Re: 48kW DRSSTC and RELIABILITY

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Original poster: Steve Conner <steve@xxxxxxxxxxxx>


> Could you please explain your
> GDT construction? pictures would help too.
They are made from three wires bound together and wound round a 
toroid core as usual, except one of the wires is a piece of 1/8" 
miniature coax. The core of this coax is connected to the driver chip 
outputs just like you would do with an ordinary unshielded wire. The 
screen is connected at one end to the metal box that the driver board 
is housed in, and left floating at the other end. The ground plane of 
the driver PCB is bolted to the box too.
I'm not sure if it really helps or if it is just a gimmick. :-/


> This only happens with secondary feedback... right?
Hmm, I never really thought about that. I guess it's a lot harder to 
induce weird frequencies in the primary, because it's just a lumped 
resonator, and doesn't have a whole spectrum of modes. (well not ones 
relevant to coiling anyway.)
But I was still unsure what would happen under real heavy streamer 
loading. I thought the effective Q of the circuits might get very 
low, and it was nice to know that the PLL would take a guess at the 
right frequency and keep driving anyway. I also expected that strikes 
to the primary would probably create some pretty extreme feedback "signals".

> Have you tried allowing primary strikes from the toroid?  If you need,
> i can send you some spare IGBTs :-).
I haven't provoked it on purpose, although it may well have happened 
once or twice by accident. I guess I could try it but it's a pretty 
evil test especially if the strike current passes through the 
feedback CT. Which it would on my coil :-<
I've got plenty of spare IGBTs, since I'm not in the habit of blowing 
any. :-P *knocks on wood
Steve Conner
http://www.scopeboy.com/