"Ignoramus29893" wrote:
Jon Danniken wrote:
Aye, thanks Iggy, that is a readable schem. It looks like they are using
the SCRs in place of the bridge for controlling the current, but are
using
an IC (or another unspecified group of components) to drive the gates.

Yes, that's why you need an SCR controller to go with the SCRs.

Thanks Iggy. I am going to build this myself (with some assistance from
those more experienced, of course), using available discreet components
(maybe an IC if there is a compelling reason), without purchasing any
pre-assembled circuitry or boards. This will entail building my own
"controller board" to control the SCRs, but that's part of the fun, too!

Before I can do that, however, I need to first determine the topology that
is used in this type of circuit (silicon control of current in a welder). I
am hoping I can come across an early TIG supply schematic that will give me
clue as to what methodology was used, be it pre-transformer control or
post-transformer control. That's where I'm stuck at right now.

I wonder if there were any TIG supplies that used a more simple
method of controlling the current, maybe in the pre-IC days?

Don mentioned another method. I do not recall what it is.

IIRC, he mentioned he would use IGBTs, but I think that might be more
complicated than I am williing to go, at least at this stage. SCRs don't
seem too terribly complicated for me, it's just finding out the layout of a
basic welder current control to give me a place to start that is my obstacle
right now. Eventually there will be zero-crossing detectors, but one step
at a time.

Jon