Single Phase Controls (AC or DC) for Resistance Welding

From a single phase power supply, the low frequency welding control utilizes an inversed parallel pair of Silicone Controlled Rectifiers (SCR) to control the output the welding power transformer. SCRs are turned on by pulsing a gate with a voltage signal. The welding control uses predictive algorithms to determine the best point to pulse the gate of the SCRs during the half cycle of the alternating current supply. The SCRs are turned off only when the alternating current supply is below the threshold point called "minimum holding current". This occurs near the zero crossing point of the AC power supply.