Welding power supplies

In the past, welding power supplies have been based on transformers. Transformers are relatively inefficient, operating at 50 or 60 Hertz. A lot of heat is generated in the transformer, which must be relatively large and heavy. In inverter controlled power supplies, the same incoming 60 Hertz power is used; however, instead of being fed directly into a transformer, it is first rectified to 60 Hertz DC; then it is fed into the inverter section of the power supply where it is switched on and off by solid state switches at frequencies as high as 20,000 Hertz. This pulsed, high voltage, high frequency DC is then fed to the main power transformer, where it is transformed into low voltage 20,000 Hertz DC suitable for welding. Finally it is put through a filtering and rectifying circuit. Output control is performed by solid state controls which modulate the switching rate of the switching transistors.