Abstract: A synchronous motor drive includes an inverter gating control system using three counters wherein two counters respond to 180.degree. apart zero crossings for providing units of time in terms of clock units, and the third counter is at a computed time interval preset with a count to be counted down to derive the remaining time which is to elapse until a predetermined firing angle is reached, at which time firing of the thyristor of the inverter is triggered.

Abstract: A constant current arc welder of the type in which arc current is regulated by thyristor phase angle adjustment, includes voltage feedback voltage control and current feedback current control, with automatic transfer from the voltage control mode into the current control mode when current has been established in the arc. A time delay allows smooth transfer to the desired current operative level by limiting the current inrush under an initial current reference and with a chosen feedback control dynamic characteristic current boost is also automatically provided when the arc voltage falls below a predetermined level.