Sequencing circuit for firing photoflash lamps in predetermined order

Claim 1

A sequencing circuit for sequentially flashing a plurality of photoflash lamps which normally become open-circuited upon flashing, said circuit comprising a plurality of semiconductor switch devices respectively adapted to be connected in series with the lamp circuits of said plurality of flash lamps, and sequencing circuitry stages successively connected between said semiconductor switch devices, said switch devices having the characteristic of drawing leakage current when said circuit is sequencing, said leakage current for each said switch device being drawn through its series-connected lamp if the lamp is unflashed and has a relatively low resistance and being drawn through the succeeding sequencing stage if its series-connected lamp has a relatively high resistance, wherein the improvement comprises a plurality of resistors successively connected between said switch devices so as to be successively connected between the junctions of the series-connected circuits of the switch devices and lamp circuits when the lamp circuits are connected to said sequencing circuit, said resistors having resistance values to provide said leakage current to any of said switch devices having in series therewith a defectively high resistance lamp, thereby assuring that the lamps will flash in a predetermined order.