I'm currently working on a design to convert a DC inverter welder to AC, and have just completed the low voltage (25-50V), high current (5-140A) circuitry using EWB5.

It's desirable to also have a built-in high frequency/high voltage (c.10-20KV, negligible current) arc facility across the output cables to make starting the welding arc that much easier, especially when using TIG. However, my output switching stage uses cross-coupled high power MOSFETs which are intolerant of such high voltages. (they *do* have reverse diodes built-in, but it's the forward direction when not conducting I'm concerned about)

Does anyone know of a method of preventing such a high frequency/voltage from finding it's way back down the cable to the MOSFETs ? Maybe it's obvious, but my brain's dried-up. Would a fistful of ferrite rings do it ?


Colin

 

A friend of mine was a fabricator for GM and NASA and he taught me a little about the way welders work. He explained that the Hi-Freq component would eat the switching transistors. AFAIR the schema was a filter of a Hi-V cap and a 10 or so watt Resistor making a ground path for the noise backfeed . I really can't help you but my suggestion would be to find a source of schematics for any welder and study the methods use by those manufacturers to eliminate that effect . I'm sorry that I can't give you any more information.