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Re: [TCML] Non-DR SSTC primary - interesting facts



You might also consider some late model, more robust MOSFETs.

Fuji just came out with some small monsters with an incredible low "on"
resistance of only 0.11 Ohms!

They are p/n 2SK3680-01 in a TO-247 package and rated 500 V, 52 Amps
continuous, and 208 Amps pulsed.

They have just been released and I'm anxiously awaiting my samples which I
intend to use in an 8" x 40" SSTC system.
Pri is 6.5 turns tapped for resonance at 5.2 turns.

Dr. Resonance

On Tue, Aug 26, 2008 at 4:32 AM, TheBypasser <bypasser@xxxxxxx> wrote:

> Well, upon an attempt of further civilizing my flower-pot primary I removed
> a turn (getting 6 turns instead of 7) and blew two fets (was a pretty stupid
> idea - even the primary itself lost ~25% of it's inductance, first blow on
> the finished construct btw) - and the interesting part is - the spark almost
> didn't grow (was up to 60cm - remained the same). Of course I put the turn
> back and replaced the fets (working fine again, same spark - and the heating
> of the bridge is very subtle btw, even with my really bad cooling), but it
> led to some interesting thoughts, also based on my older research.
> The idea is - you have a fixed-height primary with a significant number of
> turns and start reducing that number one by one, keeping the height
> constant. At first you get a low transformation coefficient and high
> inductance, thus the power is too low. As you remove the turns, the
> transformation coefficient gets higher and therefore the power transfer into
> the secondary increases. That's good, but - you slowly increase the
> reflected power by doing that, therefore the SWR gets worse and worse,
> making LESS power supplied into the secondary. The question is - is the
> resulting power supplied into the resonator rising all the time, or there's
> a peak after which you start making the coil be able to transfer less power
> again? By the way (didn't test that on my new coil, actually as far as it's
> working well and never blows I'm not going to change much - 60cm on a bps up
> to around 30 with a pretty high pulse length feels like a proper result for
> a bridge of 30a fets ;) - and the secondary heats up pretty much anyway) the
> tests on the previous version of this coil (there was no feedback at the
> point, and the secondary was much smaller and ran at ~300kHz instead of the
> present ~150) showed that the primary height (meaning not how high the top
> turn is, but the distance between the top and the bottom turns - eg the top
> turn remained at ~1/4th of the secondary, but I tried both spreading the
> primary to the bottom of the secondary and winding it tight) doesn't affect
> much as long as the winding remains close to the secondary..
> So, is there a point of an "optimal" primary, at which further turn
> reduction has only negative effects?
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