Electronic flash apparatus

Claim 2

Electronic flash apparatus for photographic purposes, comprising a flash tube, a thyristor in series with said tube for controlling flow of current through said tube, means for igniting said tube, there being a voltage drop occurring in a discharge section of said flash tube when it is ignited, and means responsive to said voltage drop for causing said thyristor to become conductive so that discharge current may flow through said tube and through said thyristor to create a light flash in said tube, said means for causing said thyristor to become conductive comprising means for supplying said thyristor with a control grid potential which is less than the initial potential applied to the cathode of said thyristor immediately before the ignition of said flash tube, and means effective immediately upon ignition of the flash tube for reducing the cathode potential of said thyristor to a potential sufficiently lower than said control grid potential so that said thyristor becomes conductive.

Claim 3

Apparatus as defined in claim 1, further comprising a storage capacitor arranged in parallel with said flash tube and thyristor, integrating measuring means responsive to light reflected from a subject being photographed for producing a termination signal pulse when the integrated reflected light reaches a desired value, and means responsive to said signal pulse for producing a commutating flow of counter-current in said flash tube and thyristor, to cause said thyristor to become non-conductive and to extinguish the flash in said flash tube, said last named means comprising an impedance arranged in a connection between said storage capacitor and said flash tube and thyristor, said impedance having an intermediate tap, a second capacitor (11) and a second thyristor (12) in series with each other and in parallel with said storage capacitor and connected to said tap, a resistor (13) in parallel with said second capacitor (11), and a connection for conveying said termination signal pulse to the control grid of said second thyristor to cause said second thyristor to become conductive, said impedance and second capacitor being so dimensioned and arranged that when said second thyristor becomes conductive, said impedance generates a quenching current surge of commutating counter-current in said flash tube and first thyristor.

Claim 4

Apparatus as defined in claim 1, wherein there is a capacitor (9) having a higher potential side and a lower potential side, and the cathode of said thyristor (4) is directly connected with the anode of said flash tube (3), and the control grid of said thyristor is connected to said lower potential side of said capacitor (9), and the potential of said lower potential side exceeds the cathode potential of said flash tube (3) by an amount at least equal to the sum of the maintaining voltage of the flash tube plus the ignition voltage of the thyristor.

Claim 5

Apparatus as defined in claim 3, whereIn there is a series circuit comprising a first resistor (6), a second resistor (7), and a third resistor (8) in series with each other and in parallel with said flash tube (3) and thyristor (4), and the control grid of said thyristor and the lower potential side of said capacitor (9) are connected to each other and to said series circuit between said second resistor (7) and said third resistor (8), and the cathode of said thyristor and the anode of said flash tube are connected to each other and to said series circuit between said first resistor (6) and said second resistor (7).