JPS6230410B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electronic flash device useful for photography, and in particular to an electronic flash device that stops the operation of a transistor converter circuit for a certain period of time after a synchro switch is activated by pressing a shutter release button. This relates to flash devices.

Conventionally, electronic flash devices have a transistor converter circuit, and a thyristor, which is a switching element, is connected in parallel to a flash discharge tube and a main discharge capacitor, and the thyristor is made conductive when the amount of light emitted from the flash discharge tube reaches a predetermined amount. 2. Description of the Related Art A so-called parallel automatic dimming electronic flash device is known in which the charge remaining in the main discharge capacitor is bypassed and discharged to stop the flash discharge tube from emitting light.

However, if we consider when the thyristor becomes conductive in the automatic dimming electronic flash device as described above, the output current of the transistor converter circuit also flows through the thyristor at the same time as the residual charge of the main discharge capacitor. Even after the charge is released, the value of the current flowing through the thyristor may not become equal to or less than the holding current of the thyristor itself. That is, there is a problem in that the thyristor may not be turned off.

In addition, when the low voltage power supply of an electronic flash device having a transistor converter circuit is shared as a power supply for a circuit that operates within a certain period of time after the flash discharge tube is emitted, such as a dimming circuit, a dimming display circuit, or a camera winder, Considering the power consumption after the flash discharge tube is emitted in an electronic flash device, it is extremely large, so the terminal voltage of the low-voltage power supply, which normally uses dry batteries, drops significantly, and the voltage value at which each of the above-mentioned circuits can operate is reduced. However, it is difficult to obtain the above-mentioned circuits, and there is a problem in that each of the above-mentioned circuits may not operate at all.

The present invention has been made to solve the problems in the electronic flash device as described above, and by stopping the operation of the transistor converter circuit for a certain period after the synchro switch operates, the above-mentioned parallel type automatic light control When the thyristor in an electronic flash device is turned off reliably and the battery used as a low-voltage power source for the electronic flash device is shared with the power source for other circuits, other circuits that are stable even after the flash discharge tube is emitted are required. It is designed so that a voltage value sufficient to operate the device can be supplied.

This will be explained below with reference to the drawings.

The figure is an electric circuit diagram showing one embodiment of an electronic flash device according to the present invention, and it is a parallel type automatic dimming electronic flash device in which a thyristor 8 is connected in parallel with a flash discharge tube 6 and a main discharge capacitor 7. Of course.

In the figure, 1 indicates a power switch that controls the supply of a battery 2, which is a low-voltage power source, to the transistor converter circuit 3, and 4 and 5 indicate an oscillation transistor and an oscillation transformer, respectively, which constitute the transistor converter circuit 3. . Reference numeral 9 designates a dimming circuit that turns on the thyristor 8 when the amount of light emitted from the flash discharge tube 6 reaches a predetermined amount, and reference numeral 10 designates a transistor that is a switching element that short-circuits between the base and emitter of the oscillation transistor 4.

Reference numeral 11 indicates a resistor connected to both ends of a capacitor 12, which will be described later, via a high potential side electrode, ie, an emitter, and a control pole, ie, a base, of the transistor 10, which is the switching element.

12 indicates a capacitor, and this capacitor 12
is connected at one end to the battery 2 via the power switch 1, and at the other end to the anode of a diode 13 whose cathode is connected to the high potential end of the synchro switch 15.

14 is a resistor, 16 is a trigger capacitor, 17
indicates a trigger transformer.

The operation of the electronic flash device according to the present invention having the configuration described above will be described.

Now, when the power switch 1 is closed, the battery 2 is supplied to the transistor converter circuit 3, so that charging of the main discharge capacitor 7 is started, and similarly, charging of the trigger capacitor 16 is also started.

Thereafter, when the synchro switch 15 is closed while the charging progresses and the charging of the main discharge capacitor 7 and the trigger capacitor 16 is completed, the charge of the trigger capacitor 16 is transferred to the primary of the synchro switch 15 and the trigger transformer 17. A high voltage is induced in the secondary winding 17b of the trigger transformer 17 because it is released through the winding 17a,
The flash discharge tube 6 is excited by this induced high voltage, and the flash discharge tube 6 is activated by the main discharge capacitor 7.
It consumes the charged charge to emit light.

At this time, a current flows through the battery 2, power switch 1, capacitor 12, diode 13, and synchro switch 15, so that the emitter and base of the transistor 10 are forward biased, and the transistor 10 becomes conductive. .

It is clear from the circuit diagram that when the transistor 10 becomes conductive, the base and emitter of the oscillation transistor 4 are short-circuited, and since the oscillation transistor 4 is made non-conductive, the operation of the transistor converter circuit 3 is stopped. It will be done.

The operation of the transistor converter circuit 3 is stopped because even if the synchro switch is opened, the reverse current is blocked by the diode 13, and the charge in the capacitor 12 is discharged between the emitter and the base of the transistor 10 via the resistor 11. Therefore, the discharge of the charge in the capacitor 12 is completed, and
This will be maintained until transistor 10 becomes non-conductive. That is, the capacitor 12 described above
and resistor 11 form a time constant circuit that controls the operation of transistor 10, and by setting their respective values appropriately, the operation stop period of transistor converter circuit 3 can be controlled in various ways.

The light control circuit 9 receives the reflected light from the subject that is used to cause the flash discharge tube 6 to emit light, and when the amount of light received reaches a predetermined amount, it supplies a gate signal to the thyristor 8 to turn the thyristor 8 into a conductive state. None, the amount of light emitted from the flash discharge tube 6 is automatically controlled.

In addition, if the electrical circuit 18 such as the above-mentioned dimming confirmation display circuit is connected as shown by the broken line in the figure, the above-mentioned The electrical circuit 18 will be supplied with the battery 2, which maintains a stable voltage since it is not used in any other way.

Furthermore, the ground of the electric circuit 18 can be shared with the ground of the battery 2 and the main discharge capacitor 7, and the voltage of the battery 2 can be easily utilized without any electrical consideration.

As described above, the electronic flash device according to the present invention is capable of stopping the operation of the transistor converter circuit 3 for a certain period determined by the resistor 11 and the capacitor 12 after the synchro switch 15 is closed. In the case of a parallel automatic dimming electronic flash device that uses a thyristor as a switching element, the thyristor can be turned off reliably, and the low voltage power supply of the transistor converter circuit 3 can be used for a dimming display circuit, etc. If it is shared as a power source for other circuits, a stable voltage can be supplied to the other circuits even after light emission, and at this time, the ground can be shared.

[Brief explanation of the drawing]

The figure is an electrical circuit diagram of an electronic flash device according to an embodiment of the present invention. 1...Power switch, 2...Low voltage power supply, 3...
...Transistor converter circuit, 4...Oscillation transistor, 6...Flash discharge tube, 7...Main discharge capacitor, 8...Thyristor, 9...Dimmer circuit, 1
0... Transistor, 11, 14... Resistor, 15
...Synchro switch, 16...Trigger capacitor.

Claims (1)

[Claims] 1 A transistor DC-DC converter circuit having an oscillation transistor connected to the high potential side of a low voltage power supply via a power switch, and boosting the low voltage power supplied by closing the power switch; - A main discharge capacitor that is connected between the high potential side output end of the DC converter circuit and the low potential side end of the low voltage power supply and is charged, and a synchro switch that flash-discharges the charge of the main discharge capacitor. a trigger circuit connected to both ends of the main discharge capacitor for discharging into the tube; a switching element connected between the base and emitter of the oscillation transistor; one end connected to the low voltage power supply via the power switch;
A capacitor whose other end has a cathode connected to the anode of a diode connected to the high potential end of the synchro switch, and a resistor connected to both ends of this capacitor between the high potential side electrode and the control electrode of the switching element. and a time constant circuit for controlling the operation of the switching element, and when the synchro switch is closed, the time constant circuit is operated to maintain the switching element in a conductive state, thereby shorting the base and emitter of the first oscillation transistor. An electronic flash device characterized in that the operation of the converter circuit is stopped for a certain period of time after the synchro switch is closed.