In fact, it is a transformer with reduced external characteristics, which converts 220V and 380V AC into low-voltage DC. General electric welding machines can be divided into two types according to the types of output power, one is AC power supply; One is DC. DC welding machine can also be said to be a high-power rectifier. When alternating current is input, it is transformed by a transformer, then rectified by a rectifier, and then the power supply with reduced external characteristics is output. When the output is turned on and off, there will be a huge voltage change. When the two poles are short-circuited, the arc will be ignited, and the generated arc will be used to melt the covered electrode and welding materials, and then the combination will be achieved after cooling. Welding transformer has its own characteristics. The external characteristic is that the voltage drops sharply after covered electrode ignition.