Design for Simultaneous Pulse Triggering of SCRs in Three-Phase Bridge Configuration

The production of common pulse triggering for a three-phase SCR bridge, which features a control circuit that derives its synchronization and power from the ripple potential of a three-phase half-wave rectifier, is the subject of this paper. The ripple potential is separated from the average dc by clamping and after clipping is utilized as bias for a pulse forming UJT circuit. After firing the UJT is made to conduct for the balance of the bias waveform in order to prevent further pulses from forming and being applied to the SCRs through the pulse transformers. The threephase half-wave rectifier is conveniently in parallel across the delta-wye transformer bank that powers the output load. This design provides 25 to 100 percent control over the conduction angle.