Patent ID: 8796585

Claim:
A welding power source, comprising: a fan transformer comprising a primary winding coupled to a fan motor and a secondary winding having a primary supply voltage; a main transformer comprising a main primary winding and a main secondary winding having a main voltage configured to supply a weld power output; at least two semiconductor-controlled rectifiers (SCRs) each comprising a gate and each being configured to remain in a non-conductive state to restrict current to the main primary winding when a trigger pulse has not been applied to the respective gate and to enter a conductive state to allow current to the main primary winding when the trigger pulse has been applied to the respective gate; a circuit breaker configured to be tripped to disallow current through the welding power source; and a controller coupled to the secondary winding of the fan transformer and the at least two SCRs and configured to selectively apply the trigger pulse to at least one gate of at least one SCR to saturate the main transformer when the primary supply voltage exceeds a predefined threshold, wherein saturation of the main transformer trips the circuit breaker.