Want to know why some welders for a given output are much bigger than others. Already found one of the big reasons is needing to run on 120V instead of 220V
How much space does a 220V AC input power supply save compared to a 120V one?
But one thing I could be overlooking is the switching frequency – the faster, the smaller the transformer & capacitors have to be. I know IGBTs have higher switching losses. I did an initial calculation of losses for 400V input (approximate voltage after rectifying 220VAC) @ 15amps (avg) & 100% duty cycle (unrealistic but for sake of maximizing conduction loss). I'm assuming a welding power supply uses the same design as a computer power supply like described here and here.
- IGBT (STGP15H60DF):
conduction loss = 15A * 1.6V = 24W
switching loss = 30KHz * (0.14 + 0.21 mJ) = 10.5W
- MOSFET (STW70N60DM2):
conduction loss = 42mOhm * 15A^2 = 9.5W
switching loss = Vds * Idrain * freq * (Qgate_drain + Qgate_source) / Igate (don't know what Igate is, but probably much lower than IGBT)
I can't say for sure, but it seems the MOSFET even switching @ 100KHz will be more efficient than the IGBT, and will allow a smaller transformer & capacitors. So why aren't welders using them?
Best Answer
It's silicon carbide mosfets that have made high amperage/high voltage circuits possible. Now they don't have to use (what I think is, I never tore one open ) transformers and capacitors. Carbide is near indestructible. I had a wielding class a few years back and the high amperage welders ranged from the size of the night stand to a large kitchen desk. Now they can fit the same functionality into something the size of a microwave oven, not only can they do that, but the machines have more switching functionality and they have so much room left over, they combine the same funtionality of 3 welders (tig,mig and stick) into one. It is increadible.
Source: https://www.researchgate.net/publication/300408761_Next_generation_arc_welding_machines_based_on_Silicon_Carbide_MOSFETS_and_high_frequency_planar_magnetics