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Re: Solid state TC working! But.



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Hi Jeff,
           The resonance(s) experienced with the flyback transformer
are mostly due to the high inter-winding capacitances experienced
with the layered winding and also capacitance to the core. In my 
experience these cores are mostly 3C3/3C6 (Philips numbers) material 
and are rather lossy at high frequencies. I don't see any major 
problem with using the circuit as you suggest. It would pay to get 
the flyback primary inductance to the same value as Duane's original 
transformer as you will start blowing transistors due to excessive 
magnetizing current if it is too low. Also, check whether his 
transformer core was gapped or not. It is usual practice to gap cores 
in SMPS circuits to prevent core saturation due to various conditions 
that can arise. The primary inductance should be measured with the 
core in its final (gapped?) condition.

Malcolm

> OK, here's the catch. The circuit drives a hand-wound ferrite core
> transformer T2 (see schematic) that hooks directly to the secondary ala
> magnifier fashion, but I would like to be able to interchange this
> transformer with a flyback transformer to drive a large plasma globe I have
> already built. T2 has a 10 turn primary, so I hand wound 10 turns around
> this hefty flyback transformer I have (an older one rated for 25 kV or so)
> and hooked it up.
> 
> When I turned up the juice with my variac, I got absolutely no output from
> the flyback transformer at first. As I varied the frequency of the circuit,
> I hit a "resonant" frequency of the flyback somewhere around 100 khz and
> the transformer went from dead to producing a crackling 3" output
> discharge. But it remained practically dead for all other frequencies.
> Also, the spark output at the resonant freq. was the kind of crackling,
> pulsed type spark you might expect from a capacitive-discharge TC, but not
> the continuous, rather smooth spark I am used to getting from a flyback
> transformer. Also, I should mention that I replaced D1 with a full-bridge
> rectifier for this experiment so that the power transistors Q3 and Q4 have
> continuous 160 VDC power, so I would expect continuous output from the
> flyback.
> 
> Question is, is this circuit feasible for driving a flyback, and if so, how
> should I go about it? Anybody have a good explanation for what is
> happening? All comments and suggestions would be greatly appreciated! Also,
> I just wanted to thank Malcolm and Bert Hickman again for all their help
> already.
> 
> Jeff Detweiler






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