Cascaded thyristor quenching arrangement for a pulsed flash device

Claim 3

Apparatus as defined in claim 1, in which the first generating means comprises, in combination, a capacitor, a transformer having a primary winding in series with the flash tube and a secondary winding connected across the capacitor, and a voltage divider including a photosensitive element connected acRoss the secondary winding and the capacitor.

Claim 4

Apparatus as defined in claim 2, in which the first coupling means comprises a diode connecting a tap point of the voltage divider to the control electrode of the first thyristor.

Claim 5

Apparatus as defined in claim 1, further comprising a pair of current-limiting resistors individually connected in the transconductive paths of the first and second thyristors, respectively.

Claim 6

Apparatus as defined in claim 4, in which the second generating means comprises an additional resistor connected in the transconductive path of the first thyristor.

Claim 7

A flash tube ignition control circuit comprising, a capacitor connected across the flash tube for supplying operating current thereto, means coupled to the flash tube for igniting said flash tube, first and second substantially identical normally nonconductive load sharing semiconductor controlled conduction devices each having a rated current capacity which is insufficient by itself to safely pass the normal expected operating discharge current of said capacitor during a tube quenching operation, means connecting said first and second semiconductor devices in parallel across the flash tube, a light integrating circuit responsive to the flash tube current for generating a control signal upon ignition of the flash tube, said integrating circuit including a photosensitive element arranged to respond to a portion of the flash tube light reflected by an object thereby to cause said control signal to vary as a function of said reflected light, means for coupling said control signal to the control electrode of the first semiconductor device to trigger same into conduction to initiate the quenching operation when the control signal attains a predetermined value, means responsive to the current flow through the first semiconductor device for generating a voltage of a magnitude to trigger the second semiconductor device into conduction, and means for coupling the trigger voltage to the control electrode of the second semiconductor device to immediately trigger same into conduction upon conduction of the first semiconductor device thereby to share the discharge load current of said capacitor between said semiconductor devices.

Claim 8

A flash tube ignition control circuit comprising, a capacitor connected across the flash tube for supplying operating current thereto, means coupled to the flash tube for igniting said flash tube, first and second substantially identical normally nonconductive load sharing semiconductor controlled conduction devices each having a rated current capacity which is insufficient by itself to safely pass the normal expected operating discharge current of said capacitor during a tube quenching operation, means connecting said first and second semiconductor devices in parallel across the flash tube, a light integrating circuit responsive to the flash tube current for generating a control signal upon ignition of the flash tube, said integrating circuit including a photosensitive element arranged to respond to a portion of the flash tube light reflected by an object thereby to cause said control signal to vary as a function of said reflected light, means for coupling said control signal to the control electrode of the first semiconductor device to trigger same into conduction to initiate the quenching operation when the control signal attains a predetermined value, means responsive to the current flow through the first semiconductor device for generating a voltage of a magnitude to trigger the second semiconductor device into conduction, and means for coupling the trigger voltage to the control electrode of the second semiconductor device to immediately trigger same into conduction upon conduction of the first semiconductor device thereby to share the discharge load current of said capacitor between said semiconductor devices.

Claim 9

An ignition circuit as claimed in claim 6 wherein said integrating circuit further comprises, a second capacitor and means responsive to the flash tube current for supplying a charge current to the second capacitor that is a function of the flash tube current.

Claim 10

An ignition circuit as claimed in claim 7 wherein said integrating circuit further comprises means for electrically isolating said second capacitor from any electrical energy source so that the second capacitor voltage returns to approximately zero value in the absence of current flow through the flash tube.

Claim 11

An ignition circuit as claimed in claim 7 wherein said charge current supply means comprises a transformer with a primary winding in series with the flash tube and a secondary winding connected across said second capacitor.

Claim 12

An ignition circuit as claimed in claim 9 wherein said integrating circuit further comprises a resistive voltage divider connected in series with said photosensitive element across the terminals of said second capacitor, and said igniting means comprises an igniter electrode for the flash tube that is energized independently of said integrating circuit.