Arc welding transformer power regulation schematic

Power variation schematic for arc welding transformer. The schematic shows a typical circuit for welding equipment.

Potentiometer P2 is used for accurate control of the maximum turn-on delay. DB1 diode bridge and R6-R7
resistors are used to discharge C1 at each line zero voltage. This resets the voltage charge at each new half line cycle, and keeps the same turn-on delay. The Transil reduces power dissipation through both potentiometers.
 

Pulse-train triggering circuit