Abstract: Included in the circuit are a pulse generator and an electronic output switch for providing machining power pulses across the EDM gap. The circuit includes an opti-coupling system intermediate the pulse generator and the output switch to pass triggering pulses to control the conduction of such switch. The opti-coupling system includes a light emitting device operably coupled to a light responsive device for controlling the triggering pulses passed to the output switch. In a further embodiment, a multiple gap set-up includes a single pulse generator for triggering pulses and a plurality of machining gaps, each having a separate opti-coupling system between the pulse generator and the associated gap.