Current-sensing circuit for determining flashing of a photoflash lamp

Claim 2

A current-sensing circuit for determining the occurrence of lamp-flashing current flow in a current-sensing element connected in series with an array of flash lamps, comprising a differential amplifier having its two inputs respectively connected to the two ends of said current-sensing element, said differential amplifier being adapted to produce a signal at the output thereof in response to a current flow of predetermined magnitude in said current-sensing element.

Claim 3

A circuit as claimed in claim 1, for use with a circuit having means to provide a trigger pulse and cause a lamp to flash upon the occurrence of the trigger pulse, and further comprising an enabling circuit connected to said differential amplifier and adapted to render said differential amplifier normally inoperative so as not to draw operating current, and means for applying said trigger pulse to said enabling circuit, said enabling circuit being adapted to enable said differential amplifier for operation upon the occurrence of said trigger pulse.

Claim 4

A circuit as claimed in claim 1, including first and second operating voltage terminals and means connecting said current-sensing element in a current path between said first operating voltage terminal and said array of flash lamps, and in which said differential amplifier comprises a pair of transistors having their base electrodes connected together electrically, a resistor connected in a current return path between said base electrodes and said second operating voltage terminal, means connecting the emitter electrodes of said transistors repsectively to the two ends of said current-Sensing element, means connecting the collector electrode of one of said transistors to the base electrode thereof, and means connecting the collector electrode of the other transistor to said output of the differential amplifier.

Claim 5

A circuit as claimed in claim 3, for use with a circuit having means to provide a trigger pulse and cause a lamp to flash upon the occurrence of the trigger pulse, and including an enabling circuit comprising an enabling transistor having its emitter and collector electrodes interposed in series in said current return path, means biasing said enabling transistor to be normally non-conductive, and means for applying said trigger pulse to the base electrode of said enabling transistor thereby rendering it conductive and enabling said differential amplifier for operation.

Claim 6

A circuit as claimed in claim 3, including a source of reference voltage interposed between the emitter electrode of one of said pair of transistors and its connection to an end of the current-sensing element.

Claim 7

A circuit as claimed in claim 5, in which said source of reference voltage comprises a diode and resistor connected in the named order in a current path between said first and second operating voltage terminals, a pair of resistors connected in series across said diode, and means connecting the emitter electrode of one of said pair of transistors to the junction of said pair of resistors.

Claim 8

A circuit as claimed in claim 6, for use with a circuit having means to provide a trigger pulse and cause a lamp to flash upon the occurrence of the trigger pulse, and further including an enabling circuit comprising an enabling transistor having its emitter and collector electrodes interposed in series in said current return path, means biasing said enabling transistor to be normally non-conductive, and means for applying said trigger pulse to the base electrode of said enabling transistor thereby rendering it conductive and enabling said differential amplifier for operation.

Claim 9

A circuit as claimed in claim 3, including a pair of zener diodes respectively connected between said second operating voltage terminal and said two ends of the current-sensing element, said zener diodes being adapted to suppress undesired transient voltages at the current-sensing element.