source battery in response to the electric flicker signal supplied from said flickering circuit.

Accordingly, electric current necessary to generate flickering certainly flows through said flickering circuit, but power consumption by the circuit arrangement is substantially smaller than for the known device through which the circuit current continuously flows to generate the signal indicating readiness for light emission.

Once said flickering has ceased, the main discharge capacitor cannot be discharged through the flickering circuit, since said flickering circuit includes the neon tube and the capacitor. In consequence, the main discharge capacitor maintains a considerably high charging voltage even after the source switch has been opened to suspend the flash for a long period until the flash device is required to be used. Thus the energy stored in the main discharge capacitor is not wasted, and a relatively short charging time suffices for the next flash.

Claims (5)

1. A photographic flash apparatus including a main discharge capacitor; means for charging said capacitor; indicating means capable of indicating when the capacitor has been charged to a level at least as high as a predetermined level; means for transferring the apparatus to a non-operative state; charge releasing means operable to release charge stored in said capacitor when the apparatus is transferred to its non-operative state; and blocking means arranged to block further release ofthe stored charge from said capacitor in response to a drop ofthe charging voltage to a level below the predetermined level, said blocking being removable by recharging the capacitor so that said indicating means is reset.

2. Apparatus according to claim 1 including: a DC-DC converter for boosting a low voltage of a source battery; a trigger capacitor connected through a resistor member to said main discharge capacitor and arranged to be charged by said converter; a flash discharge tube arranged to be triggered by a trigger circuit including said trigger capacitor and to be supplied with energy stored in said main discharge capacitorsoastoemitlight; and a discharging circuit for said trigger capacitor established via an operating switch; said blocking means comprising a current regulating member arranged in said discharging circuit so that the latter is opened by this member when said main discharge capacitor has been discharged together with said trigger capacitor through a partial section of said discharging circuit down to a predetermined level.

3. Apparatus according to claim 1 wherein said charge indicating means comprises a circuit including a neon lamp adapted to be lit in response to said predetermined level of charging voltage on the main discharge capacitor; the apparatus including a switch actuable to prevent a flash emission in advance, a discharging circuit for the main discharge capacitor established via said switch; and wherein said blocking means comprises a switching member having a lower constant voltage characteristic relative to a discharge maintaining voltage of said neon lamp and connected to said disharging circuit, wherein the switching member is activated, after the neon tube lamp has been turned off, so asto open said discharging circuit.

4. Apparatus according to claim 1 including: DC source means; a DC-DC converter connected thereto for boosting the voltage; a flash discharge tube adapted to be triggered by trigger means and to be supplied with energy stored in said main discharge capacitor so as to emit light; a flickering circuit adapted to be started in response to said predetermined level of charging voltage; a holding circuit comprising a switching element and a capacitor adapted to be charged with flicker signals of said flickering circuit; and a load member connected to said DC source means through a switching element adapted to be turned conductive in response to an output from said holding circuit, wherein a predetermined train of signals appearing at said load member can be taken out as a preparatory signal for light emission.

5. Photographic flash apparatus substantially as any described herein with reference to or as illustrated in any of Figures 2to 6 or any of Figures 8to 14.