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Re: Scopes Away! - mosfet diode



Hi Alan,
          I realized immediately after posting this it was a totally 
dumb question. I was expecting some flak.

> >>  Question - is there an easy way of destroying the diode without
> >>ruining the MOSFET? (Alan, anybody?). Alternatively, are there any 
> >>devices without this built-in nuisance available (type/s please)?
> 
> The substrate diode is a property of the actual working
> bits of the MOSFET - it's not a separate component.

In fact they enhance it and characterize it and extoll its virtues
as a protection device.
 
> The simplest way to get rid of it is to put a diode in series with
> the mosfet.
> The alternative would be to go for a bipolar or IGBT device.

A better one is two wire two in series with the sources and gates
commoned (which is what I'll do for this weekend's expts - thanks 
to Jim for the suggestion). The problem with a series diode is you 
don't get a peak to peak ring, just rectification.
     I will using 4 in series-parallel for bidirectional resistance 
of around 40 milliOhms. Be surprised if I can't get a Q of around 19 
from the test setup (abysmal L/C ratio) and _much_ better with a
higher L/C ratio. The nice thing about this "gap" is that it doesn't 
suffer the non-linear characteristics of the spark gap.
     I consider the gap to be the worst possible part of any coil 
system (bar 7000 turn secondaries of #40 wire :)  I expect to show
that anyone who makes a primary with Q>>10 in a real system is going 
to blow established records and rules-of-thumb out of the water.

Thanks,
Malcolm