JPS58125028A - Electronic flash device for series dimming system - Google Patents

Abstract

PURPOSE:To continue the light emission due to a main capacitor, by connecting a small-capacity starting capacitor in parallel to a series circuit consisting of a flash discharge tube and a switching element and charging the capacitor to a voltage higher than the discharge start voltage immediately after light emission and starting the flash discharge tube when the residual voltage of the main capacitor is higher than the discharge stop voltage. CONSTITUTION:When residual voltages of a main capacitor 8 and a starting capacitor 38 are lower than the discharge start voltage and are higher than the discharge stop voltage in the light emission, a time constant due to a resistance 41 and a capacitor 40 is set to a value sufficiently longer than the light emission time. Consequently, the charged electric charge of the capacitor 40 is hardly discharged, and the capacitor 40 is held in the voltage before light emission. Since the interval to the next light emission is about 0.1sec at least, the time constant due to the resistance 41 and capacitors 38 and 40 is so set that the capacitor 38 and etc. are charged to a voltage higher than the discharge start voltage during the interval of light emission.

Description

Detailed Description of the Invention The present invention stops the light emission of the flash discharge tube by cutting off the discharge current of the main capacitor using a series control switching element when the integrated value of reflected light from the subject reaches a predetermined value. This invention relates to an improvement of a series dimming type electronic flash device.

In the series dimming type electronic flash device, only a part of the charge charged in the main capacitor is used for light emission, so it can respond to high-speed continuous shooting. On the other hand, in a flash discharge tube, there is a large difference between the discharge starting voltage (approximately 250 V) at which discharge can start and the discharge stopping voltage (approximately 50 V) at which discharge stops. Therefore, when performing high-speed continuous shooting using a series dimming type electronic flash device, if the residual voltage of the main capacitor falls below the discharge start voltage due to the previous light emission, it will exceed the discharge stop voltage and the main capacitor will not be sufficiently charged. There was a problem that even if there was energy left, the light could not be emitted for the next shot.

The object of the present invention is to solve the above-mentioned problems and ensure that even if the residual voltage of the main capacitor becomes below the flash number's discharge start voltage, as long as it is above the discharge stop voltage, light can be emitted reliably. It is an object of the present invention to provide a serially dimmable electronic flash device.

To achieve this objective, the present invention provides a starting capacitor having a smaller capacity than the main capacitor, connected in parallel to the series circuit of the flash discharge tube and the series-controlled switching element, and in such a way that no discharge current flows through the main capacitor. The present invention is characterized in that a starting power source is provided which charges the starting capacitor to a voltage equal to or higher than the discharge starting voltage of the flash discharge tube immediately after the light is emitted.

Hereinafter, the present invention will be explained in detail based on illustrated embodiments.

The drawing shows an embodiment of the invention. An oscillating booster circuit 2 is connected to the DC low voltage power supply 1 . The oscillating booster circuit 2 includes a transistor 3, a capacitor 4, an oscillating transformer 5, and a resistor 6. The output side of the oscillating booster circuit 2 is connected to a main capacitor 8 via a diode 7. Both ends of the main capacitor 8 are
Through diode 9, resistor 10, trigger thyristor 11
, a series circuit of a resistor 12 and a constant voltage diode 13, a series circuit of a flash discharge tube 14 and a main thyristor 15, and a resistor 16.
and is connected to the series circuit of the commutating thyristor 17. A transistor 18 for controlling the trigger thyristor is connected between the positive end of the DC low voltage source 1 and the gate of the trigger thyristor 11.
The emitter and collector of the transistor 18 are connected.
A resistor 19 and a synchro contact 20 are connected between the base of the DC low voltage power supply 1 and the negative end of the DC low voltage power supply 1.

A capacitor 21 is connected in parallel to the series circuit of the trigger thyristor 11, the resistor 12, and the constant voltage diode 13 for causing the constant voltage diode 13 to generate a constant voltage for a fixed period of time. A capacitor 22 is connected in parallel to the constant voltage diode 13. In parallel with the trigger thyristor 11, a trigger capacitor 23 and a trigger transformer 240 primary winding 2
A series circuit of 4a is connected. trigger transformer 2402
The next winding 24b has one end connected to the trigger electrode 2 of the flash discharge tube 14.
5, and the other end is connected to the flash discharge tube 14 and the main thyristor 1.
5, and is also connected to the resistor 26.

The main thyristor 15 is used as a series control switching element of the present invention, and the main thyristor 15 and the commutating thyristor 1
7 and the like form a light amount control circuit 27. 28 is a commutating capacitor, 29 is a capacitor, and 30.31 is a resistor.

The output side of the photometric circuit 32 is connected to the gate of the commutating thyristor 17 . The side light circuit 32 is formed by a comparator 33, resistors 34, 35, a light receiving element 36, and an integrating capacitor 37. The light control circuit 27 and the photometry circuit 32 constitute a light control circuit.

A starting capacitor 38 is connected in parallel to the series circuit of the flash discharge tube 14 and the main thyristor 15. A diode 39 is connected to the connection point Pk between the diode 9 and the flash discharge tube 14. A capacitor 40 is connected thereto. Both ends of the starting capacitor 38 are connected to a capacitor 40 via a resistor 41. The capacitance of the capacitor 40 is set to be sufficiently smaller than that of the main capacitor 8, and the capacitance of the starting capacitor 38 is set to be smaller than that of the capacitor 40. For example, the main capacitor 8 is 600 μF.

The capacitor 40 is 30 μF, and the starting capacitor 38 is 1
μF, respectively.

Next, the operation will be explained. When a power switch (not shown) is turned on, the oscillating booster circuit 2 operates and charges the main capacitor 8 via the diode 7, and also charges the capacitor 21 and trigger capacitor 23 via the diode 9.
, the commutating capacitor 28, the capacitor 29, and the starting capacitor 38, and further charging 40tf of capacitors via 39 diodes.

When the charging voltage of the main capacitor 8, the starting capacitor 3° 8, and the capacitor 40 reaches a voltage sufficient for light emission,
When the synchro contact 20 is turned on, the transistor 18 is turned on, the trigger thyristor 11 is turned on, and the charge in the trigger capacitor 23 is transferred to 1 of the trigger transformer 24.
Discharge occurs through the secondary winding 24a, and a high voltage is generated in the secondary winding 24b. This triggers the flash discharge tube 14 and connects the commutating capacitor 28, the resistor 30 and the capacitor 2.
Since the gate current flows to the main thyristor 15 via 9,
The main thyristor 15 turns on and the flash discharge tube 14 starts emitting light.

At the same time, the charge in the capacitor 21 is discharged through the trigger thyristor 11 and the resistor 12 into the parallel circuit of the voltage regulator diode 13 and the capacitor 22, and the voltage regulator diode 13
A constant voltage that continues for a certain period of time (several ms to several tens of m5) is generated across both ends, and this constant voltage is applied to the photometry circuit 32 as a power supply voltage.

The light reflected from the subject by the flash irradiation of the flash discharge tube 14 is received by the light receiving element 36, and the integrating capacitor 37 is charged by the photogenerated current corresponding to the amount of light received. When the charging pressure of the integrating capacitor 37 reaches the partial voltage potential at the connection point of the resistors 34 and 35 (preset according to the sensitivity of the film and the aperture of the lens), the output of the comparator 33 changes from low level to low level. - The output level is reversed and the A thyristor 17 is thereby turned on.

Therefore, the discharge current of the commutating capacitor 28 flows through the main thyristor 15 in the opposite direction, the main thyristor 15 is turned off, and the discharge current of the main capacitor 8 flowing through the flash discharge tube 14 is cut off, so that the flash discharge tube 14 stops emitting light. Stop.

Next, a case will be described in which the light is emitted twice in succession with a very short emission interval. By the first light emission, the main capacitor 8
Even if the residual voltage of the starting capacitor 38 is below the discharge start voltage and above the discharge stop voltage, the time constants of the resistor 41 and capacitor 400 are set sufficiently large compared to the light emission time (several ms). The charge in the capacitor 40 is hardly discharged during light emission, and is almost maintained at a value corresponding to the voltage (sufficiently higher than the discharge start voltage) before the first light emission. Therefore, immediately after the first light emission, the capacitor 40 charges the starting capacitor 38, capacitor 21, trigger capacitor 23, commutating capacitor 28, and capacitor 29 via the resistor 41. Since the light emission interval until the second light emission is short (about 0.1 seconds), the resistor 41 is connected so that the starting capacitor 38 etc. are charged to a voltage higher than the discharge start voltage during this light emission interval time.
and capacitor 38.400 time constant is set. Since the ratio between the light emission time and the light emission interval is approximately 0°, the charging voltage of the capacitor 40 hardly decreases during the light emission, and the starting capacitor 38 etc. is charged to the discharge start voltage or higher during the light emission interval time. Thus, it is easy to set the values of the resistor 41 and capacitor 40. Note that a diode 9 prevents current from flowing from the capacitor 40 to the main capacitor 8.

When the synchro contact 20 is turned on when the starting capacitor 38 is charged to a discharge starting voltage or higher and the main capacitor 8 is not charged to the discharge starting voltage, a flash discharge occurs due to the charging voltage of the starting capacitor 38. tube 14
is started. When the voltage of the starting capacitor 38 becomes equal to the voltage of the main capacitor 8, the charge in the main capacitor 8 is discharged to the flash discharge tube 14, and light emission is continued. The operation from receiving the reflected light to stopping the light emission is exactly the same as the first operation, so the explanation will be omitted.

If the capacitance of the capacitor 40 is made sufficiently larger than that of the starting capacitor 38, it is possible to perform high-speed continuous light emission three or more times. Even in that case, since the capacitance of the capacitor 40 can be made sufficiently smaller than that of the main capacitor 8, the initial charging time only needs to be slightly longer.

In the illustrated embodiment, the capacitor 40 corresponds to the starting power source of the present invention.

Instead of the capacitor 40, a separately provided DC-DC converter can be used, or a stacked battery can also be used. As the series control switching element, a gate turn-off thyristor or other switching element can be used instead of the main thyristor 15, which is a one-way thyristor.

As explained above, according to the present invention, a starting capacitor having a smaller capacity than the main capacitor is connected in parallel to the series circuit of the flash discharge tube and the series control switching element, and in such a manner that no discharge current flows through the main capacitor. However, since the starting capacitor is immediately charged to the starting voltage of the flash discharge tube by the starting power supply at the light emitting stage, even if the residual voltage of the main capacitor falls below the starting voltage of the flash discharge tube during the previous light emission,
If the voltage is below the discharge starting voltage, the flash discharge tube is activated by the charging charge of the starting capacitor, and the main capacitor lights up!
Light emission can be sustained by the charge. Therefore, it is essential to reliably take photographs of objects at close range with appropriate exposure using high-speed continuous light emission.

[Brief explanation of drawings]

The drawing is a circuit diagram showing an embodiment of the present invention. 8... Main capacitor, 9... Diode, 14...
- Flash discharge tube, 15... Main thyristor, 27... Light amount control circuit, 32... Photometric circuit, 36... Light receiving element, 37... Integrating capacitor, 38... Starting capacitor, 40 ...Capacitor. Patent applicant: Canon Co., Ltd. Agent Nakamura”;3

Claims (1)

[Claims] 1. In a series dimming electronic flash device that stops the flash discharge tube from emitting light by cutting off the discharge current of the main capacitor using a series control switching element when the cumulative value of reflected light from the subject reaches a predetermined value. , a starting capacitor with a smaller capacity than the main capacitor is connected in parallel to the series circuit of the flash discharge tube and the series control switching element in such a way that no discharge current flows through the main capacitor, and the starting capacitor is flash discharged immediately after the light is emitted. A series dimming type electronic flash device characterized by being equipped with a starting power source that charges the tube to a voltage higher than the discharge start voltage.