JPH0128496Y2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to an electronic flash device that is useful as an artificial light source for photography, and in particular has a sub-capacitor that performs discharge to make up for the lack of light emission due to discharge of the main discharge capacitor. This invention relates to an electronic flash device.

Conventionally, as an electronic flash device having two capacitors as described above, the one shown in FIG. 1 is well known.

In FIG. 1, when the power switch 1 is turned on now, the low voltage power supply 2 is supplied to the DC-DC converter circuit 6 consisting of an oscillation transistor 3, an oscillation transformer 4, a diode 5, etc., and this circuit 6 starts operating. Then, the voltage of the low voltage power supply 2 is increased, and charging of the sub capacitor 15 and the trigger capacitor 10 via the main discharge capacitor 7 and the diode 14 is started.

When the charging voltage of the main discharge capacitor 7 reaches a state in which light can be emitted, the neon tube 8 lights up to notify that the state in which light can be emitted is enabled.

When the synchro switch 9 of the trigger circuit 12 is turned on in the above state, the charge charged in the trigger capacitor 10 is discharged via the trigger transformer 11, so the flash discharge tube 13 is excited and the charge charged in the main discharge capacitor 7 is discharged. It consumes and emits light.

At this time, if the amount of light emitted is insufficient due to the distance to the subject or the aperture setting of the camera, etc. due to the discharge of the main discharge capacitor 7, the charge in the sub capacitor 15 is transferred to the flash discharge tube 13 via the thyristor 16.
In other words, a light emitting operation is performed to compensate for the deficiency.

Now, to describe the light emitting operation by the sub-capacitor 15 in more detail, as is clear from FIG. 1, a thyristor 16 is inserted in the discharge loop of the sub-capacitor 15. Therefore, unless this thyristor 16 is first made conductive, the sub capacitor 15 will not be discharged.

Incidentally, an inverting circuit 17 is connected between the gate and cathode of the thyristor 16, and needless to say, when the inverting circuit 17 is brought into operation, the thyristor 16 is rendered conductive.

On the other hand, the inverting circuit 17 is configured such that its operation is controlled by the transistor 18 and the detection section 19, and its operation is brought into operation when the transistor 18 is turned on.

The detection unit 19 receives a signal from inside the camera (not shown)
Specifically, in response to the aperture value setting operation of the camera or the distance setting operation to the subject, if the amount of light emitted by the discharge of the main discharge capacitor 7 is insufficient under the set conditions, the operation of the transistor 18 is controlled by It operates as if turning on 18.

Due to the relationship between each structure as described above, when the light emitting operation as described above, that is, the amount of light emitted by discharging only the main discharge capacitor 7, causes an insufficient amount of light, the light emission by discharging the sub capacitor 15 to make up for the shortage. Therefore, an electronic flash device of very high practical value can be obtained.

However, considering the following cases, there are still problems in putting the electronic flash device shown in FIG. 1 into practical use.

That is, in the circuit configuration shown in FIG.
The charging voltage value of thyristor 5 becomes high, and the charging voltage value of thyristor 1 increases.
6 becomes conductive, for example, once a light emission operation is performed that does not use the charge charged in the sub capacitor 15, and the next shooting condition setting requires the charge charged in the sub capacitor 15, the sub capacitor 15 becomes conductive. A phenomenon occurs in which the charged charges of 15 instantaneously flow into the main discharge capacitor 7.

At this time, the sub capacitor 15, the thyristor 16,
The value of the current flowing through the closed loop consisting of the main discharge capacitor 7 is extremely large. Therefore, if you do not pay attention to the withstand capacity of thyristor 16, this thyristor 1
6 will be destroyed. Therefore, when the circuit shown in FIG. 1 is put into practical use, the thyristor 16 must be selected taking into account the withstand capacity necessary for regular discharge as well as the withstand capacity sufficient to form the closed loop. It was hot.

Also, considering the energy usage efficiency from the perspective of the low-voltage power supply 2, from the perspective of the sub-capacitor 15 once charging is completed, the phenomenon of the formation of the closed loop described above is due to the operation of instantaneous discharging and subsequent charging. There is nothing but
The capacitor is charged and discharged, which not only does not contribute to the light emitting operation at all, but also causes energy loss, and the power source is not being used effectively, resulting in extremely poor efficiency.

As a device that prevents the secondary capacitor from discharging other than when the flash discharge tube is discharging light, a current detection element connected in series with the flash discharge tube detects the discharge current at the time of light emission, and turns on a switch element after a predetermined delay time. Some devices are configured to discharge a secondary capacitor through a flash discharge tube. (Utility Model Publication No. 50-24128).

However, this device uses a current detection element to detect the discharge current itself when the flash discharge tube emits light. Therefore, the current detection element not only needs to withstand a large current of several hundred amperes, but also This also causes a loss of charging energy of the capacitor for discharging and emitting light.

The present invention is intended to solve such problems, and will be explained below using the drawings.

FIG. 2 is an electric circuit showing an embodiment of an electronic flash device according to the present invention, and the same numbers as those in FIG. 1 are constituent elements having the same functions.
0 is resistance 21, 24, 26, capacitor 22, 2
8. A lock circuit consisting of a diode 23 and transistors 25 and 27; 29 is a switch having almost the same function as the inverting circuit 17, transistor 18, and detection section 19 in FIG. 1; The switches 30 and 31 are connected to the low voltage power source 2 via the power switch 1 and are turned off when the shooting conditions in the camera are set such that the amount of light emitted from the main discharge capacitor 7 alone is insufficient. A thyristor 16 is connected to the thyristor 16 and is a voltage applying means that functions to apply a conduction voltage to the gate of the thyristor 16 when the power switch 1 is turned on.
The gate resistors are shown respectively.

Next, the operation will be explained.

Now, when the power switch 1 is turned on, the DC-DC converter circuit 6 starts operating, and charging of the main discharge capacitor 7, trigger capacitor 10, and sub-capacitor 15 starts, as in the conventional example explained earlier. . At the same time, as is clear from the drawing, the capacitor 22 of the lock circuit 20 is also charged via the diode 23 and the resistor 21.

Further, since a base current is supplied to the transistor 27 by the low voltage power supply 2 via the resistor 26, the transistor 27 is rendered conductive. The fact that the transistor 27 is in a conductive state means that the gate and cathode of the thyristor 16 are short-circuited, and in this embodiment, the thyristor 16 is forcibly maintained in a non-conductive state at the same time as the power switch 1 is turned on. It turns out.

For this reason, when the power switch 1 is turned on, even if the switch 29 is turned off by the settings in the camera, the thyristor 16 is not made conductive.

On the other hand, when the synchro switch 9 of the trigger circuit 12 is closed in a state in which the charging of each capacitor described above progresses and the charging of the main discharge capacitor 7 is completed, the flash discharge tube 13 is excited and the main discharge capacitor 7 is charged. It consumes charge and emits light.

At this time, the charge stored in the capacitor 22 is discharged through the resistor 24, the base-emitter of the transistor 25, the flash discharge tube 13, and the resistor 21, so that the transistor 25 becomes conductive. When the transistor 25 is made conductive, the current flowing from the low-voltage power supply 2 through the resistor 26, which had previously been supplied to the base current of the transistor 27, is bypassed by the transistor 25, and the current that had been supplied to the base current of the transistor 27 is bypassed by the transistor 25. The transistor 27 which was in the state becomes non-conductive, and as a result,
The short circuit between the gate and cathode of the thyristor 16 is released.

In other words, the forced non-conduction state of the thyristor 16 is released only after the flash discharge tube 13 emits light, and it is only in this released state that the thyristor 16 can be controlled by operating the switch 29. That's why.

In the state where the flash discharge tube described above emits light,
If the settings in the camera are such that the amount of light emitted by the main discharge capacitor 7 alone is insufficient for exposure, the switch 29 is turned off, so the gate of the thyristor 16 is connected to the resistor 30,
31, a voltage obtained by dividing the voltage of the low voltage power supply 2 is applied, and the thyristor 16 is made conductive.

Conversely, if a sufficient amount of exposure can be obtained from the amount of light emitted by the main discharge capacitor 7, the short circuit caused by the transistor 27 is canceled but the switch 29
is turned on, so the thyristor 16 maintains a non-conducting state.

The conduction period basically depends on the discharge time constant of the capacitor 22 via the resistor 24, the capacitor 28, the flash discharge tube 13, and the resistor 21, and the discharge time constant between the base and emitter of the transistor 25 of the capacitor 28. In other words, the short-circuit release period between the gate and cathode of the thyristor 16 by the transistor 27 is controlled by the above-mentioned time constant, and can be set appropriately.

However, since the discharge time constant of the former capacitor 22 is the time constant with the longest light emission period of the flash discharge tube 13, if it is set short, there is a risk of malfunction even when combined with the period due to the latter time constant. The conduction period of 25 is actually
It goes without saying that it is desirable to set the former discharge time constant to be longer than the longest light emitting time of the flash discharge tube 13, and to set it to a period in which the latter discharge time constant is added thereto.

The electronic flash device according to the present invention shown in FIG.
It operates as described above,
Considering the backflow of the charge in the sub-capacitor 15 to the main discharge capacitor 7, which was a problem with the conventional device shown in FIG. Since it is maintained in a conductive state, the time when the charge in the sub capacitor 15 can be discharged is only when the flash discharge tube 13 emits light, and during that period, the charge in the sub capacitor 15 can be discharged.
2 and the discharge time constant of the capacitor 28, the possibility of the above-mentioned backflow occurring can be almost eliminated.

As described above, the electronic flash device of the present invention can be used to set shooting conditions that require the charge of the sub-capacitor after performing light emission photography by discharging the main discharge capacitor without using the charge of the sub-capacitor. This eliminates the risk of malfunctions such as the charge in the sub capacitor flowing into the main capacitor.

[Brief explanation of the drawing]

FIG. 1 is an electric circuit diagram of a conventional electronic flash device, and FIG. 2 is a circuit diagram of an embodiment of an electronic flash device according to the present invention. 6...DC-DC converter circuit, 7... Main discharge capacitor, 12... Trigger circuit, 13... Flash discharge tube, 15... Sub-capacitor, 16... Thyristor, 20... Lock circuit, 22... Auxiliary Capacitor, 25, 27...transistor.

Claims (1)

[Scope of utility model registration request] Flash discharge tube and DC boosting voltage of low voltage power supply
- a main discharging capacitor and a sub capacitor charged by a DC converter circuit, a first switching element discharging the sub capacitor via the flash discharge tube when brought into conduction; The control electrode is connected to a control electrode, and is turned off when the shooting conditions in the camera are such that the amount of light emitted by the flash discharge tube is insufficient due to the charge charged in the main discharge capacitor, and turned on when the amount of light is not insufficient. a switch for controlling application of a conduction voltage to the DC-DC
An auxiliary capacitor charged by the converter circuit is connected to the control electrode, and is made conductive at the same time as power is supplied from the low-voltage power source to the DC-DC converter circuit to prevent application of conduction voltage to the control electrode. A second switching element and a third switching element are electrically connected to each other when the flash discharge tube emits light, and the auxiliary capacitor is electrically discharged to the flash discharge tube via a control electrode, thereby making the second switching element non-conductive. The switching element starts operating at the same time as the power is supplied, and generates the conduction voltage only when the switch is turned off and the second switching element is made non-conductive, and the control electrode of the first switching element An electronic flash device having a voltage applying means for applying a voltage to the electronic flash device.