JPS5826633B2 - electronic flash device - Google Patents

Description

[Detailed description of the invention] The present invention relates to an electronic flash device that regulates the light emission period.

Conventionally, in this type of electronic flash device, as shown in FIG. 1, a silicon-controlled rectifying element 5CR1 is connected in series to a flash discharge tube 1 as a first switching element, and both are activated at the same time so that the voltage is accumulated in a main capacitor 2. The electric charge is discharged into the series circuit of the flash discharge tube 1 and SCR, and during the process of light emission of the flash discharge tube 10 due to this discharge, the silicon controlled rectifier 5CR2, which is the second switching element, is activated, and the charging including the resistors R1 and R2 is started. It is known that the electric charge of the commutation capacitor 3, which has been previously charged to the polarity shown in the path, flows in the opposite direction to 5CR1 via 5CR2, and the SCR is made non-conductive to terminate the light emission from the flash discharge tube 1. There is.

However, even when 5CR1 turns off, the internal impedance of flash discharge tube 1 does not immediately become high impedance.
Until the flash discharge tube 1 becomes non-conductive, the commutation capacitor 3 is reversely charged along the path from the flash discharge tube 1 to the commutation capacitors 3 to 5CR2.

Therefore, after the flash discharge tube 1 becomes non-conductive, the resistance R1
, R2, it takes a long time until the commutating capacitor 3 is charged again to the polarity shown.

The present invention is intended to solve the above-mentioned drawbacks, and in order to form a path for quickly discharging the charge reversely charged in the commutation capacitor, the first switching element is temporarily turned on during the non-emission period of the flash discharge tube. The present invention provides an electronic flash device that can be used in various states.

An embodiment of the present invention will be described below with reference to FIGS. 2 and 3.

FIG. 2 is a main circuit diagram showing an embodiment of the present invention, and the same parts as in FIG. 1 are given the same reference numerals.

This embodiment differs from FIG. 1 in that a series circuit of resistor R3 and capacitor 4 is connected in parallel with 5CR1, and this series circuit and trigger diode 5 constitute a timer circuit, so that the charging voltage of capacitor 4 is When the predetermined value is reached, the trigger diode 5 is made conductive, and only 5CR1 is started and made conductive, so that the charge reversely charged in the commutation capacitor 3 is immediately transferred through the path from capacitor 3 to SCR to diode 6. The point is that it is made to discharge.

The operation of the electronic flash device configured as described above will be explained with reference to the time chart of FIG.

5CR1 in FIG. 3 is the first switching element 5CR.
It shows an impedance change of 1, OFF is non-conducting, and ON is conducting.

Further, FT indicates a change in the internal impedance of the flash discharge tube 1, and OFF means a non-conducting state and ON means a conductive state.

Furthermore, C3 represents the charged state of the capacitor 3 with the polarity on the 5CR2 side, and C4 represents the charged state of the capacitor 4 with the polarity on the resistor R3 side.

In the initial state, capacitors 2 and 3 are charged to the polarity shown,
Both flash discharge tubes 1.5CR1 and 5CR2 are in a non-conducting state.

Now, when the flash discharge tubes 1 and 5CR1 are activated simultaneously at time t1 in conjunction with pressing the camera shutter,
The internal impedance of flash discharge tube 1 rapidly decreases, and at the same time 5CR1 turns on, causing flash discharge tubes 1 and 5CR to turn on.
The charge from the main capacitor 2 is discharged through the flash discharge tube 1, and the flash discharge tube 1 starts emitting light.

Then, at the time t2 when a certain amount of reflected light from the subject is detected or after a certain period of time has elapsed from the start of light emission, 5CR is detected.
When SCR 2 is turned on, the charges that have been charged in the commutation capacitor 3 with the polarity shown flow into the SCR□ through 5CR2 in the opposite direction, turning off 5CR1.

However, at time t3 when 5CR1 turns off, the internal impedance of the flash discharge tube 1 is not sufficiently high, and the commutation capacitor 3 is connected to the flash discharge tube 1 to capacitors 3 to 5CR.
It is reversely charged via route 2.

Then, at time t4 when the commutation capacitor 3 is reversely charged, the flash discharge tube 1 becomes non-conductive.

However, when the commutation capacitor 3 starts to be reversely charged,
The capacitor 4 begins to be charged, and its charging value increases according to the time constant of the resistor R3 and the capacitor 4, and at the time t5 when it reaches a predetermined value, the trigger diode 5 becomes conductive and the 5CR1
start it again.

At this time, the flash discharge tube 1 is already in a non-conducting state and is not activated, so it will not emit light even if 5CR1 becomes conductive.

Then, the charge reversely charged to the commutation capacitor 3 through the conductive 5CR1 and the diode 6 is quickly discharged, and when both ends of the commutation capacitor 3 have the same potential, the SCR1 is turned off, and the commutation capacitor 3 is turned off. begins to be charged again to the polarity shown in the charging path including resistors R1t and R2.

This charging final stage is t5, and compared to the conventional charging final stage t7 without a reverse charging means, the time to complete charging is shortened by T1.

The period T2 between the time t when 5CR1 is re-ignited and the time t4 when the flash discharge tube 1 becomes non-conductive is a protection period to prevent the flash discharge tube 1 from re-lighting, and the commutation capacitor 3
It is necessary to set it to the minimum value in order to speed up the charging completion time.

Similarly, the second switching element may be a switching element such as a cold cathode cycitron, and the means for re-igniting the first switching element 5CR1 is such that 5CR1 becomes non-conductive due to reversal of the charging polarity of the commutation capacitor 3, etc. After a certain period of time (corresponding to t in Figure 3), 5CR is detected.
The present invention is not limited to the configuration of the above embodiment, as long as it is a timer circuit that provides a trigger signal to the timer circuit 1.

As described above, with the electronic flash device of the present invention that makes the first switching element conductive again immediately after the flash discharge tube becomes non-conductive, the charge reversely charged in the commutation capacitor is quickly discharged. Therefore, the period until the same current capacitor is charged in the normal direction again is shortened, and it becomes possible to regulate the light emission period and shorten the repetition cycle during exposure photography.

[Brief Description of the Drawings] Fig. 1 is a partial circuit diagram showing an example of a conventional electronic flash device;
FIG. 2 is a main circuit diagram showing an embodiment of the present invention, and FIG. 3 is a time chart used to explain the operation of the embodiment. 1...Flash discharge tube, 2...Main capacitor, 3...Commuting capacitor, 4...
Capacitor, 5...Trigger diode, 6...
...Diode, 5CR1...First switching element, 5CR2...Second switching element, R1* R2* R3...Resistance.

Claims (1)

[Claims] 1. A main capacitor, a flash discharge tube that emits light upon receiving the charged charge of the main capacitor, a first switching element connected in series with the flash discharge tube and activated and conductive at the same time as the flash discharge tube, a commutation capacitor, one end of which is connected to one end of the switching element connected to the flash discharge tube, and which accumulates a charge in a predetermined charging path to make the first switching element non-conductive; It is connected between the other end of the flash discharge tube and the other end of the first switching element, conducts during the light emission process of the flash discharge tube, and transfers the charge charged in the commutation capacitor through the charging path to the first switching element. a second switching element that causes the first switching element to become non-conductive by discharging in the opposite direction; and a timer circuit that makes the first switching element conductive again, and from when the first switching element becomes non-conductive due to the conduction of the second switching element until the flash discharge tube becomes non-conductive. The electric charge that has been charged in the commutation capacitor through the flash discharge tube and the second switching element in a polarity opposite to the charging polarity through the charging path is discharged through the first switching element which is made conductive again by the timer circuit. An electronic flash device characterized by: