JP2003186092A - Stroboscope circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a stroboscope circuit hardly receiving noise from a trigger switch and easy to obtain a desired light control performance. <P>SOLUTION: A light control circuit is provided with a constant voltage generating element for generating a constant voltage in synchronization with a trigger to a discharge tube, a photometric circuit constituted of a photo-detector and a capacitor connected in parallel with the constant voltage generating element, and a switching circuit comprising a 1st switching element to be turned on when the light control circuit detects a predetermined light quantity and a 2nd switching element to be turned on when the 1st switching element is turned on, and is characterized in being configured so as to stop emitting light from the discharge tube by turning on the 2nd switching element of the switching circuit, and also connecting a series circuit of capacitance and resistance for power supply and noise prevention of the light control circuit between the light control circuit and the trigger switch. <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 In a camera loaded with film such as a film unit with a lens in advance, in order to obtain a better print photograph, the aperture switching mechanism and the amount of strobe light emitted by stopping the light emission during light emission according to the shooting distance. In recent years, a camera equipped with a strobe having a dimming function that changes the light intensity has been proposed.

In such a strobe, a thyristor is turned on at the same time as the trigger switch is turned on in order to activate the dimming circuit almost at the same time as the trigger to the discharge tube and to prevent the influence of noise due to chattering of the trigger switch of the dimming circuit. There is one that connects in parallel with the trigger switch.

[0004]

A strobe circuit having a dimming function mounted on such a camera uses inexpensive parts as much as possible and has a small number of parts.
There is a demand to construct a camera with stable quality.

However, the thyristor used in the above-mentioned prior art is expensive and large, and the noise prevention circuit by the thyristor sometimes causes trigger noise to act on the dimming circuit, and in some cases the dimming circuit malfunctions.

The present invention has been made in view of the above problems, and an object of the present invention is to propose an inexpensive and small strobe circuit which is easy to obtain desired dimming performance without malfunction.

[0007]

The inventor has found that noise at the time of triggering acts on the dimming circuit and the conventional thyristor does not sufficiently prevent noise, and that the time for operating the dimming circuit is very long. Focusing on the fact that only a short time is required, the present invention has been accomplished by considering noise prevention and power supply to the dimming circuit by using only a capacitor without using a thyristor.

That is, the above object of the present invention is achieved by the following means. A booster circuit for boosting the voltage of the battery, a light emitting circuit for causing the discharge tube to emit light, and the discharge tube when the light receiving element receives the reflected light of the discharge tube reflected by the subject and the received light amount reaches a predetermined amount. In a strobe circuit having a dimming circuit for stopping the emission of light, the dimming circuit includes a constant voltage generating element that generates a constant voltage in synchronization with a trigger for the discharge tube, and the constant voltage generating element in parallel. A photometric circuit composed of a connected light receiving element and a capacitor, a first switching element that is turned on when the photometric circuit detects a predetermined amount of light, and a second switching element that is turned on when the first switching element is turned on. And a second switching element of the switching circuit that is turned on to stop the emission of light from the discharge tube and perform the trigger. By turning on the trigger switch, wherein a portion of the charge of the main capacitor to said constant voltage generating device via the trigger switch and the trigger capacitor and the noise suppressing capacitor is supplied.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The present embodiment is a flash control type strobe circuit which changes the strobe light emission amount by stopping the light emission during the strobe light emission in accordance with the shooting distance.

Hereinafter, description will be made with reference to the dimming type strobe circuit diagram shown in FIG. In FIG. 1, T is an oscillating transformer, T _R is an oscillating transistor, R ₁ is a resistor, S ₁ is a main switch turned on by an external operation, D is a rectifying diode, D _L is a light emitting diode, and R ₂ is These are resistors, and a booster circuit that boosts the voltage of the battery B is configured by them.

Also, C_MIs the main capacitor, Xe is
Electric tube, C_TIs the trigger capacitor, R ₃Is resistance, S_TIs
Rigger switch, T_CIs the trigger transformer, S₂Is light emission prevention
It is a stop switch, and these make up the light-emitting circuit.
There is.

When the main switch S ₁ is turned on by an external operation, the light emission prevention switch S ₂ is also turned on, and the current of the battery B flows through the resistor R ₁ to the transistor T _R to start oscillation. The secondary side of the oscillating transformer T is boosted to a high voltage. By rectifying the current on the secondary side by the diode D, a high DC voltage of 300 to 350 V is obtained,
The trigger capacitor C _T connected in series with the main capacitor C _M and the resistor R ₃ is charged. 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.

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 in which the primary winding of the trigger transformer T _C and the light emission prevention switch S ₂ are connected in series is formed, 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 further high 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 considered to be electrons ejected from the cathode. The discharge tube Xe emits light as the main capacitor C _M is discharged due to collision.

Next, the dimming circuit 12 will be described. R
₁₂ , R ₁₃ and R ₁₄ are resistors, D ₁₁ is a Zener diode, P
_T is a phototransistor, C _E is a noise prevention capacitor,
C _P and C _N are capacitors, T _RP is a Darlington-connected transistor, Th ₁ is a thyristor, and C _C is a thyristor T.
It is a choke coil for protection of h ₁ .

The Zener diode D ₁₁ which is a constant voltage generating element constitutes a constant voltage power source, the phototransistor P _T , the resistor R ₁₃ and the capacitor C _P constitute a photometric circuit, which is connected in Darlington which is the first switching element. The transistor T _RP , the resistor R _14, and the thyristor Th ₁ which is the second switching element constitute a switching circuit, and the resistor R ₁₂ and the capacitor C _E constitute a noise prevention circuit and a power supply circuit to the constant voltage power source. There is.

Here, the phototransistor P _T , the resistor R _13, and the capacitor C _P, which are connected in series with each other, are connected in parallel with the Zener diode D ₁₁ whose anode is connected to the negative terminal of the main capacitor C _M. . The phototransistor P _T receives the strobe light reflected by the subject. Connection portion between the phototransistor P _T and the resistor R ₁₃ is connected to the base of transistor T _RP which are Darlington connected, an emitter of the transistor T _RP is connected to the gate of the thyristor Th _1, the collector of the transistor T _{R P} phototransistor is connected to the collector of the P _T, and resistance R ₁₄ between the cathode of the junction and the thyristor Th ₁ and the gate of the emitter and the thyristor Th ₁ of the transistor T _RP is connected, the cathode and the resistor of the thyristor Th ₁ R ₁₄ Is connected to the anode of the Zener diode D ₁₁ . The thyristor Th ₁ is connected in series with a bypass choke coil C _C whose one end is connected to the plus terminal of the main capacitor C _M , and these are connected in parallel with the discharge tube Xe.

The capacitor C _N connected in parallel with the Zener diode D ₁₁ is a Zener diode D _11.
The capacitor is a capacitor that prevents the Zener diode D _{11 from} being damaged by a sudden voltage applied to _11, and reduces the influence of noise.

Therefore, when the thyristor Th ₁ is turned on, a current larger than the current flowing through the discharge tube Xe flows through the choke coil C _C, and the electric charge of the main capacitor C _M is rapidly consumed, and the discharge tube Xe is discharged. The light emission of is stopped.

A current i, which will be described later, is applied to the Zener diode D _11.
When a Zener voltage is generated across both ends of the Zener diode D ₁₁ , a current flows through the phototransistor P _T according to the reflected light of the object. If the shooting distance is short, the strobe light reflected by the subject becomes strong and the current flowing through the phototransistor P _T becomes large, so that the charging of the capacitor C _P becomes faster and the connection between the phototransistor P _T and the resistor R ₁₃ becomes faster. The voltage generated in the part also rises rapidly.

On the other hand, if the shooting distance is long, the strobe light reflected by the subject becomes weak, the current flowing in the phototransistor P _T becomes small, the charging of the capacitor C _P becomes slow, and the phototransistor P _T and the resistor R _T become slow. ₁₃
The rise of the voltage generated in the connection portion with and becomes slower than that in the short distance.

As a result, at a short distance, the voltage generated at the connection between the phototransistor P _T and the resistor R ₁₃ reaches the predetermined voltage for turning on the transistor T _RP quickly,
Since the thyristor Th ₁ that is turned on when the transistor T _RP is turned on also turns on quickly, the discharge tube Xe
The electric charge of the main capacitor C _M is rapidly consumed during the light emission of, and the light emission of the discharge tube Xe is stopped early.

On the other hand, for a long distance, the transistor T _RP
Is slow to turn on and thyristor Th ₁ is slow to turn on, so that the discharge tube Xe stops emitting light later. Therefore, even if the diaphragm is constant, the reflected light from the subject changes according to the shooting distance, and the total amount of light emitted from the flash changes, so that a substantially constant exposure amount can be obtained even if the shooting distance changes.

Note that chattering occurs when the trigger switch S _T is turned on, and high-frequency noise generated at this time acts on the dimming circuit, which tends to make the dimming circuit unstable. A resistor R ₁₂ and a noise prevention capacitor C _E are connected in series between the cathode of the Zener diode D ₁₁ and the junction of the trigger switch S _T and the trigger capacitor C _T as a power supply to D ₁₁ and a preventive measure. There is.

This operation will be described below. When the trigger switch S _T is turned on, a part of the electric charge of the main capacitor C _M passes through the primary side of the trigger transformer T _C , the trigger switch S _T and the noise prevention capacitor C _E, and the charging current i ₁ of the noise prevention capacitor C _E. And flows into the resistor R ₁₂ . Also, after the trigger capacitor C _T is discharged,
A part of the electric charge of the main capacitor C _M becomes a current i ₂ to charge the trigger capacitor C _T and flows into the resistor R ₁₂ .

In the present embodiment, the resistance R₁₂Side of
Zener diode D with sword ₁₁Is resistance R₁₂And series
Zener diode D₁₁There is no electricity
Flow i ₁And current i₂And a part of the current i added flows through
A voltage is generated and this voltage serves as a driving source for the dimming circuit.

[0026] Here, can be set by the charging time of the noise prevention capacitor C _E is to select the component values of the electrostatic capacity of the resistance value and the noise prevention capacitor C _E of the resistor R ₁₂ appropriately, the discharge tube Xe The current i for generating the Zener voltage in the Zener diode D ₁₁ is selected so that it can be made to flow through the resistor R ₁₂ for a time shorter than or substantially the same as the light emission time of, and the voltage cannot be made constant by the Zener diode D ₁₁ generated by the trigger switch S _T. Such high frequency noise has its voltage divided by the noise prevention capacitors C _E and C _N ,
As a result, the voltage of the high frequency noise applied to the Zener diode D ₁₁ is lowered, and at the same time, it is absorbed by the noise prevention capacitor C _E and the influence on the dimming circuit is reduced.

In the present invention, the resistance R ₁₂ is 1 kΩ to 22.
kΩ, preferably 4 kΩ to 10 kΩ, the trigger capacitor C _T is generally 0.022 μF to 0.033 μF, and the noise prevention capacitor C _E is 0.01 μF to
0.1 μF, preferably 0.02 μF to 0.05 μF, and the capacitor C _N is 0.01 μF to 0.22 μF, preferably 0.047 μF to 0.1 μF.

The noise prevention capacitor C _E may be replaced with a choke coil. Here, the resistance R ₁₂ becomes a cause of the the resistance value is too small to damage the Zener diode D ₁₁ becomes large current flowing into the Zener diode D ₁₁ or deterioration, the supply current is too large dimmer circuit becomes small It causes a delay in response. Further, if the capacitance of the noise prevention capacitor C _E is too small, the noise prevention effect is reduced and the supply time of the electric power supplied as a charging current to the dimming circuit is shortened so that the predetermined dimming performance cannot be obtained, which is too large. Therefore, the outer shape of the capacitor becomes large and the cost becomes high. Further, if the capacitance of the capacitor C _N is too small, the noise prevention effect is reduced, and if it is too large, the voltage rise of the dimmer circuit becomes a cause of delay and response delay.

[0029]

According to the strobe circuit of the first to fourth aspects, the power supply to the dimming circuit and the noise prevention function are required.
Since two functions have been realized by a series circuit of a capacitor and a resistor, an expensive and large thyristor is unnecessary for noise prevention by a conventional thyristor, the influence of high frequency noise of the trigger switch is reduced, and dimming performance by noise is improved. Since the influence can be reduced, a small-sized strobe with stable performance can be provided at low cost.

[Brief description of drawings]

FIG. 1 is a dimming strobe circuit diagram.

[Explanation of symbols]

T Oscillation transformer T _R , T _RP Transistor D Rectification diode C _M Main capacitor Xe Discharge tube C _T Trigger capacitor S _T Trigger switch T _C Trigger transformer D ₁₁ Zener diode P _T Phototransistor C _P , C _N capacitor C _E Noise Prevention capacitor Th ₁ Thyristor C _C Choke coil R _{1 to} R ₃ , R _{12 to} R ₁₄ Resistance

─────────────────────────────────────────────────── ─── Continued Front Page (51) Int.Cl. ⁷ Identification Code FI Theme Coat (Reference) H05B 41/32 H05B 41/32 F H

Claims (4)

[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 reflected light of the discharge tube reflected by an object is received by a light receiving element, and a light receiving amount reaches a predetermined amount. In a strobe circuit having a dimming circuit that sometimes stops the light emission of the discharge tube, the dimming circuit includes a constant voltage generating element that generates a constant voltage in synchronization with a trigger to the discharge tube, and the constant voltage. A photometric circuit composed of a light receiving element and a capacitor connected in parallel to the generating element, a first switching element that is turned on when the photometric circuit detects a predetermined amount of light, and an on state when the first switching element is turned on. A second switching element having a second switching element, the second switching element of the switching circuit being turned on to stop the emission of light from the discharge tube. A strobe circuit, wherein a part of the electric charge of the main capacitor is supplied to the constant voltage generating element through the trigger switch, the trigger capacitor, and the noise prevention capacitor when the trigger switch for triggering is turned on. 2. A means for supplying a part of the electric charge of the main capacitor to the constant voltage generating element via the trigger switch for triggering the discharge tube, the trigger capacitor and the noise prevention capacitor, The strobe according to claim 1, wherein a resistor connected in series between the cathode of the constant voltage generating element, the junction of the trigger switch and the trigger capacitor, and the noise prevention capacitor are used. circuit. 3. The strobe circuit according to claim 2, wherein a noise removing capacitor is connected in parallel with the constant voltage generating element. 4. The strobe circuit according to claim 2, wherein the constant voltage generating element is a Zener diode.