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Re: Dump the RSG!


From: 	terryf-at-verinet-dot-com[SMTP:terryf-at-verinet-dot-com]
Sent: 	Tuesday, November 04, 1997 10:10 PM
To: 	Tesla List
Subject: 	Re: Dump the RSG!

>
>From: 	Malcolm Watts[SMTP:MALCOLM-at-directorate.wnp.ac.nz]
>Sent: 	Tuesday, November 04, 1997 2:41 PM
>To: 	Tesla List
>Subject: 	Re: Dump the RSG!
>
>Greg, all,
>             I've been sitting on some Westcode devices (SCRs and 
>diodes) for some time now while agonizing over exactly how to use 
>them without destroying them. The kind of ratings I am talking about 
>(from memory) are 2.5kV holdoff/device (fwd and rev) with current 
>ratings around 2kA or so. di/dt should not be a problem with a 
>sufficiently low frequency coil. The agonizing bit comes from the 
>implications of stacking them. If one turns on fractionally before 
>the other (say two stacked), what happens to the sluggard? Bit of a 
>worry I think?

I know the answer to that all too well!

        If they recieve too high of voltage at these currents the junctions
will breakdown and the device will go to a permanant short.  The die will
simply arc and shatter.  They will not handle multiple hits and survive.
The first over voltage and it is all over.  No room for error.  Worse yet,
when one part shorts the rest now see a higher voltage and you risk loosing
the whole stack.  Its sort of sad.  They don't make much noise or anything.
It just stops working and when you go and test them with a multimeter they
are all just dead. :-(

        You really need a voltage protection device across the SCRs.  We use
very fast, high power, and very high frequency transorbs that may be an
option but ours are custom and very expensive.  There are off the self
devices that may work and be cheap (we buy the bare die and package them
ourselves).  The bad part is that you may need some trial and error
experimentaion to get it right.  During development of a RF power supply
design, we went through $250,000 worth of parts in one month trying to
getting it right.  In the end it worked out great but it's not for the faint
of heart or wallet.  

If you really want to play this game, let me know and I'll give you some
tips on things not to do! 

>snip<

        Terry