JP2003207822A - Stroboscope circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a stroboscope circuit capable of performing a suitable dimming operation even at a small distance. <P>SOLUTION: The stroboscope circuit is provided at least with a boosting circuit for boosting the voltage of a battery; a light emitting circuit for making a discharge tube emit light; and a dimming circuit for receiving, by a light receiving element, the reflected light of the discharge tube which is reflected from a subject and, when the quantity of received light reaches a prescribed quantity, stopping the light emission of the discharge tube. The dimming circuit is provided with a constant voltage generation element for generating constant voltage synchronously with the light emission start of the discharge tube; a photometric circuit connected in parallel with the constant voltage generation circuit and constituted of a series connection circuit consisting of the light receiving element, a resistor and a capacitor; a 1st switching element to be turned on when the photometric circuit detects a prescribed quantity of light; and a 2nd switching element to be turned on when the 1st switching element is turned on. The 2nd switching element is constituted of a thyristor the gate current of which is ≤2 mA. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flash circuit having a dimming function.

[0002]

2. Description of the Related Art Conventionally, a film unit with a lens, which is preloaded with an unexposed film and configured so that anyone can easily photograph, has been sold. Many film units with lenses have a built-in flash so that you can shoot at night or indoors. In recent years, there is a lens unit equipped with a reflecting mirror in front of the film unit, which is used to hold the film unit with the lens in the left hand when the arm is extended, and after the framer projects the photographer himself on the reflecting mirror. , You can take a picture of yourself by pressing the release button with your left hand.

The conventional film unit with a lens with a built-in strobe has a constant aperture during strobe photography,
Since the strobe light emits full light, there is a problem that a subject at a short distance is overexposed. In order to prevent this, a film unit with a lens with a built-in strobe, which has a dimming function of controlling so that the total amount of strobe light emission decreases as the distance becomes shorter, has been sold in recent years.

Further, although there are various circuit types for the dimming function, after the discharge tube emits light, an electric charge is stored in a capacitor with the start of the dimming operation, and the thyristor is driven by the electric charge to drive the thyristor. Japanese Patent Application Laid-Open No. 2001-2001 discloses that light emission is stopped halfway
It is disclosed in Japanese Patent Publication No. 13558. The circuit configuration will be described below with reference to the strobe circuit diagram of FIG.

In FIG. 2, the voltage of a battery (not shown) is boosted by the booster circuit 21, and the main capacitor C
_M is charged. During shooting, the trigger circuit 22 operates in conjunction with the opening operation of the shutter blades, and the main capacitor C _M discharges through the discharge tube Xe, whereby the discharge tube X.
e emits strobe light. Simultaneously with the start of strobe light emission, the capacitor C ₂₁ starts discharging, and a constant voltage is generated in the Zener diode D ₂₁ , which charges the capacitor C ₂₅ and the charging voltage thereof gradually increases.

The strobe light is projected onto the main subject and
Part of the emitted light is the phototransistor P. _T2Incident on
Phototransistor P_T2Depends on the intensity of the incident reflected light
A large amount of current is passed through the capacitor C_{twenty three}Is phototransi
Star P_T2Charged by the photocurrent from. Capacitor
C_{twenty three}When the charging voltage of the
T_R21And transistor T_R22Turns on the capacitor
C_{twenty five}Discharges. As a result, the resistance R₂₇Occur at both ends of
Voltage is Thyristor Th₂Becomes the gate voltage of
Star Th₂Turns on.

Therefore, when the main subject is at a short distance, the reflected light reflected by the main subject becomes strong and the current flowing through the phototransistor P _T2 becomes large, so that the capacitor C ₂₃ is charged quickly and the transistor T _R21 and The transistor T _R22 turns on sooner, the capacitor C ₂₅ also discharges faster, and as a result the thyristor Th ₂ turns on earlier. Therefore, during the light emission of the discharge tube Xe, the electric charge of the main capacitor C _M is rapidly consumed by the resistor R ₂₈ , and the light emission of the discharge tube Xe is stopped earlier. Also, if the main subject is a long distance, the reverse of the above,
The light emission of the discharge tube Xe is stopped halfway during the light emission.

Therefore, when a strobe unit having such a strobe circuit is incorporated in a camera, the total amount of light emitted by the strobe changes depending on the shooting distance even if the camera diaphragm is constant, so the shooting distance changes. Even with this, a constant exposure amount can always be obtained.

If the capacitor C ₂₃ is charged to a predetermined voltage before the capacitor C ₂₅ is charged to a predetermined voltage, the transistors T _R21 and T _R22 are turned on and the capacitor C ₂₅ is charged. Even if discharged, the gate voltage required to turn on the thyristor Th ₂ cannot be obtained between the terminals of the resistor R ₂₇ . Therefore, since the thyristor Th ₂ does not turn on, the discharge tube Xe cannot be stopped from emitting light halfway and emits full light. When the distance to the main subject is short or the reflectance of the main subject is high, The subject is overexposed.

Therefore, in this publication, the capacitor C ₂₁ is provided to suppress the voltage applied to the phototransistor P _T2 for a predetermined time immediately after the start of strobe light emission.
Capacitor C ₂₃ even when the distance to the main subject is short
Slowly charges, and the capacitor C ₂₅ becomes a thyristor Th.
After reaching the voltage required to turn on the _2, capacitor C ₂₃ reaches a predetermined voltage. Therefore, when the capacitor C ₂₅ is discharged, the thyristor T is connected between the terminals of the resistor R _27.
The gate voltage required to turn on h ₂ can be obtained, and normal dimming corresponding to the distance of the main subject can be performed.

[0011]

However, normal light adjustment can be performed only when the distance to the main subject is up to about 1 m. As mentioned above, when shooting the photographer himself, the shooting distance is around 60 cm, so
If the above strobe circuit is used unconditionally in such a short distance, the timing of stopping the strobe light emission will be delayed, so that after the capacitor C ₂₅ is charged to a predetermined voltage, the capacitor C ₂₃ is changed to a predetermined voltage. Even if the thyristor Th ₂ is turned on by being charged, the subject of 60 cm has already been overexposed, resulting in overexposure.

The present invention has been made in view of the above problems. After the discharge tube emits light, electric charge is stored in a capacitor with the start of the dimming operation, and the thyristor is driven by the electric charge to emit light from the discharge tube. SUMMARY OF THE INVENTION It is an object of the invention to propose a strobe circuit in which a gate current of a thyristor is regulated in a strobe circuit of a type in which the light is stopped midway, and a proper dimming operation is possible even at a short distance.

[0013]

The above object can be achieved by the following means.

At least a booster circuit for boosting the voltage of the battery, a light-emitting circuit for causing the discharge tube to emit light, and the reflected light of the discharge tube reflected by the subject being received by the light-receiving element, and the amount of light received reaches a predetermined amount. And a dimming circuit for stopping light emission of the discharge tube, wherein the dimming circuit generates a constant voltage in synchronization with the start of light emission of the discharge tube; A photometric circuit composed of a series connection circuit of a light receiving element, a resistor and a capacitor connected in parallel with the constant voltage generating element; a first switching element which is turned on when the photometric circuit detects a predetermined light amount; First
The second that is turned on by turning on the switching element
And a switching element, wherein the second switching element is a thyristor having a gate current of 2 mA or less.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION The present embodiment is a strobe circuit of a dimming system in which light emission is stopped in the middle of light emission and the amount of strobe light emission is changed according to the shooting distance.

Hereinafter, description will be given with reference to the strobe circuit diagram shown in FIG. First, the basic configuration of the strobe circuit will be described.

T is an oscillating transformer, T _R is an oscillating transistor, R ₁ is a resistor, S ₁ is a main switch which is turned on by an external operation, D is a rectifying diode, and D _L emits light when charging is completed. The light emitting diode, R _2, is a resistor, and these constitute a booster circuit that boosts the voltage of the battery B.

Further, C _M is a main capacitor for storing electric charges for emitting strobe light, R ₃ is a resistor, C _T is a trigger capacitor, S _T is a trigger switch which is turned on in association with the opening operation of the shutter blades, T _C is a trigger transformer, S ₂ is a light emission prohibiting switch that prevents light from being emitted even when the main capacitor C _M is charged when the main switch S ₁ is turned off, and Xe is a discharge tube that emits strobe light, A light emitting circuit is configured by these.

In this strobe circuit, the total amount of light emitted by the strobe is changed according to the shooting distance even if the aperture is a constant value, so that the main photographed subject is always exposed properly. It has an optical circuit.

Next, the dimmer circuit will be described. D ₁₁ is a Zener diode that generates a constant voltage for performing the dimming operation. The Zener diode D ₁₁ , the resistor R ₁₁ and the capacitor C ₁₁ are connected in series, and the main capacitor C ₁₁ is connected.
It is connected in parallel with _M and the discharge tube Xe. Further, with respect to the Zener diode D ₁₁ , a capacitor C ₁₂ and a resistor R ₁₂
Are connected in parallel.

[0021] The capacitor C ₁₂ is to absorb the current when instantaneous large current is generated to prevent an overcurrent from flowing in the Zener diode D _11, to prevent destruction of the Zener diode D ₁₁ Is a capacitor for.

P _T1 is a phototransistor that receives the strobe light reflected by the subject, and its collector terminal is connected to the cathode terminal of the Zener diode D ₁₁ via the resistor R ₁₃ . On the other hand, a resistor R ₁₄ , a resistor R _15, and a capacitor C ₁₃ are connected in series between the emitter terminal of the phototransistor P _T1 and the anode terminal of the Zener diode D ₁₁ , and are connected in series with the resistor R ₁₅ and the capacitor C ₁₃ . The resistor R ₁₆ is connected in parallel.

A photodiode may be used instead of the phototransistor P _T1 . Transistor T _R11
Also, the transistor T _R12 performs a switching action, and when turned on, emits a light emission stop signal. And the resistance R
The collector terminal of the transistor T _{R11 and} the base terminal of the transistor T _R12 are connected to the connection between the resistor ₁₄ and the resistor R ₁₅ , respectively, and the emitter terminal of the transistor T _R11 is connected to the collector terminal of the phototransistor P _T1 and the transistor T _R12. The emitter terminal of is connected to the anode terminal of the Zener diode D ₁₁ . Furthermore, the transistor T
The base terminal of _R11 is connected to the collector terminal of the phototransistor P _T1 via the capacitor C _14, and the base terminal of the transistor T _R11 and the collector terminal of the transistor T _R12 are connected.

The capacitor C ₁₄ is a transistor T
_This is a capacitor to prevent _R12 from turning on due to electrical noise.

Th ₁ is a thyristor, which is turned on to stop the light emission of the discharge tube Xe. The gate terminal of the thyristor Th ₁ is connected to the connecting portion of the resistor R ₁₇ and the capacitor C ₁₅ , the other end of the resistor R ₁₇ is connected to the cathode terminal of the Zener diode D ₁₁ , and the other end of the capacitor C ₁₅ is the Zener diode D _11. Connected to the anode terminal of. The cathode terminal of the thyristor Th ₁ is connected to the cathode terminal of the Zener diode D ₁₁ , and the anode terminal of the thyristor Th ₁ is connected to the positive terminal of the main capacitor C _M via the resistor R ₁₈ .

Here, a thyristor having a gate current of 2 mA or less is used as the thyristor Th ₁ , and a capacitor having a capacitance of 1500 pF or more and 0.015 μF or less is used as the capacitor C ₁₅ .

[0027] In the flash circuit of the above configuration, when turning on the main switch S ₁ by an external operation, turns on in conjunction also Flash Off switch S _2, transistor current of the battery B via a resistor R ₁ T _R To start oscillation, and the secondary side of the oscillation transformer T is boosted to a high voltage. By rectifying the current on the secondary side with the diode D, 3
To obtain a DC high voltage of 00V～350V, it charges the trigger capacitor C _T connected main capacitor C _M, and in series with resistor R _3. When the main capacitor C _M is charged to a predetermined voltage, the light emitting diode D _L connected in series with the resistor R ₂ lights up, so that the photographer can confirm that the photographing is possible.

Further, the trigger capacitor C _T and the capacitor C ₁₁ are also charged along with the charging of the main capacitor C _M.

During shooting, the trigger switch S _T is turned on in conjunction with the opening operation of the shutter blades. As a result, the trigger capacitor C _T , the trigger switch S _T ,
A closed circuit is formed by connecting the primary side winding of the trigger transformer T _C and the light emission prohibiting switch S ₂ in series, and the electric charge charged in the trigger capacitor C _T is discharged to the primary side of the trigger transformer T _C. As a result, a higher voltage is generated on the secondary side of the trigger transformer T _C and is applied to the trigger electrode of the discharge tube Xe, so that the ionized xenon atoms in the discharge tube Xe are ejected from the cathode. When the main capacitor C _M is discharged, the discharge tube Xe emits light.

As a result, the stroboscopic light emission is started, and the stroboscopic light emitted from the discharge tube Xe is directed toward the main subject. Further, with the start of discharging the main capacitor C _M , the capacitor C ₁₁ starts discharging through the discharge tube Xe, the Zener diode D ₁₁ and the resistor R ₁₁ , and a constant voltage is generated across the Zener diode D _11. . With this voltage, the capacitor C ₁₅ is charged by the current flowing through the resistor R _17, and the charging voltage of the capacitor C ₁₅ is gradually increased.

The stroboscopic light emitted toward the main subject is reflected by the main subject, and a part of the reflected light is incident on the phototransistor P _T1 . Phototransistor P _T1
Causes a current of a magnitude corresponding to the intensity of the incident reflected light,
The capacitor C ₁₃ is charged by the photocurrent from the phototransistor P _T1 . When the charging voltage of the capacitor C ₁₃ reaches a predetermined voltage, the transistor T _R11 and the transistor T _R12 are turned on, and the capacitor C ₁₅ is discharged through the resistor R ₁₇ , the resistor R ₁₃ , the transistor T _R11 and the transistor T _{R 12} . As a result, the voltage generated across the resistor R ₁₇ becomes the gate voltage of the thyristor Th ₁ .

Here, if the distance to the main subject is a short distance, the reflected light reflected by the main subject becomes strong and the current flowing through the phototransistor P _T1 becomes large, so that the capacitor C ₁₃ is charged quickly, The transistors T _R11 and T _R12 turn on sooner, and the capacitor C ₁₅ also discharges faster, so that the thyristor Th ₁ turns on earlier. Therefore, during the light emission of the discharge tube Xe, the electric charge of the main capacitor C _M is rapidly consumed by the resistor R ₁₈ , and the light emission of the discharge tube Xe is stopped earlier.

If the distance to the main subject is long, the reflected light reflected by the main subject becomes weaker,
Since the current flowing through the phototransistor P _T1 is small, the charging of the capacitor C ₁₃ is delayed, and the transistor T _13
The turn-on of _R11 and the transistor T _R12 is also delayed, the capacitor C ₁₅ is also discharged slowly, resulting in a slow turn-on of the thyristor Th ₁ . Therefore, the light emission of the discharge tube Xe is stopped in the middle of light emission.

When a strobe unit having such a strobe circuit is incorporated in a camera, even if the aperture of the camera is constant, the total amount of light emitted by the strobe changes according to the shooting distance, so that even if the shooting distance changes. A constant exposure amount can always be obtained.

Further, since the gate current is used the following thyristor Th ₁ 2mA, 0.015μF small capacitors following capacity becomes available as a capacitor C ₁₅ for driving the thyristor Th _1, the capacitor C ₁₅ The time required for charging is shortened, and the dimming operation can be performed even at a short distance of about 60 cm. Further, the capacitor C ₂₁ as described in the prior art becomes unnecessary.

The capacitor C ₁₅ is 1500 pF.
If a smaller capacitor is used, the thyristor Th ₁
Will not be able to obtain the gate current required to turn on the.

It is more desirable to use a thyristor Th ₁ having a gate current of 1 mA or less, and a capacitor C ₁₅ of 2200 pF or more and 0.01 μF or more.
It is more preferable to use the following.

Finally, the correspondence between the terms used in the claims and the terms used in the embodiments of the invention will be explained. The constant voltage generating element corresponds to the Zener diode D ₁₁ , and the light receiving element is It corresponds to the phototransistor P _T1 and is
The switching element corresponds to the transistor T _R11 and the transistor T _R12 , the second switching element corresponds to the thyristor Th ₁ , and the capacitor for driving the thyristor corresponds to the capacitor C ₁₅ .

[0039]

According to the strobe circuit of the present invention, since the thyristor having a gate current of 1 mA or less is used as the second switching element, a capacitor having a small capacity can be used as a capacitor for driving the thyristor.
The time required to charge the capacitor is shortened to 60 cm
It became possible to perform dimming operation even at a short distance.

[Brief description of drawings]

FIG. 1 is a strobe circuit diagram according to an embodiment of the present invention.

FIG. 2 is a prior art strobe circuit diagram.

[Explanation of symbols]

C _M Main capacitor Xe Discharge tube D ₁₁ Zener diode C ₁₁ , C ₁₅ capacitor P _T1 Phototransistor T _R11 , T _R12 Transistor Th ₁ Thyristor R ₁₇ , R ₁₈ Resistance

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 2H053 BA08 BA64                 3K098 AA05 BB10 BB13

Claims (2)

[Claims] 1. A booster circuit for boosting the voltage of a battery, a light emitting circuit for causing a discharge tube to emit light, and a light receiving element for receiving the reflected light of the discharge tube reflected by a subject so that a predetermined amount of light is received. In a strobe circuit including a dimming circuit that stops the light emission of the discharge tube when the discharge lamp reaches a constant voltage generating element, the dimming circuit generates a constant voltage in synchronization with the start of light emission of the discharge tube. A photometric circuit composed of a series connection circuit of a light receiving element, a resistor and a capacitor, which is connected in parallel with the constant voltage generating element, and a first switching element which is turned on when the photometric circuit detects a predetermined amount of light. And a second switching element which is turned on when the first switching element is turned on, and the second switching element is configured by a thyristor having a gate current of 2 mA or less. Strobe circuit. 2. The strobe circuit according to claim 1, further comprising a capacitor having a capacitance of 0.015 μF or less for driving the thyristor.