JP2872762B2 - camera - Google Patents

Description

The present invention relates to a camera provided with a flash device.

2. Description of the Related Art Conventionally, in a camera having a flash device, there has been proposed a tuning switch for flash light emission used for dimming control or the like, which is a so-called synchro switch realized by a semiconductor switch. A thyristor (hereinafter, referred to as SCR) is used (for example, US Pat. No. 4,839,686).

[Problems to be Solved by the Invention] Incidentally, an SCR as a semiconductor switch has a characteristic that if the anode current is equal to or more than a predetermined current value, the anode current continues to flow even when the gate current is cut off, that is, keeps ON.

Therefore, when an SCR, for example, is used as a tuning switch for flash emission of a camera, the current flowing through the SCR after the operation of the tuning switch needs to be equal to or less than the holding current.

However, since there is a flash device that does not become lower than the holding current after light emission, in order to solve this, a mechanical contact switch is inserted in series with the SCR, the contact switch is turned off after tuning light emission, and the current flows to the SCR. It has been proposed to reduce the current below the holding current.

However, in this case, not only the configuration becomes complicated, but also the reliability of the contact switch becomes a problem.

An object of the invention according to the present application is to provide a camera in which an IGBT is used as a switch for tuning a built-in strobe and a switch for controlling a flash tube, and the IGBT is also used as a switch for tuning when the strobe is mounted on the camera. To provide.

[Means for Solving the Problems] The configuration of a camera that achieves the object of the invention according to the present application is as follows.
A light emission start signal formed by the switching of the synchro switch is applied to the gate, and the signal is turned on by the signal.
An IGBT, a flash tube connected in series to the IGBT, a main capacitor connected in parallel to the flash tube and the IGBT in series, and a trigger circuit for forming a discharge path of the trigger capacitor by turning on the IGBT. Built-in flash circuit,
An accessory shoe portion for mounting an external strobe device, a terminal provided on the accessory shoe portion for connecting to a trigger terminal of the external strobe device, and the discharge path when the external strobe device is mounted on the accessory shoe portion. Switching means for shutting off and connecting a connection point between the IGBT and the flash tube and a terminal provided on the accessory shoe portion is provided.

[Embodiment] FIGS. 1 and 2 show an embodiment of the present invention.

FIG. 1 is a circuit diagram of a flash device incorporated in the camera of this embodiment.

In the figure, reference numeral 1 denotes a power supply battery, and 2 denotes a booster circuit. The voltage of the power supply battery 1 is boosted by the booster circuit 2, and the main capacitor 4 is charged to a high voltage via a diode 3. Reference numeral 5 denotes a resistor, reference numeral 6 denotes a trigger capacitor, and reference numeral 7 denotes a trigger transformer. The resistor 5, the capacitor 6 and the trigger transformer 7 constitute a known trigger circuit.

Reference numeral 8 denotes a flash discharge tube, 10 denotes an insulated gate bipolar transistor (referred to as an IGBT in this specification), and the flash discharge tube 8 and the IBGT 10 are connected in series to form a flash current control circuit.

Reference numeral 11 denotes an accessory shoe for detachably connecting an external flash device provided on the upper portion of the camera body, and has terminals 11a and 11b as synchro contacts as shown in the center and the outer peripheral portion, respectively, as described above. Connected to the trigger circuit of the internal flash device.

Reference numeral 9 denotes a transfer switch. When an external flash device is connected to the accessory shoe 11, the transfer switch 9a is used.
And 9c, and use contact 9 when using the internal flash device.
Connect a and 9b. The transfer switch 9 may be switched manually, or may be automatically switched to the external flash device side by automatically detecting that the internal strobe is not used.

Reference numeral 18 denotes a so-called sync switch which is turned on when the shutter is fully opened. Reference numeral 17 denotes a one-shot multivibrator, to which a synchro switch 18 is connected at the input. When the switch 18 is closed, the output of the waveform of FIG. 2B, that is, a high-level signal for a predetermined time (T) Is output.

Reference numeral 16 denotes a transistor, a base is connected to an output of the multivibrator 17 via an inverter 19, and a collector is connected to a connection point of a photodiode 14 and an integration capacitor 15 described later.
Further, the emitters are respectively connected to the ground. The photodiode 14 is provided so as to receive light reflected from the subject on the film surface.

Reference numeral 15 denotes an integration capacitor for integrating the photocurrent of the photodiode 14. Reference numeral 13 denotes a comparator. One end of the input is connected to the integration capacitor 15 and the other end is a reference voltage source.
Connected to V _ref , the output changes from a high level to a low level when the voltage on the integrating capacitor 15 exceeds the reference voltage. Reference numeral 12 denotes an AND gate, one end of which is connected to the output of the comparator 13, the other end is connected to the output of the multivibrator, and the output of the AND gate 12 is connected to the gate of the IGBT 10. I have.

The operation of the camera according to the present embodiment having the above-described configuration will be described below.

When the internal flash device is operated When the contacts 9a and 9b of the transfer switch 9 are connected, the release button (not shown) of the camera is pressed while the main capacitor 4 is sufficiently charged by the booster circuit 2. Then, a shutter (not shown) operates, and when the shutter reaches a fully open position, the switch 18 is closed. Switch 18
As described above, the multivibrator 17 outputs a high level signal for a predetermined time (usually about 3 to 10 ms longer than the flash time).

At this time, since the output of the comparator 13 is also at a high level, the high-level signal is output to the AND gate 12. AND
The high level output from the gate 12 is set to about 30 V, and the IGBT 10 is turned on. By this ON operation, the electric charge charged in the trigger capacitor 6 is discharged through the IGBT 10 and the primary winding of the trigger transformer 7, and an oscillating high voltage is output to the secondary winding of the trigger transformer 7.

The high voltage causes the flash discharge tube 8 to be in a dischargeable state, and the electric charge of the main capacitor 4 is discharged via the flash discharge tube 8 and the IGBT 10 to start flash light emission.

On the other hand, the output of the aforementioned multivibrator 17 is applied to the base of the transistor 16 via the inverter 19 and the resistor 20, and the base voltage becomes low level.
Is turned off, the reflected light from the subject by the flash discharge tube 8 is reflected on the film surface through a lens (not shown) and is irradiated on the photodiode 14, and the photocurrent is transmitted to the integrating capacitor 15.
Is integrated by

Then, when the integrated voltage is given to a predetermined value, that is, an appropriate flash light amount is applied to the subject, the output of the comparator 13 changes from a high level to a low level, the IGBT 10 is turned off, the flash current is cut off, and the flash stops.

The above operation is shown by a solid-line waveform in FIG. However, when the reflected light from the object is small and the output of the comparator 13 does not become low within a predetermined time T determined by the multivibrator 17 (see the dotted line in FIG. 2c), the output of the AND gate 12 becomes low after a predetermined time. (See the dotted line in FIG. 2d). Therefore, when the switch 18 is closed, it is always turned off within a predetermined time (T).

When the external flash device is operated When the contacts 9a and 9c of the switch 9 are connected and the release button of the camera is pressed as described above, the shutter is fully opened, the switch 18 is opened, and the AND gate 12 is opened. A high level signal is output to the output, and the IGBT 10 is turned on. At this time, since the contact 9b is not connected, the trigger circuit of the internal flash device does not operate, so that the internal flash device does not emit flash light.

On the other hand, when the IGBT 10 is turned on, the trigger output terminal of the external flash device connected to the accessory shoe and connected to the terminal 11a goes low, so that the external flash device starts emitting light.

In this case, the integration circuit composed of the photodiode 14 and the integration capacitor 15 operates in the same manner as described above, and the output of the AND gate 12 always goes low within a predetermined time, and the IGBT
10 is OFF.

By the way, depending on the trigger circuit of the external flash device connected to the accessory shoe, there is a flash device of a type in which a relatively large current continues to flow when the trigger terminal is set to a low level and connected.

For this reason, it was usual to use an SCR suitable for flowing a large current as a switching element in a camera for causing an external flash device to emit light, but once the SCR is turned on with the above-described relatively large current, Even if the gate current does not flow, the ON state is maintained, and the next light emission may not be performed.

On the other hand, in the present embodiment, when the gate voltage is set to a low level, the IGBT can be turned off without fail and can flow a large current equivalent to the SCR.
To cause the external flash device to emit light, so that the next light emission is always possible.

[Effects of the Invention] According to the present invention, an IGBT is used as a switch for tuning a built-in strobe and for controlling a flash tube.
The effect that the IGBT can be used also as a tuning switch when the strobe is mounted on the camera is obtained.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a flash device portion showing an embodiment of the camera of the present invention, and FIGS. 2a to 2d are diagrams showing current waveforms at points a, b, c and d in FIG. It is. 1 ... Battery power supply 2 ... Boost circuit 4 ... Main capacitor 7 ... Trigger transformer 8 ... Flash discharge tube 9 ... Transfer switch 10 ... IGBT 11 ... Accessory shoe 13 ... Comparator 14 ... Photo Diode 17 Multivibrator 18 Synchro switch

Claims (1)

(57) [Claims] An IGBT which is applied to a gate by a light emission start signal formed by switching of a synchro switch and which is turned on by the signal, a flash tube connected in series to the IGBT, a flash tube connected to the flash tube and the IGBT. A built-in strobe circuit having a main capacitor connected in parallel with the series body, a trigger circuit for forming a discharge path of the trigger capacitor when the IGBT is turned on, an accessory shoe unit for mounting an external strobe device, and an external strobe device. A terminal provided on the accessory shoe for connection to the trigger terminal; and a discharge path when the external strobe device is mounted on the accessory shoe, the connection point between the IGBT and the flash tube and the accessory shoe. A switching means for connecting a terminal provided to the camera.