Electronic Flash Charging And Triggering Circuitry

Abstract

A charging and triggering circuit for an electronic flash device of the type in which a voltage for triggering the flash is stored by a condenser comprises structure for generating a feedback signal in response to the triggering of the flash tube to actuate an oscillating circuit for charging the condenser with the rectified oscillatory output. A circuit disables the oscillator when the condenser has reached a voltage sufficient to actuate the flash tube thereby reducing the power consumed from a battery which energizes the circuitry.

Parent Case Text

This is a continuation of application Serial No. 30,828, filed Apr. 22, 1970, now abandoned.

Description

BACKGROUND OF THE INVENTION

In flash discharge equipment wherein a battery is used as a power source, in order to miniaturize and lighten the equipment battery of a small volume and capacity is generally used, so that if for example the power switch is left closed, the battery is wasted on account of the leakage current running through the condenser for lighting the flash discharge tube in the secondary high voltage circuit and the current running through the oscillator in the primary circuit.

SUMMARY OF THE INVENTION

The present invention relates to electronic flash equipment of the type using an oscillator operated by a battery and a circuit for charging a condenser for lighting a flash discharge tube by boosting and rectifying the output from the oscillator. A power switch connected between a power source and the oscillator initially actuates a SCR to energize the oscillator and charge the condenser. The current running through the SCR is eventually reduced below its holding current when the condenser for lighting the flash discharge tube is charged.

The first object of the present invention is to provide electronic flash circuitry wherein the power source battery consumption is considerably reduced, by opening automatically a power switch when the charging condenser for lighting a flash discharge tube is substantially completed.

The second object of the present invention is to provide electronic flash circuitry for recharging a condenser for lighting a flash discharge tube by closing automatically a power switch when the condenser is discharged after energizing the flash discharge tube.

The third object of the present invention is to provide electronic flash circuitry wherein a power switch is opened and closed automatically so as to charge a condenser for lighting a flash discharge tube within the limit of a constant voltage at all times.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit diagram of a first embodiment of the present invention.

FIG. 2 is a graph showing the change in the charging current of a condenser for lighting a flash discharge tube in the embodiment shown in FIG. 1.

FIG. 3 is a circuit diagram of a second embodiment of the present invention.

FIG. 4 is a graph showing the oscillating voltage characteristic of the oscillator in the embodiment shown in FIG. 3.

FIG. 5 is a circuit diagram of the primary side oscillation circuit of a modified embodiment provided with a circuit for holding the conduction of the SCR in the second embodiment of the present invention.

FIG. 6 is a circuit diagram of a third embodiment of the present invention.

FIG. 7 is a circuit diagram of a fourth embodiment of the present invention, which is arranged to maintain the charging voltage of a condenser for lighting a flash discharge tube within the limit of a constant voltage.

FIG. 8 is a graph showing the voltage of the trigger condenser caused by the relaxation oscillation circuit in the embodiment shown in FIG. 4.

FIG. 9 is a graph showing the charging voltage of the condenser for lighting a flash discharge tube in the embodiment shown in FIG. 8.

FIG. 10 is a circuit diagram of a fifth embodiment of the present invention .

DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 is a circuit diagram of the first embodiment of the electronic flash circuitry in accordance with the present invention, wherein lighting circuit b is formed as follows. Flush discharge tube 13, on which the voltage of condenser 8 for lighting is impressed, is provided with trigger electrode 12 and when the charging voltage of trigger condenser 9 is discharged to the primary side of trigger transformer 11 by closing synchro switch 10 the secondary side voltage of trigger transformer 11 is impressed on trigger electrode 12 to discharge condenser 8 for lighting flash discharge tube 13, and accordingly lighting circuit b is momentarily lit.

The charging of condenser 8 is effected by oscillator a wherein transistor 3 is connected to the primary circuit of transformer 4, and the secondary current of transformer 4 is rectified by diode 7. And, to the base of transistor 3 there is connected the oscillation circuit composed of resistance 5 and condenser 6 and the negative side of power source battery 1 is connected to the collector of transistor 3. The positive side of power source battery 1 is connected to the emitter of transistor 3 through SCR 2.

A trigger circuit for the gate of SCR 2 is formed through resistance 21. One part of the SCR trigger circuit is a series circuit composed of battery 18 and normally open starting switch 19 and the other part is provided with rectifier 23 and one winding 20 coupled magnetically with trigger transformer 11.

In lighting circuit b, condenser 8 is connected in parallel with indicating neon tube 17 connected in series to protective resistance 16, and to both sides of trigger condenser 9 in parallel with condenser 8 adjusting resistances 14, 15 are connected in series with each other.

The gate of SCR 2 is connected to battery 18 by closing starting switch 19 and thereby made conductive, and accordingly condenser 8 and trigger condenser 9 are charged through transistor 3, transformer 4, and diode 7. As shown by curve m in FIG. 2, the charging current decreases during the time required for increasing of the charging voltage of conenser 8, and when the charging voltage is sufficient to flash discharge tube 13, neon tube 17 for indicating the conclusion of charging lights.

Meanwhile, when the charging current gets below a fixed value the current running through the base of transistor 3 also decreases gradually and at last drops down below the current value necessary to hold SCR 2 in the conductive state, and accordingly SCR 2 is turned off and the operation of the oscillator is automatically stopped. That is, with condenser 8 and trigger condenser 9 charged above the constant voltage necessary to light the flash discharge tube, the circuits prevents power source battery 1 from wasting current, and thus, even without opening manually the power switch.

Next, when synchro switch 10 is closed, the high voltage is impressed on trigger electrode 12, flash discharge tube 13 is lit, and condenser 8 is discharged. However, in this case AC voltage is induced in coil 20 which is one winding for trigger transformer 11 so that SCR 2 is turned on, oscillator a is connected to power source 1, and condenser 8 is charged again. When condenser 8 is charged to the constant voltage SCR 2 is shut off again as described above.

Therefore, every time the flash is ignited condenser 8 is also charged automatically and even when used repeatedly there is no need for the manual opening and closing of the power switch.

With reference to FIG. 3, in order to initially effect the conduction of SCR 2, while in the first embodiment battery 18 is provided, in the second embodiment shown in FIG. 3 the positive side of power source battery 1 is connected to the gate of SCR 2 through starting switch 19 and resistance 21 In all other respects the second embodiment is essentially the same as the first embodiment.

In the first and second embodiments, the time for the SCR to be shut off from a conductive state is generally from 10 to 20 .mu.sec. Therefore, when the half period of oscillation frequency shown by curve n in FIG. 4 is longer than that turn off time, the SCR is shut off and the circuit does not operate as described above. In order to make the half period shorter than the turn off time, the oscillation frequency must be made above 25 KC, however, in view of the conversion efficiency of a transistor oscillator the suitable oscillation frequency should be below 5 KC.

In the embodiments mentioned above, therefore, it is necessary to use a SCR having a long turn off time, or the oscillation frequency must be increased.

In the modification of the second embodiment shown in FIG. 5 this matter is solved, and between the base and emitter of transistor 3 of the oscillator, holding condenser 22 is connected in parallel with SCR 2 so as to form a holding circuit. In this manner, even though the oscillation frequency of oscillator a is low as compared with the turn off time of SCR 2, in the conductive state condenser 22 is charged and the charging current is discharged during phase to of the oscillator, so that SCR 2 is not shut off.

The third embodiment shown in FIG. 6 in accordance with the present invention is an embodiment in which the base and collector of transistor 3 are coupled with transformer 4. That is, the base of transistor 3 is connected to a coil on the secondary side of transformer 4, and the oscillation circuit composed of resistance 5 and condenser 6, and power source battery 1 are connected to the emitter through SCR 2. And, the collector circuit of transistor 3 is connected to the negative side of power source battery 1 through the coil on the primary side of transformer 4 and connected to one electrode of condenser 8 from the coil on the secondary side of transformer 4 through diode 7.

In every embodiment described above, when condenser 8 reaches a substantially constant voltage SCR 2 shuts off the oscillation circuit, so that in order to effect again the conduction of SCR 2 it is necessary to light flash discharge lamp 13 or close manually starting switch 19.

However, after condenser 8 is charged once to the constant voltage, even though flash discharge lamp 13 is not lit charging current is discharged gradually through neon tube 17 for indicating the charging condition, and on account of the internal leakage of condenser 8 and trigger condenser 9 the charging voltage drops gradually and at last gets below the voltage possible to light flash discharge lamp 13. Therefore, as long as starting switch 19 is not closed flash discharge lamp 13 cannot be flashed.

The embodiments shown in FIGS. 7 and 10 remove such a drawback as mentioned above, and when condenser 8 reaches a substantially constant voltage, the SCR shuts off automatically the oscillator, however, when the charging voltage drops below a certain voltage the SCR is adapted to effect automatically the operation of the oscillator so as to furnish charging current.

In the lighting circuit b shown in FIG. 7, there is connected in parallel with condenser 8 trigger condenser 9 having on its both sides respectively resistances 14 and 15, and in parallel with the primary winding of trigger transformer 11 connected through the synchro switch, there are series connected resistance 16' and neon tube 17' for indicating the charging condition. The junction between neon tube 17' and resistance 16' is connected to the gate of SCR 2 together with the starting circuit, and relaxation oscillator C is formed by condenser 8, trigger condenser 9, and neon tube 17' and resistance 16'.

Therefore, after condenser 8 is charged, the appropriate charging voltage is divided by resistances 14, 15 to charge trigger condenser 9, however, the charging voltage of trigger condenser 9 is discharged gradually through neon tube 17' and resistance 16', and the terminal voltage of trigger condenser 9 drops and neon tube 17' is extinguished. After that, condenser 9 is charged through resistances 14, 15 by condenser 8 and neon tube 17' is lit again.

In this manner, relaxation oscillation is repeated and while the voltage of trigger condenser 9 is changing as shown by curve p in FIG. 8 the charging voltage of condenser 8 also damps gradually.

However, when neon tube 17' is lit the voltage drop in resistance 16' is fed to the gate of SCR 2, so that SCR 2 is turned on to replenish charging to condenser 8. And thus, the charging voltage of condenser 8 is shown by curve q in FIG. 9 and is maintained between voltages V.sub.1 and V.sub.2, which is sufficient for enabling flash discharge tube 13 to discharge by closing synchro switch 10.

And thus, in this embodiment, when the excitation condenser reaches the substantially constant voltage oscillator a and power source battery 1 are shut off by the SCR, and when the charging voltage of the excitation condenser drops to some extent the SCR is turned on to replenish charging and maintain it within the limits of the constant voltage.

Switch 24 is a manual power source switch and is normally opened, however, even if it remains closed it the power source battery is used only for replenishing a portion in which the charging voltage of condenser 8 is low, so that it is possible to prevent unnecessary consumption of the power source battery.

In the embodiment shown in FIG. 10, the charging voltage of condenser 8 is maintained within the limits of the constant voltage in the same manner as the previous embodiments, and the base and the collector connections of transistor 3 in oscillator a are the same as those coupled with transformer 4 in FIG. 6. The modified embodiment of FIG. 5 may be used with any of the other embodiments.

Claims

I claim:

1. A charging and triggering circuit for an electronic flash device comprising:

an electric power source;

a transformer connected to said power source and including a winding for generating an oscillatory output;

means for rectifying said oscillatory output;

a flash circuit including means for storing the rectified output of said rectifying means, a flash tube, said transformer including primary and secondary windings for triggering said flash tube, and said transformer further including an additional winding for generating a feedback signal in response to the triggering of said flash tube; and

means for controlling said oscillating means including an SCR having its gate connected to said additional winding to be made conductive by said feedback signal to oscillate said oscillating means, and said SCR is made non-conductive with said means for storing at a voltage sufficient to actuate said flash tube whereby said oscillating means are de-actuated.

2. A circuit as in claim 1 further comprising means for initiating the operation of said transformer for generating an oscillatory output.

3. A circuit as in claim 2 further comprising means for maintaining said SCR conductive at all operating frequencies of said transformer during charging of said means for storing.

4. A circuit as in claim 2 wherein said flash circuit further includes means for indicating the condition of said means for storing and means interconnecting said indicating means with said SCR, whereby said SCR is inoperative to actuate said transformer with the actuation of said means for indicating and are operative with said means for indicating non-conductive to actuate said transformer.

5. A circuit as in claim 3 wherein said means for maintaining conduction of said SCR at all frequencies is a capacitor connected across said SCR.

6. A circuit as in claim 1 further comprising means for indicating that said means for storing is at a voltage sufficient to actuate said flash tube.

7. A circuit as in claim 4 wherein said means for indicating is parallelly connected with said transformer, said means for initiating operation of said transformer comprising a manually operated switch interconnecting the gate of said SCR to said power source, and further comprising a circuit interconnecting said gate with said means for indicating.