Inside A Plasma Cutter (Must See Pictures for SSTCers!)

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Original poster: "Jim Mitchell" <Electrontube-at-sbcglobal-dot-net> 

Hello List,

Today I opened up my Speedway 30A plasma cutter to see what sort of 
topology it used to work.  To my surprise,  I found a small IGBT brick, and 
a unusually simple driver board,  with a very small gate drive 
transformer.  Does anyone know how the brick would be driven?  As I 
couldn't find a single Gate Drive IC or any other means of gate drive on 
the board.  The brick does look small,  I believe it's a 100A 
halfbridge.  The 6 diodes you see on the edge of the heatsink are 
RURG30120, 30A 1200v.  Pictures:

<http://www.hot-streamer-dot-com/electrontube/plsmc/1.jpg>www.hot-streamer-dot-com/electrontube/plsmc/1.jpg
Closeup of gate drive transformer, the right hand molex connector goes to 
the gates. Note bridge rectifier connections on left.
<http://www.hot-streamer-dot-com/electrontube/plsmc/2.jpg>www.hot-streamer-dot-com/electrontube/plsmc/2.jpg
Closeup of the Brick,  sorry for the blurry picture.
<http://www.hot-streamer-dot-com/electrontube/plsmc/3.jpg>www.hot-streamer-dot-com/electrontube/plsmc/3.jpg
Closeup of the high frequency step up transformer.
<http://www.hot-streamer-dot-com/electrontube/plsmc/4.jpg>www.hot-streamer-dot-com/electrontube/plsmc/4.jpg
Left view of the electronics.
<http://www.hot-streamer-dot-com/electrontube/plsmc/5.jpg>www.hot-streamer-dot-com/electrontube/plsmc/5.jpg
Top view of the electronics,  Note the current sense transformer on the 
cable going to the step up transformer.
<http://www.hot-streamer-dot-com/electrontube/plsmc/6.jpg>www.hot-streamer-dot-com/electrontube/plsmc/6.jpg
Rear view of the Brick and heatsink.  Note the Fairchild logo on the 
Brick.  Sorry the part number is illegible,  I meant to write it down 
before I closed the case, but I forgot to.
<http://www.hot-streamer-dot-com/electrontube/plsmc7.jpg>www.hot-streamer-dot-com/electrontube/plsmc7.jpg
Right view of the driver electronics,  Note the bank of 6 RUR30120 
diodes.  As well as the six blue capacitors above them.
<http://www.hot-streamer-dot-com/electrontube/plsmc8.jpg>www.hot-streamer-dot-com/electrontube/plsmc8.jpg
Right view of the high voltage transformer.


Regards - Jim Mitchell