Variable Strobe Light

In this strobe-light, two circuits are needed; one circuit charges a capacitor placing 320 Vdc between the cathode and anode of the flashtube. The other circuit provides bursts of approximately 4000 V to trigger the flashtube into conduction. The voltage-doubler works by summing two equal voltages in series, which results in a doubling of the voltage. The 4000 V needed to trigger the flashtube is provided by transformer T1--a voltage step-up transformer that develops 4000 V across its secondary coil when current flows in the primary coil. Silicon-controlled rectifier SCR1 controls the current flow in the primary coil of T1. When SCR1 conducts, current flows suddenly in the primary coil and 4000 Vac spikes appear across the secondary coil. For conduction, SCR1 needs a negative and positive voltage on the cathode and anode, respectively, and a positive voltage on the gate. It is the function of components R2, R3, C3, and NE1 to provide that positive gate voltage and turn on SCR1. Potentiometer R2, resistor R3, and capacitor C3 form an RC timing circuit. Control of charging time of C3 is accomplished by varying that resistance in the circuit. When the voltage on C3 reaches the firing voltage of the neon bulb, it causes NE1 to conduct, thus placing a positive voltage, from C3, on the gate of SCR1. The SCR now turns on and C3 discharges through SCR1 and the primary coil of T1. The 4000 V that is developed across the secondary coil of T1 fires the xenon tube, causing a bright flash. The whole process then repeats itself with C3 charging up, NE1 firing to short out SCR1, and T1 developing 4000 V to trigger the xenon flashtube.

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