Re: Large ferrite cores for SSTC work

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Original poster: "Justin Hays by way of Terry Fritz <twftesla-at-qwest-dot-net>" <pyrotrons2000-at-yahoo-dot-com>

Hi All,

I think most power electronics engineers would agree that SMPS design
literally rotates around the magnetics. You can see this in many
datasheets and application notes from manufacturers of SMPS-related
components. And since a magnifier-based SSTC design qualifies as a
switcher, design of the output transformer is a big deal. I tend to
agree with Jan Wagner that high power, high frequency, high voltage
magnetics design is not easy. (even without it driving a high-Q
resonant air core transformer...)

> Actually, a transformer based feed with one wire going to a 
> magnifier coil has a very important advantage.  If wound so that 
> its self resonance is much higher than that of the coil, the driver

> only draws large current at coil resonance.  Whereas the direct 
> primary approach looks like a short circuit everywhere but at 
> resonance, unless you use a huge number of turns, in which case the

> whole scheme is sort of useless. 

Absolutely true, but put simply, who runs their coil out of tune? If
you wanted an efficient ZVS converter, this would be wonderful. But
it's not that...it's an SSTC!

My comments may be discredited by the fact that I have never used an
output transformer in my SSTC designs. But I know one thing, I had
enough to worry about without having a transformer to deal with.

Don't get me wrong, I think magnetics is a great thing. Transformers
are required in most SMPS's to get the required output voltages and
currents. You can do a million things with a good output transformer:
you can make a HV power supply for your spark gap coils (as in
project THOR = awesome!!!). You can drive an SSTC if you wish. And
you can isolate everything. So if you think you might head into this
area, I would definately consider the bulk buy that Steve mentions.

Take care,

Justin Hays
KC5PNP
Email: justin-at-hvguy-dot-com
Website: www.hvguy-dot-com







Actually, a transformer based feed with one wire going to a magnifier
coil has a very important advantage.  If wound so that its self
resonance is much higher than that of the coil, the driver only draws
large current at coil resonance.  Whereas the direct primary approach
looks like a short circuit everywhere but at resonance, unless you
use 
a
huge number of turns, in which case the whole scheme is sort of
useless. 

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