JPH062600U - Electronic flash device trigger circuit - Google Patents

Abstract

(57) [Abstract] [Purpose] The purpose of the electronic flash device is to prevent each circuit from being damaged by the excitation voltage output from the trigger circuit. A trigger circuit for applying an excitation voltage to a control electrode 16a of a xenon discharge tube 16 to start light emission is provided with voltage cut means for extinguishing the excitation voltage immediately after the xenon discharge tube 16 starts light emission.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a trigger circuit provided in an electronic flash device for photography.

[0002]

[Prior art]

 FIG. 4 is a circuit diagram showing a conventional example of an electronic flash device. The converter 11 shown in the figure forms a DC-DC converter together with the rectifying diode 12 on the output side thereof. By turning on the power switch 13, the DC voltage of the battery power supply 14 is boosted. To charge the main capacitor 15.

The xenon discharge tube 16 discharges the charging energy of the main capacitor 15 and emits flash light, and a light emission stop circuit 17 is connected to the xenon discharge tube 16.

The light emission stop circuit 17 forms a dimming circuit together with the light emission detection circuit 18, the light receiving / integrating circuit 19, the comparator 20, the reference voltage circuit 21, and the like.

In the dimming circuit thus formed, the light emission stop circuit 17 to which the High output of the comparator 20 is input is provided until the dimming signal Sr from the light receiving / integrating circuit 19 reaches a predetermined level. When the light control signal Sr becomes conductive and reaches a predetermined level, the comparator 20 outputs Low and the light emission stop circuit 17 becomes non-conductive.

The xenon discharge tube 16 starts emitting light when its control electrode 16a receives an excitation voltage from the trigger circuit. This trigger circuit is composed of a charging resistor 22, a trigger switch (or a trigger switch circuit) 23, a trigger capacitor 24, and a trigger coil 25.

In the above trigger circuit, the trigger switch is turned on by the trigger signal S o which is input when the camera shutter is opened. As a result, the charging load of the trigger-capacitor 24 is discharged all at once using the primary coil 25P of the trigger-coil 25 as a path, and the high voltage generated in the secondary coil 25S is applied to the control electrode 16a.

In the electronic flash device described above, the DC-DC converter is oscillated to precharge the main capacitor 15. Further, even if the DC-DC converter oscillates, unless the xenon discharge tube 16 emits light, the dimming signal Sr is not output. Therefore, the light emission stop circuit 17 can be turned on by the high output of the comparator 20. It is in a state.

When the trigger signal So is input and the trigger switch 23 is turned on while the main capacitor 15 is charged to a predetermined charging voltage (for example, 330 volts), the charge of the trigger capacitor 24 is discharged. The output voltage of the trigger coil 25 generated by the above is applied to the control electrode 16a as an excitation voltage.

As a result, the impedance of the xenon discharge tube 16 is lowered, and the charged load of the main capacitor 15 is discharged through the xenon discharge tube 16 to start light emission.

The light emission detection circuit 18 detects the light emission start of the xenon discharge tube 16 and operates the light receiving / integrating circuit 19. That is, the reception of the reflected light of the subject and the integration of the reception signal are started.

Since the light receiving / integrating circuit 19 outputs the dimming signal Sr according to the integrated value of the light receiving signal, the dimming signal Sr reaches a predetermined level as the integration of the light receiving signal progresses, and at this time, the comparator -Outputs Low, and the light emission stop circuit 17 becomes non-conductive.

As a result, the emission of light from the xenon discharge tube 16 stops according to the distance to the subject and the voltage setting value of the reference voltage circuit 21.

[0014]

[Problems to be solved by the device]

 In the electronic flash device as described above, the excitation voltage output from the trigger coil 25 is an alternating voltage of 5 to 15 kilovolts (voltage between peaks).

Then, as shown in FIG. 2 (A), this excitation voltage is gradually attenuated from the oscillating voltage of several kilovolts after the xenon discharge tube 16 starts to emit light.

Therefore, while the excitation voltage continues, the light receiving / integrating circuit 19 starts receiving light and integrating the light receiving signal, and the influence of this excitation voltage appears in the light emission stop control.

In other words, the above-mentioned excitation voltage passes through the ground line or is transmitted as an induced voltage thereof, and acts as noise on each circuit such as the light receiving / integrating circuit 19 and the reference voltage circuit 21. The operation of such a circuit becomes unstable.

The present invention has been made in view of the above circumstances, and an object thereof is to develop a trigger circuit of an electronic flash device capable of preventing a failure to each circuit caused by an excitation voltage by a simple means configuration.

[0019]

[Means for Solving the Problems]

 In order to achieve the above-mentioned object, in the present invention, in a trigger circuit of an electronic flash device for starting emission of a xenon discharge tube in which a charging voltage of a capacitor is applied to a main electrode, an excitation voltage is applied to its control electrode. We propose a trigger circuit for an electronic flash device, which is equipped with a voltage cut-off means for extinguishing the above-mentioned excitation voltage immediately after the xenon discharge tube starts to emit light.

[0020]

[Action]

 In the electronic flash device described above, the voltage cutting means operates immediately after the emission start of the xenon discharge tube to extinguish the excitation voltage of the xenon discharge tube. For this reason, each circuit can be stably operated without any trouble in each circuit caused by the excitation voltage.

[0021]

【Example】

 Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a circuit diagram of the electronic flash device shown as the first embodiment. In this embodiment, since the electronic flash device of the conventional example is provided with the voltage cut switch 26, the same parts and circuits as those of the conventional example are designated by the same reference numerals and the description thereof will be omitted.

The voltage cut switch 26 uses a switching element such as a thyristor or a transistor, and this switching element is connected in parallel to the primary coil 25P of the trigger coil 25.

The voltage cut switch 26 is adapted to input the control signal Sc output from the light emission detection circuit 18 and turn on when the light emission of the xenon discharge tube 16 is detected.

In the electronic flash device configured as described above, when the trigger switch 23 is turned on by the input of the trigger signal So, the output of the trigger coil 25 is controlled as an excitation voltage by the charging and discharging of the trigger capacitor 24. When added to the electrode 16a, the xenon discharge tube 16 emits light.

At this stage of operation, since the control signal Sc is not generated, the voltage cut switch 26 is OFF.

The xenon discharge tube 16 emits light, and the light emission detection circuit 18 detects the start of the light emission and immediately outputs the control signal Sc. As a result, the voltage cut switch 26 inputs this control signal Sc and turns it on, thereby making the primary coil 25P of the trigger coil 25 short-circuited.

As a result, the excitation voltage generated in the secondary coil 25S of the trigger coil 25 quickly disappears. Since the control signal Sc is output from the light emission detection circuit 18 while the light emission of the xenon discharge tube 16 is being detected, the voltage cut switch 26 is kept ON for the duration of the extinction of the excitation voltage. .

FIGS. 2B and 2C show an example in which the voltage cut switch 26 is turned on and the excitation voltage disappears at the time point T after the excitation voltage is generated. In this example, the xenon discharge tube 16 starts emitting light during one cycle of the excitation voltage.

Other operations are similar to those of the conventional electronic flash device. In implementing the present invention, a timer-27 shown by a chain double-dashed line may be provided and the voltage cut switch 26 may be turned on by the timer-signal St.

That is, the timer 27 outputs the timer signal St a short time after the trigger signal So is input, and the voltage cut switch 26 to which the timer signal St is input is turned on. The configuration.

FIG. 3 is a circuit diagram of the electronic flash device shown as the second embodiment. This embodiment has a circuit configuration in which the dimming circuit is removed from the flash circuit of the first embodiment described above.

If the electronic flash device is built in the camera, the microcomputer incorporated in the camera is not affected by the excitation voltage, which is advantageous because malfunctions can be prevented. .

[0033]

[Effect of device]

 As described above, according to the trigger circuit of the present invention, the excitation voltage disappears immediately after the emission start of the xenon discharge tube due to the operation of the voltage cut means, so that the excitation voltage is applied to each circuit by prolonging it as an oscillating voltage. It is possible to surely prevent a failure, and in addition, in the present invention, since it can be simply configured by only including a voltage cut means including a switching element, it becomes a trigger circuit which is extremely advantageous in practical use. .

[Brief description of drawings]

FIG. 1 is a circuit diagram of an electronic flash device showing a first embodiment of the present invention.

FIG. 2A is a waveform diagram showing an excitation voltage output from a conventional trigger circuit. FIG. 2B is a waveform diagram showing the excitation voltage output by the trigger circuit of the present invention. Figure 2
(C) is a time chart showing the operation of the voltage cut switch.
It is

FIG. 3 is a circuit diagram of an electronic flash device showing a second embodiment of the present invention.

FIG. 4 is a circuit diagram of an electronic flash device shown as a conventional example.

[Explanation of symbols]

 11 Converter 15 Main Capacitor 16 Xenon Discharge Tube 16a Control Electrode 23 Trigger Switch 24 Trigger Capacitor 25 Trigger Coil 26 Voltage Cut Switch

Claims (1)

[Scope of utility model registration request] 1. A trigger circuit of an electronic flash device in which a xenon discharge tube in which a charging voltage of a capacitor is applied to a main electrode is started to emit light by applying an excitation voltage to its control electrode. A trigger circuit for an electronic flash device, comprising a voltage cutting means for extinguishing the excitation voltage.