JPH0712979Y2 - Sustainable discharge prevention electronic flash device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to an electronic flash device for preventing continuous discharge. More specifically, the present invention relates to an electronic flash device including a continuous discharge prohibiting circuit that prohibits the flash discharge tube from inadvertently continuing to emit light even after initial light emission by supplying power from an input terminal connected to a high-voltage external power supply.

B. Conventional Technology As a conventional continuous discharge inhibiting circuit, a type is known in which the DC-DC converter is stopped for a certain period of time starting from the X contact closure (camera release). Also, for example, 3a
The one shown in the figure is also known. If the light emission detection circuit 51 detects the light emission of the flash discharge tube and supplies a set signal to the timer circuit 52 to start the timing operation, and if the light emission is stopped before the full light emission (when dimming), The reset signal from the optical circuit 53 resets the timing operation of the timer circuit 52 so that the operation signal is not applied to the continuous discharge inhibiting circuit 54. On the other hand, when the light is fully emitted and the dimming circuit 53 does not dimm and the reset signal is not input to the timer circuit 52, the operation signal is input from the timer circuit 52 to the continuous discharge inhibiting circuit 54, and then the continuous discharge inhibiting circuit 54 is input. A light emission stop signal is supplied to a light emission control circuit (not shown) to stop light emission from the flash discharge tube.

The sustained discharge inhibition circuit 54 is configured as shown in FIG. 3b, for example.
When the transistor Q is turned on by the operation signal from the timer circuit 52, a light emission stop signal is output via the resistor R3.
The light emission control circuit has, for example, switching means for stopping light emission, for example, a commutation thyristor, and by turning on the commutation thyristor, as shown in FIG. 1a (reference numeral 21 is a commutation thyristor), the flash discharge tube 14 and The light emission control main thyristor 15 connected in series is reverse biased to extinguish the main thyristor 15 and stop light emission.

C. Problems to be Solved by the Invention However, in these conventional devices, the circuit configuration is complicated such as detecting various signals, which has been an obstacle to cost reduction and miniaturization in recent years. In addition, in consideration of the decrease in the number of full flashes of the electronic flash device every time in recent years when the automatic dimming method has become mainstream, cost reduction of the continuous discharge prohibition circuit,
This is where downsizing is strongly desired.

Further, if the continuous discharge inhibiting circuit 54 malfunctions immediately after the light emission, that is, if the transistor Q malfunctions in FIG. 3b, the above-mentioned commutation thyristor latches up and overcurrent continues to flow, which causes a failure. There is a fear. Especially in an electronic flash device with a full light emission time of 1 ms or less, a highly sensitive commutation thyristor is used to improve the responsiveness of the time from when the light emission stop signal is output to when the commutation thyristor operates. Since overshooting is prevented, the commutation thyristor is likely to turn on and latch up due to slight noise.

An object of the present invention is to provide a continuous discharge preventing electronic flash device in which the circuit configuration is simplified and a light emission stop signal is not output due to a malfunction.

D. Means for Solving the Problems Referring to FIG. 1 showing an embodiment, the present invention relates to a DC-DC converter 3 for boosting a low voltage power supply, and this DC-DC converter.
A main capacitor 9 that charges the voltage boosted by the converter 3 to store light emission energy, a flash discharge tube 14 that emits light by the charge of the main capacitor 9, and a trigger circuit 13 that triggers the flash discharge tube 14. A known light emission stopping circuit including a commutation capacitor 19 and a commutation thyristor 21 for stopping the light emission of the flash discharge tube 14, and the flash discharge tube 14
It is applied to an electronic flash device having a continuous discharge inhibiting circuit 24 for preventing the continuous discharge of. The above-mentioned problem is that the continuous discharge prohibition circuit 24 is turned on when the flash discharge tube 14 emits light and turned off when the flash discharge tube 14 does not emit light, the continuous discharge prohibition capacitor 104, and the first switch means 101 are turned on. Then, the charging path 10 for charging the continuous discharge inhibiting capacitor 104 with the current supplied through the first switch means 101.
2, 103, and discharge paths 105, 106 for discharging the charge stored in the continuous discharge inhibiting capacitor 104 when the first switch means 101 is turned off.
When the first switch means 101 is turned off and operates in a phase opposite to that of the first switch means 101, the continuous discharge inhibiting capacitor 104 is provided.
It is turned on by the charge of the
The charge of 104 is supplied to the light emission stop circuit and the flash discharge tube 14
It is solved by comprising the second switch means 107 for prohibiting the continuous discharge of.

Preferably, by adjusting the resistance value of the resistor 102 constituting the charging path, the second switch means 107 is turned on by the charging voltage of the continuous discharge inhibiting capacitor 104 only when the first switch means 101 is turned off during full light emission. In the dimming, even if the first switch means 101 is turned off, the second switch means 101 is turned off.
The switch means 107 is prevented from turning on.

E. Action When the flash discharge tube 14 emits light, the first switch means 101 is turned on and the continuous discharge inhibiting capacitor 104 is charged through the charging paths 102 and 103. When the light emission of the flash discharge tube 14 is stopped, the first switch means 101 is turned off and the continuous discharge inhibiting capacitor 104 starts discharging through the discharge paths 105 and 106. When the first switch means 101 is turned off, the second switch means 107 is turned on by the charging voltage of the continuous discharge inhibiting capacitor 104, the light emission stop signal is supplied to the light emission stop circuit, and the light emission of the flash discharge tube 14 is stopped. According to the above-described preferable configuration, in the full light emission, the continuous discharge inhibiting capacitor 104 is sufficiently charged to turn on the second switch means 107 in response to the turning off of the first switch means 101, but the dimming operation is performed. At times, the continuous discharge inhibiting capacitor 104 is not sufficiently charged,
Even if the first switch means 101 is turned off, the second switch means 107
Does not turn on.

F. Embodiment (I) Configuration of Embodiment An embodiment of the present invention will be described based on FIGS. 1a, 1b, and 2.

FIG. 1a shows the overall configuration of the electronic flash device, 1 is a power battery, 2 is a power switch, 3 is a well-known DC-DC converter for boosting the low voltage of the power battery 1 to high voltage, and 4 and 7 are rectifying diodes. is there. Between the power line l ₁ and the GND line l ₂ ,
Monitor capacitor 5 for detecting high voltage and lines l ₁ , l
A voltage detection circuit 6 that detects a potential difference between the _two and a main capacitor 9 that stores light emission energy are connected. Also,
The power line l ₁ has a GN
The external power supply input terminals 31 are directly connected to the D lines l ₂ . A flash discharge tube 14 such as a xenon discharge tube and a main thyristor 15 are connected in series between the lines l ₁ and l ₂ ,
The trigger electrode of the flash discharge tube 14 via a line l _3, also trigger circuit 13 each are connected via a line l ₄ to the gate of the main thyristor 15. The trigger circuit 13 has a line
A light emission start switch 12 forming a trigger signal is connected via l ₅ . When the switch 12 is closed and a trigger signal is input, a high voltage is applied to the flash discharge tube 14 by the trigger circuit 13 and a turn-on signal is applied to the gate of the main thyristor 15 from the line l ₄ . Line l ₄ is resistance
Connected to GND line l ₂ via 17 and capacitor 16.

Further, a resistor 20 and a commutation thyristor 21 are provided between the lines l ₁ and l _2.
And are connected in series. The gate of the commutation thyristor 21 is connected to the light emission stop signal output terminal of the dimming circuit 25 via a line l _6, line l ₆ is resistor 22 is connected to the GND line l ₂ via a capacitor 23. The light control circuit 25 measures the reflected light from the subject with a light receiving element (not shown), and outputs a light emission stop signal when the integrated value reaches an appropriate exposure amount determined by the film sensitivity, for example.

The commutation capacitor 19 is connected to the anode of the commutation thyristor 21 and the anode of the main thyristor 15, and further, the resistor 18 is connected between the anode of the main thyristor 15 and the line l ₂ . Here, when the commutation thyristor 21 is turned on, the charged charge reversely biases the anode and cathode of the main thyristor 15 to turn off the main thyristor 15. The turn-off of the main thyristor 15 causes the emission current flowing in the flash discharge tube 14 to flow in the path of the commutation thyristor 21,
When the charging of the commutation capacitor 19 is completed, the flash discharge tube
The light emission current of 14 is stopped, and the commutation thyristor 21 is also turned off.

Further, the + side terminal of the main capacitor 9 is connected to the continuous discharge inhibiting circuit 24 via the light emission detecting capacitor 10 and the protection resistor 11.

As shown in FIG. 1b, the continuous discharge prohibition circuit 24 has a switching transistor 101 which is turned off until light emission is detected and is turned on when light emission is detected. That is, the voltage V _CCL from the power supply battery 1 is applied to the emitter of the switching transistor 101, and the voltage a of the light emission detection capacitor 10 is applied to the base through the protection resistor 11. Here, the voltage a is larger than the power supply voltage V _CCL when the main capacitor 9 is completely charged. Therefore, until it emits light, a> V _CCL and the switching transistor
101 is reverse-biased and turned off, but the flash tube 14
When light emission starts, the light emitting detection capacitor 10 causes a <V _CCL and the switching transistor 101 is turned on.

The continuous discharge prohibition circuit 24 is also a switching transistor.
A resistor 102 connected in series between the collector of 101 and GND,
Having a diode 103 and a capacitor 104 for inhibiting continuous discharge,
Further, it also has a switching transistor 107 which is turned on when the switching transistor 101 is turned off when the charging voltage of the continuous discharge inhibiting capacitor 104 is equal to or higher than a predetermined voltage.

That is, the emitter of the switching transistor 107 is directly connected to the + side terminal of the continuous discharge inhibiting capacitor 104, and is also connected to the collector of the switch transistor 101 via the resistor 105. The base is connected to the + side terminal of the capacitor 104 for inhibiting continuous discharge via the resistor 105, and the switching transistor 101
Connected to each collector. The collector of the switching transistor 107 is a commutation thyristor via a resistor 108.
It is connected to the gate of 21 and can supply the light emission stop signal b.

Here, it is necessary to output the light emission stop signal b from the continuous discharge prohibition circuit 24 at the time of full light emission. When dimming without full emission, the dimming circuit 25 commutates the thyristor 21.
The light emission stop signal e is supplied to the gate of the
Although the main thyristor 15 is turned off by turning on 21, the light emission stop signal e is not output from the dimming circuit 25 at the time of full light emission. Therefore, even after full light emission, that is, even if the charge of the main capacitor 9 is exhausted, The thyristor 15 is turned on, and there is a possibility that light emission will be sustained by an external power supply. Therefore, at the time of full light emission, by turning on the switching transistor 107, the continuous discharge prohibition circuit 24
It is necessary to supply the light emission stop signal b from the above to the gate of the commutation thyristor 21 to turn off the main thyristor 15.

Therefore, the switching transistor 101
The charging speed of the continuous discharge inhibiting capacitor 104 is adjusted by the resistance value of the resistor 102 so that the switching transistor 107 is forward-biased and turned on only when is turned off.

(II) Contrast between the configuration of the embodiment and the invention In the configuration of the above embodiment, the commutation capacitor 19 and the commutation thyristor 21 form a light emission stop circuit, the switching transistor 101 forms the first switching means, and the switching transistor 107 forms the first switching means. The two switching means, the resistor 102 and the diode 103 form a charging path, and the resistors 105 and 106 form a discharging path.

(III) Operation of Embodiment Next, the operation will be described.

When the power switch 2 is closed, the step-up operation of the DC-DC converter 3 is started, and light emission energy is stored in the main capacitor 9. At the same time, an electric charge is stored in the monitor capacitor 5. The voltage of each capacitor rises, and when it reaches a certain voltage, the voltage detection circuit 6 operates to stop the step-up operation of the DC-DC converter 3. In this state, the flash discharge tube 14 can emit light.

Here, when the light emission start switch 12 is closed by operating the release button or the like, the trigger circuit 13 starts operating, and at the same time when the trigger voltage is applied to the flash discharge tube 14, the light emission start signal is sent to the gate of the main thyristor 15. It is supplied, whereby the flash discharge tube 14 starts to emit light. Dimming circuit at the same time as light emission
25 starts the operation, and when the amount of light emitted from the subject reaches a predetermined appropriate exposure amount, the light emission stop signal e is output to the line l ₆ , which is supplied to the gate of the commutation thyristor 21 to perform commutation. Thyristor 21 turns on. As a result, the anode-cathode of the main thyristor 15 is reverse biased by the commutation capacitor 19, the main thyristor 15 is turned off, and light emission is stopped. The above is the normal automatic light control operation.

On the other hand, the operation of the continuous discharge prohibition circuit 24 will be described with reference to the waveform charts of the respective parts in FIG. As shown in FIG. 2B, the base voltage a of the switching transistor 101 becomes smaller than the emitter voltage V _CCL at the same time when the light emission starts at time t _{0, the} switching transistor 101 is turned on, and the collector voltage g (second Figure (c)) appears. Because of this, the resistance
102 → diode 103 → capacitor for inhibiting continuous discharge 104 → G
Charging of the continuous discharge inhibiting capacitor 104 is started along the ND path (Fig. 2 (d)). At this time, the base of the switching transistor 107 is the collector (voltage g = V _CCL ) of the switching transistor 101 which is on, and the emitter of the switching transistor 107 is the diode 103.
Is _{maintained at} the cathode (voltage h = V _CCL ′ <V _CCL ), the switching transistor 107 is reverse-biased, and the switching transistor 107 does not turn on while the continuous discharge inhibiting capacitor 104 is being charged. That is, the light emission stop signal b does not appear in the collector of the switching transistor 107 while the continuous discharge inhibiting capacitor 104 is being charged.

When the light emission stops and the base voltage a of the switching transistor 101 exceeds V _CCL again, the switching transistor 101
Since 101 is turned off, the reverse bias of the switching transistor 107 is released. At this time, if the continuous discharge inhibiting capacitor 104 is not charged to, for example, a predetermined voltage V _CCL ′ (a voltage required to turn on the switching transistor 107), the switching transistor 107 remains off and the light emission stop signal b is not output. If the continuous discharge inhibiting capacitor 104 is charged to the predetermined voltage V _CCL ′, the switching transistor 107 is turned on and the light emission stop signal b is output.

That is, when the dimmer circuit 25 outputs the light emission stop signal e to the line l ₆ at time t ₁ before full light emission, the charging voltage h of the continuous discharge inhibiting capacitor 104 is lower than V _CCL ′ at that time. (Fig. 2 (d)), switching transistor 10
Even if 1 is turned off, the switching transistor 107 is not turned on, and the continuous discharge prohibition circuit 24 does not output the light emission stop signal b. On the other hand, after the full light emission, when the switching transistor 101 is turned off at time t ₃ , the continuous discharge inhibiting capacitor 104 is sufficiently charged at this time, the charging voltage h becomes V _CCL ′, and the switching transistor 107 is turned on. The light emission stop signal b is output from the collector. As a result,
As in the above, the commutation thyristor 21 turns on and the main thyristor
15 is turned off, which allows the flash discharge tube to be powered by an external power supply.
14 continuous discharges are definitely prohibited.

As described above, according to the present embodiment, as is apparent from FIG. 1b, the base of the switching transistor 101 whose power supply voltage V _CCL is applied to its emitter is the capacitor 10,
It is connected to the main capacitor 9 via a series body of resistors 11, and the switching transistor 101 is normally off. Therefore, there is no current consumption in the continuous discharge prohibition circuit 24. In other words, the light emission stop signal b is not normally output. Further, the flash time varies depending on the size of the flash discharge tube 14 and the capacity of the main capacitor, but by changing the resistance value of the resistor 102 and the capacity of the continuous discharge inhibiting capacitor 104, t ₀ -t _{3 in} FIG. Between the time, that is, the charging voltage of the capacitor 104 for inhibiting continuous discharge from the start of light emission
The time until V _CCL ′ can be set freely. In other words, these two elements substantially also function as a timer, and the configuration thereof is simplified as compared with the conventional device that outputs a light emission stop signal when checking whether or not full light emission is performed and then performing full light emission. Also, since all of the elements can be configured by chip parts, it is possible to contribute to downsizing and cost reduction.

In the present invention, it is sufficient that the continuous discharge prohibition circuit 24 outputs the light emission stop signal b at the time of full light emission, and even if the continuous discharge prohibition circuit 24 outputs the light emission stop signal b again immediately after the light emission is stopped by the dimming operation. Since there is no problem, the time until the charging voltage of the continuous discharge inhibiting capacitor 104 reaches V _CCL ′ does not necessarily have to correspond to the full light emission time. That is, the charging speed of the continuous discharge inhibiting capacitor 104 may be set earlier so that the switching transistor 107 is turned on after dimming.

G. Effect of the Invention Since the present invention is configured as described above, the circuit configuration is simplified as compared with the conventional device, which contributes to cost reduction and downsizing. Also, since the light emission stop signal is not output unless the continuous discharge prohibiting capacitor is charged to a predetermined voltage or more,
There is no risk of malfunction due to noise or the like superimposed on the continuous discharge inhibiting circuit, and problems such as undesired latch-up of the commutation thyristor and various elements fail can be solved.

[Brief description of drawings]

FIG. 1a is a circuit diagram showing the overall configuration of an embodiment of the electronic flash device according to the present invention, FIG. 1b is a circuit diagram showing a concrete example of the sustained discharge inhibiting circuit, and FIG. 2 is a voltage waveform of each part of FIG. It is a figure. 3a and 3b are a block diagram and a circuit diagram showing a conventional circuit. 3: DC-DC converter 9: Main capacitor 12: Light emission start switch 14: Flash discharge tube 15: Main thyristor 19: Commutation capacitor 21: Commutation thyristor 24: Sustainable discharge inhibition circuit 25: Dimming circuit 101: First Switching transistor 102: Resistor 103: Diode 104: Capacitor for inhibiting continuous discharge 107: Second switching transistor

Claims (2)

[Scope of utility model registration request] 1. A DC-DC converter for boosting a low-voltage power supply, a main capacitor for storing the light emission energy by charging the voltage boosted by the DC-DC converter, and a flash discharge for emitting light by the charge of the main capacitor. Electronic flash having a tube, a trigger circuit for triggering the flash discharge tube, a light emission stopping circuit for stopping the light emission of the flash discharge tube, and a continuous discharge inhibiting circuit for preventing continuous discharge of the flash discharge tube In the device, the continuous discharge prohibition circuit is a first switch device that is turned on when the flash discharge tube emits light and turned off when the flash discharge tube is not emitted, a continuous discharge prohibition capacitor, and the first switch device when the first switch device is turned on. A charging path for charging the continuous discharge prohibiting capacitor with a current supplied via, and a continuous discharge prohibiting capacitor when the first switch means is turned off. A discharge path for discharging the charged electric charge of the capacitor, and an operation in a phase opposite to that of the first switch means to turn on by the charged electric charge of the continuous discharge inhibiting capacitor when the first switch means is turned off, And a second switch means for supplying a charge to the light emission stopping circuit to prohibit the continuous discharge of the flash discharge tube. 2. The continuous discharge inhibiting capacitor is charged to a predetermined voltage before the main capacitor is completely discharged,
2. The continuous discharge according to claim 1, wherein the second switch means is turned on only when the continuous discharge inhibiting capacitor is charged to the predetermined voltage and the first switch means is off. Prevention electronic flash device.