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
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?