What’s an inverter? We couldn’t actually answer that until Miller provided us with these diagrams showing the differences between transformer-based (left) and newer, inverter-based TIG machines. At a basic level, think of it like the difference between a mechanical voltage regulator versus an internally regulated alternator. An inverter regulates the current from your wall outlet, taking a high-voltage low-current sine wave and changing it to a very precise digital signal that ultimately leads to a more stable weld arc and smoother starts. It can also adjust the frequency of the current, where transformer-based machines can only operate at 60hz output when welding in the AC setting.