I am sure this will be a very basic electronics question, but I am ignorant on this and would like some help. I have purchased a Chinese inverter welder/plasma cutter. The machine runs off of 24 mosfets and apparantly some people have had issues with the mosfets blowing(mostly when using the plasma). My question is- IF I were to have a problem and wanted to replace the mosfets here in the US, what would I need? I have one unit that has, I believe ,toshiba fets with the numbers FEP underneath that is the number 25N50G and below that is 70842. Here my ignorance will show. I believe the fet is a 25 amp 500 volt unit(that is all the info I could get from looking on the net). Are there different switching speeds or would any 25amp500volt mosfet work? Also I have heard that IGBT chips are more sturdy in this application would that be just a simple swap? If so what IGBT chips would I look for. I also have another unit that has a different mosfet that I may need a cross reference to as well. Thanks again Mark

 

Frequency is something to be concerned about. FET's are better for switching rates above 20 KHz, especially with longer duty cycles. IGBT's are pretty robust, but have poorer turn off times. I don't know what frequency your plasma arc generates.

If you try to run down devices based on parameters, it gets interesting - especially as I couldn't find a data sheet on a 2N50G. FET's get thin on the ground for 500 volt ratings. IGBT's all are good for 600 volts and up.

I don't know enough to make a guess, but Googling "ultra fast igbt" brings up 32,300 hits. Some rated at 600 volts @160 amps. You would think an IGBT would make a likely substitute - but I can't find specs on the original FET.

 

I did come across this obsolete Motorola part. On-semi indicates it may be available from Rochester.