Energy-saving electronic strobe flash apparatus having dual flashtubes

Abstract

Electronic strobe flash apparatus has first and second flashtubes which are fired alternately and repeatedly to produce a composite, extended light flash. A start pulse triggers the first flashtube to cause a first normally charged capacitor to discharge through a primary winding of a transformer, the first flashtube, and a second normally discharged capacitor, thereby firing the first flashtube and charging the second capacitor. The transformer is adapted to produce a flashtube trigger voltage across its secondary winding when current in its primary winding is interrupted. The second capacitor is smaller than the first capacitor so that the voltage across the second capacitor increases more rapidly than the decrease in voltage across the first capacitor during its discharge. When the difference between the voltages across the two capacitors decreases to a predetermined level, the current from the first capacitor is interrupted, which quenches the first flashtube and produces a voltage of a first polarity across the secondary winding that triggers the second flashtube. In response to triggering the second flashtube, the second capacitor discharges through the second flashtube and the primary winding, thereby firing the second flashtube. When the second capacitor is substantially discharged, current from the second capacitor is interrupted, which quenches the second flashtube and produces a voltage of a second polarity across the secondary winding that triggers the first flashtube. In response to triggering the first flashtube, the first capacitor discharges again, and the aforementioned operating cycle is repeated. A control switch, responsive to the occurrence of a predetermined exposure parameter, causes current from the second capacitor to bypass the primary winding to terminate the light pulses.