Evaluation of factors affecting the timing capabilities of the MC3858 sprytron

Abstract

The switch delay time of the MC3858 sprytron was measured using a test matrix consisting of 36 different trigger circuit configurations. The test matrix allowed the measurement of switch delay times for peak trigger voltages ranging from 47 V to 1340 V and for stored trigger energies ranging from 0.023 mJ to 2.7 mJ. The average switch delay time was independent of peak trigger voltage above approximately 800 V. Similarly, the average switch delay was independent of trigger stored energy above approximately 0.5 mJ. Below these saturation values, the average switch delay increases rapidly with decreasing trigger voltage or esergy. In contrast to the average switch delay time, the shot-to-shot variability in switch delay time does not appear to be strongly affected by peak trigger voltage as long as the trigger voltage is groater than 100 V. Below 100 V, the variability in switch delay time rises rapidly due to failure of the trigger to undergo immediate high voltage breakdown when trigger voltage is applied. The effect of an abnormally-high-resistance trigger probe on switch delay time was also investigated. It was found that a high-resistance probe behaved as a second overvoltage gap in the trigger circuit. Operation with a peak trigger voltage greater than the breakdown voltage of this second gap yielded delay times comparable to operation with a normal trigger. Operation with a peak trigger voltage less than the breakdown voltage of this second gap increased the switch delay time by an amount comparable to the time required to ramp the trigger circuit output up to the breakdown voltage of the second gap. Finally, the effect that varying the bias voltage applied to the sprytron has on switch delay time was measured. The switch delay time did not appear to depend on bias voltage for bias voltages between 725 V and 2420 V.