| 摘要 |
A normally disabled transistor gate is serially connected with the main electrodes of a flash tube for selectively coupling operating voltage thereto. A reference voltage generated when an igniting pulse is applied to the tube is coupled to one input of a comparator circuit whose output excites a Schmitt trigger, thereby causing the trigger to generate a voltage of a first polarity. The trigger output voltage opens the gate to energize the main electrodes of the flash tube, thereby causing the tube to emit a flash of light. A portion of the light reflected from an object illuminated by the flash tube is detected by a photosensitive element and integrated to form a control signal, which is coupled to a second input of the comparator circuit. After a lapse of time sufficient to permit the control voltage to exceed the reference voltage, the comparator output reverses the state of the output voltage from the Schmitt trigger to disable the gate and terminate the flash.
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