JPH06318497A - Charging circuit for stroboscope - Google Patents

Abstract

PURPOSE:To automatically perform charge ending operation by one operation of a charge switch to simplify operation and save power by opening and closing an electronic switch by the use of the charge and discharge of a capacitor. CONSTITUTION:When a switch S0 is momentarily closed, a power source voltage VDD is applied to parallel circuit of a capacitor C3 and a resistor R0, and the voltage is applied to the gate electrode of a transistor(TR)M1 according to the charge of the capacitor C3. When it reaches a predetermined voltage, the TRM1 is laid in ON state to start charge for a stroboscope. The switch S0 is in the opened state, the capacitor C23 starts discharge with the resistor R0 as a load, and after a prescribed time, the gate voltage of the TRM1 is reduced lower than a threshold to lay the TRM1 into OFF state. Thus, an oscillating TRQ1 is laid in OFF state, and the charge for a stroboscope is ended. The charge can be automatically ended by one switch operation in this way, the operation is simplified, and the consumption of power more than needed can be prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a strobe for a camera, and more particularly to a charging circuit for charging the strobe.

[0002]

2. Description of the Related Art A film with a lens was not initially provided with a strobe function. However, even in a situation where it is not possible to obtain sufficient light intensity, such as in bad weather or at night,
Films with lenses that can be photographed have been desired.
Therefore, a lens-equipped film is also provided with a strobe function as in a general camera.

FIG. 2 shows a strobe charging circuit according to the prior art. Slide the strobe charging switch provided on the lens-equipped film body to the on position, or
By continuously pressing the charging switch button, the switch S1 is closed. The main capacitor is charged only when the switch S1 is closed.

When the switch S1 is closed, current flows from the positive potential power supply terminal (VDD) to the base of the transistor Q1n via the resistor R1 and the primary winding coil TR1b of the transformer TR1. When the transistor Q1n is turned on, a current starts to flow from the positive potential power supply terminal (VDD) to the collector of the transistor Q1n via the primary winding coil TR1a of the transformer TR1. As a result, a counter electromotive force is generated in the secondary winding coil TR1z of the transformer TR1, and the base bias of the transistor Q1n is lowered to try to turn off the transistor Q1n. Then,
The current flowing through the primary winding coil TR1a is reduced, a counter electromotive force is generated in the secondary winding coil TR1z, and the transistor Q1n is turned on. In this way, the transistor Q1n and the transformer TR1 form an oscillation circuit.

The diode D1 rectifies the AC voltage generated in the secondary winding coil TR1z of the transformer TR1 and charges the capacitors C1 and C2. The capacitor C1 and the capacitor C2 are charged while the switch S1 is in the ON state.

When a predetermined amount of charge is stored in the capacitor C1, an ON current flows through the neon lamp NE through the resistors R2 and R3, and the neon lamp NE is turned on. The lighting of the neon lamp NE indicates that the charging of the strobe has been completed. When charging to the strobe is completed, switch S
Open 1 to terminate charging. The switch S1 is opened by sliding the strobe charge switch of the lens-equipped film body to the off position or releasing the charge button switch.

The strobe light can be emitted while the capacitors C1 and C2 have been charged. When the shutter release button provided on the lens-equipped film body is pressed, the switch S2 is interlocked with the shutter release button. Switch S
When 2 is closed, the capacitor C2 discharges electric charge, and a current flows through the primary winding coil TR2a of the transformer TR2.

When a current flows through the primary winding coil TR2a, a boosted voltage is generated in the secondary winding coil TR2z of the transformer TR2. The voltage is xenon lamp X
e to the trigger electrode. As a result, the xenon gas inside the tube of the xenon lamp Xe is ionized, and the internal resistance of the tube decreases. Then, the electric charge accumulated in the capacitor C1 is discharged between the electrodes of the xenon lamp Xe, and the strobe of the film with lens emits light.

[0009]

In the strobe charging circuit according to the prior art, the strobe charging switch provided in the camera body is slid to the on position or the charging switch button is continuously pressed to start the charging manually. It is a thing. When the charging is ended, the charging is manually ended by sliding the strobe charging switch to the off position or releasing the charging switch button from the pressed state.

The method of charging the strobe by continuously pressing the charging switch button is complicated for the operator.
The method using a slide requires two operations of starting charging and ending charging. Further, since it is easy to forget the operation for ending the charging, there is a possibility that the charging operation time will be made longer than necessary. This wastes power such as a battery built in the camera.

It is an object of the present invention to operate a strobe charging switch once to turn it on, thereby performing two operations, that is, an operation of starting charging and an operation of ending charging after a lapse of a predetermined time. Is to provide.

[0012]

The strobe charging circuit of the present invention comprises a switch connected to a DC power source and a capacitor connected in series, and a resistor connected in parallel with the capacitor to discharge the electric charge accumulated in the capacitor. , And a charging circuit including an electronic switch controlled by the amount of charge accumulated in the capacitor.

[0013]

By using the electronic switch, it is possible to realize the switch for terminating the charging without manual operation. As a result, charging can be started and ended by operating the strobe charging switch only once.

[0014]

EXAMPLE A lens-equipped film having a strobe charging circuit according to an embodiment of the present invention has a strobe light emitting section, a strobe charging switch, a shutter release button and a strobe charging circuit.

The strobe charging circuit starts charging by turning on the strobe charging switch. When the shutter release button is pressed after charging the strobe, light is emitted from the strobe light emitting part.

FIG. 1 shows the configuration of a strobe charging circuit according to an embodiment of the present invention. The switch S0 is normally open. When the strobe charging switch on the film body with lens is pressed, the switch S0 also forms a closed state,
When the strobe charge switch is released, it returns to the open state.

When the switch S0 is closed even for a moment, the strobe charging circuit starts its operation. The oscillation transistor Q1, the transformer TR1 and the resistor R1 form an oscillation circuit, and generate an electromotive force on the secondary side of the transformer TR1. This electromotive force charges the capacitors C1 and C2.

The switching transistor M1, the capacitor C3 and the resistor R0 have the function of a timer switch, and after a predetermined time has elapsed, the oscillation transistor Q.
1 is turned off. When the oscillation transistor Q1 is turned off, the charging of the capacitors C1 and C2 is completed.

The neon lamp NE is a display lamp for notifying that the charging of the capacitor C1 is completed. By closing the switch S2 after charging is completed,
The capacitor C2 is the primary winding coil T of the transformer TR2.
A voltage is supplied to R2a, and a high voltage is applied to the trigger electrode of the xenon lamp Xe. As a result, the capacitor C1
Is discharged between the electrodes of the xenon lamp Xe and the strobe emits light.

The circuit configuration will be described in detail below. When the switch S0 is closed for a moment, the positive potential power supply voltage VDD is applied to the parallel circuit of the capacitor C3 and the resistor R0.
The capacitor C3 has a capacitance of about 0.1 [μF],
The electric charge is accumulated in an instant. The positive potential power supply voltage VDD may be about 1.5 [V].

When the switch S0 is opened, the capacitor C3 starts discharging with the resistor R0 as a load. The voltage across the terminals of the capacitor C3 is applied to the gate electrode of the switching transistor M1. The switching transistor M1 is in the ON state while the voltage higher than the gate threshold voltage is applied. The switching transistor M1 is an enhancement type n-channel MOS type FET having a high input impedance, and its gate threshold voltage is about 0.8 [V].

When the switching transistor M1 is turned on, a current flows through the base of the oscillation transistor Q1. When the oscillating transistor Q1 is turned on, a current flows between the emitter and collector of the transistor Q1,
The oscillator circuit starts operating. Oscillation transistor Q1
Is a pnp type transistor.

The oscillation circuit has an oscillation transistor Q1, a transformer TR1 and a resistor R1. Transistor Q
The collector current of 1 flows to the ground terminal via the primary winding coil TR1a of the transformer TR1. The base current mainly flows to the ground terminal via the primary winding coil TR1b and the resistor R1. As a result, a counter electromotive force is generated in the secondary winding coil TR1z, and the oscillation transistor Q1
The magnitude of the current flowing through the base changes with the passage of time, resulting in an oscillating state.

The size of the resistor R1 determines the size of the base current of the oscillation transistor Q1. The base current depends on the on resistance of the switching transistor M1 and the resistance R1. When the resistance R1 is reduced, the base current increases and the charging time of the capacitor C1 is shortened. On the contrary, when the resistance R1 is increased, the base current is decreased and the charging time of the capacitor C1 is delayed. The resistance R1 is preferably 150 to 200 [Ω].

The capacitor C4 does not directly affect the operating function of the circuit. However, the oscillation operation described above
Since the power supply voltage is adversely affected, a sharp change in the oscillation voltage is removed by the capacitor C4 to stabilize the circuit operation. Therefore, even if the capacitor C4 is removed,
The strobe charging circuit works normally. The capacitance of the capacitor C4 is preferably about 0.01 [μF].

The diode D1 rectifies the current flowing through the secondary winding coil TR1z of the transformer TR1. The electromotive force generated in the secondary winding coil TR1z is the capacitor C
1 is also applied to the series connection of the capacitor C2, the resistor R2 and the winding coil TR2a. This allows
The capacitors C1 and C2 are charged.

When a predetermined amount of charge is accumulated in the capacitor C1, an on-current flows through the neon lamp NE through the resistor R3 and the neon lamp NE is turned on. Neon lamp N
E lights up to indicate that charging of the strobe has been completed.

Next, a means for ending the operation of charging the capacitors C1 and C2 will be described. To end the charging operation, the switching transistor M1 is turned off.

When the switching transistor M1 is turned off, the oscillation transistor Q1 is turned off.
As a result, the oscillation ends and the voltage applied to the capacitors C1 and C2 disappears. With that, the charging operation is completed.

Means for switching the switching transistor M1 to the off state will be described. The transistor M1 is controlled by the gate voltage. The transistor M1 is
If a voltage higher than the gate threshold voltage is applied to the gate electrode, the ON state is maintained.

The voltage across the terminals of the capacitor C3 is applied to the gate electrode of the transistor M1. Therefore,
The ON state and the OFF state of the switching transistor M1 can be controlled by the amount of charge accumulated in the capacitor C3.

The charge stored in the capacitor C3 is
It is discharged through the resistor R0, and the charge amount of the capacitor C3 decreases with the passage of time. Along with this, the gate voltage supplied to the transistor M1 also decreases, and the transistor M1 is turned off after a lapse of a predetermined time.

The charging operation time from the start to the end of the charging operation is almost determined by the capacitance of the capacitor C3 and the size of the resistor R0. Set the capacitor C3 to 0.1
The charging operation time is about 3 to 5 minutes when the resistance R0 is set to about [μF] and the resistance R0 is set to several tens of MΩ. The resistor R0 having such a numerical value can also be configured by the leak resistance of the capacitor C3. For example, a chip capacitor with uniform characteristics may be used.

The resistor R4 is a switching transistor M
It has the function of improving the characteristics when 1 is switched from the on state to the off state. In practical use, the transistor M
In addition to the gate voltage described above, the state switching of 1 is performed by the resistor R4.
It is also affected by the size of.

That is, the transistor R1 is connected by the resistor R4.
The charging operation time changes because the switching characteristic of the power supply to the off state changes. When the resistance R4 has a small value, the charging operation time becomes short. On the contrary, when the resistance R4 has a large value,
Charging time becomes longer. The resistance R4 is 30 to 60 [k
Ω] is appropriate.

Although the function of the resistor R4 has been described above, the resistor R4 is not always necessary. Since the state control of the transistor M1 is basically performed by the element of the capacitor C3 and the resistor R0, the resistor R4 may be removed.

Next, the flash light emitting operation will be described. The strobe light emitting unit provided on the film with lens emits light by pressing the shutter release button. When the shutter release button is pressed, the switch S2 is closed and opened again for a predetermined time in conjunction with that.

When switch S2 is closed, capacitor C2
And a closed circuit of the primary winding coil TR2a is configured. The electric charge accumulated in the capacitor C2 is discharged, and an instantaneous current flows through the primary winding coil TR2a.

Primary winding coil TR2 of transformer TR2
The secondary side winding coil T
A high voltage boosted to R2z is generated. The high voltage is
It is applied to the trigger electrode of the xenon lamp Xe. As a result, the xenon gas inside the tube of the xenon lamp Xe is ionized, and the internal resistance of the tube decreases. Then, the electric charge accumulated in the capacitor C1 changes to the xenon lamp Xe.
A discharge is generated between the electrodes of, and the strobe of the film with a lens emits light.

Next, the operation of the switching transistor M1 having the functions of a switch for starting the charging operation to the strobe and a switch for ending the charging operation will be described in detail. The transistor M1 is switching-controlled by the voltage supplied from the capacitor C3.

FIG. 3 shows the charging characteristic of the capacitor C3 after the switch S0 is closed. FIG. 3A shows the switch S.
This is a part of the circuit configuration in which 0 is closed. Switch S0
Then, the positive potential power supply voltage VDD is applied to both ends of the capacitor C3 and the resistor R0. When the voltage is supplied, the current Ic flows through the capacitor C3, and the charge is accumulated in the capacitor C3. If the wiring resistance is low, the capacitor C3 will be charged in an extremely short time.

The voltage across the capacitor also changes with the amount of charge stored in the capacitor C3. The voltage across the capacitor is applied to the gate electrode of the transistor M1,
Configure the gate voltage VG.

FIG. 3B shows the change of the gate voltage with the passage of time. The horizontal axis shows the time change after the switch S0 is closed. Gate voltage V at time t on the horizontal axis
The value of G is shown on the vertical axis.

The gate voltage before the switch S0 is closed is
It is zero. That is, the capacitor C3 is not charged. When the switch S0 is closed, the gate voltage is 0
It rises from [V] to VDD [V].

The transistor M1 is turned on when a voltage higher than the gate threshold voltage Vth [V] is applied to the gate electrode. The following expression holds for the relationship between the positive potential power supply voltage VDD and the gate threshold voltage Vth.

VDD> Vth The gate voltage VG has a time t before reaching VDD [V].
At 1, Vth [V] is reached. Therefore, after the switch S0 is closed and the time t1 has elapsed, the gate voltage becomes Vt.
The voltage rises to h [V], and the transistor M1 is turned on. After this, the oscillation transistor Q1 shown in FIG. 1 is turned on, and strobe charging starts.

The closed state of the switch S0 as described above is instantaneously ended, and then the open state is restored. Next, the operation after the open state is described. FIG. 4 shows the discharge characteristic of the capacitor C3 after opening the switch S0. FIG. 4A shows a part of the circuit configuration in the state where the switch S0 is opened.

When the switch S0 is opened, a closed circuit of the capacitor C3 and the resistor R0 is formed. The capacitor C3 starts discharging by using the resistor R0 as a load. A voltage is supplied to the resistor R0 from the capacitor C3, and a current Id flows. The amount of electric charge stored in the capacitor C3 decreases with the passage of time. The gate voltage supplied to the transistor M1 also changes according to the amount of charge accumulated in the capacitor C3.

FIG. 4B shows the change in the gate voltage with the passage of time. The horizontal axis shows the change with time after the switch S0 is opened. Gate voltage V at time t on the horizontal axis
The value of G is shown on the vertical axis.

The gate voltage before the switch S0 is opened is V
It is DD [V]. That is, the capacitor C3 is in a state of being charged by the positive potential power supply voltage VDD. When the switch S0 is opened, the gate voltage changes from VDD [V] to 0 [V]
Descend to.

The transistor M1 is turned off when a voltage lower than the gate threshold voltage Vth [V] is applied to the gate electrode. Since the positive potential power supply voltage VDD is higher than the gate threshold voltage Vth, it reaches Vth [V] at time t2. Therefore, the gate voltage is Vth [V] after the lapse of time t2 after the switch S0 is opened.
And the transistor M1 is turned off. As a result, the oscillating transistor Q1 shown in FIG. 1 is turned off, and the strobe charging is completed.

As described above, by operating the strobe charging switch once, the charging is started, and the switching transistor automatically ends the charging. That is, the charging can be started and ended by operating the strobe charging switch only once.

In the present embodiment, the strobe charging circuit has been described for the lens-attached film.
However, it is needless to say that the present invention is not limited to this and can be applied to a general camera or the like.

The present invention has been described above with reference to the embodiments.
The present invention is not limited to these. For example,
It will be apparent to those skilled in the art that various changes, improvements, combinations and the like can be made.

[0055]

EFFECTS OF THE INVENTION By operating the strobe charging switch only once, charging can be started and terminated after a predetermined time has elapsed. As a result, it is not necessary to keep pressing the switch during charging or to end charging, and the charging operation is simplified. Further, since the charging operation time is not unnecessarily lengthened, the power source such as the battery built in the camera is not wastefully consumed, and the probability of insufficient charging at the time of strobe light emission is reduced. Also, a simple circuit configuration can be realized.

[Brief description of drawings]

FIG. 1 shows the configuration of a strobe charging circuit according to an embodiment of the present invention.

FIG. 2 is a strobe charging circuit according to the prior art.

FIG. 3 shows charging characteristics of a switching transistor control capacitor. FIG. 3A shows a circuit configuration.
(B) shows the change of the gate voltage with the passage of time.

FIG. 4 shows discharge characteristics of a switching transistor control capacitor. FIG. 4A shows a circuit configuration.
(B) shows the change of the gate voltage with the passage of time.

[Explanation of symbols]

 S0, S2 switch TR1, TR2 transformer NE neon lamp Xe xenon lamp R resistance C capacitor D diode Q, M transistor

Claims (4)

[Claims] 1. A switch (S0) connected to a DC power supply.
And a capacitor (C3) in series, a resistor means (R0) connected in parallel with the capacitor for discharging the electric charge accumulated in the capacitor, and an electronic switch controlled by the amount of electric charge accumulated in the capacitor ( And a charging circuit including M1). 2. The strobe charging circuit according to claim 1, further comprising a camera body, and a body switch mounted on the camera body for controlling the switch (S0). 3. A main capacitor (C1) controlled by the electronic switch (M1), a discharge tube (Xe) having a light emitting function and discharging the electric charge accumulated in the main capacitor, The strobe charging circuit according to claim 1 or 2, further comprising a discharging switch (S2) for starting discharging. 4. The strobe charging circuit according to claim 1, wherein the strobe charging circuit has an oscillation circuit including a switching transistor (Q1) connected to a DC power source and a transformer (TR1).