Re: Self-resonant 555 astable conversion?

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Stephen Conner by way of Terry Fritz <teslalist-at-qwest-dot-net>" <steve-at-scopeboy-dot-com>

At 07:53 20/05/03 -0600, you wrote:
>Original poster: "Jolyon Vater Cox by way of Terry Fritz 
><teslalist-at-qwest-dot-net>" <jolyon-at-vatercox.freeserve.co.uk>
>
>I have posted the  diagram of my proposed  setup is at
>http://hot-streamer-dot-com/temp/555%20sr%20astable.bmp.

I didn't download this as it was an incredibly large file (2MB)


>Looking at the diagram again I am concerned about phasing - should the
>current transformer should be in one the primary leads from the H-bridge to
>the step-up transformer, rather than the secondary- this after all, is the
>position of the current transformer in half-wave converters used in compact
>flourescent  lamps and electronic halogen transformers -but what is
>implication of primary current  feedback on the TC frequency distribution/
>bandpass characteristic?

There has been a fair amount of discussion about this recently. K.C. 
Herrick, Richie Burnett and me reckon that the current transformer in the 
primary lead won't work very well. It works in simulations but once the 
corona loading is applied to the resonator, the impedance reflected to the 
primary doesn't show enough resonance. Of course a parallel-tuned primary 
(like Vladimir Mazzilli used) might fix this one.



>With the current transformer in the secondary lead- isn't there a phase
>discrepancy between the output of the current transformer and the primary
>voltage that would need to be corrected in some way e.g by connecting a
>capacitor in parallel with the secondary of the current transformer,
>perhaps?

Yes, that's why K.C.'s feedback TC scheme used a capacitor as the sensing 
element _instead_ of a current transformer. The voltage across a capacitor 
leads the current by 90deg. I'm not sure why this is needed, but I think 
it's because the mutual inductance between pri and sec causes the secondary 
current to lag the primary current by 90deg. Antenna feedback schemes like 
Justin & Aron use get the 90deg phase lead from the capacitance between 
topload and antenna.

Of course it would be nice to have an adjustable phase shift to compensate 
things like propagation delays in your switching circuit. Maybe a series RC 
circuit with a pot across the R?


>What appeared simple at first is now beginning to look rather more
>complicated...!

That's life

Steve C.