JPH0359999A - Light control flash device - Google Patents

Abstract

PURPOSE:To prevent an overexposure in a short distance photographing and to realize a compact size of the device by using a switching element as the element to carry out the light quantity control. CONSTITUTION:A converter CNV to raise the voltage of a DC power source E, a main capacitor MC connected parallel to the converter CNV, a series connecting body of a discharge tube Xe, a diode D, and a switching element FE1 connected parallel to the converter CNV and the main capacitor MC, and a capacitor CB connected parallel to the diode D are provided. Furthermore, a series connecting body of a resistance R3 connected to apply the negative voltage to an anode of the diode D and the positive voltage to a cathode, the primary winding side of a trigger coil T, and a trigger capacitor CT, which is connected parallel to the switching element FE1 is provided. And as the element to carry out the light quantity control, the switching element FE1 which can improve the light quantity control function and simplify the circuit composition easily is used. Consequently, an overexposure in a short distance photographing can be prevented, and the device can be made in a compact size.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Application of the Invention) The present invention relates to a light amount control flashlight emitting device, and in particular, a field effect transistor (FET), an insulated gate bipolar transistor (IGBT), an electrostatic induction The present invention relates to a series control type light amount control flashlight emitting device using switching elements such as type transistors (SIT) or bipolar transistors.

(Background of the Invention) A flash light emitting device called a series control system is known in which the amount of light emitted is adjusted by controlling the conduction of a thyristor connected in series with a discharge tube to control the discharge time, that is, the flash time.

In conventional flashlight emitting devices that perform dimming control using this type of thyristor, when turning off the thyristor, the charge accumulated in the commutation capacitor is applied in the opposite direction to the thyristor, thereby forcing the thyristor to commutate. , the discharge current is cut off to stop light emission. At this time, the current in the discharge tube flows into the commutation capacitor,
The current at this time causes an unexpected increase in light emission. As a result, the control characteristics in a small light amount region are poor, resulting in the problem of overexposure in photography, especially in close-range photography.

Therefore, it was necessary to limit the shooting distance at close range.

Further, in the above-mentioned dimming operation, in order to turn off the cyrisk, a commutating capacitor, a switching element for commutating, etc. are required, making it impossible to simplify the circuit and downsize the device.

(Object of the Invention) An object of the present invention is to provide a light quantity control flashlight emitting device that can prevent overexposure during close-range photography and can achieve miniaturization of the device.

(Features of the Invention) In order to achieve the above object, the present invention includes a converter that boosts a DC power supply, a main capacitor connected in parallel to the converter, a discharge tube connected in parallel to the converter and the main capacitor, A series connection body of a diode and a switching element, a capacitor connected in parallel to the diode, and a resistor connected in parallel to the switching element so as to apply a negative voltage to the anode and a positive voltage to the cathode of the diode. , a primary winding of a trigger coil and a series connection body with a trigger capacitor;
The present invention is characterized in that, as an element for controlling the light amount, a switching element is used which can improve the light amount control performance and simplify the circuit configuration.

(Example of the invention) FIG. 1 is a circuit diagram showing an embodiment of the present invention.

In the journey, E is a DC power source that generates low voltage such as a battery, and CNV is a DC power source that boosts the DC power source E and converts it to high voltage.
/DC converter, MC is a main capacitor, Xe is a discharge tube that emits light by the discharge charge of the main capacitor MC, and D is a diode connected in series with the discharge tube Xe and provided to reduce the light emission voltage of the discharge tube Xe. , FET is discharge tube
This is a field effect transistor connected in series to E, and the DC power source E is directly applied to its input electrode as a drive power source (a voltage before being boosted is applied).

T and CT constitute a trigger circuit for exciting the discharge tube Xe, and are a trigger coil and a trigger capacitor, respectively. CB is a reverse bias capacitor for applying a negative bias to the cathode side of the discharge tube Xe when the discharge tube Xe is excited, R4 is a trigger capacitor CT, a resistance for charging the reverse bias capacitor CB, and R3 is a charging resistor for the reverse bias capacitor CB. A resistor connected for the path, R2, is connected between the gate and source of the field effect transistor FET, and is a resistor for removing the charge of the capacitance between the gate and source when the field effect transistor FET is non-conducting.1 is a resistor connected to the DC power supply E. This is a gate drive circuit for driving the gate of a field effect transistor FET using the power source.

Next, the operation of the apparatus having the above configuration will be explained using the timing chart of FIG.

DC power supply E is boosted by converter CNV, main capacitor MC is charged, and at the same time, trigger capacitor CT is charged via resistor R4 and the primary winding of trigger coil T, and reverse bias capacitor CB is charged via resistors R4 and R3. Ru. At this time, at time T1 in FIG. 2, the light emission control signal S1
By falling to L°, the transistor Q of the gate drive circuit 1 is turned on, and the gate of the field effect transistor FET is driven from the DC power supply E through the resistor R1 as shown in FIG. 232. The field effect transistor FET becomes conductive. Also, when starting this drive,
The DC power supply E is connected to the DC power supply E through the resistor R1 in advance.
Since the charge of the capacitor CG in the gate drive circuit 1 charged to the same potential as the voltage is applied to the gate of the field effect transistor FET at the same time as the transistor Q is turned on, the same voltage as the DC power supply E is applied to the gate immediately after the start of driving. After that, a voltage E' obtained by dividing the DC power supply E by resistors R1 and R2 is applied. By driving the gate of the field effect transistor FET in this manner, the turn-on operation of the transistor FET is performed smoothly without being affected by the gate-source capacitance.

When the field effect transistor FET becomes conductive in this way, the primary current of the trigger circuit can be sufficiently passed through without being restricted, and a sufficient trigger current can be generated for the discharge tube Xe.
The next output can now be applied. Due to the conduction of the field effect transistor FET, the resistors R4 and R3 are pre-loaded as shown in FIG.
By discharging the reverse bias capacitor CB, which had been charged via the Same opposite voltage (-EMC)
Since the voltage between the electrodes of the discharge tube Xe is twice the voltage EMC of the main capacitor MC, it is possible to make the discharge tube Xe emit light with a lower voltage than before. Become. Also, since current flows through the trigger capacitor CT of the trigger circuit and the primary winding of the trigger coil T at the same time as the reverse bias operation, the trigger secondary output is generated from the secondary winding of the trigger coil T as shown in Figure 2 S3. The voltage is applied to the discharge tube Xe. A voltage twice that of the main capacitor MC is applied between the electrodes, and the discharge tube Xe excited by the application of the trigger secondary output becomes conductive, and from the time point T2 in FIG. 2, the voltage of the main capacitor MC is applied via the field effect transistor FET. While discharging the charge, it emits light as shown in Fig. 2S.

When the amount of light emitted from the discharge tube Xe reaches a predetermined amount (time point T3 in FIG. 2), the light emission control signal SI is changed from "L" to "
By raising the high level, the transistor Q of the gate drive circuit 1 is turned off, and the gate potential of the field effect transistor FET also falls as shown in FIG.
becomes non-conductive, and the discharge tube Xe instantly stops emitting light. When turning off the field effect transistor FET, the higher the gate voltage just before turning off, the longer it takes for the turn off to occur and the worse the control characteristics become. Therefore, the gate drive voltage of the field effect transistor FET is discharged as shown in FIG. Resistors R1 and R2 are set so that the discharge current of the tube Xe reaches the lowest voltage E'.

According to this embodiment, the discharge current of the discharge tube is turned on.

Since an input electrode controlled element such as a field effect transistor FET (or an insulated gate bipolar transistor IGBT, a static induction transistor SIT, etc.) is used as a switching element for off-conduction control, a commutating capacitor is not required, and the control performance is improved. This improves the image quality and eliminates problems such as overexposure when shooting at close range. Moreover, control performance can be further improved by reducing the current of the discharge tube to about 1/2 of the conventional current value.

The discharge current of the discharge tube can be reduced by increasing the rare gas pressure within the discharge tube. If this is done, a problem arises in that the voltage at which the discharge tube starts emitting light increases, making it impossible to emit light using the conventional voltage. Therefore, if the voltage applied to the discharge tube is increased, the discharge current increases and controllability deteriorates, creating a paradox.

Furthermore, since an input electrode controlled switching element is used to which a power supply voltage before being boosted is applied as a driving power supply, the light amount control circuit can be simplified and the device can be miniaturized.

(Effects of the Invention) As explained above, according to the present invention, a switching element that can improve light amount control performance and simplify the circuit configuration is used as an element for controlling the amount of light. Overexposure during distance photography can be prevented, and the device can be downsized.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, and FIG. 2 is a timing chart thereof. CNV...Converter, MC...Main capacitor, Xe...Discharge tube, D...Diode, FET...Field effect transistor,
CB... Capacitor, T... Trigger coil, CT... Trigger capacitor.

Claims (2)

[Claims] (1) A converter that boosts a DC power supply, a main capacitor connected in parallel to the converter, a series connection body of a discharge tube, a diode, and a switching element connected in parallel to the converter and the main capacitor, and a series connection body connected in parallel to the diode. a negative voltage at the anode of the diode connected in parallel to the connected capacitor and the switching element;
A resistor connected to apply a positive voltage to the cathode, a primary winding of a trigger coil, and a series connection body with a trigger capacitor, the secondary winding of the trigger coil being connected to the trigger electrode of the discharge tube and the cathode. A light amount control flashlight device connected to an electrode. (2) The light amount control flashlight emitting device according to claim 1, characterized in that a direct current power source is directly applied to the input electrode of the switching element as a driving power source for the switching element.