Electric lamp and discharge devices: systems – Condenser in the supply circuit – Condenser in shunt to the load device and the supply
Patent
1985-01-16
1989-01-17
Moore, David K.
Electric lamp and discharge devices: systems
Condenser in the supply circuit
Condenser in shunt to the load device and the supply
315151, 315159, 354417, H05B 3700
Patent
active
047989963
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a control circuit for an electronic photoflash apparatus used in photographic applications.
BACKGROUND ART
Electronic photoflash guns have been extensively used for some years to provide extra illumination for photography in low ambient light conditions. A requirement of control circuits associated with photoflash guns has been to time accurately the firing of the photoflash tube(s) and also to provide a definite cut-off or quench of the photoflash tube when sufficient light has been generated. This latter cut-off can be either fixed to provide one or more discrete levels of generated light (whereupon exposure settings within the camera may need to be varied to compensate) or may be automatically provided when a quantity of light sufficient for a predetermined exposure setting of the camera has been generated by the tube.
Prior control circuits for photoflash guns as will hereinafter be described operate on the principle of charging and discharging capacitors in order to switch thyristors in order to initially fire the flash gun and to cut off or quench the flash gun. However, operation by charging and discharging capacitors can be slow, particularly where fast recycling times are required, for example in motor driven cameras where it may be necessary to take sequential exposures very rapidly and a photoflash gun must be able to recycle in a very short time between exposures.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a control circuit for a photoflash gun which is capable of fast recycling times.
The present invention provides a control circuit for a photoflash gun, the circuit including a flashtube, a switching circuit for initiating operation of the flashtube, a switch means coupled with the flashtube which when operated permits current flow through the flashtube, and reset means for resetting the switch means after a predetermined time to cut off current flow through the flashtube. The reset means includes an inductance and a charge storage means coupled to the switch means such that when the switch means is operated current flow occurs through said charge storage means and said inductance to create a voltage across said charge storage means which is of a polarity such as to reset the switch means.
In accordance with the invention, the inductance and the charge storage means provide a resonant like circuit which permits fast recycling time of operation.
BRIEF DESCRIPTION OF DRAWINGS
Features and advantages of the present invention will become apparent from the following description of a prior arrangement and preferred embodiment of the invention, together with the accompanying drawings. in which:
FIG. 1 is a basic block diagram of a prior art control circuit;
FIG. 1A shows the electronic switch circuit of FIG. 1 in greater detail;
FIG. 1B shows the light-sensing calculation circuit of FIG. 1 in greater detail;
FIG. 2 is a block diagram of the preferred embodiment of the invention;
FIGS. 2A and 2B show two forms of electornic switch circuit which can be used in the circuit of FIG. 2;
FIGS. 2C and 2D show two further developed forms of electronic switch circuit which can be used in the circuit of FIG. 2;
FIGS. 2E and 2F show two forms of light-sensing calculation circuit which can be used in the circuit of FIG. 2; and
FIG. 2G shows a voltage controller circuit which can be used in the circuit of FIG. 2F.
DESCRIPTION OF PREFERRED EMBODIMENT
Referring to Figure 1, a previously-proposed circuit includes a voltage source 10 arranged to charge an energy storage capacitor CM (and other capacitors elsewhere in the circuit) to a voltage V1. Also connected across the storage capacitor CM are a series combination of energizing switch SW and resistor R1, and a capacitor C1 with triggering coil L1 also connected across switch SW. A secondary of the triggering coil L1 triggers a flash tube FT which is also connected to electronic switch circuit 11 for controlling cut-off of the flash tube FT. The switch circuit 1
REFERENCES:
patent: 3875471 (1975-04-01), Buck
patent: 3974419 (1976-08-01), Adams, Jr. et al.
patent: 4092565 (1978-05-01), Neal
patent: 4132923 (1979-01-01), Gahler et al.
patent: 4288722 (1981-09-01), Ikawa
Macek, "Einige Anwendungen Schneller Thyristoren", Siemens-Bautelle-Informationen, vol. 10, No. 5, 1972 Munich, FRG.
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